es_battery_voltage_saadc.c

/**
 * Copyright (c) 2016 - 2017, Nordic Semiconductor ASA
 * 
 * All rights reserved.
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 * 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
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 */
#include "es_battery_voltage.h"
#include "nrf_drv_saadc.h"
#include "sdk_macros.h"

#define ADC_REF_VOLTAGE_IN_MILLIVOLTS  600  //!< Reference voltage (in milli volts) used by ADC while doing conversion.
#define DIODE_FWD_VOLT_DROP_MILLIVOLTS 270  //!< Typical forward voltage drop of the diode (Part no: SD103ATW-7-F) that is connected in series with the voltage supply. This is the voltage drop when the forward current is 1mA. Source: Data sheet of 'SURFACE MOUNT SCHOTTKY BARRIER DIODE ARRAY' available at www.diodes.com.
#define ADC_RES_10BIT                  1024 //!< Maximum digital value for 10-bit ADC conversion.
#define ADC_PRE_SCALING_COMPENSATION   6    //!< The ADC is configured to use VDD with 1/3 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_10BIT) * ADC_PRE_SCALING_COMPENSATION)

static nrf_saadc_value_t adc_buf;                   //!< Buffer used for storing ADC value.
static uint16_t          m_batt_lvl_in_milli_volts; //!< Current battery level.

/**@brief Function handling events from 'nrf_drv_saadc.c'.
 *
 * @param[in] p_evt SAADC event.
 */
static void saadc_event_handler(nrf_drv_saadc_evt_t const * p_evt)
{
    if (p_evt->type == NRF_DRV_SAADC_EVT_DONE)
    {
        nrf_saadc_value_t adc_result;

        adc_result = p_evt->data.done.p_buffer[0];

        m_batt_lvl_in_milli_volts =
            ADC_RESULT_IN_MILLI_VOLTS(adc_result) + DIODE_FWD_VOLT_DROP_MILLIVOLTS;
    }
}


void es_battery_voltage_init(void)
{
    ret_code_t err_code = nrf_drv_saadc_init(NULL, saadc_event_handler);

    APP_ERROR_CHECK(err_code);

    nrf_saadc_channel_config_t config =
        NRF_DRV_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_VDD);
    err_code = nrf_drv_saadc_channel_init(0, &config);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_buffer_convert(&adc_buf, 1);
    APP_ERROR_CHECK(err_code);

    err_code = nrf_drv_saadc_sample();
    APP_ERROR_CHECK(err_code);
}


void es_battery_voltage_get(uint16_t * p_vbatt)
{
    VERIFY_PARAM_NOT_NULL_VOID(p_vbatt);

    *p_vbatt = m_batt_lvl_in_milli_volts;
    if (!nrf_drv_saadc_is_busy())
    {
        ret_code_t err_code = nrf_drv_saadc_buffer_convert(&adc_buf, 1);
        APP_ERROR_CHECK(err_code);

        err_code = nrf_drv_saadc_sample();
        APP_ERROR_CHECK(err_code);
    }
}