RE: NRF52832, NRF_SAADC negative values

Karl Ylvisaker — Mon, 08 Mar 2021 14:16:43 GMT

Hello,

[quote user=""]Is there an error in my declaration?[/quote][quote user=""]What can I do to avoid the strange value of sample 0?[/quote]

It is recommended that you always perform a calibration upon initialization of the SAADC, and when the ambient temperature has changed more then 10 C in either direction. Other than that, you configuration looks alright. Please keep Errata 86 for the nRF52832 in mind when doing this, as it may produce an invalid initial sample.

[quote user=""]Since I set the ADC to 8 Bit, I expect a 8 Bit value, -128....127 or 0...255.[/quote][quote user=""]If I connect to 3.3V I see value 235/236 which is, what I expect.[/quote]

This sounds correct to me as well - as expected. Your current input range is 0 - 3.6 V. When you connect it to 3.3 V, that should yield something close to 235 as its output.

Regarding the occasional -1 value you see when sampling GND, you should always account for some LSB of noise, which in this case could cause you to see slightly negative values when measuring ground.

Best regards,
Karl