[mordae]

Hey, you can also arrange 2 GPIO pins in 1st order sigma delta topology with two external resistors, a capacitor and disabled hysteresis.

With RP2040 (and an LDO for supply), using two such channels for pseudo differential measurement (the second one just tracks threshold noise) I typically obtain 16 ENOB at 1 kHz, more at DC.

It is critical to avoid any periodic activity on the chip, though. Putting cores to sleep and then waking them up again causes huge spurs. One has to e.g. sleep for random intervals to spread them around. Same with flash. USB can be used, it's noise doesn't normally exceed -100 dB for me.

Fun stuff!

PS: I have not tested DC accuracy. One would likely use a channel with reference and hope that GPIOs are well matched. Could be used to e.g. sense CC lines on USB or analog joysticks and other non-critical, low accuracy stuff.

[nerdsniper]

Can you post any resources for understanding this? I have basic understanding of circuits.

Is this essentially trading time resolution for voltage resolution? Would just doing an exponentially weighted moving average in firmware achieve the same results?