controlling a pump width PWM
Have you scoped your input pin before and after your PWM circuit is causing it to go crazy? If you run PWM without anything plugged into the PWM pin and you don't see the problem then I wouldn't be on this being a timer issue.
If you haven't yet, you should read up on the LM1815 chip as it is designed specifically for what you're doing.From the LM1815 datasheet:The LM1815 is an adaptive sense amplifier and default gatingcircuit for motor control applications. The sense amplifierprovides a one-shot pulse output whose leading edgecoincides with the negative-going zero crossing of a groundreferenced input signal such as from a variable reluctancemagnetic pick-up coil.
you have electrical noisewhat is the spec of the rpm sensor ?is it a VR sensor with analogue or digital output ?
It is diffucult to see from the video but, it looks like you are sharing 1 ground wire with you Mosfet and your Schmitt trigger. I would recommend that the Schmitt trigger have it own power,signal,ground wires to the Arduino to eliminate noise from other loads on the wire.Mark