[rcheshire (Rowland)]

Noise is presenting as spikes in analog sensor input values during setpoint modulation - switching - and occasional chirping through the 12v supply - I will refer to your diagram on this one.

I think the connection DGND to GND is necessary, but could that also be through an inductor?

On the mosfet gate side, I'm thinking inductor in series with the current limiting 100R.

Simple enough with an on-line aircore inductor calculator to wind my own.

I've used that smoothing algorithm before, but I think first, sort out the hardware. As you rightly point out, my application is flawed in places.

Attached with proposed changes/queries.

EDIT: had an hour spare so whipped up a 100nh inductor to replace the resistor. Possibly my imagination, but temperature control is more consistent - that is; less pwm hunting as it endeavours to push the temperature up or down.

Chirping is however, more consistent - resonance in the circuit I guess.