Get weird value back when read ADC

RE: Get weird value back when read ADC

Vidar Berg — Fri, 11 Nov 2022 09:20:39 GMT

Glad to hear that it works now. Yes, the voltage will fluctuate if you leave the input floating. It should become stable if you connect it to ground or VDD.

RE: Get weird value back when read ADC

Wols — Fri, 11 Nov 2022 09:16:01 GMT

I expected it should be zero, I leave it in the air, I think that is why I got negative voltage.

By the way, this two node is necessary in DTS on 2.1.2.

		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_SAADC_AIN3>;

I just move my project to 2.1.2, and rewritten adc part as your example, it works well now, thanks.

RE: Get weird value back when read ADC

Vidar Berg — Fri, 11 Nov 2022 08:00:13 GMT

What is the expected voltage on the channel 2 input? Is it tied to ground?

RE: Get weird value back when read ADC

Wols — Fri, 11 Nov 2022 03:42:01 GMT

Sorry for lat reply, this example work for me on 2.1.2

Some time adc@40007000, channel 2 got negative voltage, but it's better than now what happened on my board at 2.0.2.

I'll try to move the project to 2.1.2 and see what will happen, thank you Vidar.

adc@40007000, channel 2: -3 = -3 mV 
adc@40007000, channel 2: -1 = -1 mV

RE: Get weird value back when read ADC

Vidar Berg — Wed, 09 Nov 2022 10:17:34 GMT

Alternatively, you can try to just remove the "zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;" lines from your overlay and see if it is enough to let you build the sample.

RE: Get weird value back when read ADC

Wols — Wed, 09 Nov 2022 10:15:05 GMT

Well

I would like to have a try but need some time.

If any updates I'ii that you know of, thanks : )

RE: Get weird value back when read ADC

Vidar Berg — Wed, 09 Nov 2022 10:08:11 GMT

I forgot to add that my sample was tested with SDK v2.1.2. Are you able to try with this version instead?

RE: Get weird value back when read ADC

Wols — Wed, 09 Nov 2022 09:43:30 GMT

Sorry,

I got a error like this.

It's a include problem, there is no any like define in my ncs2.0.2 folder.

adc_52832/nrf52dk_nrf52832.overlay:35 (column 30): parse error: expected number or parenthesized expression

	35 zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;

RE: Get weird value back when read ADC

Vidar Berg — Tue, 08 Nov 2022 14:03:14 GMT

Hello,

I did not manage to reproduce this here with a test sample I made based on the ADC driver sample. Please try this sample and see if you get the same result.

ADC demo sample

devzone.nordicsemi.com/.../1884.adc_5F00_nrf52dk_5F00_nrf52832.zip

Expected log output

ADC reading:
- ad007000, channel 0: 230 = 202 m
- adc@40007000, channel 1: 174 = 152 mV
- adc@40007000, channel 2: 8 = 7 mV
- adc@40007000, channel 3: 121 = 106 mV
- adc@40007000, channel 4: 181 = 159 mV
ADC reading:
- adc@40007000, channel 0: 191 = 167 mV
- adc@40007000, channel 1: 185 = 162 mV
- adc@40007000, channel 2: 26 = 22 mV
- adc@40007000, channel 3: 121 = 106 mV
- adc@40007000, channel 4: 187 = 164 mV
ADC reading:
- adc@40007000, channel 0: 158 = 138 mV
- adc@40007000, channel 1: 200 = 175 mV
- adc@40007000, channel 2: 22 = 19 mV
- adc@40007000, channel 3: 129 = 113 mV
- adc@40007000, channel 4: 198 = 174 mV
ADC reading:
- adc@40007000, channel 0: 127 = 111 mV
- adc@40007000, channel 1: 166 = 145 mV
- adc@40007000, channel 2: 18 = 15 mV
- adc@40007000, channel 3: 144 = 126 mV
- adc@40007000, channel 4: 194 = 170 mV
...

Best regards,

Vidar