Zephyr Battery Voltage Measurement

[bojan]

Hello, guys!

My goal is to monitor battery voltage by using a voltage divider and ADC peripheral of nRF51822 SoC. I find that this example perfectly fits my needs. Consequently, I included the device tree node that describes the voltage divider for battery monitoring:

/ {
	vbatt {
		compatible = "voltage-divider";
		io-channels = <&adc 6>;
		output-ohms = <1000>;
		full-ohms = <(1000 + 3000)>;
		power-gpios = <&gpio0 6 GPIO_ACTIVE_HIGH>;
	};
};

prj.conf file contains the following ADC-related line:

CONFIG_ADC=y

However, when I try to build the example, I get the Unsupported ADC error that is a consequence of this part of the code (in battery.c file):

#ifdef CONFIG_ADC_NRFX_SAADC
	*accp = (struct adc_channel_cfg){
		.gain = BATTERY_ADC_GAIN,
		.reference = ADC_REF_INTERNAL,
		.acquisition_time = ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 40),
	};

	if (cfg->output_ohm != 0) {
		accp->input_positive = SAADC_CH_PSELP_PSELP_AnalogInput0
			+ iocp->channel;
	} else {
		accp->input_positive = SAADC_CH_PSELP_PSELP_VDD;
	}

	asp->resolution = 14;
#else /* CONFIG_ADC_var */
#error Unsupported ADC
#endif /* CONFIG_ADC_var */

I tried including CONFIG_NRFX_SAADC=y or CONFIG_ADC_NRFX_SAADC=y lines in prj.conf file but to no avail. Adding #include <nrfx_saadc.h> in battery.c file did not help as well.

Do you have any idea what I am missing here in order to be able to compile and try this example with nRF51822 SoC?

Thanks in advance for your time and efforts.

Cheers

Bojan.

[Priyanka]

Hi Bojan,

This could be because you are trying with the nRF51 and this does not support the SAADC and as you can see

the code is written for the SAADC peripheral.

Regards,

Priyanka

[bojan]

Hello, Priyanka!

I did not know that nRF51 does not support SAADC.

Would it be possible to adapt the existing battery voltage measurement approach for nRF51 (basically just to avoid using SAADC)?

Regards,

Bojan.

[bojan]

Hello, Priyanka!

Where can I find an appropriate example of reading ADC voltage with nRF51 SoCs in the Zephyr environment?  I started looking at the Analog-to-Digital Converter (ADC) sample from here but the Note says that:

The sample does not work on Nordic platforms where there is a distinction between channel and analog input that requires additional configuration. See samples/boards/nrf/battery for an example of using the ADC infrastructure on Nordic hardware.

However, samples/boards/nrf/battery is using SAADC peripheral which is not supported in nRF51 SoCs. Can you help me find the appropriate way of using the ADC peripheral of nRF51 SoCs in the Zephyr environment?

Thanks in advance.

Regards,

Bojan.

[Priyanka]

Hi Bojan,

We don't generally support the Zephyr for nRF51 series. But you could try building the adc samples that we have in Zephyr for the nRF51, or at least it works well for the nRF51DK_nRF51422.

Regards,

Priyanka