SDK 1.6.1 Zephyr, How Read nRF52832 AIN7 and configure prj.conf and overlay file.

[Fb62]

Hello, how do I configure the prj.conf file and the overlay file and how do I read the AIN7 analog input (P0.31) of the nRF52832. It is the first time that I use the micro to read an analog voltage. I did various research on DevZone, but I couldn't figure out how to do it. Thanks in advance.

[Heidi]

Hi!

I'm having some trouble flashing the application to the board to actually test this, but I will provide the basics here to start with. 

In the prj.conf file, you will need to enable CONFIG_ADC=y.

Then we need an overlay file to enable the adc and to create a node and set the correct io-channel:

&adc {
	status = "okay";
};


/ {
	n: node {
		io-channels = <&adc 31>;
		io-channel-names = "AIN7";
	};
};

The main will look something like below. 

/*
 * Copyright (c) 2020 Nordic Semiconuctor ASA
 * SPDX-License-Identifier: Apache-2.0
 */

#include <stdio.h>
#include <zephyr.h>
#include <sys/printk.h>
#include <drivers/adc.h>


#define ADC_RESOLUTION			12
#define ADC_GAIN				ADC_GAIN_1
#define ADC_REFERENCE			ADC_REF_INTERNAL
#define ADC_ACQUISITION_TIME	ADC_ACQ_TIME_DEFAULT

#define ADC_CHANNEL_ID		7

static uint16_t adc_raw;
static const struct device * dev_adc;

struct adc_channel_cfg channel_cfg = {
	.gain 				= ADC_GAIN,
	.reference 			= ADC_REFERENCE,
	.acquisition_time 	= ADC_ACQUISITION_TIME,
	.differential 		= 0,
	.channel_id			= ADC_CHANNEL_ID,
	.input_positive 	= SAADC_CH_PSELP_PSELP_AnalogInput7,
};


void main(void)
{
	int err;
	dev_adc = device_get_binding("ADC_0");
	if (!device_is_ready(dev_adc)) {
		printk("ADC device not found\n");
		return;
	}
	err = adc_channel_setup(dev_adc, &channel_cfg);
	if (err) {
		printk("adc_channel_setup() failed with error: %d\n", err);
	}
	struct adc_sequence sequence = {
		.channels    = BIT(channel_cfg.channel_id),
		.buffer      = &adc_raw,
		.buffer_size = sizeof(adc_raw),
		.resolution  = ADC_RESOLUTION,
	};

	while (true) {
		err = adc_read(dev_adc, &sequence);
		if (err != 0) {
			printk("ADC reading failed with error %d.\n", err);
			return;
		}
		printk("ADC reading: %d\n", (int16_t)adc_raw);
		k_sleep(K_MSEC(1000));
	}
}

[Fb62]

Hello Heidi,

I test it,

Thanks

Fausto

[Heidi]

Great! I was able to test it now, and it seems to work. I modified the main.c just now, so try that one instead.

[Fb62]

Hello Heidi,

can you share your test code project.

Thanks 

Fausto

[Fb62]

Hello Heidi,

I tested the code sample, but whit 0.5V in input I have 3430 of adc_raw data, it's normal,

What is the input voltage range of AN7 (P0.31)?

Best regards

Fausto

[Heidi]

Hi!

You can add the following code snippet to convert the raw ADC reading to millivolts. 

mV = (int16_t)adc_raw;
err = adc_raw_to_millivolts(adc_ref_internal(dev_adc), channel_cfg.gain,
			   sequence.resolution, &mV);
if (err) {
	printk("ADC conversion failed: %d\n", err);
	return;
}
printf("ADC raw %d => %d mV\n", (int16_t)adc_raw, mV);					   

I attached a zip file of the application below.

adc_sample.7z

[Fb62]

Hi,

I compiled the last adc_sample code, but I get

*** Booting Zephyr OS build v2.6.0-rc1-ncs1 ***
ADC raw 4095 => 599 mV
ADC raw 4095 => 599 mV
ADC raw 4095 => 599 mV
ADC raw 4095 => 599 mV
ADC raw 4095 => 599 mV
ADC raw 4095 => 599 mV

In input of AN7 I have 1.7 Volt but the ADC reaches full scale with only 0.6 volts

Is there any other settings to be made?
My hardware is the pine watch which has a resistive divider which halves the battery voltage which is about 3.7Volt

Best Regards

Fausto

[Heidi]

Hi!

Try setting the gain to ADC_GAIN_1_6 to get a range of 0V - 3.6V.