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The following is a list of the schematic elements for your parabolic microphone:

The circuit starts with the electret microphone, which transforms sound

waves into electrical signals.

R1 connects the microphone to positive voltage and supplies the 3 volts

required to make the microphone function.

C1 is a capacitor that blocks the DC voltage on the input signal and

allows the AC signal to pass.

IC1,an LM386N-1 audio amplifier, takes the electrical signal generated

by the electret microphone and amplifies it to provide sufficient power

to generate sound through the headphones.

R2is a potentiometer you use to control the sound volume.

C2sets the voltage gain of IC1 to 200. Therefore the voltage out is 200

times the voltage in.

C3improves the stability of the LM386 amplifier to prevent problems,

such as oscillation. Oscillation can turn that nice little birdcall into a

hodgepodge of unintelligible sounds.

C4removes any DC offset from the output of the LM386 amplifier.

C5 acts as a current bank for the output. This capacitor drains when

sudden surges of current occur and refills with electrons when the

demand for current is low.

Building Alert: Construction Issues ...........................................................

The electret microphone cartridge used in this project is about^1 ⁄ 4 " in diame-

ter. Therefore, the contact pads on the cartridge to which you solder wires

are very small. Review the methods for soldering to contact pads that we

cover in Chapter 4. And don’t forget to use your magnifying glass after solder-

ing to check for solder bridging(a clump of solder that could short out the

connection) between the two pads.

If you find bridging solder, try using a utility knife to gentlyclean it out. Also,

you might subscribe to the better-safe-than-sorry theory and consider order-

ing two of these microphone cartridges. That way, if you ruin one while learn-

ing how to solder to these small contact pads, you have a second one at the

ready, saving you time and shipping fees for a second order.

The parabolic dish comes with a reflective finish. We recommend spray paint-

ing it to avoid blinding yourself or others with the sun’s reflection from the

118 Part II: Sounding Off!