On Sat, Nov 16, 2013 at 09:26:10AM -0800, Chris Albertson wrote:
> The signal is 120 volts. You hardly need to amplify it.
I tried this a slightly different way. Since there is mains noise
everywhere, I made a small loop and connected it to a 3.5mm jack
and then plugged that into the mic socket on a sound card. You can
get lots of (slightly noisy) samples per second. I took chunks of
this data and took the Fourier transform to find the dominant
frequency:
http://www.maths.tcd.ie/~dwmalone/time/leap2012/#mains
but I guess you could filter it and count crossings too?
David.
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