I'm experimenting with an electret microphone, specifically this one. I put it on my scope and I see what I expect - a really small voltage, typically under 20mV, that varies appropriately with sound.
However, when I put it into my Arduino (connecting signal pin to A0, V to 5V, and G to GND) and read it using analogRead on the appropriate pin, I end up getting a strange offset. The analog read should read 0 more or less constantly, due to the low voltage coming out of the board. However, I get an offset of around 425 counts on the ADC, implying that the voltage is somewhere around 2.5V.
What's going on? Why would the arduino be reading a voltage when there isn't any?