Guru
Joined: 05/03/2018
Location: NetherlandsPosts: 5994
| Posted: 06:18am 28 Sep 2022 |
Hi OA47.
Your circuit will work (I have used similar many times before), there is however one thing you should pay attention to. The protection diode. For this diode to work, it should be a shottky diode. And these tend to have high leakage (1uA). If you put that against 1Mohm input impedance, you will see a non-linearity error (that is also temperature dependent). That is why real multimeters use different protection methods, i.e. with silicon diodes (or even si transistors used as a diode) that have leakage currents in the pA...nA range.
Most microcontroller IO pins have very high impedance when in input mode, despite the fact that the datasheet may say different. Not sure about the pico IO pins, but microchip pins where exceptionally low leakage when tested for it.
Regards,
Volhout