Mic experimenting has been interesting, and by interesting I mean a lot of me cursing at circuitry. I’ve been tinkering with a few options, trying to find a light-weight circuit suitable for use in a tiny portable device. Finally, I have a circuit that’s working well for me, and it’s more or less this:
(Thank you Soyoung Park and ITP Sensor Wiki!)
I’m using a 386 because they’re cheap, low-power, and easy (insert a “your mom” joke here). They don’t require negative voltage, they can do a variety of functions, and they’re easy to find at pretty much any electronics retailer. The circuit is very similar to what Tom Igoe has in the Physical Computing book, with a bridge rectifier added to turn negative-and-positive readings into all-positive (as mics measure input by swinging voltage both positively and negatively) and a low-pass filter to get rid of some of the high-frequency noise that was giving me ugly spikes in the readings.
Breadboarded, that looks like this:
Lots more pictures in that Flickr set too.
I keep finding a ton of better ways to do what I’m doing, so consider this to be one of a million work-in-progress listings, but here’s what I’ve been all up ons the past week or so:
From Rason.org — Designing Op Amp Audio Preamplifiers
At the moment I’m using an lm386 rather than 741, but for the second draft I think I’ll try that route. It’s a much more powerful amp, so I can only imagine the improved clarity and response. For now though, the 386 is so simple, cheap and low-power that it’s hard to argue with.
I’ve also been reading a pile of other op-amp things, including:
Wikipedia — Operational amplifier applications
Ron Mancini — Op Amps for Everyone (and free PDF here)
Don Lancaster — Active Filter Cookbook
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