Electret Microphone Question

sunblock

I've attached a picture of a schematic of a voice IC module that has an electret microphone attached to it. The schematic shows both the positive and negative leads of the electret mic connected to the voice IC module (ISD3900)--directly. My question(s): why would the negative lead be attached to the IC? Is it not true that the variation on the positive side reflects the sound pressure on the electret mic? And if one wanted to use this as simply a sound sensing device, would it not be better to run the(+) side through a ADC to get get fluctuation readings, and simply ignore the (-)? Similar in concept to the sound impact sensor from Parallax... Thoughts....

VR/JW--Sunblock

Beau Schwabe

This is a basic Electric Microphone (or regular 'coil' microphone for that matter) differential connection which essentially provides better noise immunity (esp with long wires) . In your circuit, the first 1.5k connected to Vcca and the 220uF provide a 'quiet' voltage reference to the Microphone. The other two 1.5k resistors provide the necessary balance for the differential mode of operation.

Of course it's patented ...

http://www.faqs.org/patents/app/20120140956

...but on several occasions I have been able to pull prior art proving that someone else did it first. Funny thing is that the schematic in the patent isn't even correct on the "Ground" side. Ahh well that's another discussion.

http://www.faqs.org/patents/imgfull/20120140956_02



Another very similar differential configuration:
http://www.datasheetdir.com/MAX4061+Microphones

Publison

I have always found this to be faithful when dealing with a condenser mic with ISD/Nuvoron/Windbond chips.

Let it be known that I only have interfaced with Radio Shack 270-092 and 270-090 thus far.

Jim