Mains Power Frequency Monitor
Ages ago, I had built a tool to monitor the mains power frequency with resolution of some microseconds. I looked at my old assembly code, and realized with better optimization and optocoupler choice, I could probably get that down to some hundreds of nanoseconds. The original idea was to try and correlate phase jitter to space weather, essentially using the mains power system as a sort of radio telescope. I never did get it working (although I did not have much time to try, either). I was able to see interesting things like generators spinning up to maintain the frequency though. Will open source the hardware when done. I am not an astronomer, just some random fellow that investigates things at depth for no particular reason.