Understanding a circuit diagram

Question

I am trying to use an electret mic with beaglebone. Instead of making a preamp, I am using a locally made 'audio board'. This is the instruction slip that came with it :

However, I do not understand how to connect an electret mic to this. The "1 core pickup wire to V.c" is supposed to do the job. I'm attaching a picture of the wire :

I tried connecting the outer strand to the ground of the electret mic and the inner strand to the other terminal. The blue wires are supposed to go the speaker. I connected one to the ground of the beaglebone and the other to an analog pin. Reading the pin did not give me any meaningful results (yelling at the mic didn't increase the value).

Assuming (arbitrarily) that the problem is not with the BBB, can I be wiring the audioboard correctly? I gave 6 v power supply to the board. In any case, I do not understand how my configuration (outer strand ground, inner strand other terminal of mic) can be equivalent to that in the instruction (there are sort of 3 lines in the diagram, and a resistor). What, do you think, could be wrong here?

Answer 1

I tried connecting the outer strand to the ground of the electret mic and the inner strand to the other terminal. The blue wires are supposed to go the speaker. I connected one to the ground of the beaglebone and the other to an analog pin.

Two problems (more than likely)

• Your electret mic needs a polarizing current to activate the circuit inside it.
• Don't connect the speaker wires to ground - you may (have) damage(d) the amplifier

Try a 10 kohm resistor to positive supply for biasing the electret microphone and try using an audio transformer for pulling off the signal from the amp (assuming it isn't now damaged).

It could easily work without the audio amp just by biasing the electret has mentioned above. I have no-idea what the input is on the beaglebone so I can't comment on where you need to AC couple it via a capacitor and/or dc bias it to midrail.