The ADC settings on the nRF52840 with Zephyr are malfunctioning for certain parameters.

[Mr.tang]

"The nRF52840 is developed using NCS v2.6.1. When the ADC is set with the reference voltage as (.reference = ADC_REF_VDD_1_4, .resolution = 10), the ADC sampling output is 0 and malfunctions. However, when set to (.reference = ADC_REF_VDD_1_4, .resolution = 12), it works normally. Additionally, when set to (.reference = ADC_REF_INTERNAL, .resolution = 10), it also works normally. Why does the combination of (.reference = ADC_REF_VDD_1_4, .resolution = 10) cause a malfunction?"

[Kenneth]

Hello,

When using VDD as reference, then you need to add .zephyr,vref-mv = <nnnn>; where nnnn depends on the vdd/4 voltage (e.g. 750mV if VDD=3V). Make sure to use pristine build, it's not allways that changes in devicetree is picked up otherwize.

Kenneth

[Mr.tang]

First of all, thank you very much for your reply. However, I also noticed .vref_mv and configured it accordingly. Regrettably, when the ADC parameters are set to (.reference = ADC_REF_VDD_1_4, .resolution = 10), the ADC collection does not work properly.

To troubleshoot, I bypassed the devicetree ADC attribute configuration and directly used the adc_dt_spec structure variable to configure the ADC sampling parameters (struct adc_dt_spec adc_channels). Even with this configuration, it still doesn't work properly.

[Kenneth]

Adding this to the overlay this seems to work here. Sometimes the build system doesn't pick up changes automatically, so if --pristinebuild doesn't work, then try to delete the build folder after the change.

Kenenth

[Mr.tang]

Thank you for your reply. I tried your method, but the ADC is not working as expected. The overlay configuration is as follows:

channel@7 {
reg = <7>;
zephyr,gain = "ADC_GAIN_1_6";
zephyr,reference = "ADC_REF_VDD_1_4";
zephyr,vref-mv = <750>;
zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
zephyr,input-positive = <NRF_SAADC_AIN6>;
zephyr,input-negative = <NRF_SAADC_AIN7>;
zephyr,resolution = <10>;
};

[Kenneth]

Mr.tang said:

but the ADC is not working as expected.

Allways 0?

Kenneth