Grounding for arduino, measuring phase controllled 240V I would like to measure a phase controlled 240Vac waveform as a digital PWM input for an arduino. The signal would look something like this:



My intent was to use a zener clipping circuit to limit the positive portion of the waveform to 5V, and measure that signal. However, I want to make sure I'm properly grounding these items. This is what my proposed circuit looks like, with all components inside a metal chassis.



I feel like ideally I would isolate this waveform from the system controller/light with a 1:1 transformer, but I'm unsure if that is feasible given its irregularity. Can I safely connect the arduino ground to the system's neutral, or am I barking up the wrong tree?

Thanks!
your circuit will work, and can be simplified a little bit further. But it will work.

it is safer to use isolation, however. there are multiple ways to go about doing it.

the key here is to detect zero crossing, and start counting from there.