/diy/ - Do It Yourself

>>2398861
>I tried running the valve at 120Hz and the noise was still very much there.
Makes sense. If signal has fast edges it wouldn't really matter if pulses happen at 120 or 300kHz because in both cases the edge is what's causing noise.

Here is simulation of what might be happening with your system. Ringing on voltage bus will happen due to parasitic elements of the wire and solenoid. If you add a diode, you mainly prevent big voltage spikes on the pin which might introduce additional noise, but noise on supply line will still remain. You should be able to fix it by adding a capacitor close to solenoid to ground like in third example. Try adding 10-100nF from solenoid voltage supply to ground and see if it helps.