Zephyr "battery" example using VDD as the ADC input

Question

I am trying to use the battery example in "/ncs/zephyr/samples/boards/nrf/battery" to measure my 3V coin cell via VDD. I am using P0.14 to enable a set load on VDD before the battery measurement.

In the past I have used NRF_SAADC_INPUT_VDD to successfully read the battery voltage via VDD.

What do I need to put for the "io_channel" in the dts file for the following vbatt? Is anything else missing.

	vbatt {
		compatible = "voltage-divider";
		io-channels = <&adc 4>;
		output-ohms = <180000>;
		full-ohms = <(1500000 + 180000)>;
		power-gpios = <&sx1509b 4 0>;
	};

Following is my "battery_def.h" file. I haven't done the calculations for the battery voltage state of charge yet, this is just my modified version of the one from "nrf52840gmouse_nrf52840".

battery_def.h

The following is from my proj.conf file.

CONFIG_GPIO=y

#Enable Battery Readings https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/applications/nrf_desktop/doc/battery_meas.html
CONFIG_ADC=y
CONFIG_ADC_ASYNC=y
#CONFIG_ADC_0=y
CONFIG_ADC_NRFX_SAADC=y
# P0.31 is the Battery measurement enable pin.
CONFIG_DESKTOP_BATTERY_MEAS_HAS_ENABLE_PIN=31
CONFIG_DESKTOP_BATTERY_MEAS_MIN_LEVEL=2
CONFIG_DESKTOP_BATTERY_MEAS_MAX_LEVEL=3
# Difference in mV between the adjacent elements in the conversion lookup table.
# CONFIG_DESKTOP_VOLTAGE_TO_SOC_DELTA=
# The amount of time between the subsequent battery measurements (in ms).
CONFIG_DESKTOP_BATTERY_MEAS_POLL_INTERVAL_MS=1000

matt_C · Accepted Answer

After looking around for a bit longer I found from https://github.com/zephyrproject-rtos/zephyr/tree/master/samples/boards/nrf/battery that if the device tree has a "vbatt" node then the battery voltage is measured with the divider defined there. Otherwise the internal source for VDD is assumed to be directly connected to the battery and as such is used for the battery measurements. 
 So, simply don't include a "vbatt" node if you want to use VDD to measure the battery.

Zephyr "battery" example using VDD as the ADC input

Top Replies