nrf52 SAADC single ended samples GND returns 65535 indicating mode configuration errors.

[shanyechungu]

I used the example code on nrf52840 DK (PCA10056) to sample GND signal in Single-Ended mode. The returned value sometimes is 65535 which indicates potential wrong configuration of the sampling mode. Maybe set still as Differential instead of Singel-Ended when configured as Single-Ended.

Please help check, test and fix this issue.

Thanks,

[shanyechungu]

Never mind. This seems like a hardware issue.

In their SDK->SAADC (https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.nrf52832.ps.v1.1%2Fsaadc.html)

It states the following:

The assumption in single-ended mode is that the internal ground of the ADC is the same as the external ground that the measured voltage is referred to. The ADC is thus sensitive to ground bounce on the PCB in single-ended mode. If this is a concern we recommend using differential measurement.

I am using PCA10056 which is the official DK board. I still have this ground bounce issue. For developers, they may want to avoid this issue by using differential mode.