NRF52840 DK SAADC PIN A0 Reading

[Radio]

Hi All,

I am trying to use the saadc example given in nRF5_SDK_17.0.0_9d13099\examples\peripheral\saadc.

I have built the project and now I want to read some values from some voltages from one of the output pins in nRF52840 DK.

As suggested https://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v15.0.0/nrf_dev_saadc_example.html

(**To use VCC. In the hardware I see only VDD pins. Is it the same?)  in  

I tried to connect A0 pin to VDD (There are three VDD) pins however, value I read is,

<info> app: SAADC HAL simple example started.
<info> app: ADC event number: 0
<info> app: 19
<info> app: 19
<info> app: 18
<info> app: 19
<info> app: 17

However, if I connect to the 5V pin, I read,

<info> app: ADC event number: 22
<info> app: 559
<info> app: 560
<info> app: 559
<info> app: 560
<info> app: 559

Is it possible to know, why there is no output from the VDD pins? What is the expected voltage output of this pin?

Should I configure anything in the hardware?

Also is it ok to connect the 5V pin to the A0 pin?

Thanks a lot!!

[haakonsh]

There is only one VDD pin, on aQFN73 ball assignments it's A22, on WLCSP ball assignments it's B3. You're confusing regulator decoupling pins with a supply pin. 

Also, Jörg is correct, you've likely fried the analog input when you supplied 5V to it, I suggest you consider it broken (for now) and use one of the other analog input pins when testing the SAADC. 

[Radio]

Hi Haakonsh/ Jorg,

Thanks for the reply. Hope A0 pin is not burnt even though I connected to the 5V for few seconds. I first connected A0 pin to the 3.0 V. It still did not show a valid output.

I was referring to the VDD pins in nRF52840 DK highlighted in Red in the above diagram. When I measured using the Multimeter it reads 3.0V. But ADC reading values don't seems to be correct. I simply connected a wire as shown above in Green.

I am now using A1 pin. Still the same observation. Any idea what could be the reason? 

Thanks a lot!!

[haakonsh]

Do you mind sharing your code and the hex file you've compiled? 

[Radio]

Hi Haakonsh,

Herewith attaching my source code and the hex file. It's the exact example from Nordic.

saadc_nrf.rar

Thank a lot!!

[haakonsh]

I measure ~850 when connected to VDD (~3.0V):

With a gain of 1/6 and an internal voltage reference of 0.6V the input voltage range is 0-3.6V, and the expected output from an 3.0V input with 10-bit resolution is 3.0/3.6 * 1024 = 853.34. 

If you do not see ~850 as the output when connecting the analog input to a 3V source then the pin is most likely fried. 

[Radio]

Hi,

I now can see ~850 when I define NRF_SAADC_INPUT_AIN1 in the code and use pin "P0.03" to measure VDD (3.0V).

However, when I define NRF_SAADC_INPUT_AIN0 I am unable to measure from pin "P0.03".

Isn't "A0" = P0.03 = NRF_SAADC_INPUT_AIN0 ?

If I define NRF_SAADC_INPUT_AIN2 in the code, I can use pin "P0.04" to measure VDD.

 

[haakonsh]

See Mapping of analog pins.

AIN0 is the p0.02 pin on the opposite side of the DK.