Fig.1: four Mosfets, Q1-Q4, are used to switch up to fifteen 47W resistors, applying a varying load resistance across CON1. IC1 and the 15mW shunt allow the load current to be measured, while the 33kW/10kW divider measures the voltage, allowing the dissipation to be calculated. voltage sources up to 12V nominal. But Fig.1 shows the circuit we came up a catastrophic failure. Otherwise, the we’ve kept in mind that there can be with. Four N-channel Mosfets, Q1-Q4, circuits are entirely separate, apart some variation in voltage; for exam- switch the resistors in and out of cir- from their common grounds. ple, a 12V battery could put out up to cuit. Their sources are connected to 14.4V during charging, and a 12V LED circuit ground, and their drains go to The other end of the load resistors might require 13V or more to produce the groups of one, two, four or eight connects to a 15mW current-m easuring full power. So we’ve selected compo- resistors, respectively. Their gates are shunt and then to the Load’s positive nents that will handle up to 15V con- held low by 10kW resistors, so they terminal. The connection to the exter- tinuously (more on a pulsed or inter- usually are off. nal circuitry is via the screw terminals mittent basis). at CON1. The gates also connect to four dig- 47W is the lowest E24 series resis- ital I/O pins (D3, D4, D5 and D6) of Also connected to the top of the load tor value that produces less than 5W an attached Arduino board via 470W resistors is a 33kW/10kW divider with a of dissipation with 15V applied across resistors. The resistors provide a 100nF capacitor across the lower resis- it, hence our use of 47W resistors. degree of protection in the event of tor. This allows the attached Arduino siliconchip.com.au board to measure up to 21.5V, assuming Australia's electronics magazine June 2022 49 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
it has a 5V analog-to-digital converter IPP80N06S4L-07 or similar Mosfets otherwise, adjust it using tweezers (ADC) reference voltage. as the CSD18534KCS are not suitable until you can do so. The 15mW shunt for 3.3V gate drive. resistor adjacent to CON1 can also be The divided and smoothed voltage handled similarly, although it is not is fed to the attached Arduino board’s Secondly, change the 33kW resistor as fiddly to mount. A0 analog input pin. This divider to 56kW and change the 15mW shunt means that the Arduino Programma- to 10mW. This is to avoid overloading Clean up any excess flux at this ble Load always presents a minimum the ADC pins with voltages above 3.3V point as the remaining parts are all load of 43kW. and assumes a default ADC reference through-hole. Note that the PCB will of 3.3V (as per the Due). also accept a through-hole resistor The voltage across the shunt is mea- for the shunt if that suits you better. sured by IC1, an INA282 current shunt In the sketch, change the V_CONST You will have to tweak the calibration monitor with a gain of 50. A current define to 0.0212695 and the I_CONST in the software if changing its value, of 1A results in a 15mV drop across define to 0.0064453 to account for the though. the 15mW shunt resistor, and thus an different component values. output of 750mV at IC1’s pin 5. The Next, fit the remaining small axial maximum measurable current with a Construction resistors, as marked on the PCB silk- 5V reference is therefore 6.67A. screen. Check the resistors with a The Load is presented as a bare multimeter if you are unsure of their This voltage goes to another ADC shield PCB with external screw termi- values. channel at the Arduino A1 pin via a nals. It’s expected to be used similarly 10kW resistor, and it is filtered by a to the Arduino PSU (February 2021; Follow with the three 100nF capac- 100nF capacitor. The output voltage siliconchip.com.au/Article/14741), itors, all of which are near IC1. These of IC1 is set to be referred to circuit as a bare board on top of an Arduino- are not polarised. Trim all leads close ground by its pins 3 and 7 being con- compatible microcontroller board. on the underside of the PCB. Screw nected to ground. terminal CON1 can be soldered next. The lack of enclosure actually Ensure that the lead entries face out IC1 is fed with a 5V supply to its pin helps us somewhat. With up to 70W of the board. 6 with a 100nF bypass capacitor from of dissipation, a good amount of free the attached Arduino board, and its air convection is necessary to avoid The next tallest components are power ground connection is at pin 2. overheating. Ideally, a fan should Mosfets Q1-Q4, all of which are the be pointed at the module when it is same type. Make sure to orientate By changing which of Arduino used at or approaching its maximum them correctly, with the tabs align- pins D3-D6 are high or low, the load power rating. ing to the silkscreen markings. You presented can be varied between the can also refer to the photos and Fig.2 value of 1-15 parallel 47W resistances, The Load is built on a double-sided to confirm the mounting arrangement or even disconnected completely. The PCB coded 04105221 that measures 89 for these Mosfets. Arduino monitors the voltage and cur- x 54mm, and Fig.2 shows where all the rent and reports them along with cal- components go. The Mosfets are mounted freestand- culated power dissipation. ing and vertically. They do not drop Start by fitting the small compo- much voltage when on and do not han- Depending on its programmed nents. IC1 is an SMD part in a SOIC-8 dle much current relative to their rat- mode, the Load can provide a fixed package and is best soldered with ings, so they do not need heatsinking. resistance or attempt to emulate con- the aid of flux paste and tweezers, stant current, or even a changing load although you might get by without Prepare the 5W ceramic resistors by to check the response of the supply. them. bending one lead 180° down one side so that they can be slotted vertically Arduino board selection Apply flux to the pads and tack one onto the PCB. Bending the lead down lead in place with a clean iron tip, the side opposite the markings gives We’ve specified an Arduino Uno ensuring pin 1 is aligned with the dot the neatest result. in the parts list, but any 5V Arduino on the PCB. If the part is still correctly board, including other AVR-based aligned, solder the remaining pins; When fitting the 5W resistors, it will R3 shield-compatible boards like the Leonardo or Mega, should work fine. We suggest that the Load is used The sample code doesn’t use any without a case, although you pin-specific peripherals, so it isn’t tied should ideally add some tapped to a particular board. But 5V digital I/O spacers to stand it off your work levels are necessary to ensure that the surface. There isn’t any point in Mosfets turn on fully. using stackable headers, as there is no room If you really want to use a 3.3V for a shield above, board, you could do so with some and it would limit changes, but note that many are not convection cooling of compatible with the R3 shield form the resistors. factor (they typically use the MKR form factor instead). One exception is Australia's electronics magazine siliconchip.com.au the Due. We have not tested the design with a 3.3V Arduino board, but we believe it will work with the follow- ing changes. Firstly, ensure you use the 50 Silicon Chip Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
also help to stand them slightly above Parts List – Arduino Programmable Load the PCB to allow more room for air to circulate; you can see this in our pho- tos. We’ve made a 3mm gap, although 1 double-sided PCB coded 04105221, 89 x 54mm the length of their leads might limit 1 5V Arduino-compatible board (eg, Uno, Leonardo or Mega) you in this. 1 10-way 2.54mm-pitch pin header 2 8-way 2.54mm-pitch pin headers Start with the resistors near the cen- 1 6-way 2.54mm-pitch pin header tre of the PCB and work outwards, try- 1 2-way 5/5.08mm pitch screw terminal block (CON1) ing to keep the tops level for unifor- mity and square up the parts within Semiconductors their pads. Note that some parts are 1 INA282 current shunt monitor, SOIC-8 (IC1) not on the ‘grid’ to provide clearance 4 CSD18534KCS, IPP80N06S4L-07 or similar N-channel logic-level Mosfets, from the DC socket and USB socket. TO-220 (Q1-Q4) [2 x Cat SC4177 or 4 x Cat SC6184] Trim the leads neatly and flush Capacitors against the rear of the PCB. 3 100nF MKT capacitors The only remaining parts are the Resistors (all 1% 1/4W axial unless otherwise stated) pin headers. First, plug them into the 1 33kW Arduino board so that they are cor- 6 10kW rectly aligned, then slot the shield 4 470W on top. 1 15mW 1-3W M6332/2512-size SMD Before soldering them, check for any [Cat SC3943] conflicts below. The in-circuit serial 15 47W 5W 10% wirewound programming (ICSP) headers on the Uno board are exposed high points and are the most likely to foul any pins Q1-Q4 could be just about any logic-level (ie, suitable for 5V drive) N-channel on the Load PCB that are not trimmed Mosfets in TO-220 packages with sufficient voltage and current ratings. short enough. Also ensure that the PCB is down firmly against the pin headers, and select your board (eg Uno, Leon- The positive multimeter lead should then solder them together from above. ardo or Mega) and serial port from the connect to the ‘+’ terminal and the neg- Tools menu. Upload the sketch and ative to ‘-’. Note that if a reverse current Programming it then open the Serial Monitor from is applied, it will be conducted by the Our fundamental control sketch the Tools menu. Set the baud rate to Mosfet body diodes (and thus all the (program) for the Load is controlled 115200. resistors) and will appear as a 3W load. through the Arduino Serial Monitor You should start to see an output There are three modes that our soft- for simplicity. The voltage, current similar to Screen 1, with updates ware can operate in. The first is man- and power are also reported this way. occurring several times per second. ual mode, selected by typing the letter Screen 1 shows a typical display on the Note that the measured voltage is ‘m’ into the Serial Monitor, followed Arduino Serial Monitor during use. across the Load itself, so the power by a number from 0 to 15. This is sim- If you don’t have the Arduino IDE shown is what is being dissipated in ply the number of resistors that will be (integrated development environ- the Load. paralleled and presented as the load. ment), start by downloading it from So for “1”, Q1 is switched on, while siliconchip.com.au/link/aatq and then Testing and usage “2” means that Q2 is on, “3” results install it. A good way to test the Load is to con- in both Q1 and Q2 being on etc. This Now open the sketch file (download nect a multimeter to CON1 to measure continues up to “15”, when all the from siliconchip.com.au/Shop/6/6330) the resistance between its terminals. Mosfets are switched on. For example, typing “m1” and press- ing Enter (ensuring the ‘CR’ line end- Fig.2: the board is ing is selected) will cause a 47W load easy to assemble, to be presented on CON1. Entering but it’s best to “m2” will choose a 23.5W load. You take some care can check these with your multime- to line up the 5W ter, although you might see slightly resistors neatly or it will look messy. higher values than expected due to Watch out for the orientation of lead resistance. the Mosfets and At any time, the “m0” command IC1. Also, check the underside of will disconnect all resistors, so that’s the PCB when a good one to remember if something it is fitted to the goes wrong. Arduino board to The second mode is where a resis- tance is entered using the “r” com- mand. The software finds the nearest ensure that none of possible resistance value to the entered the shield component leads short against anything on the Arduino. The 15mW shunt can be fitted as an SMD or through-hole resistor. value. Of course, there are only 15 siliconchip.com.au Australia's electronics magazine June 2022 51 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
discrete steps, so it will hardly ever be Screen 1: the Serial Monitor (or another serial terminal program of your choice) exact. But it is a good way to approxi- is used to control the unit and show its status. It has current, voltage and power mate resistive loads of a known value. read-outs, and the applied load is displayed as both ohms and the number of 47W units. In the ‘constant current’ mode used here, the load resistance is The emulated constant-current controlled to keep the current near a setpoint. mode is started with the “i” command, and it attempts to match the measured inserted in series, they should be con- can offer, so stay tuned for that in the current to the setpoint by ramping up nected between the PSU “+” and Load near future. and down the number of unit loads. “+” to ensure that the Load “-” stays at ground potential. Making modifications With the limited number of steps, it too can only approximate the set cur- The Load is well suited to testing The software is written with most rent, and will not respond to rapidly solar panels, with the proviso that parameters set by #define statements changing conditions. In practically all the Mosfet drain-source voltage is near the start. cases, it will jump between two adja- respected, especially under open- If you wish to modify the load resis- cent load levels, and the current will circuit conditions when panels pro- tors, all must remain the same resis- zigzag around the setpoint. Screen 1 duce their highest voltages. This limits tance (unless you make significant shows this, with the Load switching it primarily to solar panels with a nom- changes to the software). The unit between 3 & 4 resistors to maintain a inal 24V output; these can produce up load resistance is specified by the R_ current near 70mA. This was set using to 44V under open-circuit conditions. CONST value. the “i0.07” command. A higher test voltage might require A manual scan of the sixteen differ- a different divider to change the range If the voltage rises above 15V or the ent load levels will create sixteen data (although you will need to check that power goes over 70W for an extended points that can be plotted on an I/V or the Mosfets can also handle a higher period, shut the Load down with the P/V curve. But note that we are also voltage). A different divider will mean “m0” command to avoid damage to designing a Solar Panel Tester which that the V_CONST multiplier will the resistors. There should not be any will have more features than the Load need to change. damage to the Mosfets as long as the voltage stays below the Mosfets’ rated To calculate the new value for V_ drain-source voltage, which is 60V for CONST, work out what applied volt- the recommended types. age will deliver 5V to the A0 pin of the Arduino, then divide that higher Remember that the displayed volt- voltage by 1024. The default value of age cannot go above 21.5V, so it might 0.0209961 is simply 21.5V divided be much higher than shown if it is by 1024. above 20V. We have used (as much as possible) PWM-capable pins so that it is possi- More usage tips ble to emulate intermediate resistance values by applying PWM signals to the Connect the Arduino Programmable Mosfets. We have not tried this tech- Load’s negative terminal to your cir- nique, but you could experiment with cuit ground (remember that it is also it if you need finer resistance controls commoned with the computer con- than the discrete steps presented here. trolling it) and the “+” terminal to a Note that this will present a pulsed positive output. load to the current/voltage source, and depending on what it is, it might react For example, a power supply should in an unexpected manner. simply be connected “+” to “+” and SC “-” to “-”. If other loads need to be Australia's electronics magazine siliconchip.com.au 52 Silicon Chip Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
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500 POWER WATTS AMPLIFIER PART 3 BY JOHN CLARKE To finish our new 500W Amplifier, we shall now describe the power supply configuration and the complete assembly details. That includes mounting all the modules and parts in the enclosure, wiring it up, checking that it works and making the calibration adjustments. T he 500W Amplifier module The transformer has two indepen- Considerable capacitance is used we’ve described over the last dent 115V primary windings and two to filter the DC supply, with four two issues cannot operate independent 55V secondary windings. 10,000uF 100V capacitors filtering the alone. It needs a power supply and The two 115V windings are connected positive supply and another four for added circuitry to protect the loud- in series so it can be powered from the negative supply. This is to remove speaker and keep it cool. the nominally 230V AC mains. Simi- much of the ripple from the DC sup- larly, the two 55V windings are con- ply rails, especially when under load, We are using two projects for these nected in series with a centre tap so as the Amplifier can draw many amps tasks: the Amplifier Clipping Indica- that after rectification and filtering, we when delivering the peak power it is tor (March 2022; siliconchip.com.au/ get approximately ±80V DC. capable of. Article/15240) and the Fan Control- ler & Loudspeaker Protector (Febru- Danger: High Voltage ary 2022; siliconchip.com.au/Article/ 15195). The 160V DC supply across the filter capacitor bank and the amplifier supply rails is potentially lethal! After the power sup- The final circuitry to be described ply wiring is complete and before you apply power, mount is the Amplifier’s power supply, and a clear Persp ex sheet over the capacitor bank to protect its circuit is shown in Fig.9. As you against inadvertent contact – now or in the future! Note would expect for this Amplifier, the that the capacitors take some time to discharge after power supply uses a large transformer, the power is switched off. rated at 800VA. siliconchip.com.au Australia's electronics magazine June 2022 61 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Fig.9: the only remarkable aspect of the power supply circuit is the large 800VA transformer and relatively high ±80V supply rails. Several 15kW discharge resistors are needed due to the high total capacitance. Three 15kW 1W resistors are con- The transformer is a toroidal type, the amplifier heatsink to be mounted nected in parallel from both supply and a slow-blow fuse is required to inside the enclosure with three cooling rails to ground, to discharge the capac- prevent it from blowing when power fans that draw air in from one side of itors when the amp is switched off. is initially applied, as the inrush cur- the lid and pass this air across the heat- LEDs are included in series with one rent can be very high. For this trans- sink fins. That forces airflow upwards, resistor on each side of the supply, as former, a 3.15A M205 slow-blow fuse to remove heat from the heatsink. voltage presence indicators. is specified. It is installed within the IEC power connector housing. This The fans are taller than the heatsink, They ensure that the capacitors do has a safety fuse enclosure, where the so any air coming up past the fins is not remain charged to high voltages for fuse cannot be accessed until the IEC blown sideways and then out through too long after the power is switched off. power lead is unplugged. the vented lid on the other side. This is for safety reasons since the total of around 160V DC is an electrocution The power supply is installed and There are quite a few holes that risk. Additionally, a plastic cover over wired up within a 3U rack case that need to be drilled for all the mount- the capacitors (removed in some pho- houses the Amplifier Module, heatsink ing hardware, various cutouts made tos for clarity) prevents accidental con- fans, the Amplifier Clipping Detector, for the power switch, XLR and IEC tact with the high-voltage wiring and Loudspeaker Protector & Fan Speed sockets, the loudspeaker terminals and capacitor terminals. Controller and other necessary com- clipping indicator LED. The locations ponents. for these are shown in Fig.10, and the The bridge rectifier is rated at 35A close-up detail drawings in Figs.11-13. 400V. This rating is sufficient to handle Enclosure layout the initial surge current that charges Begin with the front and rear panels. the capacitors at power-up, and the The internal layout for the Ampli- Some of the required cutouts are not repetitive capacitor charging cur- fier and associated parts is shown in circular; you can cut these by drilling a rent peaks that occur near the peak Fig.10. The Amplifier is built into a series of small holes around the inside of the rectified waveform each mains 3U rack case with a solid baseplate of the required perimeter, knocking out half-cycle. and vented top lid. This layout allows the piece of metal and filing to shape. Note that you could dispense with At left is a close-up of the power supply section of the Amplifier, with the rest of it, transformer and all, shown adjacent. 62 Silicon Chip Australia's electronics magazine siliconchip.com.au Downloaded by Mike Blake (#19283) Copyright © 2022 SILICON CHIP Publications.
IEC CONNECTOR REAR PANEL LOUDSPEAKER XLR INPUT Please note that WITH FUSE (inside view) TERMINALS SOCKET inductor L1 is + wound using 13.5 turns of 1.25mm N E INSULATION diameter wire, A BOOT not 30.5 turns or 1mm diameter Earth as stated in two places on p64 & THIS SECTION SHOWN ENLARGED IN FIG.13 Piezo p65 last month. Transducer Around 900mm of wire will be Earth Cooling Fan and Loudspeaker Clipping Indicator Protector Controller consumed. To FAN3 SILICON CHIP Cooling Fan and Loudspeaker Protector Controller 01111211 SILICON CHIP Indicator THIS * REV.C C 2021 4004 Clip SECTION 4.7V SHOWN To FAN2 4 ENLARGED To FAN1 3 NC 4148 IN FIG.11 2 NO 1 COM Fig.10: here’s an coil overview of the 5819 4004 chassis layout and RLY1 wiring; more details A 4 4.7V 4148 are shown in the 3 15V close-up drawings * 2 4148 of Figs.11-13. 1 Use this diagram to arrange the 3.9V 4.7V REV.B components in the C 2021 chassis and to get 5819 01112211 an idea of where the wires and cables 4 15V run, then use the 3+ following figures to determine where 4004 exactly each wire 2+ connects. Note: the wiring 1 between the fans and thermistors 5819 TH1 & TH2 (mounted to the + heatsink), the Cooling Fan TP1 TP2 TP3 A Controller module and fan wiring has To To been omitted for TH1 TH2 clarity. The corner instrument feet 0.47W 5W + mounting holes are 0.47W 5W also not shown. CON2 June 2022 63 FAN 1 0.47W 5W 12V SUPPLY 0.47W 5W * 0.47W 5W * A N E 0V12V 3.3kW A 0.47W 5W ++FAN 2WARNING! HIGH VOLTAGES PRESENT ++ 4148 ~ 4148 + ~ THIS SECTION SHOWN ENLARGED IN FIG.12 Earth 0.47W 5W + ALUMINIUM 0.47W 5W + ANGLE 0.47W 5W CON1 Insulation 0.47W 5W Board 0.47W 5W RCA PLUG: 0.47W 5W RED TO CENTRE, Transformer BLUE TO BODY. T1 M8 nut BASE PLATE 500W AMPLIFIER REV.B Mounting FAN 3 C 2021 Plate 01107021 FRONT PANEL (inside view) CLIPPING LED Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
All of the various modules are attached to the case by mounting screws. The wiring between these modules are also cable tied to the case. It’s a good idea to be generous with cable ties as it keeps everything secure and neat. Note that the XLR input socket has a 560nF capacitor soldered to it as shown above. the XLR input socket and just use an panel for the power switch and clip- terminals and 162 x 162mm for the insulated panel-mount single RCA ping indicator LED bezel similarly. transformer. socket. This depends on your intended You can make a copy of the front panel application; XLR would be better label (Fig.14) and use that as a tem- An 8mm hole is needed in the centre suited for PA use, while RCA might plate for positioning those two holes. of the transformer insulator. That can be fine for home use. If using an RCA be made using a wad punch (giving a socket, a single-core shielded cable is Next, prepare the insulating mate- cleanly cut hole) or an 8mm drill, after all that’s needed to connect internally rial sections to go under the trans- which you can clean up the resulting to the Amplifier Module input. former, the 3-way mains terminal strip furry edges with a hobby knife. and the 12V switchmode supply. The We specify an insulated RCA socket insulation for the transformer prevents 3mm holes are also needed in the because the connections need to be voltage flash-over to the Earthed chas- other insulation pieces for the mount- isolated from the chassis. Otherwise, sis should there be an insulation break- ing holes of the 3-way terminals and a hum loop will be caused by Earth- down. The other insulators prevent a those on the underside of the 12V ing the signal ground to the chassis in live wire from contacting the chassis if supply. Again, a small wad punch is two places, since it is already Earthed it disconnects from its terminal. ideal for making these holes. A 3mm by the Amplifier Module. drill can be used instead, although the Cut the required insulation pieces resulting holes will not be clean. If using the XLR socket, the main from the 208 x 225mm sheet with scis- XLR cutout can be made using a 22mm sors or a sharp knife and ruler. The Arranging the parts Speedbor drill and then filing the hole sizes required are 63 x 97mm for the shape. Now make holes in the front 12V supply, 57 x 45mm for the 3-way At this point, it’s a good idea to place all the major components in the Equipment feet four M3 x 10mm machine screws, four Bridge rectifier one M4 x 20mm machine screw, one hex nuts M4 hex nut Amplifier PCB six M3 x 5mm machine screws, three Earth three M4 x 15mm machine screws, mounting 9mm M3-tapped Nylon standoffs connections three 4mm star washers, four M4 hex nuts, 3 5.3mm diameter crimp eyelets Heatsink four M3 x 10mm machine screws mounting Transformer one M8 x 75mm bolt, M8 washer, M8 mounting hex nut Table 1: Screw & nut usage Speaker eight M3 x 5mm machine screws, four Protector PCB 9mm M3-tapped standoffs Aluminium angle two M4 x 10mm machine screws, two Clipping eight M3 x 5mm machine screws, four mounting M4 hex nuts Indicator PCB 9mm M3-tapped standoffs Relay two M3 x 10mm machine screws, two 12V switchmode M3 hex nuts supply two M3 x 6mm machine screws two M3 x 12mm countersunk head 20 M4 x 10mm machine screws, IEC connector machine screws, two M3 hex nuts 32 M4 hex nuts, eight M4 x 50mm Capacitor machine screws, four M4-tapped XLR connector two M3 x 12mm countersunk head mounting joiners (for mounting protective cover) machine screws, two M3 hex nuts 3-way mains two M3 x 15mm machine screws, two two No.4 x 6mm self-tapping screws terminal block M3 hex nuts Piezo transducer or two M2 x 6mm machine screws and two M2 hex nuts 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Fig.11: a close-up of the chassis’ right rear corner showing the wiring between the three main PCB modules, the speaker protection relay, the warning piezo, the loudspeaker terminals and the XLR input socket. chassis and make sure you’re com- The holes required in the alumin- bracket for mounting the fans near the fortable with all their positions. Mark ium baseplate include the mounts heatsink (4mm). It’s best to locate it them out with a fine felt-tip pen. That for the four corner equipment feet after the heatsink has been mounted. way, you can be sure everything is (3mm), the three PCBs (3mm), the The aluminium bracket itself will positioned correctly before you start heatsink (3mm), the relay (3mm) and also need holes to attach the fans that making holes. piezo transducer (2.5mm), the Earth are spaced evenly along the 400mm lug holes (4mm), capacitor mounting length, with one fan in the centre and When initially laying out the parts holes (4mm), the 12V supply (3mm), the others at each end. in the baseplate, be sure to allow room the three-way mains terminals (3mm), for the equipment feet to be secured in the bridge rectifier (4mm) and trans- The angle piece is secured to the the corners with M3 screws and nuts. former (8mm). Refer to Figs.10-13 to base by two 4mm screws in the gaps In particular, check that the trans- see the locations. between the fans. We made a small former can be positioned without the semicircular cutout for each fan to pre- screw and nut for the equipment foot You’ll also need to make holes vent the lower portion of the bracket in that corner interfering. to hold the aluminium right-angle from covering the fan blade area. But siliconchip.com.au Australia's electronics magazine June 2022 65 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Fig.12: a close-up of the chassis’ that is not strictly necessary; it’s just left front corner showing the nice to have. wiring of the toroidal transformer, bridge rectifier, mains terminal While there needn’t be any particu- block and front panel. lar order to install the parts within the case, it is easier to mount the lighter 66 Silicon Chip Australia's electronics magazine ones first. The transformer is the heavi- est part, so attach it last. There is a list Copyright © 2022 SILICON CHIP Publications. of the screws and nuts in Table 1 to help you select the correct hardware for each job. Install the IEC socket, the speaker terminals and the XLR socket on the rear panel. Then mount the switch and clipping indicator LED bezel on the front panel. However, leave these panels detached from the enclosure until the rest of the wiring is complete. Now is a good time to mount the thermistors for the Cooling Fan Con- troller. These are mounted against the amplifier heatsinks behind the Q25 and Q26 transistor clamp screws. The wires from the thermistors will need extending with an approxi- mately 350mm length of light-gauge figure-eight wire; insulate the joints with heatshrink tubing. Next, mount the three PCBs in the chassis on 9mm Nylon standoffs using M3 x 5mm screws. The Ampli- fier Module’s primary mounting is via the screws into the heatsink. The Amp Module has three PCB mount- ing locations at the edge away from the heatsink that attach using spacers and short machine screws, but these should be installed last to avoid stress- ing the PCBs. Before mounting the capacitors, cut out the capacitor plastic covering piece measuring 295 x 125mm, place this on the base plate and mark out the four 4mm mounting holes. These coincide with the capacitor mounting clamp screws marked with asterisks in Fig.10 & Fig.13. Now mount the capacitors. These must be orientated with the correct polarity. The negative side is marked with a minus symbol down one side of the capacitor body. When orientated correctly, tighten down the clamps to prevent them from rotating. Note that the four capacitor bracket mounting locations marked with aster- isks are secured using 50mm-long screws and nuts. Once all the capaci- tors are mounted, place M4 joiners on the end of these four 50mm screws, ready to attach the capacitor cover- ing piece using four more M4 x 50mm screws. Now mount the 12V switchmode siliconchip.com.au Downloaded by Mike Blake (#19283)
supply with the insulation board Australia's electronics magazine Fig.13: a close-up of the chassis’ beneath it, and the three-way mains left rear corner showing the terminal block, also with the insula- wiring of the capacitor bank, 12V tion underneath. switchmode supply, mains IEC input socket and the Earthing. Next, attach the fans to the alumin- ium bracket using the securing screws June 2022 67 supplied with each fan, then mount Downloaded by Mike Blake (#19283) the bracket and fan assembly to the baseplate. To improve heat transfer, when attaching the bridge rectifier to the base, smear a little heatsink compound on the mating surface and the chassis. Transformer mounting Place a washer onto the M8 bolt for the transformer and insert it from the underside of the baseplate. Place the insulation square onto the base- plate over the screw, then add a Neo- prene washer on top of this, followed by the transformer, the second Neo- prene washer, the mounting disc and then the M8 nut. Orientate the trans- former as shown in Figs.10 & 12 and tighten the nut. Wiring it up Most of the work left involves the heavy-duty power supply wiring. Wire the two banks of four capaci- tors in parallel using strands of 0.5mm diameter copper wire. We twisted two strands together using a drill and then bent this in half, interweaving the wire around the capacitor terminals as shown in the photos. Solder the wires securely to the terminals. Both sides of the filter capacitor bank have two 15kW 1W bleed resis- tors connected across them. Also, a red LED is connected across each side of the capacitor bank in series with another two 15kW resistors. The LEDs are positioned to protrude through 5mm holes in the capacitor cover plate. If your cover plate is made from clear or translucent plastic, you could skip making those holes. These LEDs indicate when voltage is present across the capacitors. As you will find, even with these bleed resistors, it takes quite a while for the capacitors to discharge after the Amplifier is switched off. The whole Amplifier uses single- point Earthing, so it is important to follow the wiring details in Figs.10- 13 closely. Mains wiring The mains supply is via the IEC power socket, then a length of siliconchip.com.au Copyright © 2022 SILICON CHIP Publications.
For safety, the capacitor bank needs a sheet of Perspex mounted on top of it to Earth connection to the chassis using prevent accidental contact. This photo shows the capacitors without the cover, an eyelet secured to the baseplate with to clearly present how they are arranged. an M4 screw, star washer and nut. twin-core mains flex rated at 7.5A or The mains wires from the IEC Transformer wiring more. This wire needs to pass through socket connect to the power switch the IEC insulation boot before being using crimp spade connectors on the We’ve shown the transformer wir- terminated (soldered) to the IEC socket top two terminals. It is important to ing using the colour coding of the rec- terminals. wire this switch the right way around; ommended transformer. But check on otherwise, the neon LED will be lit, the transformer label that your wind- The Earth wire also passes through regardless of whether the Amplifier ing colours are the same as we used; if the insulation boot and is secured to is on or off. not, wire it up according to the colours the Earth terminal on the IEC socket, for your transformer. and to the chassis using a crimp eyelet We placed unused insulated crimp secured with an M4 screw, star washer spade connectors on the lower two Connect the two 115V primary and nut. Note that this Earth contin- switch terminals just for safety. The windings in series by joining the pur- ues to also connect to the baseplate via mains wires from the power switch ple and grey wires using the centre another eyelet. at the centre terminals run to an insu- terminal of the 3-way terminal block. lated three-way terminal block. Fur- Tie the mains wires with a cable ther mains wiring connects to the 12V Run the wiring to the filter capaci- tie before placing the insulating boot switchmode supply. The mains wires tors from the bridge rectifier using the cover over the rear of the IEC socket. must all be cable tied together so that 2.9mm2 (cross-sectional area) wire A third eyelet and Earth wire con- if one comes loose, it will not cause with red for positive and black for nects from the baseplate Earth point a safety issue by shorting to chassis. negative. You will find that the yel- to the star Earth between the capac- low and black transformer wires are itor banks. Note that the 12V supply also has an not long enough to reach the star Earth point, so extend them using one of the 2.93mm2 figure-8 cables. The power supply wiring is basi- cally complete at this stage, but it is not connected to the Amplifier Mod- ule. Check for continuity between the chassis and the Earth connection on the IEC connector. You should get a reading very close to 0W. Next, install the 3.15A slow-blow fuse into the IEC socket. Check your work to ensure every- thing is connected correctly. Be sure that the capacitors are all orientated correctly. Check that the positive ter- minal on the bridge rectifier connects to the positive side of the capacitor bank, and that the negative terminal of the bridge rectifier connects to the negative side of the capacitor bank. The 120mm PWM fans for the 500W Australia's electronics magazine siliconchip.com.au Amplifier are attached via a metal Downloaded by Mike Blake (#19283) bracket on the base of the case. These types of fans are quite common in computers, and be purchased at a low cost. Smaller fans (eg, 80mm) could be used, but they will probably be louder and, due to how common 120mm fans are, likely more expensive too. 68 Silicon Chip Copyright © 2022 SILICON CHIP Publications.
It’s important to check the winding colours for the transformer, as your transformer might not match the colours we’ve used here. Safety precautions overheats and vents to the atmosphere. If all is OK, remove the capacitor Before powering it up for the first safety shield and, taking great care (as After the power supply wiring is the capacitor voltages are dangerous), complete and before you apply power, time, wear safety glasses or a face switch on power again and measure we suggest that you mount the cover shield. Briefly apply power and check the capacitor voltages. The readings sheet over the bank of capacitors. This that both LEDs light. Then switch off you get should be close to ±80V DC. will prevent accidental contact with the power and allow the capacitors to Check also that the 12V supply pro- the 160V DC supply. The total DC sup- discharge completely. It should take vides 12V DC at its output terminals. ply is potentially lethal. a while for the LEDs to stop glowing, Switch off the power, and again, wait and they should go out at around the for the voltage to drop to near zero. The cover will also provide a degree same time. of safety if one of the capacitors Now you can complete the remain- Australia's electronics magazine ing wiring. Run the wiring from the siliconchip.com.au filter capacitors to the Amplifier using the 2.9mm2 wire, with red for posi- tive, black for negative and one of the 2.93mm2 figure-8 wires for the 0V connection. Similarly, use 2.9mm2 or 2.5mm2 wire for the loudspeaker output wiring to the speaker terminals via the relay. The remaining wiring can be com- pleted using lighter-duty wire. Follow the wiring diagram carefully to com- plete it. Use cable ties and the chassis mount ties to bundle the wires together where needed. We don’t show all the cable ties on the diagram; be gener- ous and use them wherever required. Connect the XLR input socket to the amplifier module via dual-core June 2022 69 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
The completed Amplifier with its vented lid attached. The functions of the three connections on the rear of the case can be made more obvious by printing out small labels. microphone shielded cable as per wiring against the circuits and dia- one of the 56W 1W resistor ends closest Fig.15. If using an RCA input socket grams in this series of articles. Then to the edge of the amplifier PCB. There instead, use single-core shielded cable. reattach the capacitor safety shield. should be less than ±20mV DC at the output. You can adjust this using VR1, The enclosure can now be assem- Remove fuses F1 and F2 on the to get a reading close to 0V. bled by attaching the side panels, rear amplifier module and replace these and front panels to the baseplate. with blown fuses with 390W 5W resis- Now connect your multimeter tors soldered across the fuse ends. across the 390W 5W resistor across fuse Final checks and adjustments Ensure that trimpot VR2 is rotated F1, and adjust trimpot VR2 clockwise fully anti-clockwise. to obtain 30V. This provides a total You are now ready to power up the quiescent current of 77mA or about amplifier module and make voltage Apply power and measure the volt- 13mA per output transistor. checks. First, double-check all your age on the amplifier speaker output, at Fig.14: the front panel label (shown at 85% actual size) can be used as a template to drill the holes for the power switch and the clipping indicator LED. You can also print a copy on overhead transparency film or photo paper (laminated after printing) and affix it to the front of the Amplifier. This label only covers the left-hand half of the panel, as it would be too wide to easily print otherwise. 70 Silicon Chip Australia's electronics magazine siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
The 500W Amplifier chassis as presented is designed to operate with a reasonable amount of free air above the case, as the fans draw in cool air and exhaust hot air through the substantial vent area in the lid. If it is installed in a constricted space, such as an equipment rack or cabinet without much space above the lid, modifications need to be made, especially if it’s run flat-out. Airflow in a rack can be increased by expanding the small holes on either side of the case in front of and behind the fans. Internal ducting may also be required to prevent hot air recirculation. Now measure the voltage across each. If not correct, verify that the other 390W 5W resistor in place they are the right transistor types. of fuse F2. It should be within 10% Additionally, the voltages across of the reading across F1. the 68W emitter resistors for Q3 and Q4 should be about 50-60mV each, You now need to leave the Amplifier and both voltages should be the same ► running for at least an hour. This will allow it to warm up gradually. Measure provided VR1 is adjusted for mini- It’s a good idea to attach the front the voltage across the 390W resistors mum output offset. If these are not panel label (Fig.14) so everyone again and readjust VR2 to give 30V. correct, check the transistors for the knows what the behemoth is. If you correct type. don’t want to do that you can at least Troubleshooting If the correct transistors are in place, affix a small label near the Clipping but the voltages are incorrect, consider Indicator LED in the centre. If these voltages cannot be realised, replacing these transistors with repu- switch off the power and recheck your table brand-name devices. Fig.15: the wiring details for the XLR construction and wiring. You will Once the problems are found and socket. For home use, an RCA socket need to measure voltages around the fixed, you can adjust the quiescent could be fitted instead, in which Amplifier Module to see where there current again for 30V across the 390W case you could even use a panel- could be a problem. To do this, first resistors. mount female-female RCA socket. A reduce the quiescent current by turn- Once it all checks out, power it standard RCA cable can then connect ing VR2 anti-clockwise so that there is down, wait for the capacitor banks to from the inside of this socket to the minimal voltage across the 390W resis- fully discharge, then remove the fuses Amplifier Module input, avoiding tors that are across each fuse holder. with the 390W resistors attached and soldering. install the correct ceramic fuses; 5A First, check for +80V, 0V and -80V for use with 8W speakers or 10A for June 2022 71 at the Amplifier Module supply ter- 6W or 4W speakers. minals. Check the voltages across the Finally, follow the instructions for 470W resistor at Q5’s emitter and the setting up the Fan Controller & Loud- 39W resistor at Q7’s emitter. If these speaker Protector in the February aren’t between 0.6 and 0.8V, check 2022 issue. transistors Q5 and Q6 for about 0.6- SC 0.7V between the base and emitter of Australia's electronics magazine siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Using Cheap Asian Electronic Modules By Jim Rowe MOS metal oxide semiconductor Air Quality Sensors Our recent article took a look at low-cost air quality sensors and sensing modules, explaining what they do and how they work. Here’s a more detailed investigation of some of the currently available MOS (metal oxide semiconductor) type sensor modules. MOS type air quality sensors the oxide layer is reduced. low-cost MOS sensors currently avail- (sometimes called MOx sensors) So the current passed by the oxide able is the Hanwei MQ-135, which is rely on the behaviour of particles of a designed to be sensitive to ammonia metal oxide (usually tin oxide) when layer varies proportionally with the (NH3), nitrous oxides (NOx), carbon heated in the presence of air and/ amount of reducing gas in the air sur- dioxide (CO2), alcohol, benzene and or other gases. The basic principle rounding the oxide layer. The higher smoke. Like the other sensors in the is shown in Fig.1, which depicts a the reducing gas level, the higher the Hanwei series, the MQ-135 sensor cross-section of a typical MOS sensor. current. Therefore, the basic MOS sen- comes in a cylindrical 6-pin package sor essentially behaves as a reducing 19mm in diameter and 15mm high. The silicon substrate of the sensing gas to DC analog current transducer. chip has a thin layer of tin oxide on the Most modules using the MQ-135 top, placed there by chemical vapour We already mentioned several of simply take the current output from deposition. Electrodes at each end these modules in the article last month the sensor and convert it to a propor- allow its resistance to be measured. On (siliconchip.au/Article/15309) along tional voltage using a fixed load resis- the underside of the chip is a heater with some basic specifications. But tor. The output voltage can then be element, used to heat the oxide layer we did not go into detail regarding measured using a DMM, or fed into to around 200-250°C, to speed up the how they work and how to use them. one of the ADC inputs of a microcon- sensor’s response. troller unit (MCU). The Hanwei MQ-135 When the oxide layer is heated in Fig.2 shows the circuit of Hanwei’s the presence of clean air, donor elec- Probably the most common of the Fig.1: shows the trons in the oxide attract oxygen mol- cross-section of a ecules from the air, and they are ‘cap- MOS (metal oxide tured’ by the oxide particles. As a semiconductor) result, a depletion layer forms on the sensor and how it surface of the oxide layer, and its elec- works. trical resistance rises. But if reducing gases such as car- bon monoxide (CO) and some volatile organic chemicals (VOCs) are present in the air, oxygen molecules in the surface of the oxide are released, and the depletion layer becomes thinner. As a result, the effective resistance of 72 Silicon Chip Australia's electronics magazine siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
own air sensor module using the Fig.2: the circuit of Hanwei’s sketch using no libraries, but just MQ-135. The MQ-135’s heater pins (H) MQ-135 air sensor module. showing the current analog voltage are connected between the +5V (Vcc) provided at the module’s A0 pin (at line and the GND line via a 5.1W series The lead photo shows a group https://arduinolearning.com/amp/ current-limiting resistor. of MQ-model sensors. code). One end of the tin oxide sensing just need to connect the module’s Vcc I adapted this sketch slightly, and resistor (Rs) is connected to the +5V and GND pins to the corresponding its listing is replicated below along line via the two A pins, and the other pins on the Arduino, plus the mod- with some of the sample output from end goes to the GND line via the two B ule’s A0 pin to one of the Arduino’s when this sketch is running. When I pins and a 1kW load resistor. The two ADC input pins; in this case, we’re breathed on the MQ-135, that caused B pins are also connected to the A0 using A2. the voltage reading to rise from under analog output pin, to allow the voltage 700 to about 728 before falling back across the load resistor to be sent to a There are quite a few Arduino librar- down again. DMM or an MCU’s ADC input. ies and sketches available to work with the MQ-135 module. You’ll find links As you can see, there’s no attempt The rest of the components are so to some of them in the list of links to convert the A0 voltage readings to that the module can also be used as a at the end of this article. However, equivalent gas levels – for that, you simple gas level alarm. One half of the I found many of them a bit tricky to would need one of the fancier sketches LM393 dual comparator (IC1b) com- negotiate. relying on their dedicated libraries. pares the voltage across the 1kW load resistor with a reference voltage set But I did find some very helpful The SGX Sensortech using trimpot VR1, so whenever the information on Rob’s blog (at https:// MiCS-5524 A0 voltage rises slightly above the ref- blog.robberg.net/mq-135-arduino/). erence voltage, the output of IC1b (pin Then I came across an elementary Another MOS sensor found in low- 7) drops to near ground level, causing cost air/gas sensing modules is the the D0 LED to begin glowing. MiCS-5524, made by SGX Sensortech (an Amphenol company) in Switzer- The voltage level at the D0 output land. This is much smaller than the pin is pulled down simultaneously. MQ-135, coming in an SMD package measuring only 7 x 5 x 1.6mm. One change should ideally be made to the module if you want to use it The MiCS-5524 detects CO, etha- with an MCU for monitoring the gas nol, hydrogen, ammonia and meth- level, rather than simply using it as a ane. It is used in an 18 x 13mm gas gas level alarm. This involves replac- sensing module with the same name ing the sensor’s 1kW load resistor with available from various internet suppli- a 22kW resistor, to give a higher out- ers, including Banggood, which cur- put voltage swing and improve read- rently has it priced at US$11.00 with ing accuracy. free shipping (about $16). This resistor is an M2012/0805- Fig.3: the connection diagram for size (2.0 x 1.2mm) SMD component, the MQ-135 sensor module with an so you’ll need a fine-tipped soldering Arduino Uno or similar. iron and either a magnifying glass or a microscope. MQ-135 Sketch Program Fig.3 shows how to hook it up void setup() { to an Arduino Uno or a compatible Serial.begin(9600); MCU after making that change. You Serial.println(“Silicon siliconchip.com.au Chip’s MQ-135 demo!”); } void loop() { int reading = analogRead(A2); Serial.println(reading); delay(1000); } Sample Output Silicon Chip’s MQ-135 demo! 696 694 694 691 692 710 June 2022 73 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Fig.4: the circuit diagram for the MiCS-5524 module, which is simpler than the previous MQ-135 sensor and detects fewer gases. Next to the circuit are two different modules that use this chip. The circuit of the MiCS-5524 mod- arduinolearning.com/amp/code I couldn’t find any circuit diagram ule is shown in Fig.4. It’s basically just for the MiCS-VZ-89TE module, but its the sensor itself with an 82W current The SGX Sensortech layout is shown in Fig.6. limiting resistor for the sensor’s heater MiCS-VZ-89TE and a 91kW load resistor for its sens- I found it fairly easy to connect to ing resistor Rs, with a 100nF capacitor SGX Sensortech also makes a fan- this module by using two 5-pin sec- across the latter for noise reduction. cier and slightly larger module (23 tions of SIL header strip, with the top x 14mm) called the MiCS-VZ-89TE, of the second and fourth pins of each P-channel Mosfet Q1 is so that the available from suppliers like ele- strip cut short, allowing the tops of the power to the sensor can be controlled ment14 for $24.65, including GST remaining three pins to be soldered to using the module’s EN pin. This pin but not delivery. This module incor- the notches on one side of the mod- can be left floating if the module is to porates its own dedicated MCU with ule. You can then plug the complete operate continuously. ADCs (analog to digital converters) assembly into a small breadboard for and embedded conversion algo- testing and use. Fig.5 shows how easy it is to connect rithms. the MiCS-5524 module to an Arduino Fig.7 shows how the MiCS-VZ-89TE Uno, while the sketch is shown below As a result, this module can provide module can be connected to an Ardu- with the sample output. The sketch is both PWM and I2C digital outputs for ino Uno or equivalent MCU. The GND almost identical to the MQ-135 pro- CO2 equivalent and TVOC (isobuty- connection goes to one of the Ardu- gram and is similarly based on https:// lene equivalent). ino’s GND pins, while the module’s Fig.6: the layout diagram for the MiCS-VZ-89TE module, which is shown above. Fig.5: MiCS-5524 connection diagram. MiCS-5524 Sketch Fig.7: MiCS-VZ-89TE connection diagram to an Arduino Uno. void setup() { Serial.begin(9600); 74 Silicon Chip Serial.println(“Silicon Chip’s MiCs-5524 demo!”); } void loop() { int reading = analogRead(A0); Serial.println(reading); delay(1000); } Sample Output Silicon Chip’s MiCs-5524 demo! 40 39 40 39 Copyright © 2022 SILICON CHIP Publications. siliconchip.com.au Downloaded by Mike Blake (#19283)
3.3V power connection goes to the from about 414 ppm (parts per mil- Fig.9 shows the circuit for many of Arduino’s +3.3V pin. lion). these CCS811 sensor modules. Along with the CCS811 sensor itself, there’s The module’s I2C connections SDA Then I sprayed a tiny amount of voltage regulator REG1, which steps and SCL are wired to the Arduino’s isopropanol (spectacle cleaning fluid) down the incoming +5V power to pro- pins A4/SDA and A5/SCL, respec- a few centimetres above the sensor, vide the 3.3V needed by the CCS811, tively. Each of these pins needs an causing the VOC reading to jump up plus Mosfets Q1 and Q2 which, external 4.7kW pullup resistor con- to its maximum figure of 1000ppb. So together with four 10kW pullup resis- necting to the +3.3V pin, because the the MiCS-VZ-89TE and the sketch and tors, perform logic level conversion for MiCS-VZ-89TE module doesn’t pro- library certainly seem to be working! the I2C digital communication lines vide the pullups itself. (SDA and SCL). The ScioSense CCS811 I found an Arduino sketch and Diodes D1 and D2, together with the library to read the CO2 and VOC lev- Another MOS sensor found in sev- two 100kW pullup resistors, allow the els from a MiCS-VZ-89TE, written by eral low-cost air/gas sensing modules WAKE and RST pins of the CCS811 to H.Grabas and available on his website is the CCS811, made by ScioSense BV be pulled low. The WAKE pin must at https://github.com/HGrabas/MICS- in Eindhoven, The Netherlands. The be pulled to ground to allow the chip VZ-89TE CCS811 is in a tiny SMD package, mea- to operate. suring only 4 x 3 x 1.2mm. This sketch and its library worked Note that pin 1 of the CCS811 is so well that I adapted it to produce the Despite this tiny size, it incorpo- pulled low by a 100kW resistor to set sketch listed below along with a sam- rates both an ADC and a dedicated the I2C address to 90d/5Ah. Also, as ple of the output from the Arduino IDE MCU with built-in conversion algo- mentioned earlier, pins 4 and 5 are Serial Monitor. For this to work, you rithms, plus an I2C digital interface tied together and pulled high via two need to download Mr Grabas’ library to link directly to a PC or an MCU more 100kW resistors. from his website and install it as a like an Arduino or a Micromite. It’s library in the Arduino IDE. described by ScioSense as an “ultra- Incidentally, some CCS811-based low power digital gas sensor” and modules (such as the CJMCU-811) When running, it gives you a VOC detects a range of VOCs and provide have an additional pin on the I/O con- reading and a CO2 reading approx- both eTVOC (equivalent total VOC) nector, with the extra pin connected imately once per second. I eventu- and eCO2 (equivalent CO2) levels. to pin 1 of the CCS811 and labelled ally breathed on the module’s sensor, “ADD”. This allows the I2C address of causing the VOC readings to rise to Fig.8 is a block diagram of the the module to be changed to 91d/5Bh around 270.4ppb (parts per billion), CCS811. Pins 4 (PWM) and 5 (SENSE) by pulling the pin high. while the CO2 reading barely moved must be connected together for correct operation of the MOX sensor’s heater It’s quite easy to connect the SEN- MiCS-VZ-89TE Sketch: control circuit. Pin 1 (ADDR) is to CCS811 and most of the other CCS811- allow the CCS811’s I2C address to be based air quality modules to an MCU #include <MICS-VZ-89TE.h> set to either 90d/5Ah (ADDR pin low) like an Arduino Uno, as shown in #include <Wire.h> or 91d/5Bh (ADDR pin high), while Fig.10. The Vcc and GND pins con- the AUX pin (8) has no internal con- nect to the +5V and GND pins of the MICS_VZ_89TE voc; nection. Arduino, while the SDA pin goes to the Arduino’s A4/SDA pin and the void setup() { The CCS811 sensor is used in many SCL pin to the Arduino’s A5/SCL voc.begin(); air quality sensing modules, includ- pin. Finally, the module’s WAKE pin Serial.begin(9600); ing the Keyestudio KS0457 CO2 Air connects to another GND pin on the Serial.println(“Reading the Quality module, the Duinotech SEN- Arduino. CCS811 Air Quality Sensor module MiCS-VZ-89TE sensor”); (Jaycar Cat XC3782), the Adafruit Some modules have the pins in a dif- } CCS811 Air Quality Sensor and the ferent order, so make sure you check CJMCU-811 CO2, Temperature and the connections for the module you void loop() { Humidity Sensor from Banggood. are using. voc.readSensor(); Serial.print(“VOC =”); Australia's electronics magazine Fig.8: the block diagram Serial.print(voc.getVOC()); for the CCS811 module. Serial.print(“ | ”); One type of this module Serial.print(“CO2 = ”); is shown below, with a Serial.println(voc. larger variant shown getCO2()); overleaf. delay(1000); } June 2022 75 Sample Output Reading the MiCS-VZ-89TE sensor VOC = 0.00 | CO2 = 413.97 VOC = 135.37 | CO2 = 413.97 VOC = 270.74 | CO2 = 413.97 VOC = 1000.00 | CO2 = 420.96 siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Fig.9: the circuit diagram for the CCS811 module. Several Arduino libraries are avail- Overall, I prefer the ‘smarter’ mod- to any of the modules based on the able to support a sketch communi- ules like the SGX Sensortech MiCS- ScioSense CCS811 sensor, like the cating with these modules. I found VZ-89TE or most of those using the Duinotech SEN-CCS811 from Jaycar the easiest one to use was the Keye- CCS811 sensor. These modules are (Cat XC3782), the CJMCU-811 from studio KS0457 library (CCS811.h and all much easier to get going with an Banggood (ID 1157216), the Keyestu- CCS811.cpp), available from https:// MCU like an Arduino as a reliable dio KS0457 or the Adafruit CCS811 fs.keyestudio.com/KS0457 CO2/VOC sensor. (www.adafruit.com/product/3566). I will describe some of the NDIR and I also downloaded Keyestudio’s I would give first prize to the PAS type air quality sensor modules “readData.ino” sketch and adapted it MiCS-VZ-89TE module (element14 in a future article. to produce the sketch “read_CCS811_ 2925865). But second prize would go SC data.ino”, which you can download from the Silicon Chip website. It’s Sample Output Fig.10: CCS811 connection diagram. a bit too long to reproduce the list- siliconchip.com.au ing here. Getting data from the CCS811... Shown at right is the output of that sketch. The Arduino provides a stream eCO2: 400ppm, eTVOC: 0ppb of measurements for both the eCO2 eCO2: 410ppm, eTVOC: 1ppb level in ppm and eVOC in ppb. eCO2: 414ppm, eTVOC: 2ppb eCO2: 1743ppm, eTVOC: 384ppb At one point, I blew in the direction eCO2: 1345ppm, eTVOC: 143ppb of the CCS811 sensor to give it some eCO2: 977ppm, eTVOC: 87ppb extra CO2. That’s the reason for the sudden rise in eCO2 and eTVOC read- Useful Links ings, from around 400ppm and 1-2ppb MQ-135: up to peaks of 1743ppm and 384ppb • www.arduinolibraries.info/ a second later. Then the readings fell slowly after that. libraries/mq135 • https://github.com/ Summary Phoenix1747/MQ-135 After trying several of these mod- • siliconchip.com.au/link/abct ules, I’m less keen on those based on • https://blog.robberg.net/ the MQ-135 sensor than on the Sen- sortech MiCS sensors or the ScioSense mq-135-arduino CCS811 sensor. That’s mainly because MiCS-5524: of the scarcity of easy-to-u nderstand • www.sgxsensortech.com software if you want to do more than • siliconchip.com.au/link/abcu simply ‘raise the alarm’ if the CO2/ • https://github.com/HGrabas/ VOC level rises above a preset ‘safe’ level. MiCS-VZ-89TE CCS811: I’m also not that keen on modules • https://fs.keyestudio.com/ based on the SGX Sensortech MiCS- 5524 sensor for much the same reason. KS0457 • siliconchip.com.au/link/abcv 76 Silicon Chip Australia's electronics magazine Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
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Universal BatteryUPDATED Charge Controller We have made some changes to our Universal Battery Charge Controller published in December 2019 (siliconchip.au/Article/12159) so that it can be built using parts that are actually available. The changes are modest, and the total cost for parts has been reduced. By John Clarke Once upon a time, we at Silicon Chip semiconductor devices and ICs and and us. We put considerable effort lived in the land of plenty where dramatically increased the demand into maintaining parts supply for our electronic components were plenti- for electronics. This has impacted projects via our Online Shop. But once ful and readily available, blissfully the supply of motor vehicles, mobile they are sold, we may not be able to unaware of future events that would phones and many white goods such as replenish the supply straight away, alter our lives. But all that changed washing machines and refrigerators, especially if someone buys up all our when the COVID-19 pandemic sud- amongst other items, all of which now stock at once. denly disrupted many markets and depend on semiconductors. manufacturers. Turning to the Universal Battery The resulting lack of semiconductor Charge Controller, we used one Si8751 This affected the production of supply is also impacting our readers isolated Mosfet driver IC in the circuit. While it was available when the article Fig.1: construction is much the same as before, except you can skip soldering was first published, this is no longer the SMD IC (IC2) and a few associated capacitors. Instead, install the TO-92 the case, and we don’t expect these to transistor (Q4), two resistors and zener diode ZD3. These components are all in be available for at least another year, the upper right-hand corner. The rest of the PCB is identical to the original. if not longer. siliconchip.com.au Australia's electronics magazine So we have come up with a new cir- cuit that performs the function of the Si8751 in another way. Fortunately, the changes are straightforward. Our discrete Mosfet driver comprises small-signal NPN transistor Q4, a few resistors and zener diode ZD3. The N-channel Mosfet is replaced with a P-channel type. These changes are highlighted in a cyan box in the updated circuit dia- gram, Fig.2. The revised PCB, shown in Fig.1, is essentially identical to the original, except for the Mosfet and gate driver component changes. Also see the panel below outlining the changes in the parts required to build this project. These changes do not affect the operation of the Charge Controller as far as the user is concerned. Original design The original circuit using the Si8751 June 2022 81 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Fig.2: the only changes in this circuit from the original on page 27 of the December 2019 issue are in the box at upper right. All the components there have been replaced; the N-channel Mosfet is now a P-channel type. This simplifies the driving scheme greatly; it is now an NPN transistor with a few resistors and a zener diode to limit the drive voltage and current to safe levels. (IC2) would drive the N-channel Mos- Fast switching was not required in on top of the battery voltage. fet gate (Q1) positive whenever the this application, as we’re only switch- RB3 output of microcontroller IC1 was ing the Mosfet on and off once every Revised Mosfet driver high, switching Q1 on. This allowed two seconds. current to flow from the charger to the With the revised Mosfet driver cir- battery. When the RB3 output went The main reason for using this spe- cuit, the RB3 output signal from IC1 low, Q1’s gate voltage dropped to its cialised driver (IC2) was that, with Q1 still controls the Mosfet on and off source voltage, so the Mosfet was off, being an N-channel type and its source periods. The Mosfet is now a P-chan- and no current flowed to the battery. connected to the battery, it needed a nel type, so the higher voltage is gate voltage of around 20V to switch unnecessary. It is switched on by pull- The Mosfet switch on-time with on. This is not present anywhere in ing its gate voltage below the charger this arrangement was 5ms and the the circuit; it was generated by stack- output voltage, which connects to its switch-off time was typically 15μs. ing the isolated power output of IC2 source terminal. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Switching from an N-channel type Parts List – Updated Battery Charge Controller to a P-channel type means we have to swap the drain (D) and source (S) ter- 1 double-sided PCB, code 14107192, 111 x 81mm minal connections. That is so that the 1 diecast aluminium box, 119 x 94 x 34mm [Jaycar HB5067] parasitic internal diode is still facing 1 2A DPDT 5V coil telecom relay (RLY1) [Altronics S4128B] in the right direction to block current 1 PCB-mount SPDT momentary pubutton switch (S1) flow to the battery when the channel is not conducting. [Jaycar SP0380, Altronics S1498] 1 pushbutton switch cap for S1 [Jaycar SP0596, Altronics S1482] Now, when the RB3 output is low, 1 SPST micro tactile switch with 0.7mm actuator (S2) transistor Q4 is off and the gate of Mos- fet Q1 is held at its source voltage via [Jaycar SP0600, Altronics S1122] the 47kW resistor. The Mosfet is there- 1 PCB-mount 3.5mm stereo switched socket (CON1) fore off. When the RB3 output goes high, transistor Q4 is switched on via [Jaycar PS0133, Altronics P0092] base current through the 10kW resistor. 2 PCB-mount M205 fuse clips (F1) The transistor conducts, and the gate 1 10A M205 fuse (F1) of Q1 is pulled toward the ground via 2 NTC thermistors (10kW at 25°C) (TH1 and external thermistor) a 4.7kW resistor. 1 2-way header with 2.54mm spacing (JP1) 2 3-way headers with 2.54mm spacing (JP2, JP3) The 47kW resistor between the 3 jumper plugs/shorting blocks (JP1-JP3) source and gate forms a voltage divider 1 18-pin DIL IC socket (for IC1) with the 4.7kW pull-down resistor, but 1 3.5mm stereo jack plug since its value is ten times higher than 1 TO-220 silicone insulating washer and mounting bush (for Q1) the 4.7kW resistor, the gate is pulled 4 6.3mm-long M3 tapped spacers near to ground. Zener diode ZD3 is 3 M4 x 10mm machine screws included to limit the gate to source 3 M4 star washers voltage to 13V to prevent damage to 3 M4 hex nuts the Mosfet, as it has a gate-source volt- 2 M3 x 10mm machine screws age limit of -16V. 8 M3 x 5mm machine screws 2 M3 hex nuts The switch-on time for the Mosfet 4 insulated crimp eyelets (wire size 4mm, eyelet for M4 screw) is much faster than before, less than 2 cable glands for 4-8mm diameter cable 27μs, and the switch-off time is under 1 2m length of 15A figure-8 automotive cable 270μs (it’s higher because the pull-up 1 1m length of twin-core shielded cable (for thermistor) resistor value is ten times high than 1 20mm length of 6mm diameter heatshrink tubing the pull-down resistor). 2 large insulated battery terminal alligator clips (red and black) 6 PC stakes (optional) So the switch-on is much faster than 4 small adhesive rubber feet with the Si8751, but the switch-off period is a bit longer. Still, as men- Semiconductors tioned earlier, the switching time 1 PIC16F88-I/P micro programmed with 1410719A.HEX (IC1) does not need to be particularly fast 1 LM317T 1.5A adjustable positive regulator (REG1) for our circuit. 1 IPP80P03P4L-07 P-channel Mosfet (Q1) [Silicon Chip SC6043] 2 BC337 NPN transistors (Q2, Q3) Part of the reason we have been able 1 BC547 or BC337 NPN transistor (Q4) to simplify the driving arrangement is 3 green 3mm LEDs (LED1, LED5, LED6) that we can now supply high-current 2 orange 3mm LEDs (LED2, LED4) P-channel Mosfets at a reasonable 1 red 3mm LED (LED3) price (see the revised parts list). Tradi- 2 18V 1W zener diodes (ZD1, ZD2) tionally, they have been harder to get 1 13V 1W zener diode (ZD3) and more expensive than equivalent 3 1N4004 1A diodes (D1-D3) N-channel types. Capacitors Construction 1 220µF 50V PC electrolytic 1 100µF 16V PC electrolytic There is very little difference in 3 100nF MKT polyester construction between the original 5 10nF MKT polyester and revised PCBs. Refer to Fig.1 and simply fit the new components in the Resistors (all 1/4W, 1% metal film unless otherwise stated) upper right-hand corner as shown. The Mosfet mounting is identical. As 1 51kW 1 47kW 4 10kW 1 4.7kW a bonus, this change eliminates the only SMD component in the design, 1 3.3kW 1 2kW 7 1kW 1 330W the Si8751 (IC2). 1 120W 1 100W 1W, 5% 1 56W Testing, setting up and using the charger are identical to the original 4 10kW multi-turn top adjust trimpots, 3296W style (VR1-VR4) (code 103) and are described in the original article (siliconchip.au/Article/12159). SC 1 100W multi-turn top adjust trimpot, 3296W style (VR5) (code 101) siliconchip.com.au Items in bold have been changed or added Australia's electronics magazine June 2022 83 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Altium Designer 22 Review by Tim Blythman We use Altium Designer to design all our project PCBs and have done so for many years. New versions and updates are released regularly, with new releases coming yearly for some time now. Therefore, 2022 sees the release of Altium Designer 22, and we installed it immediately to see what new features are available. You might not think that there is users, such as the Schematic Editor allow shared access to projects and much need for PCB software to being completely rewritten to make libraries and includes a version con- change. While it is true that some peo- it quite a bit faster. trol system. ple continue to use older versions of Altium Designer, there are good rea- In fact, the entire suite was rewrit- We weren’t sure that our small team sons to stay up to date, as improve- ten, with numerous features and at Silicon Chip would use this sort of ments and new features appear with enhancements. Notably, the new soft- feature, but it has been a handy tool, each version. ware base allowed integration with the especially with work-from-home now then-upcoming Altium 365 ‘cloud’ being common. In particular, we have Altium Designer 20 (reviewed software. found it a great way to keep our com- December 2019; siliconchip.com.au/ ponent libraries consistent and up to Article/12176) was a significant mile- We reviewed Altium 365 and date. We expect that it is even more stone. There were substantial improve- Altium Designer 21 in January 2021 helpful for larger workplaces. ments from Altium Designer 19 for (siliconchip.com.au/Article/14705). Altium 365 is an online platform to Even through 2021 and after the release of Altium Designer 21, they Screen 1: here’s where you’ll find the setting to enable Automatic Cross brought out multiple updates and References at the bottom of the Options tab (highlighted in yellow). The dialog minor releases, so some of the features window can be easily be reached by right-clicking on a sheet and selecting we mention here might have been seen “Sheet Actions → Automatic Cross Reference Settings”. in previous updates. It’s also worth noting that Altium provides numerous 84 Silicon Chip Australia's electronics magazine training and development webinars to ensure that its users are making the most of the software. For those readers who do not have an Altium subscription, it’s possible to use some of the online features of Altium365 by simply visiting the web page at www.altium.com/viewer/ The YouTube channel “Altium Academy” (www.youtube.com/c/ AltiumAcademy) is another good way to get a glimpse at Altium Designer and pick up some PCB design tips too. Altium Designer 22 Altium Designer 22 was released in February and was followed closely by the Altium Roadshow, an online event that consisted of a series of technical sessions over two days. Importantly, siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
this included a guided overview of Screen 2: the automatically-generated Cross References include the sheet name Altium Designer 22’s new features. and a grid reference that indicates the X/Y location of the object on that sheet. The Port Actions menu option also provides selections to jump to the location of We always find the Roadshow to be any of the Cross References. a great way to learn the best way to use Screen 3: counterhole settings are found under Pad properties in the Pad Altium Designer and stay up to date Features section. Here, a 90° countersunk hole is specified (45° per side), with with the newest features. We’re cur- the adjacent 3D view showing what it would look like. rently using Altium Designer version 22.2.1, the most recent release avail- Screen 4: the same countersunk hole in the Draftsman view shows several able at the time of the Roadshow. You dimensional callouts. You can place just about any linear, angular or diameter might find some changes or improve- dimension on any part with such properties, so it is not limited to counterholes. ments if you install a later version. with straight sides can be added to create separate files for counterholes Schematic Editor pads or holes on the PCB. Of course, on the top and bottom of the board. the ability to implement such features One feature that was added to the will depend on your board manufac- Screen 3 shows the appearance of a Schematic Editor in Altium Designer turer’s capabilities. 90° (45° slope on each side) counter- 22 appears minor. Still, we think it is sunk hole in the 3D view and its cor- quite handy and indicates the broad Countersinks have the advantage responding size and angle properties range of incremental improvements that the bevel of the screw against the adjacent in the Pad Features section. Altium provides. hole will positively locate the PCB at A counterbore has a diameter (size) its mounting point. However, that may and depth properties. This is the Automatic Sheet Cross not always be required, especially if Referencing setting. You can enable movement is expected or needs to be Screen 4 shows the same counter- it with a right-click on a schematic, accounted for. sunk hole in a Draftsman view. This then “Sheet Actions → Automatic view was quickly and easily created Cross Reference” settings, as shown Counterbores allow simple pan- by adding a new counterhole view to a in Screen 1. head screws to be recessed, among Draftsman document and then adding other jobs. some diametrical, linear and angular When Automatic Cross References measurements. are enabled, references are shown on When the design is exported, it will the schematic as seen in Screen 2. Note the grid coordinates on the sheet (3B Australia's electronics magazine June 2022 85 and 3C) identifying the location within the target sheet. A right-click on the reference allows the reference to be followed like a hyperlink. Exporting such a schematic sheet as a PDF will include the cross-references as hyperlinks, allowing signals to be followed throughout the design, even if they aren’t on the same sheet. As it can be pretty frustrating trying to track signals otherwise when using ports, this is a powerful feature. They do tend to clutter the sche- matic a bit during the design stage, but it was handy to turn this setting on during the later verification stages to simplify broad checking of the design and also when PDFs are generated. PCB counterholes The PCB editor now allows coun- terholes to be added to a pad or hole. A counterhole is a machining process that does not extend through the full depth of the PCB laminate. A typical example would be a countersunk hole to allow a countersunk screw to be recessed into the laminate. The remaining laminate allows the board to be secured by the screw, but the recess means that the head of the screw does not protrude as much. As well as countersunk holes, which have an angled wall, counterbores siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Screen 5: IPC 4761 Via Types can be found under Via Properties; a drop-down IPC 4761 menu lists the types available according to the standard. These types can also be set as templates. IPC 4761 is a standard created by the IPC (founded as the Institute for Screen 6: an IPC 4761 Type 1A via Printed Circuits) regarding the pro- on a four-layer PCB is shown here in tection of vias (connections through the Draftsman view. This makes it the PCB) on printed circuit boards. clear that it consists of a simple solder Without delving too deeply into the mask on the top side of the PCB. Other specifics of the standard, it specifies types have different degrees of filling, seven different levels of treatment plugging and covering. that can be applied to a via to protect it and the PCB. Screen 7: Gloss and Retrace settings now have their own panel, which can be opened from the Panels button. This makes it simple to quickly adjust these We alluded to the tenting of vias settings while tweaking the final location of the PCB tracks. in our review of Altium Designer 20. This involves covering the bare metal 86 Silicon Chip Australia's electronics magazine of the via with a plastic solder mask layer. That is equivalent to the lowest (Type I and Type II) of the seven lev- els covered by the IPC 4761 standard. Other levels include various cover- ings and degrees of plugging (to cover or fully seal the hole left by the via). These may be needed to protect the vias from contact, moisture, corro- sion or even to ensure that there are no holes to allow anything to pass through the PCB. Many specialised designs demand higher levels of protection than what our readers and we generally require. For example, boards that operate in very humid environments and with rapid temperature changes could be subject to condensation, and vias are often the first parts of a board to cor- rode away. So Altium Designer 22 now allows the IPC standard types to be directly chosen from a Via Types & Features section of the via properties. This is shown in Screen 5, a menu that lists the IPC 4761 types with a brief description of each. Those types with an “a” suffix have the treatment applied to one side only (it appears to be the top side), while the “b” suf- fixes have the covering applied to both sides of the via. The various types can also be cho- sen as via templates to streamline via placement. You can also add via lay- out views to a Draftsman document, as seen in Screen 6. The upshot of all this is that the design intent can be better communicated to the PCB man- ufacturer, and more consistent results can be achieved. PCB design Other improvements to the PCB editor include more flexibility in the Pad properties editor when using top- middle-bottom or full-stack views. Each layer now has its own options siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
relating to things like corner radius Screen 8: the Mixed Simulation extension is not installed by default, but can be and thermal relief, and they can now added from the Extensions and Updates tab of the License Management page. As be set for each individual layer. you would guess, it lets you simulate the circuit represented by your schematic, so you can get an idea of whether it will work before you build it. A Gloss and Retrace panel has been added (accessible from the Panels Screen 9: the Simulation button) to allow finer control of the Dashboard is a panel options that are used for the “Route accessible from the → Gloss Selected” and “Route → Panels button and is Retrace Selected” actions. The panel actually a ‘wizard’ can be seen in Screen 7. (Glossing is as it works through where the routing of the track is auto- the steps necessary to matically ‘fixed up’ to be as clean and complete a simulation. direct as possible.) As well as defining a circuit, you might need Bringing up this panel allows the to add voltage source(s) glossing and retracing settings to be to provide simulated tweaked interactively as the track lay- power or signals to that out is finalised. circuit. There is also a new routing algo- expect that the simulation models come in very handy while checking rithm that now prevents loops from will be missing unless you have them these designs. forming if a trace is brought back on in your libraries, but Altium Designer It appears that counterholes are not itself. includes many inbuilt models that yet widely available amongst PCB can be used. manufacturers. But we can see that They also added design rules for being a handy feature as it becomes SMD pad entry location and angle, Of course, the usefulness of these more accessible. For example, designs which make it easier to produce neat models will depend on how closely that use a PCB as a lid on a Jiffy box can designs by keeping SMD pads consis- they match the parts you’re using in be streamlined and improved by using tent. Since these are usually not criti- your design. But, at the very least, the a counterhole to recess the screws that cal criteria, there is also the option to included models for resistors, capaci- secure the lid. disable the rules if they cannot be met. tors and inductors will be usable. A good number of new and handy features have appeared in Altium Mixed simulations Summary Designer 22, making it well worth the time to install the latest version and The simulation extension, accessed We have some complicated multi- remain up to date. directly from the Schematic Editor, is board projects coming up, so the sche- SC not new. But it was a point of interest matic cross-referencing feature has during the Altium Roadshow event as June 2022 87 this feature has had some upgrades. Australia's electronics magazine If you have not seen the simulation feature before, that might be because it is not installed by default. It can be installed from the Exten- sions and Updates tab of the License Management page, as seen in Screen 8. Altium Designer might need to be restarted after installation. The Mixed Simulations extension is based on the well-known SPICE program (“Simula- tion Program with Integrated Circuit Emphasis”). We mentioned in our previous review that Altium Designer 21 added a Simulation Dashboard, while Altium Designer 22 adds measurements and plots of many intrinsic and inferred circuit properties. You can open the Simulation dash- board from the Panels button. Apart from your schematic, you may need to add some voltage or current sources; these can be found under the “Simu- late → Place sources” menu item. As you can see from the dashboard shown in Screen 9, Altium Designer leads you through the steps needed to complete the simulation. You might siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. RF burst power meter You could likely use any AD8318- The resolution is approximately based module, but it’s worth checking 0.3dB per servo step. This calculation The circuit presented here enables that they do not have a low-pass fil- is described in the source code. As an reasonably accurate and repeatable ter capacitor fitted (CLPF) on pin 5 (if example, with a large 80mm pointer RF burst transmission and continu- they do, remove it). attached to the servo, the dial scale will ous wave power measurements with a have approximately 4mm between simple and low-cost circuit. Although The benefit of using a servo as a dis- 1dB increments over a range of about far simpler than the Silicon Chip Low play is the ability to calibrate the meter 60dB. I made another version using a Cost Wide Band Digital RF Power scale regardless of linearity changes Holden speedometer stepper motor Meter (August 2020; siliconchip.com. over the dynamic range of the AD8318. and pointer, with code changes to suit. au/Article/14542), it has a large ana- For enhanced accuracy, multiple log display and can make burst mea- scales for different frequency bands The BASIC source code for the surements. could also be made. The drawback of PICAXE is in a file named “rf-servo_ an analog display is the resolution. v1.bas” that can be downloaded from The circuit has two novel features: siliconchip.com.au/Shop/6/6479 it uses a servo to provide the readout I built the meter by attaching a with a dial of any size, and the burst pointer to the servo motor over a cal- George Mackiewicz, measurement function, implemented ibrated dial scale. Calibration was Vermont, Vic. ($100) as a peak-hold. The peak-hold function performed by temporarily attaching is enabled by a mode switch. a sheet of paper to the meter face and using a pen to mark measured points It was designed to measure the trans- around the dial at the frequency of mit power of 2.4GHz WiFi AP beacons interest. (peak envelope power) and was also tested with other burst transmissions Multiple frequency arcs can be cal- formats and in different bands, eg, pro- ibrated on one scale, mitigating fre- prietary frequency-hopping protocols quency response issues; eg, you could in the 2.4GHz and 910MHz ISM bands. have 2.4GHz and 910MHz scales. The implementation is straightfor- After that, I removed the paper and ward, consisting of a PICAXE-08M2 scanned it, then loaded it into a draw- microcontroller (eg, Altronics Cat ing software package. I then redrew the Z6111A) and a miniature servo motor dial scale using the measured mark- (eg, Altronics Cat Z6392 or Jaycar Cat ers in appropriate arcs. I extrapolated YM2758). The AD8318 module cost intermediate points between the mea- about $18 from AliExpress and came sured marks. I then printed the new with a metal shield around the AD8318 dial and fitted it to the servo. and input components. 88 Silicon Chip Australia's electronics magazine siliconchip.com.au Downloaded by Mike Blake (#19283) Copyright © 2022 SILICON CHIP Publications.
Artificial candle is ‘ignited’ by a real flame This 3D-printed artificial candle is comprises four main pieces: the cyl- The bottom piece has a small rect- not turned on using a switch; instead, inder, base, top and flame cover. The angular opening to accommodate the it is ignited using the flame of a real main cylinder is hollow, and it houses small slider of our mini DPDT power matchstick or lighter, just like an ordi- all the electronics. The top and bot- switch. Insert the slide switch from nary candle. When a flame is brought tom pieces are designed to be a snap- the inside of the bottom part, aligning near the tip of the artificial candle, the fit onto the main cylinder. it such that the slider can properly be LED bulbs magically light up. They moved from the outside, then fix it in also flicker like a real candle. The bottom piece has a small rectan- place using hot glue/silicone etc. Once gular opening for the USB port of the that’s solid, push the bottom piece into The trick here is simple: a hidden Arduino Nano board. There are four the main cylinder. flame sensor is installed at the top of small holes in the top part: three for the candle. This signals an Arduino the LEDs and one for the flame sen- Add the flame cover to the top, and Nano board inside the candle to turn sor's IR diode. the candle is ready for programming. on the LEDs. The flame cover acts as a cap and The Arduino sketch required is rel- It uses two yellow LEDs and one red diffuses the light from the three LEDs. atively short, but we don’t have space LED to produce the flickering effect. It needs to be printed in white plastic, for it here, so download the file “Artifi- They are switched off in a pattern, one and it has very thin walls so that it is cial candle.ino” from siliconchip.com. after another, to create the flickering translucent. You can download all the au/Shop/6/6478 effect. These features make our artifi- 3D printing files from www.tinkercad. cial candle look almost real. com/things/4iuOdy6Wpmp Fire up the Arduino IDE, open this file, select the Nano board from the It is powered by a small 3V coin After printing these pieces, insert menu and set up your COM port, then cell for portability. I've also added a the LEDs in the central holes in the choose Upload. Check that you get a small slide switch at the bottom of the top piece in no particular order. Also success message in the window at the candle to switch it off. The plan is to insert the flame sensor's IR diode half- bottom of the IDE. eliminate this in a future version of way through the remaining outer hole, this project where you can blow on it then fix the module to the underside Ensure the slide switch is on, then to turn it off! But until then, it has to using hot melt glue, silicone or another bring a flame near the top of the can- be manually switched off. adhesive. dle and check that it switches on and then flickers. When finished, switch Note that a few slightly different IR You can now connect the wires from off the slide switch in the base. flame sensor modules are available, the LEDs and the flame sensor to the but they all work similarly. If using Arduino Nano board, then wire up You can use the same principle to another type, check the pinout and the button cell via the slide switch. light up any other shaped lamp. You adjust the wiring as necessary. Insert the circuitry into the candle could also use different coloured LEDs body, then push the top piece onto in the candle to get different effects. The body of the candle is 3D printed. the main cylinder. I designed the model in Tinkercad. It Aarav Garg, Hyderabad, India. ($120) siliconchip.com.au Australia's electronics magazine June 2022 89 Downloaded by Mike Blake (#19283) Copyright © 2022 SILICON CHIP Publications.
Digital volume control using discrete logic This circuit is based upon a submis- held low by a 1kW resistor, keeping the lower threshold detected at pin 2. sion from Raj. K. Gorkhali from Nepal. timers in reset with their pin 3 out- The process repeats with pin 3 going It expands on his concept, providing puts low. When the associated switch high again. 16 steps of logarithmic attenuation, is pressed, the reset input goes high, a power-up preloaded attenuation and the pin 3 output immediately goes When the switch is released, the pin setting and end stops for the volume high (near 5V). 3 output immediately goes low. The control. 555 timers allow the volume level to Oscillation starts with the pin 3 out- change immediately when the switch The analog switches are low dis- put staying high for around 700ms, is pressed and continue to change if tortion types and op amp buffering is until the 10µF capacitor at pins 2 and the button is held down. included for the attenuator. 6 charges via the 100kW resistor to the upper threshold. The upper thresh- The signal from output pin 3 of The volume is controlled via up and old is detected at pin 6; then the pin IC1 goes through two 2-input NAND down switches S1 & S2. These connect 3 output goes low for around 700ms gates (IC3c and IC3d). The first gate to the reset inputs of 555 timers IC1 as the capacitor is discharged to the has its pin 8 input connected to the & IC2. Their reset inputs are typically borrow output of a 4-bit binary up/ 90 Silicon Chip Australia's electronics magazine siliconchip.com.au Downloaded by Mike Blake (#19283) Copyright © 2022 SILICON CHIP Publications.
down counter, IC4. The borrow output since the following analog switches An easy way to at pin 13 is usually high, so the pin 3 may be overdriven. measure SMDs voltage level from IC1 is inverted by IC3c and then inverted again by IC3d. The output from IC3 is applied to Here is an idea inspired by the SMD This causes the counter to decrement a 16-level attenuator controlled by Test Tweezers project (October 2021; on the initial press of S1. the Q0-Q3 binary outputs from IC4. siliconchip.com.au/Article/15057). The attenuation is logarithmic, and When using fat leads from a multime- If the counter’s output at Q0-Q3 we have set the range to be from zero ter or similar to test small individual reaches 0000, the borrow output goes attenuation down to 45dB attenuation SMD components, they have a habit low, forcing the IC3c output high and in 3db steps. of acting like a circus flea and jumping hence IC3d’s output goes low, prevent- out of sight, never to be found again. ing further decrementing. This is the There are four attenuation stages. negative ‘end stop’ which prevents the The first stage provides 24dB atten- To solve this, I added a thin copper volume from jumping from maximum uation, the second stage, 12db, the film recovered from an SMPS trans- volume to minimum. third stage 6dB and the final stage, former to the teeth of a cheap set of 3dB attenuation. With various com- callipers (which should be made from A similar operation occurs with binations of these attenuators, we can an insulating material) and secured the IC2 and NAND gates IC3a and IC3b. obtain 16 steps. test leads to the copper. I used super The difference is that the counter is glue to hold the film to the callipers. incremented instead of decremented, Each attenuator comprises two and stops when outputs Q0-Q3 reach or three resistors and a changeover The smallest SMD component can (1111) or minimum volume. switch. With the switch in the ‘NO’ be firmly captured and restrained from position, it completes a resistive escaping. I modified a second calli- Note that the counter counts down divider from the preceding stage to per with longer leads to connect to a to increase volume and counts up to ground, with the attenuated signal multimeter for holding and measur- decrease volume. That’s because max- appearing at the resistor junction feed- ing resistors. imum volume (minimum attenuation) ing into the next stage. With the switch occurs when Q0-Q3 are all low. in the ‘NC’ position, the divider is dis- Michael Harvey, connected, and the upper resistor(s) Albury, NSW. ($60) IC4 includes a preload feature, are ‘shorted out’, so the stage has no where the Q0 to Q3 outputs can be attenuation. June 2022 91 set to a particular value during pow- er-up. Jumper links JP1-JP4 set the Calculating the required resistor val- power-up volume level. If no jumpers ues is done assuming that the source are inserted, the preload inputs at P0 impedance is zero for the first stage, to P3 are all held high via 10kW resis- which is reasonable as it is from an op tors and the unit is at minimum vol- amp output. ume (maximum attenuation). The second stage calculation is To determine the initial attenuation for 12dB attenuation, and the source setting, take the binary number formed impedance is now 25kW (due to the by jumpers JP1-JP4 (with a shorting 25kW output impedance of the first block being 0 and open-circuit being stage). The stage output impedance 1), convert it to decimal and multiply also 25kW. The following stages are it by three. calculated using the 25kW input and output impedance values. This is the initial attenuation in dB. For example, with JP1 & JP3 in and JP2 The output from the attenuators & JP4 out, the binary number is 0101, is applied to another op amp buf- five in decimal, and times three gives fer, IC5b. 15dB attenuation. The attenuator switches are Volume control TS5A22362 dual-channel SPDT analog switches. These are interesting because The audio signal is applied to a not only are they very low resistance buffer circuit (IC5a for the left chan- switches (0.65W typical), with low dis- nel) operating as a unity-gain ampli- tortion (below 0.0041% at 1kHz) but fier. The op amp needs ±5V supplies also the signal can be below the supply which can be obtained from existing rails for the switch. So while we run supplies in a preamplifier. Regulators each switch IC from a 0-5V supply, the may be required to reduce the voltages applied signal can be up to -5V with- (eg, 7805 and 7905 types). out causing extra distortion. The TL072 type op amps shown can If you plan to use a different ana- handle signals up to about 2.5V RMS log switch, make sure the supplies before clipping with such a supply. If (and control voltage) for the switch you use rail-to-rail op amps instead, are suitable. that would allow for signals up to about 3.5V RMS. You could also con- John Clarke, sider using lower distortion op amps. Silicon Chip. Do not use a higher supply voltage Original concept: Raj. K. Gorkhali, Nepal. ($75) siliconchip.com.au Australia's electronics magazine Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
SERVICEMAN’S LOG Ion with the wind Dave Thompson Servicing can be a strange industry. These days, much of what comes through the door is not designed to be repaired. You can imagine how that makes the job a bit of a challenge! I understand that companies want to protect their designs. Some took them so seriously that hospitals utilised Still, if someone wants to clone a product, unless it uses them as part of their air-conditioning systems to minimise cutting-edge technology, they can do it without too much or neutralise airborne infections. The recent pandemics difficulty. (SARS, COVID etc) have resulted in a considerable boost in air ioniser sales. Making devices unrepairable usually has the most signif- icant impact on the customer – someone that the company As is typical these days, ‘mileage’ varies with any ‘health’ making the goods probably should want to keep happy! product. If using one makes one feel better, why not use it? Regardless of the health and well-being implications, Someone, somewhere, always has the wherewithal, making and setting them up is fun and educational. That resources and ability to ‘deconstruct’ or ‘reverse engineer’ (for me) makes up for any of the controversies. Many com- something to find out how it works. If the mood or the mercial variants are still sold today for use in the health promise of commercial gain takes them, they will repli- and horticulture industries. cate it and sell it, likely at a lower price. Many countries’ economies are seemingly reliant on copying the ‘intellec- The premise of these devices is simple: apply a high tual property’ of others. voltage to an array of sharp metal “emitters”, and a corona or ion wind will stream from those points. Many airborne Some of these ‘clone jobs’ are so shameless that they pollutants are electrostatically charged by this wind and replicate the external appearance of the original product, are attracted to a nearby ground. So the theory of air puri- down to the shape, the colours and even the font. They just fication by negative ions is sound. replace the original company’s name with their own and sell it for a fraction of the price! I have seen this for myself; I built several ionisers in the early 1980s for a friend who had a small greenhouse/ I think this is a basic human instinct, illustrated by the hydroponic setup for producing cabbages and cauliflowers. fact that I (like many others who would be reading this This guy wanted to improve the air quality in his setup, column) pulled many things apart when I was a wee fella and when he heard me going on (as was my wont) about to see what made them tick. Dad had to put most of them this new-fangled method I’d been reading about, he was back together – that is, until I could do it myself. keen to bankroll a couple to see how it worked for him. My first guitar builds were attempts at making copies of I scaled up a project from an American magazine and set existing models as I tried to make an instrument I could them up in his greenhouse. They sat on a large baking-tray afford, hopefully as good (if not better) than those available type metal plate that was Earthed through the mains, and for what were, to me at the time, vast amounts of money. sandwiched between that and the ioniser was a sheet of white paper. After just two days, that paper was turning Whatever the motivation behind copying others’ work, grey, and when the ioniser was moved, there was a stark it still happens a lot today. white outline where it had been sitting. That said, finding an epoxy resin-potted ‘module’ in a That proof was good enough for me. Those ionisers ran commercial unit may have another more practical expla- for the next 15 years until the guy moved, and I was sold nation than obfuscation. on the idea. Ionisers are positively great The last one I built was for a person here who suffers from a seasonal complaint we call “Nor’ West Syndrome”. Recently, a client brought in a device I’ve not seen for We get a very hot, dry, gusty wind during the spring and many years; a commercially-produced air purifier/ioniser. summer months, prevailing from the northwest. It is loaded These devices were all the rage as far back as the 60s and with pollens and dust picked up by roaring over the nearby 70s, in a jet-age, sci-fi sort of way, and were the ‘go-to’ Canterbury Plains. gadget for a while. They were also popular as a project in magazines back then. As it blasts through Christchurch, it dumps that pollen in buildings, on the ground and anywhere the air reaches. It got me, too; the subject of purifying air using electron- It looks like yellow, granular dust and is sometimes every- ics fascinated me. The result was that I built many nega- where. Those with hay fever or any sensitivity to pollen tive ion generators over the years, with varying success. or dust can have serious health impacts due to this phe- nomenon. However, that didn’t mean all was well in the state of negative ion generators. There have been hundreds of stud- When this person complained to me about it, I suggested ies showing that negative ions have no real benefit to peo- an ioniser might be the answer, especially if set up near ple or pets, while a similar number of studies have proven that they are beneficial. 92 Silicon Chip Australia's electronics magazine siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
Items Covered This Month so we can only assume the particles find something else grounded enough to be attracted to. • Ion with the wind • A nomadic TV antenna Also, some of these commercial devices are tiny, about • Repairing a microswitch in a washing machine the size of a small mobile phone, so it is hard to see how they can be as effective as those boasting a decent-sized Dave Thompson runs PC Anytime in Christchurch, NZ. pin array. Website: www.pcanytime.co.nz Email: [email protected] Either way, this device wasn’t running, and there was Cartoonist – Louis Decrevel nothing I could do. They are pretty cheap to purchase off Website: loueee.com the internet, so I wasn’t sure this would be a feasible job anyway. I talked to the client about it (good communica- their bed. I initially built one ion generator for them, then tion is essential to a serviceman). In the end, they commis- another for their home office; they swear by their use now. sioned me to make one of the models I’d produced before (and likely harped on a bit too much about!). Unrepairable but not unbreakable Do it yourself! The one that came into the workshop recently is a com- mercial unit, made in China, and is quite small compared While not overly complex in the models I build, the actual to others I’ve encountered. It runs from a 9V battery and electronics involved are pretty interesting from a theoreti- is designed to sit on a bedside table or similar. cal point of view and are good fodder for the home exper- imenter. Anyone who likes watching big arcs and making After determining the battery was good, the only real circuits with the potential (!) for lots of high-voltage exper- option was to pull it apart and have a look. There were no imentation can use a very similar layout to power up the screws; it was clipped together, so I got the client’s per- likes of Tesla coils and Jacob’s Ladders. mission to (literally) crack it open. The main difference with this circuit is that we want to Inside was a solid mass of black potting compound. keep arcs out of the equation as much as we can and feed There was absolutely nothing I could do with it repair- all that juicy HV energy to the pin array. If we get a flash- wise. Many such devices are potted like this inside, not over at any of the connections on the multiplier, not only to mask the circuitry (although that might be a useful do we create a fire and shock hazard, we lose any sem- byproduct) but more likely to prevent corona bleeding or blance of decent ion emission at the output. arcing between all the components that are in very close proximity. The circuit I use consists of three sections: a driver/ oscillator section, a multiplier/output section and the pin Most of these devices work the same way, though there array. Each section has its own circuit board. are different lines of thought regarding the power input. Some apply a relatively low DC voltage (usually from a Anyone familiar with such things would recognise a plugpack supply), via a simple switching circuit, to the pri- Cockroft-Walton arrangement of high-voltage capacitors mary of a transformer. The stepped-up transformer output and diodes in a characteristic criss-cross ladder outlay. then goes through a voltage multiplier circuit. This is actually a line of half-wave rectifiers connected in series, with each stage boosting the previous stage’s out- The resulting HV output terminates at the pin array, put ever higher. though sometimes it can just be a single-pointed elec- trode/antenna. Theoretically, you can just keep adding stages. As long as your components can handle the resulting voltage (and The other method is to use mains power directly into the the spacing between components and stages multiplier circuit, sans transformer (although some use a is enough to prevent arcing between them), 1:1 transformer for isolation). But I doubt that is legal here; the whole circuit would run at mains potential; perhaps another good reason to pot everything solid! The output voltage (around -3kV to -10kV depending on the circuit) is safe for anyone touching it (the output pins may be accessible through holes in the case), yet it’s high enough to cause an ion wind to stream from the points. This wind can usually be felt by placing a (wet) finger close to the emitter array, but note that some ionisers employ a fan to fudge/boost the ion output. You might think getting too close to the pins could be dangerous; sometimes, a tiny, weak arc to a fingertip may be visible in very low light. But a line of high-value resis- tors in series with the HV feed to the pin array limits the available current to a safe level. The idea is that the negative ions from the emitter pins charge any muck in the air, and this finds its way to the nearest ground. Most commercial units don’t come with a ground plane to sit on, or a handy connection to add one, siliconchip.com.au Australia's electronics magazine June 2022 93 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
you can get some seriously high voltages out of such a setup. neatly, insulating well between each layer. I made a jig years Practically though, it’s a different story. ago for such things and keep it handy, just in case. While the wire is still wound by hand, holding the assembly is One significant consideration is what to assemble these much easier, and the resulting windings are much neater. components on. I could use veroboard or perf-board, but I’d spend most of my time stripping tracks and arc-proofing This component is the most critical, especially when add- it. A better option is to use a printed circuit board with the ing extra stages to the multiplier because the transformer correct spacing already worked out. will break down internally – usually before anything else – should the HV output go too high. Fortunately, because I throw nothing away, I have a spare set of boards from the run of ionisers I made back in the day. The pin array is a little trickier, but I used a 0.5mm PCB These are very much home-made, meat and potatoes PCBs, drill bit and a small manual hand drill to carefully bore not like the multi-layer works of art we see today, but they the holes for modified (head cut off) dress pins through still look good and do the job, which is all I want from them. a 120mm length of 4mm brass tube. Getting them all in line is probably the worst part of it. Still, given that they The driver board boasts a board-mounted barrel jack can be easily bent into shape if they are off-angle a little, for DC input (typically from a 9-15V plugpack) powering it isn’t too onerous. a 555 timer configured to run as an astable multivibrator that, in turn, drives two NPN power transistors in a push- Soldering the pins in is also a bit of a challenge, but I use pull configuration. liquid flux and lots of solder, and it seems to stick them in OK. I also fill the ends of the tube with solder and sand The relatively square-wave output from the transistors that and each pin end smooth to ensure there are no sharp switches current through the primary of a custom-wound edges – ions will ‘leak’ from anything sharp. transformer. A few other ancillary components ensure everything runs as it should. This is also why the capacitors and diodes in the multi- plier must be soldered to the PCB with their leads cut very The secondary of the transformer runs off to the multi- close and what I would usually consider too much solder; a plier board. If this sounds familiar to some readers, that is nice round blob will be less likely to arc to another nearby because the April 1981 issue of Electronics Today Interna- joint or bleed ions. We want all the ions coming from the tional (ETI) (which we offer scans for siliconchip.com.au/ sharpest parts – the pins. Shop/17) featured a very similar circuit. This circuit is also quite close to most oscillator-based ioniser circuits from Once it is up and running and mounted in a nice case, around that time and even some I see on the web today. the question is how to know it is working. Other than stick- ing your hand in front of it and hoping to feel the corona I changed it slightly to upgrade the transistors, included wind (no, not that kind of corona!), the ion output can be heatsinking and added two extra stages to the multiplier, measured using a simple detector. altering the PCB artwork to suit. That ETI version I mentioned included a tester that sup- The rest of the build involved making the transformer posedly lit up when ions were present, but I could never and the pin array, both tasks which can put constructors get it to work. That could be because the PCB I made for it off. But while they both seem to be quite tricky to make, wasn’t good enough, the components were not quite right, neither is overly difficult. or perhaps the ioniser I built at the time didn’t work well enough to trigger it. The transformer uses a standard ferrite pot core and bob- bin, and it is just a matter of winding the coils carefully and Regardless, I ended up making a little hand-held meter with a couple of transistors and a whip antenna that picked up negative ion emissions quite well. I use that now – not that I build many of these things – but when I do, it’s nice to have the test gear to show they are working. 94 Silicon Chip Australia's electronics magazine siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
The client was happy and claimed my version worked way better than their original ever did. That’s always grat- ifying to hear, especially with something as ‘controversial’ regarding health benefits as air ionisers. The nomadic TV antenna reception I decided it was time to check the amplifier in the antenna. It was not easy to get to, as we did not bring a ladder. But by G. C., of The Gap, Qld had a lot of trouble with TV recep- lowering the antenna quite a bit, it was possible to access tion in his caravan on a trip to Far North Queensland. He the F-connector and pins securing the antenna to the struts traced it to a rather apparent electronic fault... by sticking my head out of a hatch. On the first night at Tewantin, we could not receive a sin- These antennas do not appear to be designed to be gle television channel. This was somewhat unexpected as repaired; umpteen diabolical plastic clips held the two our caravan had been in storage for several months. Before sides of the radome together, plus several plastic dow- that, we had received television stations without difficulty els from one side to the other, which were ultrasonically from the Mt Tinbeerwah transmitters near Tewantin. These welded. When I finally got to the printed circuit board, it UHF transmitters broadcast with vertical polarisation. was obvious why it was so temperamental – it was severely corroded, presumably due to moisture ingress. Most modern caravans use fractal antennas that can receive both horizontally and vertically polarised signals, I would generally clean a board in this state with iso- but our 16-year-old caravan does not have such luxuries. propyl alcohol, but the best I had on board was plain old It has a simple Winegard antenna (sometimes called a methylated spirits. After cleaning it up, there were open- batwing) with folded dipoles for VHF and UHF signals. circuit tracks that needed replacement. After re-assembling the antenna and re-installing it, it was happy days again It can be raised off the caravan’s roof and rotated in the when we could receive the ABC. direction of transmission by a mechanism on the ceiling. Inside the antenna radome is a masthead amplifier that is But our joy was short-lived, as after about 90 minutes, power-fed through the coaxial cable. there was a complete signal blackout again. The next day, I risked life and limb to again remove the antenna to access The two struts that hold and control the position of the the PCB. I checked every plated-through hole with a mul- antenna head are in a parallelogram configuration. This timeter and replaced another corroded link. Again, there enables a simple modification to be carried out that involves was apparent success, and the missus could watch her BBC raising one of the struts, causing the antenna head to rotate programs. All was well. to the vertical position, which is needed at Tewantin. At Atherton, we could pick up the VHF broadcasts from Bypassing the PVR (personal video recorder) and connect- the powerful Mt Bellenden Ker transmitters but not the UHF ing the antenna fly-lead directly to the TV did not fix the problem. Neither did changing the fly-lead or connecting it The masthead amplifier PCB and to the second antenna socket in the van. I checked that there components were badly corroded. was 12V at the “F” connector at the antenna, and it was fine. As a last resort, I removed the 694MHz filter (to block mobile phone signals) on the drop-side of the power-feed module and, surprisingly, I could then tune in all the chan- nels. It seemed unlikely that a passive device had failed, and I wondered at the time whether its insertion loss was the straw that broke the camel’s back. All went well until we arrived at Rolleston, where the caravan park had a community antenna with coax distribu- tion. Usually, we connect the audio output of the television set to the auxiliary input of the caravan’s CD/radio stereo system. However, with the external coax feed connected to the van, mains hum from an apparent ground loop made listening to the TV virtually impossible. When we reverted to using the television speakers, there was absolutely no sound. We had that problem on a pre- vious trip, and we fixed it by doing a master reset on the TV. But that did not do anything this time, and it wasn’t until a couple of days later in Charters Towers that I had time to dismantle the TV. I was surprised to find that the voice-coils of both speak- ers were open-circuit. I couldn’t replace them at the time, and when I later got home, I discovered that Sharp no lon- ger sells replacement parts for this set. Eventually, we arrived at Georgetown for a few days exploring. Once again, we could not pick up the single- channel broadcast from the transmitter just over 1km away. This ABC transmitter was in the VHF band and transmit- ted at 4W. Even manually tuning the PVR and TV, I could not find the ABC signal. siliconchip.com.au Australia's electronics magazine June 2022 95 Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
signals from the nearby transmitters at Hallorans Hill. On service manual and parts manual from the Fisher & Paykel passing through Mareeba, I was pleased to be able to buy website and printed them. Fisher & Paykel must be only one PCB lacquer at an electronics parts reseller and, when I of the few companies left that gives out service manuals. applied it, the board looked much better. But in hindsight, it may have been better to have waited a bit. The service manual shows how to enter diagnostic mode, which gives codes for the last eight cycle errors. It also has At Redlynch, Cairns, there is a local broadcast site with procedures on how to test the out-of-balance microswitch, all channels in the UHF band, but we couldn’t pick them the pump and the water valves. The error codes are dis- up. When we arrived at Wongaling Beach just south of played on the eight wash progress LEDs, with the right-most Mission Beach, my suspicions that the antenna amp had “spin” LED being the least significant bit and the left-most failed again were confirmed when we could not pick up “long wash” LED being the most significant bit. any UHF channels from the broadcast site on Dunk Island. It was just 8km away, and we could see it clearly. The code that it came up with was 00101011 binary or 53 octal. The binary decoding table indicates that 3 octal When I again removed the antenna and accessed the selects the 4th column while 5 octal selects the 6th row PCB, I had a close look at the circuit. The signal split into down. This points to error code 43, which means that the two paths from the balun: a VHF amplifier with one tran- fault is that the out-of-balance microswitch is permanently sistor and a UHF amplifier with two transistors. I quickly on or the harness to it is disconnected. sketched out the circuit of the UHF section. Since I made my repair, the Fisher & Paykel website At this stage, I got on to the internet to see if there was now has a service diagnostics manual that makes it easier any information about fixing these boards. There was infor- to read the error codes. mation about replacing corroded PCB tracks and plated- through holes, but someone had figured out that the UHF I activated the diagnostic mode to test the out-of-balance transistors were BFR93A types. switch. On manually activating the out-of-balance lever under the top deck, the short wash LED did not turn on, I connected a 9V battery to the output coax connections which indicated that the microswitch was not working. on the board so that I could make DC voltage measure- ments. It soon became evident that the second UHF tran- To get to the microswitch, I removed two screws at the sistor was not conducting at all, even though the base bias top of the back panel. I could then lift up the top section voltage was correct. I removed this transistor, which wasn’t with the eight wash progress LEDs and remove a screw easy in a caravan without a fine-tipped soldering iron etc. that holds the grey control module. I then lifted the con- trol module to reveal the microswitch, an SPST-NC type. The missus was the theatre nurse and held a magnify- The normally open (NO) contact that would have made it ing glass and LED torch so I could see what I was doing, an SPDT switch had been cut off. which definitely helped. I guess that they used an SPST-NC switch to ensure that, No wonder we were having so many issues with the during assembly, the quick connector could not be placed antenna – the collector of this transistor was missing! It onto the wrong terminal. After disconnecting the quick had totally corroded away. Where do you buy a low-noise connectors, I used a multimeter to measure the resistance RF transistor at Mission Beach? All I could do was bridge of the normally-closed contacts. This showed that the con- the base track to the collector track and see how well the tacts were open and that the microswitch was faulty. UHF amplifier would work with just one transistor. Opening the microswitch revealed that the contacts had In practice, it worked surprisingly well, and for most become severely oxidised after many years of service in an localities, either the PVR or TV signal meter displayed a environment with water and steam. I made a trip to our strength of around 70% and signal quality of 100%. There local electronics store to purchase an SPDT microswitch, was only one place when the antenna was pointing at dense and having installed that, the machine worked again. vegetation that the level of pixellation was so severe that watching the television was untenable. Some time later, after we moved to a new house, it failed with error code 43 again. I knew what to do, so I purchased By the time we got home, an online retailer had deliv- ered a few of the transistors as well as some SMD ceramic capacitors. After soldering in a new transistor, I replaced a filter capacitor that had a corroded end. I also strung an MKT capacitor across the power supply electrolytic. When re-assembling the radome, I siliconed both halves together except for segments to allow egress of any water entering when the antenna is in either the horizontal or vertical plane. The antenna is now working as well as it can, but the real question is: for how long? Washing machine microswitch repair An internal view of the GW709AU out-of-balance microswitch assembly. Replacement microswitches are not R. W., of Mount Eliza, Vic has discovered that sealed available from Fisher & Paykel. components are needed for harsh environments, including the inside of a washing machine. At least he’s had plenty of practice replacing the failing part. He can probably do it in his sleep by now... I repaired a Fisher & Paykel GW709AU washing machine that was around 17 years old. The symptom was that it would not start. I began by downloading copies of the 96 Silicon Chip Australia's electronics magazine siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
another microswitch and installed it. Due to a busy life- style, I did not realise that it was only around two years since I had first replaced it. Well, two years on and the washing machine stopped during the spin cycle. This time, the “final spin” LED and “current spin speed” LED were both flashing. On restarting the washing cycle, it would start and run then stop with the same error code. Section 10.5 of the service manual indicated that the fault could be any one of eight causes, mostly related to the machine being out of balance. One of these mentioned, “Check that the switch oper- ates correctly and the contacts measure less than 2 ohms”. I made the mistake of thinking that, as it was not that long ago that the microswitch was replaced, it was unlikely to be the problem. I also thought this because the washing machine would start and then run before stopping. I started a cycle and lifted up the lid a bit to see what was happening without activating the lid switch. I could see that the out-of-balance lever was not being activated, but the washing machine was still stopping. This indicated that out of the eight possible causes, it could only be the microswitch at fault. I measured the normally-closed contacts and got a read- ing of 8MW, not less than 2W as specified. It appears that the fault was intermittent. Sometimes the switch would be closed but then incorrectly open during a spin cycle. So the microswitch was faulty once again. Opening up the microswitch, it looked OK with no appar- ent oxidation. So what was wrong? An internet search did not reveal a data sheet for this device. I thought this type of switch might be OK when switching high-voltage, high-current loads but perhaps was no good at switching small currents in a wet and steamy environment. I started looking for a better microswitch. The Fisher & Paykel Parts Manual lists the microswitch part number as 436597 but they no longer sell that part. The replacement is the sealed OOB (out of balance) assembly, part number 420313. That includes a different switch, bracket, lever and two-wire connectors. At ~$70, this is considerably more expensive than just a micros- witch. It looks as if the switch is now sealed and requires a different bracket and lever because it is a different size. Searching for the original part number on eBay showed two sellers with photos of their microswitch that had Omron part numbers D3V-6-2C24 and V-16-2C25 on them. The Omron data sheets indicate 30mW and 15mW contact resistance, respectively. The D3V-6-2C24 data sheet also shows a graph for the micro load D3V-01 series at currents as low as 0.16mA. I think that a D3V-01 series microswitch might be suit- able in this environment. But at the moment, the washing machine is working with another generic microswitch from my local store, so we will wait to see how it goes first. Next time, the solution will be to use either that Omron device or the Fisher & Paykel replacement part if the OOB micro switch fails again. I now realise why a normally closed switch was used rather than normally open. If the contacts oxidise and the out-of-balance lever operates the switch, the circuit would not be closed, and the washing machine would not stop – it would be hopping and jumping around in the laundry. With an NC microswitch, the washing machine would just stop working with a faulty switch. SC siliconchip.com.au Australia's electronics magazine June 2022 97 Downloaded by Mike Blake (#19283) Copyright © 2022 SILICON CHIP Publications.
Vintage Television The Admiral 19A11S TV and its unique deflection circuit By Dr Hugo Holden This set features a unique horizontal deflection by Fink, Grob or Von Ardenne. As far circuit that has been sitting under everyone’s as I am aware, the only two TV sets noses for about 67 years, invented by Britons which contained this “circuitry mas- Faudell & White. Over the last 35 years, I terpiece” were the Admiral 19A11S have asked many veteran TV technicians if and the Motorola VT71; both use the they know about it but so far, none have been 7JP4 electrostatic CRT. familiar with the technique. Perhaps it was overlooked by peo- Early CRT TV sets like the Admi- vertical). In contrast, magnetic deflec- ple servicing the sets because ‘it just ral 19A11S used electrostatic deflec- tion uses coils to create magnetic fields worked’ and they put no further tion rather than magnetic deflection, that bend the electron stream. thought into it; they needed to fix the which became the standard until TV and get it back to the customer. cathode ray tubes (CRTs) were made The amount of deflection created by essentially obsolete by LCD screens. the electrostatic method depends on I recently posted this circuit on a The difference is how the electrons the applied voltage, while the mag- vintage TV internet forum, again seen in the cathode ray are deflected to netic deflection works on the current by many people with a long history land at the desired spot on the front through the coil. Either way, this volt- in TV repair, design & construction. of the screen. age/current must be carefully con- Nobody was familiar with it, and it trolled so that the electrons trace out surprised most. As you might guess from the names, a zigzag to illuminate the phosphor(s) electrostatic deflection works by cre- on the face of the cathode ray tube. Before reading this article, imagine ating an electric field to deflect the you have studied all there is to know electrons, basically by charging capac- The circuit concept used for the about designing TV sets with valves. itors placed on either side of the elec- horizontal deflection system in the You walk into an exam room and are tron beam (left and right for horizon- Admiral 19A11S has not been featured confronted with this question: tal deflection or top and bottom for or described in standard television technology textbooks such as those Design a circuit with a single triode and any other R, C & L components 98 Silicon Chip Australia's electronics magazine you wish which runs from a 250V DC supply (ignoring the triode’s heater). It must produce two anti-phase 450V peak-to-peak linear sawtooth wave- forms (one for each horizontal deflec- tion plate) and be suited to television horizontal scan and flyback timing. It needs an adjustable frequency of around 15,750Hz, and it will be synchronised to the horizontal sync pulses in the usual way. I think most engineers familiar with television scan stage design would find this question too challenging. On its face, it seems impossible. Conven- tional wisdom is that this task requires a separate oscillator and a two-triode para-phase amplifier running from plate supply voltages of 700V or more to allow enough linear amplification for generating the 450V peak-to-peak anti-phase sawtooth signals. As argued in some texts, electro- static deflection was abandoned in favour of electromagnetic deflec- tion because sets with larger CRTs required very high voltages for the siliconchip.com.au Copyright © 2022 SILICON CHIP Publications. Downloaded by Mike Blake (#19283)
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