nRF52840 ADC offset calibration on B404X

Hardware
1

Hi all,

I'm using a B404X for a precision analog measurement application and have been digging into ADC accuracy. I noticed that Nordic's nRF52840 product spec explicitly recommends running CALIBRATEOFFSET at startup and whenever ambient temperature changes by more than 10°C, since the SAADC has a temperature-dependent offset.

I took a look at the Device OS source (hal/src/nRF52840/adc_hal.cpp) and found that hal_adc_calibrate() currently just returns SYSTEM_ERROR_NOT_SUPPORTED — so it seems like no calibration is being performed at any point by the OS.

Two questions for the community:

  1. Can anyone confirm whether Device OS performs SAADC offset calibration anywhere else in the stack that I may have missed?

  2. For those doing precision analog work on B404X or similar nRF52840-based Particle devices — what's your approach to working around this? I'm considering implementing a software digital offset calibration (reading a known voltage periodically and correcting for drift), but curious if there are established patterns people use within the Particle ecosystem.

Thanks!

2

It does not appear that calibration is done. However, you can easily call it yourself from user firmware. Include this:

#include <nrfx_saadc.h>

Call this:

nrfx_saadc_calibrate_offset();