DK - Tech Lab

Generator 51 ! i Clamping the sticks Hacksaw to a scrap piece of see p.21 wood will help to hold them in place. The main pulley 5 Using a hacksaw, cut 3⁄8 in (1 cm) off one end wheel is complete. of four craft sticks. Next, cut one end off four more craft sticks at a 45° angle, starting 3⁄4 in (2 cm) 4 Once the glue has dried, push the skewer through up one side. the centers of the cardboard disks to form the shaft. Make sure there is an equal length of skewer on each side, then glue the shaft to the cardboard on each side. Make sure the !i sticks are aligned. Drilling 6 Glue together two of the straight-cut craft sticks, see p.23 then repeat with the other two. These are the legs that will support the generator’s pulley wheel. 7 Using a drill bit slightly wider than the wooden skewer, drill a hole through the middle of each of the legs, about 3⁄8 in (1 cm) from the rounded end. 8 Using a utility knife, cut two disks, Use a cutting mat each about 1⁄4 in (6 mm) thick, to protect your from an unused glue gun stick. work surface. !i Hold the glue firmly so it doesn’t roll as you are cutting it. The disks will help keep the generator’s shaft in place.

52 Generator 9 Stretch the rubber band around the tape roll. 10 Using the pointed end of a skewer, make This will be the belt of the pulley system that a hole in the center of each glue stick disk. attaches to the motor and turns the generator. Push one of the disks onto one side of the shaft of the pulley wheel. Set aside the second glue disk. Make sure the shaft can turn freely. 11 On the wooden base, make a mark about 3⁄4 in 12 Push one end of the shaft through the hole (2 cm) in from each side, about 5 in (12 cm) in the leg already in place, and feed the other from one end. Glue one of the legs on top of one of end through the hole in the other leg. Glue the second the marks, and wait for the glue to dry. leg on top of the second mark. 13 Use the angle-cut craft sticks to make supports 14 Use the wire cutters to carefully trim the for the legs. Glue the rounded ends to the legs, ends of the pulley shaft on both sides, one on each side of each leg, and the flat angled ends leaving about 11⁄2 in (4 cm) on each side of the legs. to the base.

Generator 53 15 Using the last craft stick, cut a length of about 16 Cut a piece of wooden skewer about 1 in 21⁄2 in (6 cm) from it for the generator’s crank (21⁄2 cm) long and glue it into the hole at the handle. Drill a hole about 3⁄8 in (1 cm) in from each end. rounded end of the handle. 17 Push the second glue Check that disk (see step 8) onto the shaft can the end of the pulley shaft— at the same end as the first turn freely. glue disk. The glue disks keep the pulley in place. 18 Push the crank handle onto the other end of the pulley shaft, making sure that the wooden skewer on the other end is facing outward. Secure it with hot glue.

54 Generator Make sure that the center of the pulley is in line with the motor’s shaft. 19 Find a place for the motor in the center of 20 Cut another 1⁄4 in (6 mm) thick disk from the base, far enough from the pulley that the glue gun stick. Push the point of a skewer the rubber band is taut. Glue the motor down, then into its center, but do not push all the way through. stretch the rubber band over the motor’s shaft. Push the glue stick disk onto the shaft of the motor. The resistor will help limit how much current flows through the LED. 21 Carefully bend the legs of the LED up. Next, 22 Attach one end of the 150 kΩ resistor to one glue it to the base with a blob of hot glue. of the terminals of the motor. It doesn’t matter which one. 23 Using the crocodile wires, connect the clip of 24 Connect the other ends of the two wires one of the wires to the free end of the resistor, to the two legs of the LED. The generator and the clip of the other wire to the other terminal of is ready to operate. the motor.

Generator 55 25 Turn the handle of the generator. Turning the handle spins the Make sure the shaft of the motor is pulley. This spin is transferred to turning. LEDs only light up when the current the motor via the rubber band. flows in one direction, so if it doesn’t light up, As the motor spins, it it may mean that the current is flowing the creates an electric wrong way. Try turning the handle the other current in the circuit, way, or switching the crocodile clips attached and the LED lights up. to the LED, as this will switch the direction of current from the motor. How it works Real-world inventions A motor is designed so that its shaft Hydroelectric power spins when electric current flows through it. However, this process can be Nearly one-fifth of the world’s electricity is generated reversed: spinning the motor’s shaft can by hydroelectricity (the energy of moving water). The be used to produce an electric current. machines in this picture are turbines at the Hoover Dam Inside the motor are static magnets as in Nevada. The turbines spin as water pushes through well as three coils of wire that can spin. them, turning generators that supply electricity. Two magnets with north (red) 5. The electric current and south (blue) poles sit inside the motor’s casing. passes into the motor’s terminals, supplying 1. The magnets’ magnetic power to the LED. fields exert force on the 4. The commutator is a electrons in the coils of wire. component that transfers Motor electric current from each casing of the three coils of wire to the motor’s terminals. 2. As you turn the crank handle, the 3. Inside the spinning coiled wires, the pulley transfers this force to the motor shaft. As the shaft turns, the coils spin magnets cause electrons to align and push through the wires, producing an electric rapidly through the magnetic fields. current (see p.30 for more on this). Electrons (green) moving through the copper atoms (orange) of the wire.

The propellers spin as Handheld electric current from the fan batteries passes through two motors mounted on Keep cool with this useful handheld fan! In this project, the top of the fan. you’ll be using batteries to power two motors with propellers attached, to produce a cooling breeze. You will be wiring the motors in parallel, which means that each of the motors is on a separate branch of the circuit, so that each one receives the full voltage the batteries provide.

Handheld fan 57 How to make a !i Handheld fan Using a glue gun see p.22 For this project, you will need a battery pack with a built-in switch. You will also need to find pieces 1 Glue the motor platform to the top of the battery of plastic or wood to act as a platform for the motors. pack, making sure it is in the center. Make sure that They need to be wide enough to hold the motors, you can still open the battery pack. and long enough that the propeller blades won’t touch once they are installed. 2 Glue one motor onto each end of the platform, with the shafts pointing away from the side of Time !i Difficulty the battery pack with the switch, and the motor 30 mins Easy terminals facing down. Next, slide on the propellers. Be aware Requires hot glue !i gun and soldering Preparing wires iron use. see p.24 What you need 1x AA battery From the toolbox pack with built-in switch • Hot glue gun • Wire strippers • Soldering iron and solder 2x Fans 2x 2x AA batteries 3-volt motors 6 iMnwa(1itd5etrchima1al)sxfloobrnatghtaearnnyddplseaacmk e Black 1x Platform3(8fxo3xr⁄42mincomt)ors stranded wire 3 in (8 cm) Red 3 Cut and strip two black wires and two red wires, stranded wire each about 11⁄2 in (4 cm) long, and strip the battery pack wires. 3 in (8 cm)

58 Handheld fan 4 Twist the stripped ends of the red wires onto 5 Twist the stripped ends of the black wires onto the left terminals of each motor. the right terminals of each motor. You can shorten the battery pack wires if they get in the way. 6 Twist the ends of the red wires together, 7 Twist the end of the red battery wire around and the ends of the black wires together. the twisted black wires. Then twist the end of the black battery wire around the twisted red wires. The direction the !i fans rotate in is Soldering determined by see pp.25–26 the polarity of the motors, which you can find out by testing them. 8 Flip the switch on the battery pack to test 9 Once you are happy with the flow of air, solder all whether the propellers create a forward-blowing of the wire connections. breeze. If the air is blowing backward, switch the black and red battery pack wires around.

Handheld fan 59 Make sure the fans are clear of the handle when they spin and that you can still open the battery pack. 10Glue a handle to the front of the battery pack 11 Your fan is now finished. that is the same width as the pack. When you turn it on, it will create a refreshing breeze. How it works 2. Each motor receives all When you wire circuit components in parallel, each the energy of the electrons component receives the same voltage, so in your handheld fan, each motor receives the full 3 volts that pass through it. from the battery pack. Two motors in parallel will use twice the power, however, so the batteries will run down more quickly. Real-world inventions 1. Half the electrons 3. Since the speed Car headlights flowing from the at which the motors’ negative terminal of shafts spin depends Car headlights are wired in parallel. If they were wired in series, then if one light stopped the battery pack on the voltage, working, the other one would also not work, pass through one wiring two motors in and both would gradually get dimmer as the battery drains. motor, and half parallel will make through the other. each one spin as fast The electric as if you used only current splits at one motor. this junction.

Matchbox microphone A microphone transforms sound waves into an electrical signal, and allows the original sound wave to be heard when that signal is converted back. With this matchbox microphone you’ll be using a pencil lead to capture sound waves, and some earphones to help you hear the sounds it picks up. The green and red clips are connected to the battery, which provides the base electric signal that is altered by the microphone. Sound waves make the The microphone creates box vibrate, and those an electrical signal that vibrations are passed can be heard through on to the pencil lead. the earphones.

How to make a Matchbox microphone 61 Matchbox !i microphone Using a bradawl The safest and easiest way to get the pencil leads see p.24 you need is to buy mechanical pencil lead refills. Also, it is best to use old or cheap earphones, 1 Use the bradawl to pierce two holes about in case they get damaged. 3⁄8 in (1 cm) apart in one end of the box, then repeat for the other end. Be careful not Time !i Difficulty to hurt your hand when making the piercing. 15 mins Easy Be aware !i Requires bradawl and utility knife use. Utility knife see p.20 What you need 2 Gently scratch one side of both pencil leads with From the toolbox the sharp edge of the utility knife to create a flat side on each. • Utility knife • Bradawl 3 Push the pencil leads through the holes in the box, as shown. Let the pencil leads 1x stick out from each end of the box. Twist Earphones them around so the flat side faces up. 1x Matchbox 2x Graphite pencil leads Be gentle when sliding 2x AA batteries the leads in, as they can snap easily. 3x Wires with a crocodile clip at each end 1x Battery pack

62 Matchbox microphone 4 Snap the ends of the pencil leads, so that about 5 Snap a piece of pencil lead that’s slightly 3⁄8 in (1 cm) remains sticking out from the box. shorter than the width of the box from one of Strip the battery pack the leftover pieces. Place it flat-side down across the wires if they are not other two leads, to bridge the gap between them. already stripped. !i 7 Use a different crocodile clip wire to connect to the remaining battery pack wire. Finally, take a third Preparing wires crocodile clip wire and connect it to the remaining see p.24 pencil lead. 6 Using one of the crocodile clip wires, connect one of the pencil leads to one of the battery pack wires. 8 You should have two crocodile clips that are left free. Connect one crocodile clip to the tip of the metal part of the earphone jack, and the other one to the other end of the metal part. 9 Insert the earphones into your ears, switch on the battery pack if it has a switch, and then gently tap the box. You should hear the tapping sound through one of the earphones. Next, try speaking into the box!

Matchbox microphone 63 How it works Real-world inventions Pencil “leads” are not made of lead: Audio signal they are made of a material called graphite mixed with clay. Graphite The varying electric current conducts electricity, but not very well: microphones produce is called an audio it has a high resistance to electric current. signal. It is a copy of the changes in air pressure of a sound wave. The audio signal can be recorded digitally, and No sound then be displayed and manipulated by using a computer. 1. When you connect the circuit, an electric current flows from the battery, through the 2. The bridging lead makes a good graphite and earphones, and connection with the other two leads back to the battery. when the microphone is picking up no sound, allowing the current to flow. Sound 3. Any sounds directed 4. When the contact is worse, less current at the box cause the bridging lead to jump up flows, and when the contact is better, more and down, disturbing the flow of electric current current flows. The variation in the electric through the circuit. current matches the pattern of vibration 5. The varying current causes caused by the sound waves. the tiny speakers in the earphones to move back and forth, recreating the original sound waves.

Bugbot The bugs will react to sunlight or a strong These amazing creatures seem to come alive halogen bulb, but there is in bright light. They move without being pushed, not enough energy in LED and they don’t even need batteries. But they light to make them move. are not alive: each one is powered by a solar cell, which converts light energy into electrical energy—and the electrical energy powers a motor hidden on the bug’s underside, which makes it vibrate and bounce along! In bright light, the solar cell powers the motor, causing the bug to vibrate and move. You can decorate the bug’s legs with beads or the plastic coating from wires.

Bugbot 65 How to make a The motor wires are usually very thin, so be careful not to snip Bugbot them as you’re stripping them. For this project, you need a solar cell and a vibrating !i motor. There are various kinds of these motors—look for a “coin” or “pancake” one, and make sure it has two Preparing wires leads, not three. Avoid any labeled a “linear resonant see p.24 activator,” as they will not work in this build. 1 Strip the motor’s wires. If your motor has a Time !i Difficulty self-adhesive pad, use it to stick the motor 15 mins Easy to the middle of the solar cell’s underside— Be aware otherwise use a little hot glue. Requires soldering and hot glue gun use 2 If your motor’s wires can reach the solar panel’s terminals, skip this step. If not, cut and strip two What you need 3x Large paper clips short stranded wires just long enough to reach from the ends of the motor wires to the terminals of the From the toolbox 2x solar cell, to bridge the gap. Small paper clips • Wire cutters 3 Use the short wires and solder to connect each • Soldering iron and solder motor wire to a terminal of the solar cell—it • Pliers doesn’t matter which one goes where. If your solar • Hot glue gun cell has long wires, just solder those to the motor wires. 1x Mini 3-volt solar cell 1x !i 3-volt “coin” or “pancake” Soldering vibration motor see pp.25–26 2x Small silver beads 1x Red stranded wire 11⁄2 in (4 cm)

66 Bugbot !i Using a glue gun see p.22 4 Using the pliers, unfold three paper clips, then 5 Use the hot glue to attach each pair of legs to trim the ends and bend them into wide “U” the underside of the solar cell. Make sure the legs shapes, so each one looks like a pair of insect legs. don’t touch the exposed parts of the wires, to avoid causing a short circuit. Use the pliers to bend the ends of the wire to create little feet. 6 Use the wire cutters to trim either the front or 7 If you like, you can make eyes and antennae using the back set of the bugbot’s legs so that they are smaller paper clips and beads. But don’t add too slightly shorter than the rest. This will angle the solar many things, or your bugbot will become too heavy cell, and may help it to collect more light. for the motor to move. Your bugbot will need 8 To make it move, take your bugbot to be exposed to plenty outside if it is very sunny, or place it of bright light to work. underneath a halogen lamp. It will work best on a smooth, flat surface. The vibrating bug will glide across the surface.

Bugbot 67 How it works The bugbot is a simple circuit—the solar panel provides electrons that are used to power the vibration motor, which makes the bugbot move. 1. The solar panel is made up of two layers—the N-type and the P-type, which are separated by a barrier called the depletion zone. When bright light shines on the solar panel, electrons are dislodged from their atoms in the depletion zone. N-type layer Electrons After making their Depletion zone way through the circuit, the electrons will return P-type layer to the P-type layer. 2. The electrons are pushed up through the N-type layer, and into the circuit. This is the electric current that powers the bugbot. 3. Inside the motor is an unevenly distributed weight. When electrons flow into the motor, the uneven weight spins. Its unevenness causes the motor to vibrate. Real-world inventions Uneven weight Smartphone Motor There is a vibration motor inside every casing smartphone. In most smartphones, it is the only moving part. When a call 4. The vibration makes the whole bugbot comes in, the motor activates, whirring and making the whole phone vibrate. shake, and as it does, it lifts off the This is particularly useful when the phone’s ringer is turned to silent. surface and lands again many times each second, so the bugbot bounces along the surface in tiny hops.

The spool provides a path for the chain to move. The jib is the part of a crane that holds onto the load. The coil of copper wire wound around a steel bolt is the electromagnet. The steel nails are the load that the electromagnet is lifting when it is turned on.

Electromagnetic crane Whenever an electric current flows through a wire, it causes the wire to become slightly magnetic. Wind a current-carrying wire into a coil and you have an electromagnet, which works just the same as an ordinary magnet, except that you can turn it on and off! Electric motors, computer hard drives, and loudspeakers are just some of the familiar devices that contain electromagnets. In this project, you’ll make a crane that uses an electromagnet to lift steel objects. Flicking the switch turns the electromagnet off. Winding this metal skewer lifts or drops the crane’s jib.

70 Electromagnetic crane How to make an !i Electromagnetic Using a bradawl crane see p.24 The key to this build is to make it as strong as possible, 1 Cut two strips of corrugated plastic 12 in (30 cm) so you can test the strength of the crane by lifting a heavy by 3⁄4 in (2 cm). Use the bradawl to make a hole in load. We have used corrugated plastic sheets to make the the center of each strip about 1 in (21⁄2 cm) from one box, but you can use a similar material as long as it is sturdy. of the ends. We have used a metal chain to support the crane’s jib— if you can’t get your hands on one, you could use !i string or wire. Using a glue gun Time !i Difficulty see p.22 45 mins Easy Be aware 2 Glue the strips to the inside of the box. Requires bradawl, hot glue Make sure the two holes at the top are aligned. You can glue around the holes to gun, and heat-shrink secure the skewer in place, if you like. tubing use. 3 Place one of the metal skewers through one of What you need the holes, slip the metal bobbin onto the skewer, then stick the skewer through the other hole. From the toolbox: 1x 32–36-gauge SPST switch enameled • Ruler copper wire • Utility knife 1x • Cutting mat Bolt 2 in 8 ft 81⁄2 in (28 m) • Bradawl (50 mm) • Adhesive putty 1x • Hot glue gun 1x Battery • Marker Piece of heat- snap connector • Wire cutters shrink tubing • Electrical tape • Sandpaper • Wire strippers • Double-sided tape At(1le3axst105 1x 1⁄2 1x Corrugated plastic sheet 1x 1x Grill lighter 9-volt battery x1⁄86Bxoc4mxx)2 in 6Minet(a1l5sckme)w2xers 1x 1x Metal chain Metal bobbin 1 m (3 ft)

4 Mark a dot 3⁄4 in (2 cm) down and 11⁄8 in (3 cm) Electromagnetic crane 71 in from the opposite corner of the box on both sides, as shown. Use the bradawl to poke a hole 5 Slide the other metal skewer through both dots. all the way through both holes in the box. Make sure the 6 Wrap the end of the chain around the middle of skewer can turn freely, as it will the lower skewer, and secure it in place with some be the handle for your crane. hot glue. When the glue has dried, spin the skewer to wrap the piece of the chain around it. Turn the skewer around a few times to make sure it turns freely. Tape the coil to the bolt to secure it in place. 7 Next, starting at least 6 in (15 cm) in from one end, 8 Use the sandpaper to scrape 1 in (21⁄2 cm) of wrap the enameled copper wire tightly around the the coating off both ends of the enameled bolt about 600 times. Cut the wire, leaving another 6 in wire to reveal the shiny copper. This will allow (15 cm) free at the other end. you to make an electrical connection at each end.

72 Electromagnetic crane !i Briefly heat the tubing with the lighter, until Using heat-shrink tubing it shrinks around the see p.27 two wires. 9 Strip the battery snap connector wires. Slip some 10 Wrap the other end of the copper wire around heat-shrink tubing over one of the copper wires, one of the terminals on the switch. If you want and wrap the wire around one of the battery wires. to make it more secure, you can solder it in place, but Cover the joint with the tubing and heat-shrink it. it is not necessary. 11 Wrap the remaining wire from the battery snap 12 Now, take the bolt from step 7. Tape the free connector to the other terminal of the switch. end of the metal chain securely to the smaller Again, if you wish to make it more secure, you can end of the bolt. solder it in place. 13 Attach the battery snap Make sure you firmly connector to the battery. attach the battery Turn on the switch, and check that snap connector. the bolt is magnetic by trying to pick up some paperclips or steel nails. !i Don’t leave the switch on for too long, as the wire and battery can get hot.

14 Turn off the switch, and use the Electromagnetic crane 73 double-sided tape to stick the battery and the switch inside the box. How it works Your electromagnetic crane is ready! When an electric current is flowing, a magnetic field is created. The stronger the current, the stronger the magnetic field. In your electromagnetic crane, this effect is increased by coiling the wire and adding the bolt. This increased magnetic field attracts the steel nails. 1. A magnetic field surrounds the wire when a current is running through it. 2. When the wire is coiled, the magnetic field becomes more powerful. Adding more turns increases the strength of the field. Try picking up various 3. The steel bolt increases the objects with your crane by turning on the switch and strength of the magnetic field winding the handle to bring yet again, as the bolt itself up the jib. becomes magnetized. Real-world inventions Scrap-metal crane Large, powerful electromagnetic cranes are used in scrapyards to pick up scrap metal. It only works on ferrous metals—those containing iron. Since most scrap metal is steel, which is a combination of iron and carbon, these cranes are perfect tools. Similar cranes are used in factories to move around large sheets of steel.

When the door opens, the craft stick is jerked out of the teeth of the clip, completing the circuit. These nuts attached to a motor spin and strike the bell when the circuit is completed. Door alarm Frighten intruders away from your room with this mechanical door alarm, which rings out when someone trips the system. All the trespasser needs to do is open the door: this causes an electrical circuit to complete, which triggers two metal nuts to repeatedly strike a bell, alerting everyone nearby!

Door alarm 75 How to make a !i Use a piece of scrap wood Door alarm Drilling to protect your see p.23 work surface. In this project, you’ll need to screw into a door frame— so make sure you ask permission first! We have used a call bell that we’ve taken apart, but anything that makes a ringing noise when struck will work. You also need a bolt to hold the bell slightly above the base. !i 1 Use a drill bit that is slightly wider than the diameter of your bell bolt to drill a hole in Be aware the base board about 2 in (5 cm) from two edges. Requires drill, soldering iron, Time Difficulty 45 mins and hot glue gun use. Medium What you need From the toolbox: 1x 1x Bolt SPST switch • Drill and drill bit • Scrap wood and clamps 1x 1x Bell bowl 2 Slide the bolt upward through the hole and • Ruler Battery screw three nuts all the way down the bolt to • Wire strippers snap connector hold it in place. • Wire cutters • Soldering iron 1x 3 Place the bell upside down on Screw top of the three nuts and secure and solder it with another nut. • Hot glue gun • Double-sided foam tape 2x 1x 6-volt motor AA batteries 1x Clip 9x Nuts 1x 3-volt 1x battery pack bAa6s-esibzoeadrd 1x Chain 1x Craft stick Black stranded wire 8 in (20 cm)

76 Door alarm !i Soldering see pp.25–26 Use clamps to hold 5 Cut and strip a piece of black the base board in stranded wire about 4 in (10 cm) long. place when drilling. Twist it around one of the motor terminals and then solder it in place. 4 Drill a 1⁄8 in (3 mm) hole about 11⁄2 in (4 cm) from the rim of the bell, in line with the bolt. This will create a seat for the motor to rest in. It doesn’t matter which terminal you solder to— either end can be open or closed on a SPST switch. 6 Solder the other end of the wire to one of the 7 Strip about 11⁄8 in (3 cm) of insulation off the red SPST switch terminals. wire on the battery snap connector. Strip and solder the black wire to the remaining SPST switch terminal. 8 Cut and strip both ends of a piece of black 9 Wrap the bared end of the red wire from stranded wire about 4 in (10 cm) long, taking the battery snap connector around a nut, about 11⁄8 in (3 cm) of insulation off one end. Solder the and the black wire attached to the motor other end of this wire to the remaining motor terminal. around another nut. Make sure each nut is tightly secured to each wire.

Door alarm 77 !i Using a glue gun see p.22 You might see a little spark when the nuts come near each other. 10 Insert the batteries into the battery pack and 11 Apply hot glue to one side of the clip, and stick connect the snap connector. Test the circuit by it onto the base board, so that the mouth of flipping the SPST switch: the motor should whirr when the clip is roughly in line with the battery pack. you touch the two nuts together. Turn the switch off. Turning the switch on readies the 12 Next, use the hot glue gun to glue the alarm, but no current will flow to battery, switch, and motor onto the the motor until the two nuts touch. base board. Glue the motor directly over the hole you drilled in step 4—but make sure no glue gets near the motor’s shaft. To give the motor extra stability, you can glue an L-shaped wooden bracket onto the motor’s side and the base board.

78 Door alarm Carefully glue the nuts one at a time, so they don’t end up glued together. 13 Take the two wired nuts from step 9 and glue 14 Take another nut and glue one side of it to one each to the upper and lower jaw on the the top of the motor shaft. Be careful not to clip’s mouth. let glue drip down into the motor, and make sure the hole in the middle of the nut is clear. Bend the wires so that they form a loop. 15 Cut two wires into equal lengths, which, 16 Thread the wires with the nuts through the when bent in half, are long enough to reach motor nut. Adjust the length of the wires to the motor shaft and bell. Thread the wires through a make sure that the nuts can reach the edge of the bell. nut each and then bend each wire into a “U” shape. Clamp the stick to a piece of scrap wood before drilling. 17 Now glue the wire loops closed. Each wire loop 18 Cut the craft stick in half, then drill a hole should have a nut on it, and each of these nuts near the end of one half. Attach one end should be able to hit the bell when the motor turns. of the chain to the hole, and secure the other end to the door frame with a screw (ask permission first!).

Door alarm 79 The chain must be secured to the door frame. 19 Use double-sided foam tape to attach the 20 Flip the switch. The next time the door is alarm to the door. Place the craft stick opened, the craft stick will slide out of the clip, between the nuts in the clip’s jaw. causing the circuit to complete and the alarm to sound. Open circuit How it works The piece of craft stick is made of wood, which does not conduct electricity, and when it is removed, the circuit is complete. 1. When the craft stick is holding apart the jaws of the clip, no electricity can flow to the motor— even when the switch is on. Closed circuit 3. The motor turns, Real-world inventions 2. When the door opens, the causing the two nuts Refrigerator light craft stick is pulled out, the to sound the alarm by clip closes, and electricity When you open a refrigerator door, flows around the circuit. repeatedly striking the light inside the refrigerator comes on automatically. There is the bell. a spring-loaded switch just inside the door that is off when the door is closed. When you open the door, it causes the switch’s contacts to complete a circuit, which turns the light on.

Infinity mirror Each reflection of the LED strip is dimmer and smaller than the last one, How can you make a normal mirror look like it stretches on which gives the effect of great depth. forever? All you need to achieve this illusion is a strip of LED lights, some mirrored film, a picture frame, and a mirror. The lights from the LED strip are reflected again and again inside the frame, creating images that appear to fade far into the distance!

Infinity mirror 81 How to make an !i Infinity mirror Utility knife see p.20 For this project, you will need a “deep-box” frame with a removable inner frame. Any size frame will work, but 1 Remove the glass or plastic window from the frame. the mirror must fit perfectly into the outer frame. Either Use it as a template to cut the one-way mirror film match the frame’s size to the mirror’s size, or get the mirror so that it is slightly wider than the window on all sides. cut by a professional to match the frame. Finally, be careful If the window has a protective covering, peel it off. handling the mirror and glass, as they can cut you. 2 Lay the window on a flat surface and spray it Time !i Difficulty with a little soapy water. The water will help 20 mins Easy the one-way mirror film to stick to the window. Be aware Requires utility Use both hands to ensure the mirror knife, drill, and film doesn’t stick to itself. household power use. What you need From the toolbox: 1x One-way reflective mirror film 1x Plastic card • Utility knife • Cutting mat • Ruler • Drill • 5⁄16 in (8 mm) drill bit • Scissors 1x kiCtclehaenn cloth 1x 1x Cuttable LED strip 1x with mains plug (293Mxx i92r3rxox2r5incm) 1x 9 xD9wexeit2phi-nabn(o2xi3npxni2ec3rtufxrra5emcfrmea)bmoetw,tlaeSteospraripnayyaer 3 Carefully peel off the mirror film’s backing. Place the adhesive side of the mirror film onto the window. Working out from the center, use the plastic card to smooth out any bubbles to create a flat surface.

82 Infinity mirror !i Inner frame Drilling see p.23 Outer frame Use a metal ruler to protect your fingers when cutting. 4 Dry the window with a towel, then trim 5 Drill a hole through the outer and inner frames. off the excess mirror film with a utility knife. Make it wide enough to accommodate the cord of the LED strip. You may need to drill two holes side by side to allow for this. 6 Remove the inner frame, and measure the LED 7 Cut the LED strip. Make sure you only cut the strip strip so there is enough to go around the entire on the marked cut lines. length of the inner frame’s inside. 9 Stick the adhesive side of the LED strip Press the LED inside the inner frame, removing the strip firmly into backing as you go. If your LED strip doesn’t the corners. have adhesive backing, use hot glue or double-sided tape. 8 Feed the end of the LED strip through the drilled The lighted part of the hole in the inner frame. strip should be up against the hole.

Infinity mirror 83 11 Place the mirror into the frame so that the reflective surface faces away from you. Then place the backing board into the frame and secure it in place with the tabs. Plug in the LED strip and turn on the switch. 10 Lay the window into the outer frame with the Use the metal tabs to make sure Insert the LED mirror film facing toward you. Feed the cord the backing board is secured, or cord into the plug from the LED strip through the drilled hole in the outer frame, and lay the inner frame on top of the window. else the mirror may fall out. it comes with. How it works 1. The light waves Mirror film Your infinity mirror works by bouncing from each LED on 3. When this reflected the light from the LEDs off the mirror the strip travel out and the mirror film again and again, light hits the mirror film which gives the impression of an in all directions. at the front of the frame, infinite depth to the mirror. half the light reflects 2. When the light back in and half the light passes straight through, waves hit the allowing it to be seen. mirror, they are reflected forward. 4. The reflected light Mirror reflects off the back mirror and the mirror film With every reflection again and again, forming in the mirror, the LED multiple images of the LED, each one appearing appears dimmer, as smaller and farther back light is lost through than the last one, giving the illusion of depth. the mirror film. LED Real-world inventions The mirror film allows you to look One-way mirrors into the infinity mirror, and see yourself reflected in the mirror at Some police interview rooms have a the back of the picture frame. half-mirrored window like the window at the front of your infinity mirror. To people inside the interview room, it looks like a mirror—but people watching in the next room can see through it, like a window.

AM radio The earphones play the sounds extracted by the circuit from With just a handful of components radio waves in the air. and a bit of know-how, you can catch the airwaves by making your own radio. “AM” stands for “amplitude modulation,” which is one way to send a radio signal. AM signals can travel over great distances, and were the first kind of signals used for broadcasting radio signals. A coil of copper wire wrapped around a ferrite rod captures the radio waves.

AM radio 85 How to make an 30 gauge 1x 1x enamelled copper wire Earphone Variable AM radio tuning 9 ft (23⁄4 m) socket capacitor Make sure the earphone socket is the right fit for your earphones or headphones. You’ll need to use 1x 100 kΩ resistor 1x Ferrite rod a soldering iron in several parts of the project, so 1x 1 kΩ resistor make sure you work somewhere where you can 6 x 8 in base leave it plugged in safely. 1x Time !i Difficulty 40 mins Medium Be aware Requires soldering iron and hot glue gun use. What you need 1x 1x 2x 0.1 μF Earphones or AA batteries From the toolbox: capacitor headphones Black solid- • Ruler core wire • Clear tape 71⁄8 in (18 cm) • Wire cutters • Sandpaper 1x 1x 1x 1x Red solid- • Third-hand tool 3-volt battery TA7642 Mini 0.01 μF core wire • Soldering iron and solder pack with wires AM radio IC breadboard capacitor 71⁄8 in (18 cm) • Wire strippers • Pliers • Multimeter • Hot glue gun 1 Tape the copper wire to the ferrite rod, leaving about 4 in (10 cm) of wire on the end. Next, wind the wire around the rod, making about 80 turns. Cut the wire, leaving about 4 in (10 cm) at the other end, and secure it with tape. The ferrite rod makes the coil more sensitive to radio waves.

86 AM radio !i Soldering see pp.25–26 2 Use sandpaper to remove about 1 in (21⁄2 cm) 3 Use the third-hand tool to hold of the coating at each end of the copper wire. the ends of the copper wire, This will reveal shiny copper, which will allow you then tin the exposed ends. (See p.26 to make an electrical connection at each end. for instructions on tinning.) !i The solder on the tinned ends Preparing wires will melt when see p.24 you attach the wires. 4 Cut a red wire and a black wire each at 31⁄8 in (8 cm) 5 Use solder and a soldering iron to tin one end long, then another pair each at 4 in (10 cm) long. of each of the four wires. The tinned ends of Use wire strippers to strip about 3⁄8 in (1 cm) off each the wires will connect both the tuning capacitor end of all four wires. and the headphone socket to the circuit board. 6 Trim the ends of the battery pack wires and strip 7 Use the needle-nose pliers to bend the tinned about 3⁄8 in (1 cm) off the ends. Twist the stranded ends of the copper coil wire back on themselves, wires and tin these too, using the third-hand tool to forming small hooks. hold the wires in place.

AM radio 87 The coil and the capacitor will detect radio waves. 8 Solder the tinned copper hooks 9 Use the needle-nose pliers to bend the tinned to the variable tuning capacitor ends of the shorter red and black wires into hooks. prongs. It doesn’t matter which Solder the hooks to the tuning capacitor prongs. Again, way around they are connected. it doesn’t matter which wire is connected to which side. 10 Prepare to test the terminals on your earphone 11 Use a multimeter to test the socket by plugging in the earphones. terminals on the earphone socket. Listen to the earphones to work out which terminals to solder the wires to. The correct terminals will be the ones where the static is loudest. The red measuring lead determines the positive charge. !i Using a multimeter see pp.28–29 12 Solder the tinned ends of the longer red and black wires to the terminals of the headphone socket. Make sure you connect the black wire to the negative and the red to the positive side.

88 AM radio Black battery pack wire [H8] 13 Follow this breadboard map to plug all of the individual components into the mini breadboard. Make sure the flat side of the TA7642 AM radio IC faces in towards the middle of the breadboard. Black tuning capacitor wire [G4] 0.01 μF capacitor [F4 and F8] 100 kΩ resistor [I4 and J10] TA7642 AM radio IC 0.1 μF capacitor [J8 and 10] [G8, G9, G10] Red tuning capacitor wire [H9] Red headphone socket wire H10] Red battery pack wire [A16] Black earphone socket wire [I16] 1 kΩ resistor !i [C16 and G16] Using a glue gun see p.22 14 Plug in the earphones and insert the batteries 15 If you can’t hear any static, check all the into the battery pack. If the circuit is working, connections. Once you hear the static, glue you will hear static noise through the earphones. down all the components to the base. Tune the knob on the tuning capacitor to pick up AM radio stations.

How it works AM radio 89 AM stands for “amplitude modulation.” Real-world “Amplitude” means the height of a wave, inventions and “modulation” means to change something. AM radio stations take a base FM and DAB carrier wave and change its amplitude to carry sounds, which they then broadcast Starting in the 1920s, the first radio at a specific address on the radio wave stations used AM technology, but a rival spectrum, called a station’s frequency. These method of broadcasting, called frequency waves enter your AM radio through the coil. modulation (FM), overtook it by the end of the 20th century. These days, many radio 1. Radio waves create an stations use digital audio broadcasting (DAB), which relies on computers to electric current in your create the signals they beam out. AM radio coil that is an exact copy of the original 2. When you select one of these electrical signal. signals with the tuning capacitor, it passes to the TA7642 AM radio IC. 4. The earphones You can turn then convert the the knob on the audio signal into tuning capacitor to pick up different sound waves. radio stations. The audio signal carries the 3. The TA7642 AM sound of music and speech radio IC extracts the through the earphones. audio signal from the modulated waves and amplifies it. Different radio The coil picks up the The TA7642 AM radio IC The fixed capacitor The earphones turn the stations release radio waves, and you use the amplifies the signal. smooths out the signal audio signal into sound sound as radio waves. tuning capacitor to select a to become a clear so you can hear the particular frequency. audio signal. original sounds. Many AM Specific but unclear Specific and clear radio signals radio signal radio signal

Bend the copper wire into simple or complicated shapes. The switch allows you to turn off the game when you are not using it. Inside the box are a battery and a buzzer. Buzzer game Do you have a steady hand? Find out by making this game! Try maneuvering the copper loop from one end of the twisting path to the other without the loop and wire touching. If they do, a buzzer will sound and an LED will light up to let you know that you’ve lost the game. Challenge your friends and see who can get the farthest.

Buzzer game 91 How to make a !i Buzzer game Drilling see p.23 Before you start this project, you’ll need to prepare the sides of the box. Ask an adult to help you cut out five squares from plastic or wood. Most buzzers will work at a range of voltages from about 3 volts to 20 volts— this circuit uses a 9-volt battery. Time !i Difficulty 1 Using the 1⁄8 in (3 mm) drill bit, make a hole for 60 mins Hard the LED’s legs in the center of one of the box sides. Be aware Drill two more holes big enough to fit the copper wire, Requires drill, hot glue gun, each 3⁄8 in (1 cm) from the LED hole. and soldering iron use. 2 On another box side, use the 1⁄8 in (3 mm) drill bit to make a hole in the corner. In a different What you need 1x corner, use the 5⁄16 in (8 mm) drill bit to create a 9-volt battery rectangular slot large enough for the switch to From the toolbox sit in. Use sandpaper to smooth the slot. 1x 1x • Drill SPST switch 330 Ω resistor 3 Use a hot glue gun to join four panels together • Scrap wood and clamps along their sides as shown below. • 1⁄8 in (3 mm) drill bit 1x The side with the • 5⁄16 in (8 mm) drill bit Battery snap three holes will be • Sandpaper the top of your box. • Hot glue gun connector • Wire strippers !i • Soldering iron and solder • Wire cutters Using a glue gun • Pliers see p.22 • Electrical tape 1x Thick unlaquered Buzzer copper wire 3 ft 9 in (1 m 15 cm) 1x Black stranded wire 193⁄4 in (50 cm) 5x LED 104cxm4) (10 x in panels Red stranded wire 23⁄8 in (6 cm)

92 Buzzer game !i Preparing wires see p.24 4 Slot the SPST switch and the LED into their holes. 5 Cut and strip a piece of red stranded wire Once through, widen the legs of the LED against approximately 23⁄8 in (6 cm) long. Next, strip the inside of the box to secure it in place. the battery snap connector wires. ! i It doesn’t matter Soldering which wire you solder see pp.25–26 to which terminal. 6 Tip the box on its side, so you can see into it. 7 Strip the end of the buzzer’s red wire. Twist the Glue the buzzer near the bottom of one side, red battery snap connector wire around one near enough to connect it to the switch. switch terminal, and the red buzzer wire around the other terminal. Solder both in place. 8 Solder one end of the red stranded wire from 9 Solder the other end of the stranded step 5 onto the same switch terminal as the wire to the shorter (negative) leg of the LED. red buzzer wire.

Buzzer game 93 10 Solder one end of the resistor (it doesn’t matter 11Strip about 13⁄8 in (31⁄2 cm) from the black which end) onto the longer leg of the LED. buzzer wire. This wire will wrap around a Make sure the two legs of the LED are not touching. resistor and one end of the copper wire. You can solder the Make sure you resistor to the black place the battery buzzer wire for extra stability, if you wish. where the snap connector wires can easily reach it. 12 Twist the other end of the resistor firmly 13 Attach the battery to the snap connector. around the black buzzer. Leave about Glue the LED and switch securely into their 3⁄4 in (2 cm) of stripped wire left over. slots and glue the battery anywhere inside the box. 14 Cut about 31⁄4 ft (1 m) of the thick copper wire. Use the pliers to twist the wire into whatever shape you like. Make sure you keep the last 1 in (21⁄2 cm) of each end of the wire straight. The more twists, turns, and loops you add, the more challenging the game will be.

94 Buzzer game Twist the wire tightly around the copper wire and solder if needed to secure it. 15 Insert the two ends of the copper wire into 16 Twist the end of the buzzer’s black wire the holes on the top of the box, and glue firmly around one of the ends of copper them into place. Make sure there is about 3⁄8 in (1 cm) wire inside the box. of each end sticking into the box. The wire should be 18 Thread the shorter stripped end of the black long enough to reach wire through the remaining hole in the side from the bottom of of the box, and twist it around the black battery wire. the box over the copper wire shape. 17 Cut a piece of black stranded wire about 193⁄4 in (50 cm) long. Strip about 3⁄8 in (1 cm) off one end and about 13⁄8 in (31⁄2 cm) off the other. 19 Cut another piece of the copper wire, about 6 in (15 cm) long. Use the pliers to bend the end into a loop. The tighter the loop, the more difficult the game will be. 20 Twist the stripped end of the long black wire around the straight end of the copper loop. Secure the wire connection by wrapping electrical tape tightly around it.

Buzzer game 95 Make sure no glue gets on the circuit inside. Turn the switch on to start playing. 21 Use hot glue to attach the final panel to the 22 Your buzzer game is finished. Slide the loop side of the box. The bottom of the box should onto the copper wire to play. See if you can be left open. get the wire loop from one end of the copper wire to the other. If the loop touches the wire, the buzzer will sound and the LED will light up, and you have failed. How it works 2. When the circuit is complete, current If you keep the copper loop away from flows through the resistor and the LED, the copper wire, the circuit is incomplete. lighting the LED. Some current also flows No current flows, the buzzer will not make a sound, and the LED will not light up. through the buzzer, making it buzz This means you’re winning! loudly, letting you know you have failed. 1. When the loop touches the wire, you are completing the circuit. Real-world inventions Bumper cars Inside a bumper car is an electric motor that powers the wheels and electric lights for headlamps. The floor and the ceiling of the ride are connected to an electrical power supply. A metal pole touches the ceiling, and a metal contact beneath the car touches the floor. Electric current flows through the motor and the lights, as long as you have the foot pedal pressed down.

Breadboard car This speedy car is powered by nothing more The breadboard makes it than a simple household battery. All you’ll easier to wire the circuit, as need to do is connect a few wires and basic components and wires can components on a breadboard—which also acts as the car’s frame. The car has bright LEDs simply be inserted into it. as its headlamps and a motor that turns a propeller to make the car move. The battery supplies electric current to the circuit. A resistor makes sure that just the right amount of electric current flows through the LEDs.

The electric current flowing through the circuit and into the motor causes the fan to turn.

98 Breadboard car How to make a Time !i Difficulty 35 mins Medium Breadboard car Be aware Requires hot glue gun You’ll need to follow these steps carefully to make sure and soldering iron use. you wire the LEDs and the motor correctly. The motor is powered by a 9-volt battery: if it becomes hot, switch off the car for a few minutes to let it cool down. For more information on how breadboards work, see pp.34–35. What you need 1x Apply glue along Battery snap each line where From the toolbox: a straw will go. connector • Ruler 4x Bottle tops • Scissors !i • Hot glue gun 1x • Wire cutters 510 Ω resistor Using a glue gun • Double-sided foam tape see p.22 • Wire strippers • Pliers • Soldering iron and solder 1x Red solid-core wire 1 Mark two lines on the bottom of your breadboard 3–9-volt motor 23⁄8 in (6 cm) that are at equal distances from the ends. Cut two pieces from the straws, each slightly wider than the 1x Plastic propeller breadboard. Use hot glue to stick the straws down. 2x Skewers 1x SPST switch Black solid-core wire 11⁄2 in (4 cm) 2x Red LEDs 2x Straws 1x 840-pin breadboard 2 Use the sharp end of a skewer to poke a hole through the center of each of the bottle tops. Be careful not to hurt yourself with the sharp point. 1x 9-volt battery

Breadboard car 99 3 Trim two skewers so that they are about 11⁄8 in 4 Put a small amount of glue on the ends of the (3 cm) longer than the straws. Slide the skewers skewers to hold the wheels in place. Make sure through the straws and push one bottle top onto each the wheels are at right angles to the skewer. side of each skewer, as shown. The shorter LED The battery leg plugs into a terminals should hole in the negative bus. face this way. The longer LED leg plugs into a hole in the positive bus. 5 Plug in the LEDs and resistor as shown. It doesn’t 6 Cut a piece of double-sided foam tape the same matter which way the resistor goes. Carefully size as your battery. Use it to secure the battery bend the LED legs forward at right angles to look to the board, directly behind the resistor. like headlights. 8 Solder the unbent end of the wires to the terminals on your motor. 7 Cut a piece of black wire and a piece of red wire !i about 11⁄2 in (4 cm) in length. Strip 3⁄8 in (1 cm) off the ends of each wire, and bend down the stripped Soldering end at one side of each wire. see pp.25–26

100 Breadboard car The motor’s shaft will hold the car’s propeller. The double-sided foam tape keeps the motor in place. 9 Cut a small piece of the double-sided foam tape 10 Plug the red wire into a hole in the closest and use it to secure the motor to the other end of positive bus and the black wire from your the breadboard, with the motor’s shaft pointing off the motor into a hole in the closest negative bus. end of the breadboard. Make sure the ends of the wires are firmly in place. 11 Cut a short piece of red wire about 3⁄4 in (2 cm) 12 Plug the SPST switch into the breadboard as long. Strip a little insulation off the ends, and shown. The first prong of the switch should bend the bared wire with your pliers. Push the ends be in the same row as the small red wire. into the breadboard as shown. 13 Connect the battery snap connector to the 14 Push the end of the negative (black) wire into battery. Use the wire cutters to trim the wires a hole in the negative bus and the end of the of the snap connector. Strip about 1⁄4 in (1⁄2 cm) off positive (red) wire into a hole next to the middle pin of the ends of the wires and twist the bared ends. the switch, as shown.