The issue in ADC in nrf52840

[Muqarrab]

Hi,

I am trying to integrate ADC in my project(ble_app_template) but getting garbage data. I have nothing connected with pin P0.4(NRF_SAADC_INPUT_AIN1). (Means not applied any voltage)


The behavior is the same with/without connecting NRF_SAADC_INPUT_AIN1 with input signal.
Here is my implementation.

void saadc_init(void)
{
	// A variable to hold the error code
  ret_code_t err_code;

  // Create a config struct and assign it default values along with the Pin number for ADC Input
  // Configure the input as Single Ended(One Pin Reading)
  // Make sure you allocate the right pin.
//  nrf_saadc_channel_config_t channel_config = NRFX_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN1);
 nrf_saadc_channel_config_t channel_config = NRFX_SAADC_DEFAULT_CHANNEL_CONFIG_DIFFERENTIAL(NRF_SAADC_INPUT_VDD,NRF_SAADC_INPUT_AIN1);

  // Initialize the saadc 
  // first parameter is for configuring the adc resolution and other features, we will see in future tutorial
  //on how to work with it. right now just pass a simple null value
  err_code = nrf_drv_saadc_init(NULL, saadc_callback_handler);
  APP_ERROR_CHECK(err_code);

// Initialize the Channel which will be connected to that specific pin.
  err_code = nrfx_saadc_channel_init(0, &channel_config);
  APP_ERROR_CHECK(err_code);

  

}

    // Enter main loop.
    for (;;)
    {
        idle_state_handle();
		// a blocking function which will be called and the processor waits until the value is read
		// the sample value read is in 2's complement and is automatically converted once retrieved
		// first parameter is for the adc input channel 
		// second parameter is to pass the address of the variable in which we store our adc sample value
      nrfx_saadc_sample_convert(0, &adc_val);

		// print this value using nrf log : here %d represents the integer value 
      NRF_LOG_INFO("Sample value Read: %d", adc_val);
		
		// use nrf log and float marker to show the floating point values on the log
		// calculate the voltage by this: input_sample * 3.6 / 2^n (where n = 8 or 10 or 12 or 14 depending on our configuration for resolution in bits)
      NRF_LOG_INFO("Volts: " NRF_LOG_FLOAT_MARKER "\r\n", NRF_LOG_FLOAT(adc_val  / 16384));
       
	   // give 500ms delay 
       nrf_delay_ms(2000);

    }

Any suggestions, please?

[haakonsh]

I removed the TIMER and PPI related code:

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/** @file
 * @defgroup nrf_adc_example main.c
 * @{
 * @ingroup nrf_adc_example
 * @brief ADC Example Application main file.
 *
 * This file contains the source code for a sample application using ADC.
 *
 * @image html example_board_setup_a.jpg "Use board setup A for this example."
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "nrf.h"
#include "nrf_drv_saadc.h"
#include "boards.h"
#include "app_error.h"
#include "nrf_delay.h"
#include "app_util_platform.h"
#include "nrf_pwr_mgmt.h"

#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrf_log_default_backends.h"

#define SAMPLES_IN_BUFFER 1
volatile uint8_t state = 1;

static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];
static uint32_t              m_adc_evt_counter;

void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {
        ret_code_t err_code;

        err_code = nrf_drv_saadc_buffer_convert(p_event->data.done.p_buffer, SAMPLES_IN_BUFFER);
        APP_ERROR_CHECK(err_code);

        int i;
        NRF_LOG_INFO("ADC event number: %d", (int)m_adc_evt_counter);

        for (i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            NRF_LOG_INFO("%d", p_event->data.done.p_buffer[i]);
        }
        m_adc_evt_counter++;
    }
}


void saadc_init(void)
{
    ret_code_t err_code;
    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN0);

    err_code = nrf_drv_saadc_init(NULL, saadc_callback);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(0, &channel_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[0], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(m_buffer_pool[1], SAMPLES_IN_BUFFER);
    APP_ERROR_CHECK(err_code);

}


/**
 * @brief Function for main application entry.
 */
int main(void)
{
    uint32_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();

    ret_code_t ret_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(ret_code);

    saadc_init();
    
    NRF_LOG_INFO("SAADC HAL simple example started.");

    while (1)
    {
        err_code = nrf_drv_saadc_sample();
        APP_ERROR_CHECK(ret_code);

        nrf_pwr_mgmt_run();
        NRF_LOG_FLUSH();
    }
}


/** @} */