Electronics_Projects_For_Dummies

180 Part II: Sounding Off!

3.Leaving about 8 inches of wire loose, start winding the enamel-coated wire around the rod, starting about 11⁄4" from one end.

4.When you have about 20 turns of wire on the rod, secure that end with one of the pieces of electrical tape so that it doesn’t loosen while you are finishing the coil.

5.Wind a total of 50 turns of wire around the rod, leaving another 8- inch length of wire loose at the other end.

6.Secure the wire at that end with the other piece of electrical tape.

7.At each end of the coil, use some glue to hold down the wires.

We had you cut the electrical tape 1⁄4" wide so there is enough exposed wire to glue. When the glue is dry, your coil is finished. The finished coil is shown in Figure 8-13.

Figure 8-13:

Your coil, all ready to use.

Putting it all together

Now it’s time to assemble your radio and see whether you can pick up a signal. Follow these steps to complete the project:

1.Attach Velcro to the breadboard and the box and then secure the breadboard in the box.

Chapter 8: Surfing the Airwaves 181

2.Attach Velcro to the battery packs and the box and then secure the battery packs in the box.

3.Insert the wires from the speaker, potentiometer, variable capacitor, coil, battery packs, and the on/off switch to the terminal blocks on the breadboard, as shown in Figure 8-14.

Wire from variable capacitor lug

Wire from coil

Wire from coil

Wire from variable capacitor body

Wire from left lug of potentiometer

Wire from center lug of potentiometer

Figure 8-14:

Connect the speaker, variable capacitor, on/off switch, and battery packs to the breadboard.

182 Part II: Sounding Off!

4.As you insert the wires, cut each of them to the length needed to reach the assigned terminal block and strip the insulation from the end of the wire.

Keep the wires from the potentiometer as far away as possible from the wires from the speaker or the wires from the variable capacitor/coil. You’ve no doubt experienced how having a microphone too close to a speaker can produce an awful screech; the same screech can occur if these wires get too close together.

5.Secure the wires with wire clips where needed.

The way parts are laid out in this box and the distance between some of the components (such as the speaker, potentiometer, and variable capacitor to the terminal blocks) is short enough that you won’t need wire clips.

6.Close the lid on the box and admire your finished radio, as shown in Figure 8-15.

Figure 8-15:

The finished radio.

Chapter 8: Surfing the Airwaves 183

Trying It Out

At this point, the radio is ready to go. Insert batteries and turn it on. Adjust the tuner (the knob on the variable capacitor) and the volume (the knob on the potentiometer) to find listen to your favorite radio stations.

When you tune into a station that you want to find again, mark the position of the tuning knob on the face of the radio.

If you’re not getting the signal you thought you would, here are the obvious things to check out:

Check that all the batteries are fresh and tightly inserted in the battery pack, all facing the right direction.

Check to see that no wires or components have come loose.

Rotate the radio.

When one end of the antenna points at the radio station’s transmitting antenna, the signal from that radio station will be stronger.

Taking It Further

Many people get bitten by the radio bug and want to get into ham radio in a big way. If you’re one of these, here are some variations on this project to keep you going:

You can build an FM radio to get those high-frequency stations. The TEA5710N IC can be used to build a radio that can receive both AM and FM signals.

Build a radio that will receive signals from ham radio operators.

Go to QRP/SWL HomeBuilder (www.qrp.pops.net/default.htm) for some ideas for ham radio projects, or visit www.arrl.org.

Mount an external antenna connected to the ferrite rod to boost the power of the signal if you live in the boondocks where signals are hard to come by.

184 Part II: Sounding Off!

Part III

Let There Be Light

In this part . . .

Thomas Edison discovered what fun light can be in electronics projects when he invented the light bulb.

In the projects in this part, you use light in several forms. For example, you work with tiny LED lights that dance across a display of dolphins; use infrared light to signal a go cart when to go and when to stop; and use an infrared beam to detect motion to set off lights and sound in a snazzy Halloween display.

Chapter 9

Scary Pumpkins

In This Chapter

Eyeing the schematic

Checking off the parts list

Breadboarding the pumpkin circuits

Placing the works in the pumpkins

Turning on your pumpkins

Around the end of October, many of us carve faces in pumpkins and then put candles in those pumpkins to create an eerie effect. Why not elec-

trify pumpkins to do the same thing — and add a spooky sound effect or message to the mix?

In this chapter, we use two plastic pumpkins and activate sound and light by using an infrared beam. When those trick-or-treaters come up to your doorway, won’t they be surprised?

Of course, if it’s February and plastic pumpkins are scarce, use these same techniques with some other plastic container shape to create talking dinosaurs, heart-shaped candy boxes, or whatever!

The Big Picture: Project Overview

When you complete this project, you’ll have two pumpkins:

One that transmits an infrared beam

A second one that lights up and plays back a recorded sound or message when something or somebody interrupts the infrared beam by walking between the two pumpkins

188 Part III: Let There Be Light

You can see the finished pumpkin in Figure 9-1.

Figure 9-1:

The final product: a talking pumpkin.

Here’s the big picture of this pumpkin project:

1.Put together two electronic circuits and fit them into plastic pumpkins with switches, a microphone, and a speaker.

2.Use a microphone to record a sound or message.

We like, “Welcome to Sleepy Hollow. We hope you have a good time,” followed by a spooky laugh.

3.One pumpkin transmits an infrared beam to the other. When someone walks between the pumpkins, the recorded message is triggered, along with a flickering red light.

4.To reduce the chance of this IR noise interfering with your gadget, use an IR detector tuned to detect infrared that turns on and off at 38 kHz and ignores infrared not switched at that frequency. The transmitter circuit then sends out infrared that is switched on and off at 38 kHz, and the noise problem is solved.

One complication you’ll deal with along the way is lots of infrared noise floating around. IR is given off by heaters, people, pets, and pretty much any living creature or equipment that gives off heat.

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Should you be lucky enough to have an oscilloscope perched on your workbench, you can see that a 38 kHz square wave looks something like the one shown in Figure 9-2. But don’t worry: You don’t have to have an oscilloscope to tune your IR transmitter. We tell you how to tune it in the upcoming section, “Trying It Out.”

Figure 9-2:

A square wave on an oscilloscope screen looks like this.

Scoping out the schematic

You put together two breadboards for this project: one that transmits and one that receives and sounds off.

First, you can see the schematic for the board that goes in what we call the silent pumpkin (the one with the transmitter in it) in Figure 9-3.

Here’s the nitty-gritty of the schematic elements for the silent pumpkin:

The IR LED (LED2) is one of the key components of this circuit; the purpose of the rest of the circuit is to send an electrical current, which turns on and off at a frequency of 38 kHz, through this LED. This current causes the LED to transmit IR light that turns on and off at a frequency of 38 kHz (38,000 times a second: so fast you can’t even see a flicker).