Electronic – simple microphone – speaker circuit


This is my first time creating a circuit, so forgive my poor understanding. I am trying to create a simple intercom system with a 9v battery. I have an 8 ohm speaker and a standard microphone:

(source: seeq.com.au)

My circuit looks like this currentlyMy circuit

What else is necessary to get this circuit to function.

Best Answer

Your circuit might almost work if you replace the microphone with a old carbon powder type. This is what old telephones had in the mouthpiece. That type of microphone looks like a variable resistor to the circuit, not the tiny voltage source your microphone probably is. With a variable resistor, you can just put it in series with the speaker and a battery and probably hear sounds picked up by the microphone in the speaker. If you can find a really old telephone with mechanical ringer, it might have a carbon mic in it.

Otherwise, microphones you get today produce a tiny varying voltage. This must be amplified to drive a speaker. Note that some types of microphones, called electrets, additionally need a few volts applied to it with a few kΩ imedance to produce that small varying voltage. Electrets often come in small cartidges like what you show, so you may have such a mic.