Electronics_Projects_For_Dummies

170 Part II: Sounding Off!

Figure 8-3:

Key components.

This supplies 1.5 volts to IC1 because the maximum supply voltage for the ZN416 is 1.6 volts.

Battery pack for 4 AA batteries to supply 6 volts to IC2

ZN416E AM radio receiver IC1

14–365 picofarad variable air capacitor (C2)

You could also use a variable capacitor that goes up to 500 picofarad.

3⁄8"-diameter × 31⁄2" ferrite rod

You can also use a ferrite rod with a 1⁄2" diameter and longer lengths of either 3⁄8" or 1⁄2" diameter as long as they fit in the box that you’re using for the radio. Longer ferrite rods should give you higher sensitivity to weak radio signals than shorter ferrite rods.

We found the preceding three radio-specific items above at Ocean State Electronics (www.oselectronics.com). We noticed that it was less expensive to buy this vendor’s part #LA-540 — a ferrite rod already wrapped with a wire coil — slip off the coil, and then wrap wire to the number of turns we needed on that rod. Buying a ferrite rod by itself was about three times as expensive!

Figure 8-4:

More key components.

SPST toggle switch, used as the on/off switch

830-pin breadboard

Seven 2-pin terminal blocks

Two knobs (for the potentiometer and variable capacitor)

8 ohm, 1 watt speaker

Enclosure

We used a wooden box that we found at a national craft supply store (Michael’s). You can use plastic or wood but do not use metal because it will block the radio signal from the ferrite antenna.

Four 1⁄2" long 6-32 flathead screws

Four 6-32 nuts

An assortment of different lengths of prestripped, short 22 AWG wire

A few feet of 26 gauge enamel-coated wire (used to make the coil)

Chapter 8: Surfing the Airwaves 173

2.Insert wires to connect the ICs and the terminal blocks to the ground bus and insert a wire between the two ground buses to connect them to each other, as shown in Figure 8-6.

Figure 8-6:

Six shorter wires connect components to ground bus; the long wire on the right connects the two ground buses.

3.Insert wires to connect IC2 and the terminal block for IC2’s battery pack to the +V bus, and a wire between the two +V buses to connect

them to each other, as shown in Figure 8-7.

Do not connect IC1 to the +V bus. If you do, you will probably fry the poor IC because it isn’t designed to take 6 volts.

4.Insert wires to connect the ICs, terminal blocks for the coil (L1), variable capacitor (C2) and terminal blocks for the potentiometer (R1), and terminal block for the speaker and discrete components, as shown in Figure 8-8.

5.Insert two 0.047 microfarad capacitors (C4 and C9), two 10 microfarad capacitors (C6 and C7), one 100 microfarad capacitor (C8), two 0.001 microfarad capacitors (C1 and C3), one 0.1 microfarad capacitor (C5), and one 10 ohm resistor (R2) on the breadboard, as shown in Figure 8-9.

When inserting electrolytic capacitors, be sure to check the schematic to see where to insert the longer, positive (+) lead.

174 Part II: Sounding Off!

Figure 8-7:

Connect components to the +V bus.

We discuss in Chapter 4 how you can determine how short to clip the leads of many of these components to make them fit neatly on the breadboard. Not to sound like your mother, but make sure you wear your safety glasses when clipping leads!

Making a box into a radio

After you build the circuit, it needs a home, so the next step in the process is to work with the box you purchased for your radio enclosure.

Follow these steps to get the box radio ready:

1.Drill holes in the box where you will mount the variable capacitor, potentiometer, and on/off switch.

We put both the on/off switch on one side of the box and the speaker, potentiometer and variable capacitor on another side, but the placement is really up to you. Figure 8-10 shows where we placed these components.

Chapter 8: Surfing the Airwaves 175

Open region to speaker TB

Pin 5 of IC2 to open region

Pin 5 of IC1 to R1 TB

L1/C2 TB to Pin 8 of IC1

Battery pack TB to Pin 6 of IC1

Figure 8-8:

Hook up the ICs, terminal blocks (TB), and discrete components.

2.Place the speaker against the face of the box where you want to mount it and mark positions for the four screws you’ll use to secure the speaker.

3.Drill holes to allow clearance for 6-32 screws.

We used a 9⁄64" drill bit.

4.Draw an outline about 1⁄4" smaller than the speaker shape for the opening to let sound from the speaker out.

Use a coping saw to cut the opening.

176 Part II: Sounding Off!

C8 from IC2 Pin 5 to speaker TB

C7 from Pin 7 of IC2 to ground

C9 from Pin 5 of IC2 to open region

R2 from C9 to ground

C1 from IC1 Pin 8 to ground

C3 from IC1 Pin 7 to ground

Figure 8-9:

Insert resistors and capacitors on the breadboard.

C4 from Pin 2 of IC1 to Pin 3 of IC1

See Chapter 4 for more information about choosing drill bit sizes for particular components and other pieces of wisdom on how to customize a box for your projects. Make sure you use safety glasses when drilling and clamp the box to your worktable!

5.Slip the shaft of the on/off switch through the drilled hole and secure with the nut provided.

6.Slip the shaft of the potentiometer through the drilled hole and secure with the nut provided.

Chapter 8: Surfing the Airwaves 177

Potentiometer

Figure 8-10:

Box with on/ off switch, potentiometer, variable capacitor, and speaker in place.

On/off switch

7.Slip the knob on the potentiometer shaft and secure with the set screw provided.

The tread on potentiometers is about 1⁄4" long, so if the wall of your wooden box is 1⁄4" thick, you won’t be able to use the nut to secure the potentiometer. Instead, glue the face of the potentiometer to the box, making sure that you don’t get any glue on the rotating shaft of the potentiometer.

8.Slip the shaft of the variable capacitor through the drilled hole and glue the metal body of the capacitor to the wooden box.

Make sure you don’t get any glue on the shaft or other moving parts of the capacitor.

9.Slip the knob on the variable capacitor shaft and secure with the set screw provided.

10.Secure the speaker with four 6-32 flathead screws and four 6-32 nuts.

Chapter 8: Surfing the Airwaves 179

Wires to potentiometer

Figure 8-12:

Wires soldered to potentiometer and speaker.

Wires to speaker

Be sure to heed all the safety precautions about soldering that we give you in Chapter 2. For example, don’t leave your soldering iron on and unattended. And just in case a bit of solder has an air pocket and pops, wear your safety glasses!

Coaxing the coil

Take your ferrite rod, 26 gauge enamel-coated wire, some electrical tape, and glue and get ready to make the coil by following these steps:

1.Wrap electrical tape around the ferrite rod.

This protects the enamel coating on the wire from the ridges that run along the rod.

2.Cut two small pieces of electrical tape, about 1⁄4" wide, and place them in a handy spot.