On Mon, 19 Aug 2013 18:26:52 +0100, MrWeld MrWeld wrote:
A really DIY approach would be to feed the output of mains transformer,
possibly via a potentiometer, into the audio line-in socket of a PC. A
wall-wart with an AC output (rare, but they do exist) would probably
satisfy most safety concerns. You could record the waveform with audio
software of your choice, presumably at a fairly low sampling rate. I'm
not sure whether a typical integrated soundcard can go as low as 50Hz
though.

That's an interesting thought. Mains transformers are easy enough to
find, or as you say an AC PSU. Maybe I can use a low-end CPU device
instead of a PC to keep it low-power: the raspberry pi doesn't have
audio in, but the pandaboard es does. If I've got time I might give
that a go.

Maybe there are cheap ADCs with USB or serial outputs I could use.
This is getting interesting. Thanks for the idea.