I've been trying to set up a microphone circuit for use in an AVR, essentially just to detect levels of noise. I observed some strange behavior in the amplified circuit I set up, so i elected to strip the circuit down to its base functional unit to see if I could figure out what the problem was. Schematic follows.
The resources that I've used to build this circuit all seem to indicate that the type of cap used doesn't matter, so I opted for the higher-capacitance electrolytic. This did not behave as expected.
The following is a waveform captured from the circuit using an electrolytic cap.
Now, the ceramic cap:
To be clear, these waveforms are captured while the room is quiet. blowing into the microphone produces a response.
The ceramic capacitors I have do not dampen the 60Hz noise to my liking, and it seems silly to wire a bunch of them in parallel when I have a few much larger electrolytic caps.
I've tried a few different sizes of electrolytic caps, with the same result.
I've tried reversing the polarity, with the same result.
Why am I seeing this discrepancy? How can I remedy the situation?
Additionally and secondarily, is there an established best practice for using a microphone with AVR?
EDIT turns out i'm seeing this effect because my cheap chinese power supply has a poor rectifier :^)