Trouble w. analog Read of a Mic Amplifying Circuit

I've wired up a mic amplifying circuit ...
(image to follow) and connected it to my Decimlanove. The problem is the value of successive analogRead calls starts aroung the 70-90 range, and over time, (hours) climbs to around the 420-470 range. This is with the same ambient noise level. How I can stablise the default analogRead value - it's difficult to set a threshhold value when the baseline keeps moving! Any ideas?
(first time poster) :smiley:

Here's the Circuit I'm using (exactly)

Thanks in advance for any help!

Perhaps it would be better if you first stated what you are trying to accomplish, what is the task that the Arduino will do with the audio signal?

This mic/amp generates a AC audio output voltage, that creates both positive and negitive voltages at any given instant of time. An arduino can only safely measure voltages from 0-5vdc, but not negitive voltages.

Lefty

Thanks Lefty. The purpose is simple to simply create a trigger for a voice activated night light. All I wanted to do is set a threshold at which my program could say "ok - time to turn on the light" - it works if I set the threshold high enough and shout into the mic. But I'd like to stop the analogRead values (for almost silent) from increasing over time... so I can set up a lower threshold value and not have to shout :slight_smile:

If there's other info you need - let me know. Thanks again.