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I started logging the mains waveform because I noticed when we have power outages, the power tends to flicker badly instead of simply going off, and I just really wanted to know what that looked like.

The setup is simple - a small transformer to knock the voltage down to a usable range, into a cheap USB mixer, into a laptop which runs arecord in a loop. Could easily do it using a Pi or something like that, but for me the laptop has a battery and is already on 24/7 doing some radio monitoring.

The video of the lamp was made after the fact, but is accurate to how it really looked during the outage. Since I have the recording of the outage, I can play it back through a big amplifier, calibrate it to ~120V, and connect a light bulb in place of the speakers :)

Note I put a high-pass filter on the audio in the video clip, just to make it a little more user-friendly. I have the full thing in 22k 16bit wav though...