The issue in ADC in nrf52840

RE: The issue in ADC in nrf52840

haakonsh — Sat, 03 Oct 2020 11:21:29 GMT

I removed the TIMER and PPI related code:

/**
 * Copyright (c) 2014 - 2020, Nordic Semiconductor ASA
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
/** @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();
    }
}


/** @} */

RE: The issue in ADC in nrf52840

Muqarrab — Fri, 02 Oct 2020 05:12:26 GMT

Hi haakonsh
Trying to build your code but getting the following issue.

RE: The issue in ADC in nrf52840

haakonsh — Thu, 01 Oct 2020 14:44:09 GMT

Try this:

/**
 * Copyright (c) 2014 - 2020, Nordic Semiconductor ASA
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
/** @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 "nrf_drv_ppi.h"
#include "nrf_drv_timer.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 const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(0);
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];
static nrf_ppi_channel_t     m_ppi_channel;
static uint32_t              m_adc_evt_counter;


void timer_handler(nrf_timer_event_t event_type, void * p_context)
{

}


void saadc_sampling_event_init(void)
{
    ret_code_t err_code;

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
    err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);
    APP_ERROR_CHECK(err_code);

    /* setup m_timer for compare event every 400ms */
    uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_timer, 400);
    nrf_drv_timer_extended_compare(&m_timer,
                                   NRF_TIMER_CC_CHANNEL0,
                                   ticks,
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
    nrf_drv_timer_enable(&m_timer);

    uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,
                                                                                NRF_TIMER_CC_CHANNEL0);
    uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();

    /* setup ppi channel so that timer compare event is triggering sample task in SAADC */
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
                                          timer_compare_event_addr,
                                          saadc_sample_task_addr);
    APP_ERROR_CHECK(err_code);
}


void saadc_sampling_event_enable(void)
{
    ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);

    APP_ERROR_CHECK(err_code);
}


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();
    //saadc_sampling_event_init();
    //saadc_sampling_event_enable();
    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();
    }
}


/** @} */

RE: The issue in ADC in nrf52840

Muqarrab — Thu, 01 Oct 2020 07:44:45 GMT

Hi haakonsh,
I have made function and commented timer functions.
But now the code is not working. Can you please refer to any example or guide how can I implement this nrfx_saadc_sample?
Really Thanks!

RE: The issue in ADC in nrf52840

haakonsh — Wed, 30 Sep 2020 08:21:22 GMT

Just call nrfx_saadc_sample instead of triggering the sample task via the timer.

RE: The issue in ADC in nrf52840

Muqarrab — Wed, 30 Sep 2020 05:39:39 GMT

Thanks, rmptxf

It's working perfectly fine.

Can you please mention/remove the timer? I want a function, when I call that function it gives me current ADC reading on P0.3. Can you please guide how can I do that(remove the timer from this code)? I have tried but it's not working.

Thanks again

/**
 * Copyright (c) 2014 - 2020, Nordic Semiconductor ASA
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
/*
   Author : Abdelali Boussetta @rmptxf
   Description : This saadc example uses one channel (AIN1 (P0.3)), samples at 100ms (10 samples) =  get result each (1 second).
   It uses 14Bit as a resolution.
*/

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "nrf.h"
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.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 10

static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(0);
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];
static nrf_ppi_channel_t     m_ppi_channel;
static uint32_t              m_adc_evt_counter;

// RESULT = [V(P) – V(N) ] * GAIN/REFERENCE * 2(RESOLUTION - m)
// (m=0) if CONFIG.MODE=SE, or (m=1) if CONFIG.MODE=Diff.

// V(N) = 0;
// GAIN = 1/6;
// REFERENCE Voltage = internal (0.6V);
// RESOLUTION : 12 bit;
// m = 0;

// 12bit
// V(P) = RESULT x REFERENCE / ( GAIN x RESOLUTION) = RESULT x (600 / (1/6 x 2^(12)) =  ADC_RESULT x 0.87890625;
//#define ADC_RESULT_IN_MILLI_VOLTS(ADC_RESULT) ((ADC_RESULT * 0.87890625))

// 14bit
// V(P) = RESULT x REFERENCE / ( GAIN x RESOLUTION) = RESULT x (600 / (1/6 x 2^(14)) =  ADC_RESULT x 0.2197265625;
#define ADC_RESULT_IN_MILLI_VOLTS(ADC_RESULT) ((ADC_RESULT * 0.2197265625))


void timer_handler(nrf_timer_event_t event_type, void * p_context)
{

}


void saadc_sampling_event_init(void)
{
    ret_code_t err_code;

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
    err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);
    APP_ERROR_CHECK(err_code);

    /* setup m_timer for compare event every 100ms */
    uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_timer, 100);
    nrf_drv_timer_extended_compare(&m_timer,
                                   NRF_TIMER_CC_CHANNEL0,
                                   ticks,
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
    nrf_drv_timer_enable(&m_timer);

    uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,
                                                                                NRF_TIMER_CC_CHANNEL0);
    uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();

    /* setup ppi channel so that timer compare event is triggering sample task in SAADC */
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
                                          timer_compare_event_addr,
                                          saadc_sample_task_addr);
    APP_ERROR_CHECK(err_code);
}


void saadc_sampling_event_enable(void)
{
    ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);

    APP_ERROR_CHECK(err_code);
}


void saadc_callback(nrf_drv_saadc_evt_t const * p_event)
{
    ret_code_t err_code;

    if (p_event->type == NRF_DRV_SAADC_EVT_DONE)
    {     
        uint32_t buffer_samples = 0;
        uint16_t adc_result = 0;
        uint16_t adc_voltage_mv = 0;

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

        m_adc_evt_counter++;

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

        for (uint8_t i = 0; i < SAMPLES_IN_BUFFER; i++)
        {
            buffer_samples += p_event->data.done.p_buffer[i];
        }

        adc_result = buffer_samples/SAMPLES_IN_BUFFER;
        adc_voltage_mv = ADC_RESULT_IN_MILLI_VOLTS(adc_result);

        NRF_LOG_INFO("adc result : %d.", adc_result);
        NRF_LOG_INFO("voltage : %d mV.", adc_voltage_mv);
         
        NRF_LOG_INFO("---------------------------");
    }
}


void saadc_init(void)
{
    ret_code_t err_code;
    // Using the channel default single ended (SE) config
    // pin NRF_SAADC_INPUT_AIN1 : P0.03
    nrf_saadc_channel_config_t channel_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_AIN1);

    // changing the saadc resolution to 12bit
    nrf_drv_saadc_config_t saadc_config ;
    saadc_config.resolution = NRF_SAADC_RESOLUTION_14BIT;

    err_code = nrf_drv_saadc_init(&saadc_config, 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();
    saadc_sampling_event_init();
    saadc_sampling_event_enable();
    NRF_LOG_INFO("SAADC HAL simple example started.");

    while (1)
    {
        nrf_pwr_mgmt_run();
        NRF_LOG_FLUSH();
    }
}


/** @} */

RE: The issue in ADC in nrf52840

rmptxf — Tue, 29 Sep 2020 16:42:47 GMT

haakonsh is right. there is actually an issue in this example regarding the conversion.

I fixed that in this new one saadc modified example.

RE: The issue in ADC in nrf52840

haakonsh — Tue, 29 Sep 2020 13:39:42 GMT

There's an issue in your data processing. The SAADC is not that inaccurate, even in a worst case scenario.

I suggest you print out the raw samples and convert them by hand and compare them to what you get with your data processing.

RE: The issue in ADC in nrf52840

Muqarrab — Tue, 29 Sep 2020 08:32:06 GMT

Thanks,
I have tried the above-mentioned project. Here is the ADC reading I am getting.

Applied Voltage On pin(P0.4) nRF52840 Reading
(mV) (mV)

1000 798-810
1500 1216-1225
2000 1622-1629
2500 2023-2027
3000 2425

1-Can you please suggest how can I improve its reading/accuracy?
2-I am also attaching my code. I want a function, when I call that function it gives me current ADC reading on P0.4. Can you please guide how can I do that(remove the timer from this code)?

Thanks!

/**
 * Copyright (c) 2014 - 2019, Nordic Semiconductor ASA
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 *    list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form, except as embedded into a Nordic
 *    Semiconductor ASA integrated circuit in a product or a software update for
 *    such product, must reproduce the above copyright notice, this list of
 *    conditions and the following disclaimer in the documentation and/or other
 *    materials provided with the distribution.
 *
 * 3. Neither the name of Nordic Semiconductor ASA nor the names of its
 *    contributors may be used to endorse or promote products derived from this
 *    software without specific prior written permission.
 *
 * 4. This software, with or without modification, must only be used with a
 *    Nordic Semiconductor ASA integrated circuit.
 *
 * 5. Any software provided in binary form under this license must not be reverse
 *    engineered, decompiled, modified and/or disassembled.
 *
 * THIS SOFTWARE IS PROVIDED BY NORDIC SEMICONDUCTOR ASA "AS IS" AND ANY EXPRESS
 * OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY, NONINFRINGEMENT, AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL NORDIC SEMICONDUCTOR ASA OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
 * GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */
/*
    Simplified SAADC example.
    Author : Abdelali Boussetta
 */

#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include "nrf.h"
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.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 RES_14BIT                           16384                                    /**< Maximum digital value for 12-bit ADC conversion. */
#define RES_12BIT                           4096                                    /**< Maximum digital value for 12-bit ADC conversion. */
#define RES_10BIT                           1024                                    /**< Maximum digital value for 10-bit ADC conversion. */

#define ADC_RES                             RES_12BIT
#define ADC_REF_VOLTAGE_IN_MILLIVOLTS       600                                     /**< Reference voltage (in milli volts) used by ADC while doing conversion. */
#define ADC_PRE_SCALING_COMPENSATION        5                                       /**< The ADC is configured to use VDD with 1/5 prescaling as input. And hence the result of conversion is to be multiplied by 3 to get the actual value of the battery voltage.*/                                


#define ADC_RESULT_IN_MILLI_VOLTS(ADC_VALUE)\
         ((((ADC_VALUE) * ADC_REF_VOLTAGE_IN_MILLIVOLTS) / ADC_RES) * ADC_PRE_SCALING_COMPENSATION)

#define SAMPLES_IN_BUFFER                 3  
#define SAMPLE_RATE		        100   // ms

#define   ANALOG_0         NRF_SAADC_INPUT_AIN1  // A0(P0.03)
#define   ANALOG_1         NRF_SAADC_INPUT_AIN2  // A1(P0.04)
#define   ANALOG_2         NRF_SAADC_INPUT_AIN4  // A2(P0.28)

static uint32_t adc_event_counter = 0;

static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(0);
static nrf_saadc_value_t     m_buffer_pool[2][SAMPLES_IN_BUFFER];

static nrf_ppi_channel_t     m_ppi_channel;


int count=0;
double t_mv=0;

void timer_handler(nrf_timer_event_t event_type, void * p_context)
{

}

void saadc_sampling_event_init(void)
{
    ret_code_t err_code;

    err_code = nrf_drv_ppi_init();
    APP_ERROR_CHECK(err_code);

    nrf_drv_timer_config_t timer_cfg = NRF_DRV_TIMER_DEFAULT_CONFIG;
    timer_cfg.bit_width = NRF_TIMER_BIT_WIDTH_32;
    err_code = nrf_drv_timer_init(&m_timer, &timer_cfg, timer_handler);
    APP_ERROR_CHECK(err_code);

    // setup m_timer for compare event every {SAMPLE_RATE} 
    uint32_t ticks = nrf_drv_timer_ms_to_ticks(&m_timer, SAMPLE_RATE);
    nrf_drv_timer_extended_compare(&m_timer,
                                   NRF_TIMER_CC_CHANNEL0,
                                   ticks,
                                   NRF_TIMER_SHORT_COMPARE0_CLEAR_MASK,
                                   false);
    nrf_drv_timer_enable(&m_timer);

    uint32_t timer_compare_event_addr = nrf_drv_timer_compare_event_address_get(&m_timer,
                                                                                NRF_TIMER_CC_CHANNEL0);
    uint32_t saadc_sample_task_addr   = nrf_drv_saadc_sample_task_get();

    // setup ppi channel so that timer compare event is triggering sample task in SAADC 
    err_code = nrf_drv_ppi_channel_alloc(&m_ppi_channel);
    APP_ERROR_CHECK(err_code);


    err_code = nrf_drv_ppi_channel_assign(m_ppi_channel,
                                          timer_compare_event_addr,
                                          saadc_sample_task_addr);


    APP_ERROR_CHECK(err_code);
}


void saadc_sampling_event_enable(void)
{
    ret_code_t err_code = nrf_drv_ppi_channel_enable(m_ppi_channel);

    APP_ERROR_CHECK(err_code);

}


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;

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

        adc_event_counter ++;
if(count>=33)
{

// all the channels are scanned, and the values are stored in p_event->data.done.p_buffer.

//     NRF_LOG_INFO("ANALOG_0 : ADC result = %d , Voltage = %d mV. ", p_event->data.done.p_buffer[0], ADC_RESULT_IN_MILLI_VOLTS(p_event->data.done.p_buffer[0]));   
//        NRF_LOG_INFO("ANALOG_1 : ADC result = %d , Voltage = %d V. ", p_event->data.done.p_buffer[1], ADC_RESULT_IN_MILLI_VOLTS(p_event->data.done.p_buffer[1]));  
//     NRF_LOG_INFO("ANALOG_2 : ADC result = %d , Voltage = %d mV. ", p_event->data.done.p_buffer[2], ADC_RESULT_IN_MILLI_VOLTS(p_event->data.done.p_buffer[2]));  


NRF_LOG_INFO("Voltage     : %d mV. ", t_mv/34);  
NRF_LOG_INFO("Float Value : " NRF_LOG_FLOAT_MARKER " V\r\n", NRF_LOG_FLOAT(t_mv/34000.0))
 // NRF_LOG_INFO("---------- ADC scanned %d times -----------", adc_event_counter);   
  count=0;
  t_mv=0;

 }
else
{
count++;
t_mv=t_mv+ ADC_RESULT_IN_MILLI_VOLTS(p_event->data.done.p_buffer[1]);


//NRF_LOG_INFO("ANALOG_1 : ADC result = %d , Voltage = %d V. ", p_event->data.done.p_buffer[1],t_mv );  
//NRF_LOG_INFO("---------- ADC scanned %d times -----------", adc_event_counter);   

}


    }
}

void saadc_init(void)
{

    ret_code_t err_code;
    // channels config

    nrf_drv_saadc_config_t saadc_config = NRF_DRV_SAADC_DEFAULT_CONFIG;

    // only set to 12-bit resolution, and let the other parameters to default
    saadc_config.resolution = NRF_SAADC_RESOLUTION_12BIT; 

    // saadc init
    err_code = nrf_drv_saadc_init(&saadc_config, saadc_callback);
    APP_ERROR_CHECK(err_code);

    // channel 0
    nrf_saadc_channel_config_t channel0_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(ANALOG_0);

    // channel 1
    nrf_saadc_channel_config_t channel1_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(ANALOG_1);

    // channel 2
    nrf_saadc_channel_config_t channel2_config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(ANALOG_2);

    // channels init
    err_code = nrf_drv_saadc_channel_init(0, &channel0_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(1, &channel1_config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_channel_init(2, &channel2_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);
}


static void log_init()
{
   uint32_t err_code;
   err_code = NRF_LOG_INIT(NULL);
   APP_ERROR_CHECK(err_code);
   NRF_LOG_DEFAULT_BACKENDS_INIT();

}
/**
 * @brief Function for main application entry.
 */
int main(void)
{
    ret_code_t ret_code;

    log_init();

    ret_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(ret_code);

    saadc_init();
    saadc_sampling_event_init();
    saadc_sampling_event_enable();
  
    NRF_LOG_INFO("SAADC simplified example started.");

    while (1)
    {
        nrf_pwr_mgmt_run();
        NRF_LOG_FLUSH();
        nrf_delay_ms(3000);
    }
}


/** @} */

RE: The issue in ADC in nrf52840

haakonsh — Mon, 28 Sep 2020 07:30:31 GMT

Like rmptxf says. It's a floating pin. AIN1 is p0.03 not p0.04.

RE: The issue in ADC in nrf52840

rmptxf — Fri, 25 Sep 2020 14:45:10 GMT

Hi Muqarrab,

A floating pin will normally generate random values.

Here is an saadc example that I was working on lately. You can have a look, and see how you can achieve the analog reading also for the voltage conversion.

Hope that helps.