nRF52832 - ADC Value With 0V at the Input

RE: nRF52832 - ADC Value With 0V at the Input

Jørgen Holmefjord — Fri, 20 Apr 2018 07:24:20 GMT

If you get very big and wrong number, you are not handling the sample correctly. Note that the samples are stored as int16_t, not uint16_t:

typedef int16_t nrf_saadc_value_t;  ///< Type of a single ADC conversion result.

The values 0xFFFF, 0xFFFE represents -1 and -2 in int16_t format. You can compensate for this in your software by saying all negative values should be threated as 0. You can also do offset calibration , or oversampling to average multiple samples and compensate for the noise.

RE: nRF52832 - ADC Value With 0V at the Input

sdrest — Fri, 20 Apr 2018 06:42:01 GMT

Do anyone have solution?

I have this question too. when I touch ground on ADC pin, ADC value is 1,0, 0xFFFF or 0xFFFE.

It cause my average ADC value to be a very big and wrong number.

RE: nRF52832 - ADC Value With 0V at the Input

Carsten Wulff — Wed, 01 Feb 2017 11:02:30 GMT

Could you plot the ADC output also? It would be interesting to see if that is periodic.

RE: nRF52832 - ADC Value With 0V at the Input

jk83 — Wed, 01 Feb 2017 09:48:19 GMT

Hello,

Here you can find 3 screenshots of the same 5mV input of the ADC. The screenshot are taken with different time scales.

The signal has some noise, but nothing periodic. The ADC values that I am reading: 0x199A / 0x0001 / 0x0000 / 0x4CCD / 0x3333...

RE: nRF52832 - ADC Value With 0V at the Input

Carsten Wulff — Tue, 31 Jan 2017 17:13:10 GMT

As Jørgen says, this is not expected. Could you try plotting the ADC output and see if there is a periodic signal there? It would be interesting to know the frequency (if any) of what you see.

RE: nRF52832 - ADC Value With 0V at the Input

Jørgen Holmefjord — Tue, 31 Jan 2017 14:54:01 GMT

This does not look like expected behaviour. Have you checked the input with an oscilloscope to see that the signal is in fact 0/GND and stable?