Mains waveform monitor


This circuit monitors the waveform of the connected mains supply. It does so in an isolated way so that the waveform can be recorded by an isolated, low-voltage data acquisition system. This is used as a "veto" signal in the lab to determine whether fluctuations in our sensitive instruments were caused by something intended or rather by a power spike on the mains supply to the lab.

After I built this, I discovered how rubbish the waveform from board mount transformers can be. If you can't trust the transformer, you can't trust what the circuit says the mains waveform looks like. Instead, I put the circuit in a bigger box with a toroidal transformer, with wires connecting the transformer to the board in place of the sockets for the board mount transformer. This worked much better.