Attempting to get ADC to work

Question

I am trying to get a very simple ADC reading to print to the console using the nRF5340DK. I have a voltage divider with a photoresistor and a regular resistor, and I am trying to pass the output voltage as an analog input to P0.04. I am using nRF Connect in VSCode, version v2023.4.179. I am using the onboard VDD (3V) and GND for the circuit. I have enabled ADC in the prj.conf file. I will attach my main.c file to this. When I build and flash the code to the board, I get error -22 from adc_read. I would greatly appreciate any advice to solve this issue. Thank you!

#include <inttypes.h>
#include <stddef.h>
#include <stdint.h>

#include <zephyr/device.h>
#include <zephyr/devicetree.h>
#include <zephyr/drivers/adc.h>
#include <zephyr/kernel.h>
#include <zephyr/sys/printk.h>
#include <zephyr/sys/util.h>

#define INPUT_PIN 0

#define ADC_NODE DT_NODELABEL(adc)
static const struct device * dev = DEVICE_DT_GET(ADC_NODE);

#define ADC_RESOLUTION 10
#define ADC_GAIN ADC_GAIN_1
#define ADC_REFERENCE ADC_REF_INTERNAL
#define ADC_ACQUISITION_TIME ADC_ACQ_TIME_DEFAULT
#define ADC_CHANNEL 0
#define ADC_PORT SAADC_CH_PSELN_PSELN_AnalogInput0

struct adc_channel_cfg chl_cfg = {
	.gain = ADC_GAIN,
	.reference = ADC_REFERENCE,
	.acquisition_time = ADC_ACQUISITION_TIME,
	.channel_id = ADC_CHANNEL,
#ifdef CONFIG_ADC_NFRX_SAADC
	.input_positive = ADC_PORT
#endif
};

int16_t sample_buffer[1];
struct adc_sequence seq = {
	.channels = BIT(ADC_CHANNEL),
	.buffer = sample_buffer,
	.buffer = sizeof(sample_buffer),
	.resolution = ADC_RESOLUTION
};

void main(void) {
  int err;

  if (!device_is_ready(dev)) {
	printk("device not ready\n");
	return;
  }

  err = adc_channel_setup(dev, &chl_cfg);
  if (err != 0) {
	printk("channel setup failed\n");
	return;
  }

  while (1) {
	err = adc_read(dev, &seq);
	if (err != 0) {
		printk("read failed %d \n", err);
		return;
	}

	int32_t mv_value = sample_buffer[0];
	int32_t adc_vref = adc_ref_internal(dev);
	adc_raw_to_millivolts(adc_vref, ADC_GAIN, ADC_RESOLUTION, &mv_value);
	printk("ADC-voltage: %d mV\n", mv_value);

	// sleep for half a second
	k_msleep(500);
  }
}

shamboozled · Accepted Answer

Hi all,

I was able to resolve my own issue by learning more about devicetree overlays. I simply used the zephyr adc example and wrote my own devicetree overlay because the adc example does not contain one for the nRF5340. I will attach it here as well. Runar, thank you for your help, my issue is resolved.

/ {
    zephyr,user {
		io-channels = <&adc 0>, <&adc 1>;
	};
};

&adc {
	#address-cells = <1>;
	#size-cells = <0>;

	channel@0 {
		reg = <0>;
		zephyr,gain = "ADC_GAIN_1_6";
		zephyr,reference = "ADC_REF_INTERNAL";
		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_ADC_AIN0>; /* P0.04 */
		zephyr,resolution = <12>;
	};

    channel@1 {
		reg = <1>;
		zephyr,gain = "ADC_GAIN_1_6";
		zephyr,reference = "ADC_REF_INTERNAL";
		zephyr,acquisition-time = <ADC_ACQ_TIME_DEFAULT>;
		zephyr,input-positive = <NRF_ADC_AIN1>; /* P0.05 */
		zephyr,resolution = <12>;
	};
};

Attempting to get ADC to work

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