How to measure battery voltage with my custom nrf54L15 board?

[Llama12580]

I have customed my own nrf54L15 board and it would run on button battery. I managed to measure the battery level through ADC, but I don't know how to use ADC with nrf54L15.

Firstly I tried to run demo: ncs2.8.0/zephyr/samples/boards/nordic/battery to test, but it failed to be built with target nrf54l15dk/nrf54l15/cpuapp.

So how to measure the battery voltage(nrf54l15 input voltage)?

[helsing]

Hi Barry,

Just letting you know we are looking into this. Is VDD directly connected (or at least proportional) to the battery voltage on your custom board? If so, an alternative solution could be to measure the input voltage. This could free up a pin in your desing.

[Llama12580]

Yes, it directly connects to the battery voltage. How can I measure the voltage? by ADC?

[helsing]

I tried to run demo: ncs2.8.0/zephyr/samples/boards/nordic/battery

The sample you tried is set up for Thingy:52.

Llama12580 said:

Yes, it directly connects to the battery voltage. How can I measure the voltage? by ADC?

Try this sample instead:

\v2.8.0\zephyr\samples\drivers\adc\adc_dt\README.rst

or

/v2.8.0/zephyr/samples/drivers/adc/adc_sequence/README.rst.

The adc_dt sample is configured for sampling VDD (VNRF_SAADC_VDD) on channel 2 when building for nRF54L15 DK:

https://github.com/nrfconnect/sdk-zephyr/commit/ff05708b357d3bab73668f45f88b2ed56b290796

Test this sample, and let us know if you encounter any issues. You will need to write a Device Tree overlay describing the set up of the channels.

[Llama12580]

I've run this sample successfully, but it confused me that the result of channel 2 was 0.9V. In my opinion, isn't it supposed to be 3.3V?

[helsing]

When VDD is used as an analog input for SAADC it is "divided down to a valid range". Do you see the results from channel 2 changing as the voltage at VDD is altered? I will have to look up exactly how VDD is divided down. VDD is likely divided down by 4, as for nRF52 and 53 series VDD. Please let me know if more details regarding dividing down is needed.

The adc_sequence sample is set up to measure DVDD by default. DVDD is onnected to the internal 0.9V digital supply rail.