nRF52 adc Calibration

[KingKarl237]

Hello, i'm searching for informations about calibrating the SAADC of the nRF52. And i have read here: Link

For nRF52, there are no calibration values that I know of. You need instead to periodically calibrate the SAADC by calling the TASKS_CALIBRATEOFFSET task.

I noticed calling TASKS_CALIBRATEOFFSET improves the Offset, but how often do i have to do that? Do you have some additional information on that?

Additional Info: I'm sampling every 10ms(100Hz) 4 Channels in 12Bit Single Mode.

1. Battery Voltage
2. Voltagesignal of an IC
3. Voltage of an potentiometer 1k
4. Voltagesignal of an external sensor

Thanks

[Carsten Wulff]

Seems for all of input sources you have quite low source impedance, so you should be able to do oversampling to improve the noise levels. I would recommend 16x (OVERSAMPLE=4) and BURST=1, that is a resonable tradeoff between time and noise levels.

Stefan is correct that it's about 0.1 Lsb10b per degree, and 0.4 Lsb12b per degree.

What also needs to be taken into consideration is that the noise level at gain = 1/4 is around 1.6 Lsb12b (0.4 Lsb10b), thus without oversampling I would expect the calibration to have a standard deviation of 0.4 Lsb10b, so maybe up to +-2 Lsb10b error in the calibration without oversampling.