Thanks Adrian - in order for the ADC to work it is using a VREF and scaling the measurements 0 bits at ground up to 12 bits at VREF: my guess is that it is using 3.3V input power - this is what the pico does and it is noisy but it improves if you add an external VREF - they suggest an LM4040 3V. I’m new to circuitpython and micropython so there could be a way to direct VREF to a pin in the board module but I’ve not seen any example - and nothing I’ve found shows a pin on the XIAO RP2040 labelled as ex_vref so perhaps I’m out of luck. There are 4 ADC channels so I should be able to make it work measuring the ground in one channel the reference in another and the two measurements of interest on the other two.
Thanks again