Zephyr NRF battery example on nrf52840dk

RE: Zephyr NRF battery example on nrf52840dk

Hieu — Tue, 26 Mar 2024 18:15:35 GMT

Hi BarneyH,

Good to know you figured it all out. I assume the 1199mV saturation comes from a modified battery point level struct in that sample's main.c, then.

Please feel free to close this ticket at your convenience. 🙂

RE: Zephyr NRF battery example on nrf52840dk

BarneyH — Tue, 26 Mar 2024 09:35:14 GMT

Hi Hieu

Thank you for your detailed reply.

I copied the sample from zephyr/samples/boards/nrf/battery when creating a new application within vscode and can confirm now for the next person, that it works with the nrf52840 dk with the above overlay file and a simple voltage divider hooked up to AIN7.

To solve the "saturation issue above" the key was to set the gain to 1/6 with #define BATTERY_ADC_GAIN ADC_GAIN_1_6 which I think it is by default but I might have messed it up in some initial testing, so sorry to bother you for this.

Thank you again and have a great day

RE: Zephyr NRF battery example on nrf52840dk

Hieu — Mon, 25 Mar 2024 20:57:53 GMT

Hi BarneyH,

The SAADC on the nRF52840 can only measure voltage within a range, from 0 to an upper limit. The upper limit can be configured by adjusting gain setting or choose a different reference voltage. I am guessing this is why you see the saturating kind of behavior.

You can find more details about the SAADC range in the documentation: https://infocenter.nordicsemi.com/topic/ps_nrf52840/saadc.html?cp=5_0_0_5_22_1#unique_926836493.

What doesn't make sense to me is why you read 1199mV when you meet the threshold, why that exact value. If we dived into the driver implementation, I think we will find out.

I don't remember the Zephyr ADC driver implementation by heart, and there are a few different battery samples around. If you want me to dive further with you, could you please give me the full path to the sample, and I can try to see what could be wrong.

By the way, the nRF52840 doesn't have a voltage divider. Did you make your own physical divider and connect it to AIN7?

Hieu