Example Code for A/D

Question

Hi, 
 Is there is a sample for using the nrf-9610 I/O input for A2D to read a voltage across a resistor(using P and N for differential), given that I'm having Zephyr as ROS? I had seen adc.h under Zephyr driver in Asset Tracker code but looks non of the functions are called. 
 Best Regards 
 HeTsH (Hesham)

Øyvind · Accepted Answer

Hi Hesham,

We do have a couple of ADC examples, one in the Zephyr repo, the Battery Voltage Measurement sample. This is found under zephyr\samples\boards\nrf\battery. This sample uses the ADC driver.

We also have an unofficial ADC sample found here.

Attached is an example on how to configure multiple ADC inputs:

  
/*
 * Copyright (c) 2018 Nordic Semiconductor ASA
 *
 * SPDX-License-Identifier: LicenseRef-BSD-5-Clause-Nordic
 */

#include <nrf.h>
#include <stdio.h>
#include <string.h>
#include <drivers/uart.h>
#include <drivers/adc.h>
#include <zephyr.h>

struct device *adc_dev;

#include <hal/nrf_saadc.h>
#define ADC_DEVICE_NAME DT_ADC_0_NAME
#define ADC_RESOLUTION 10
#define ADC_GAIN ADC_GAIN_1_6
#define ADC_REFERENCE ADC_REF_INTERNAL
#define ADC_ACQUISITION_TIME ADC_ACQ_TIME(ADC_ACQ_TIME_MICROSECONDS, 10)
#define ADC_1ST_CHANNEL_ID 0
#define ADC_1ST_CHANNEL_INPUT NRF_SAADC_INPUT_AIN0
#define ADC_2ND_CHANNEL_ID 1
#define ADC_2ND_CHANNEL_INPUT NRF_SAADC_INPUT_AIN1
#define ADC_3RD_CHANNEL_ID 2
#define ADC_3RD_CHANNEL_INPUT NRF_SAADC_INPUT_AIN2
#define ADC_4TH_CHANNEL_ID 3
#define ADC_4TH_CHANNEL_INPUT NRF_SAADC_INPUT_AIN3
#define ADC_5TH_CHANNEL_ID 4
#define ADC_5TH_CHANNEL_INPUT NRF_SAADC_INPUT_AIN4
#define ADC_6ST_CHANNEL_ID 5
#define ADC_6ST_CHANNEL_INPUT NRF_SAADC_INPUT_AIN5

static const struct adc_channel_cfg m_4th_channel_cfg = {
	.gain = ADC_GAIN,
	.reference = ADC_REFERENCE,
	.acquisition_time = ADC_ACQUISITION_TIME,
	.channel_id = ADC_4TH_CHANNEL_ID,
#if defined(CONFIG_ADC_CONFIGURABLE_INPUTS)
	.input_positive = ADC_4TH_CHANNEL_INPUT,
#endif
};

static const struct adc_channel_cfg m_3rd_channel_cfg = {
	.gain = ADC_GAIN,
	.reference = ADC_REFERENCE,
	.acquisition_time = ADC_ACQUISITION_TIME,
	.channel_id = ADC_3RD_CHANNEL_ID,
#if defined(CONFIG_ADC_CONFIGURABLE_INPUTS)
	.input_positive = ADC_3RD_CHANNEL_INPUT,
#endif
};


static const struct adc_channel_cfg m_2nd_channel_cfg = {
	.gain = ADC_GAIN,
	.reference = ADC_REFERENCE,
	.acquisition_time = ADC_ACQUISITION_TIME,
	.channel_id = ADC_2ND_CHANNEL_ID,
#if defined(CONFIG_ADC_CONFIGURABLE_INPUTS)
	.input_positive = ADC_2ND_CHANNEL_INPUT,
#endif
};

static const struct adc_channel_cfg m_1st_channel_cfg = {
	.gain = ADC_GAIN,
	.reference = ADC_REFERENCE,
	.acquisition_time = ADC_ACQUISITION_TIME,
	.channel_id = ADC_1ST_CHANNEL_ID,
#if defined(CONFIG_ADC_CONFIGURABLE_INPUTS)
	.input_positive = ADC_1ST_CHANNEL_INPUT,
#endif
};

#define BUFFER_SIZE 1*5
static s16_t m_sample_buffer[BUFFER_SIZE];

static int adc_sample(void)
{
	int ret;

	const struct adc_sequence sequence = {
		.channels = BIT(ADC_1ST_CHANNEL_ID) | BIT(ADC_2ND_CHANNEL_ID) | BIT(ADC_3RD_CHANNEL_ID) | BIT(ADC_4TH_CHANNEL_ID),
		.buffer = m_sample_buffer,
		.buffer_size = sizeof(m_sample_buffer),
		.resolution = ADC_RESOLUTION,
	};

	if (!adc_dev) {
		return -1;
	}

	ret = adc_read(adc_dev, &sequence);
	printk("ADC read err: %d\n", ret);

	/* Print the AIN0 values */
	for (int i = 0; i < BUFFER_SIZE; i++) {
		float adc_voltage = 0;
		adc_voltage = (float)(((float)m_sample_buffer[i] / 1023.0f) *
				      3600.0f);
		printk("ADC raw value: %d\n", m_sample_buffer[i]);
		printf("Measured voltage: %f mV\n", adc_voltage);
	}

	return ret;
}

int main(void)
{
	int err;

	printk("nrf91 saadc sampling AIN0 (P0.13)\n");
	printk("Example requires secure_boot to have ");
	printk("SAADC set to non-secure!\n");
	printk("If not; BusFault/UsageFault will be triggered\n");

	adc_dev = device_get_binding("ADC_0");
	if (!adc_dev) {
		printk("device_get_binding ADC_0 failed\n");
	}
	err = adc_channel_setup(adc_dev, &m_1st_channel_cfg);
	if (err) {
		printk("Error in adc setup: %d\n", err);
	}
	err = adc_channel_setup(adc_dev, &m_2nd_channel_cfg);
	if (err) {
		printk("Error in adc setup: %d\n", err);
	}

	err = adc_channel_setup(adc_dev, &m_3rd_channel_cfg);
	if (err) {
		printk("Error in adc setup: %d\n", err);
	}

	err = adc_channel_setup(adc_dev, &m_4th_channel_cfg);
	if (err) {
		printk("Error in adc setup: %d\n", err);
	}			

	/* Trigger offset calibration
	 * As this generates a _DONE and _RESULT event
	 * the first result will be incorrect.
	 */
	NRF_SAADC->TASKS_CALIBRATEOFFSET = 1;
	while (1) {
		err = adc_sample();
		if (err) {
			printk("Error in adc sampling: %d\n", err);
		}
		k_sleep(K_MSEC(1000));
	}
}

And its corresponding prj.conf:

CONFIG_GPIO=y
CONFIG_SERIAL=y
CONFIG_HEAP_MEM_POOL_SIZE=4096  

CONFIG_ADC=y
CONFIG_ADC_NRFX_SAADC=y
CONFIG_MAIN_STACK_SIZE=4096

Kind regards,
Øyvind

Example Code for A/D

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