Low Power Mode using SAADC with ble_app_beacon

Question

Hello !!

I have custom board on nrf52832 having 10 buttons which is pull down by default. I have achieved 22uA after modifying the ble_app_beacon example to broadcast when button is pressed.I am also having coin cell with the custom board so i want to check the battery voltage so that i could indicate the battery level (2 conditons i.e <10% & >10% ) using bi-colour led.

I have modified ble_app_beacon as per requirement and then integrated SAADC example with modified ble_app_beacon example. I am now getting more than 2 mA current consumption.

So, If anyone could help me with the code so that I could monitor the battery (on any interval) to indicate battery percentage. I am also attaching the main code so that it would be more understandable. My requirement is 3uA when there is no broadcasting.

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/** @file
 *
 * @defgroup ble_sdk_app_beacon_main main.c
 * @{
 * @ingroup ble_sdk_app_beacon
 * @brief Beacon Transmitter Sample Application main file.
 *
 * This file contains the source code for an Beacon transmitter sample application.
 */

#include <stdbool.h>
#include <stdint.h>
#include "nordic_common.h"
#include "bsp.h"
#include "nrf_soc.h"
#include "nrf_sdh.h"
#include "nrf_sdh_ble.h"
#include "ble_advdata.h"
#include "app_timer.h"
#include "nrf_drv_clock.h"
#include "nrf_pwr_mgmt.h"
#include "nrf_drv_saadc.h"
#include "nrf_drv_ppi.h"
#include "nrf_drv_timer.h"
#include "boards.h"
#include "nrf.h"
#include "nrf_delay.h"

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

/*****  Broadcast Parameters *******/

#define DEVICE_NAME                     "BLE_APP_BEACON"
#define APP_BLE_CONN_CFG_TAG            1                                  /**< A tag identifying the SoftDevice BLE configuration. */
#define NON_CONNECTABLE_ADV_INTERVAL    MSEC_TO_UNITS(400, UNIT_0_625_MS)  /**< The advertising interval for non-connectable advertisement (100 ms). This value can vary between 100ms to 10.24s). */

#define APP_ADV_DATA_LENGTH             0x15                               /**< Length of manufacturer specific data in the advertisement. */
#define APP_DEVICE_TYPE                 0x02                               /**< 0x02 refers to Beacon. */
#define APP_COMPANY_IDENTIFIER          0x0059                             /**< Company identifier for Nordic Semiconductor ASA. as per www.bluetooth.org. */

#define DEAD_BEEF                       0xDEADBEEF                    /**< Value used as error code on stack dump, can be used to identify stack location on stack unwind. */
#define HIGH 1
#define LOW  0

static ble_gap_adv_params_t m_adv_params;                                  /**< Parameters to be passed to the stack when starting advertising. */
static uint8_t              m_adv_handle = BLE_GAP_ADV_SET_HANDLE_NOT_SET; /**< Advertising handle used to identify an advertising set. */
static uint8_t              m_enc_advdata[BLE_GAP_ADV_SET_DATA_SIZE_MAX];  /**< Buffer for storing an encoded advertising set. */

uint16_t remote_led_indication;

static uint8_t      packet_buf;          /****** TX buffer for buttons ******/


/******    ADC parameters  *********/
#define SAMPLES_IN_BUFFER 1

volatile uint8_t state = 1;
static const nrf_drv_timer_t m_timer = NRF_DRV_TIMER_INSTANCE(1);
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;

#define ADC_REF_VOLTAGE_IN_MILLIVOLTS   600                                     /**< Reference voltage (in milli volts) used by ADC while doing 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 DIODE_FWD_VOLT_DROP_MILLIVOLTS  270                                   /**< Typical forward voltage drop of the diode . */
#define ADC_RES_10BIT                   1024                                    /**< Maximum digital value for 10-bit ADC conversion. */
#define ADC_RESULT_IN_MILLI_VOLTS(ADC_VALUE) \
        ((((ADC_VALUE) *ADC_REF_VOLTAGE_IN_MILLIVOLTS) / ADC_RES_10BIT) * ADC_PRE_SCALING_COMPENSATION)

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;
        nrf_saadc_value_t adc_result;
        uint16_t batt_lvl_in_milli_volts;
        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++)
        {
          adc_result=p_event->data.done.p_buffer[0];
         
          batt_lvl_in_milli_volts = ADC_RESULT_IN_MILLI_VOLTS(adc_result);

        }
        remote_led_indication = batt_lvl_in_milli_volts;  
        //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_VDD);

    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 the GAP initialization.
 *
 * @details This function will set up all the necessary GAP (Generic Access Profile) parameters of
 *          the device. It also sets the permissions and appearance.
 */
static void gap_params_init(void)
{
   uint32_t err_code;
   ble_gap_conn_sec_mode_t     sec_mode;
   BLE_GAP_CONN_SEC_MODE_SET_OPEN(&sec_mode);
   err_code = sd_ble_gap_device_name_set(&sec_mode, (const uint8_t *)DEVICE_NAME,
   strlen(DEVICE_NAME));
   APP_ERROR_CHECK(err_code);
}

/**@brief Struct that contains pointers to the encoded advertising data. */
static ble_gap_adv_data_t m_adv_data =
{
    .adv_data =
    {
        .p_data = m_enc_advdata,
        .len    = BLE_GAP_ADV_SET_DATA_SIZE_MAX
    },
    .scan_rsp_data =
    {
        .p_data = NULL,
        .len    = 0

    }
};

/**@brief Callback function for asserts in the SoftDevice.
 *
 * @details This function will be called in case of an assert in the SoftDevice.
 *
 * @warning This handler is an example only and does not fit a final product. You need to analyze
 *          how your product is supposed to react in case of Assert.
 * @warning On assert from the SoftDevice, the system can only recover on reset.
 *
 * @param[in]   line_num   Line number of the failing ASSERT call.
 * @param[in]   file_name  File name of the failing ASSERT call.
 */
void assert_nrf_callback(uint16_t line_num, const uint8_t * p_file_name)
{
    app_error_handler(DEAD_BEEF, line_num, p_file_name);
}

/**@brief Function for initializing the Advertising functionality.
 *
 * @details Encodes the required advertising data and passes it to the stack.
 *          Also builds a structure to be passed to the stack when starting advertising.
 */

static void advertising_data_update(void)
{
    uint32_t      err_code;
    ble_advdata_t advdata;
    uint8_t       flags = BLE_GAP_ADV_FLAGS_LE_ONLY_LIMITED_DISC_MODE;

    ble_advdata_manuf_data_t manuf_specific_data;

    manuf_specific_data.company_identifier = APP_COMPANY_IDENTIFIER;
    manuf_specific_data.data.p_data = (uint8_t *) &packet_buf;
    manuf_specific_data.data.size   = sizeof(packet_buf);
    advdata.p_manuf_specific_data = &manuf_specific_data;

    // Build and set advertising data.
    memset(&advdata, 0, sizeof(advdata));
    //advdata.name_type             = BLE_ADVDATA_NO_NAME;
    advdata.name_type             = BLE_ADVDATA_FULL_NAME;
    advdata.flags                 = flags;
    advdata.p_manuf_specific_data = &manuf_specific_data;

    // Initialize advertising parameters (used when starting advertising).
    memset(&m_adv_params, 0, sizeof(m_adv_params));

    m_adv_params.properties.type = BLE_GAP_ADV_TYPE_NONCONNECTABLE_NONSCANNABLE_UNDIRECTED;
    m_adv_params.p_peer_addr     = NULL;    // Undirected advertisement.
    m_adv_params.filter_policy   = BLE_GAP_ADV_FP_ANY;
    m_adv_params.interval        = NON_CONNECTABLE_ADV_INTERVAL;
    m_adv_params.duration        = 400;       // Broadcast for 4 sec.

    err_code = ble_advdata_encode(&advdata, m_adv_data.adv_data.p_data, &m_adv_data.adv_data.len);
    APP_ERROR_CHECK(err_code);

    err_code = sd_ble_gap_adv_set_configure(&m_adv_handle, &m_adv_data, &m_adv_params);
    APP_ERROR_CHECK(err_code);
}
/**@brief Function for starting advertising.
 */
static void advertising_start(void)
{
    ret_code_t err_code;

    err_code = sd_ble_gap_adv_start(m_adv_handle, APP_BLE_CONN_CFG_TAG);
    APP_ERROR_CHECK(err_code);

/**** LED indication while advertising ****/
    if (remote_led_indication > ("%d", 1920)){
        nrf_gpio_pin_write(LED_1, LOW);   // Green Led will Blink on less than 10% battery
        nrf_delay_ms(50);

        nrf_gpio_pin_write(LED_1, HIGH);
        nrf_delay_ms(50);

       }

    if (remote_led_indication < ("%d", 1920)){
        nrf_gpio_pin_write(LED_2, LOW);   // Red Led will Blink on more than 10% battery
        nrf_delay_ms(50);

        nrf_gpio_pin_write(LED_2, HIGH);  
        nrf_delay_ms(50);

       }

    //err_code = bsp_indication_set(BSP_INDICATE_ADVERTISING);
    //APP_ERROR_CHECK(err_code);
}


/**@brief Function for starting advertising.
 */
static void advertising_stop()
{
    ret_code_t err_code;

    err_code = sd_ble_gap_adv_stop(m_adv_handle);
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for initializing the BLE stack.
 *
 * @details Initializes the SoftDevice and the BLE event interrupt.
 */
static void ble_stack_init(void)
{
    ret_code_t err_code;
    err_code = nrf_sdh_enable_request();
 
    uint32_t ram_start = 0;
    err_code = nrf_sdh_ble_default_cfg_set(APP_BLE_CONN_CFG_TAG, &ram_start);
    APP_ERROR_CHECK(err_code);

    // Enable BLE stack.
    err_code = nrf_sdh_ble_enable(&ram_start);
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for initializing logging. */
static void log_init(void)
{
    ret_code_t err_code = NRF_LOG_INIT(NULL);
    APP_ERROR_CHECK(err_code);

    NRF_LOG_DEFAULT_BACKENDS_INIT();
}

/**@brief Function for initializing LEDs. */
static void leds_init(void)
{
    ret_code_t err_code = bsp_init(BSP_INIT_LEDS, NULL);
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for initializing timers. */
static void timers_init(void)
{
    ret_code_t err_code = app_timer_init();
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for initializing power management.
 */
static void power_management_init(void)
{
    ret_code_t err_code;
    err_code = nrf_pwr_mgmt_init();
    APP_ERROR_CHECK(err_code);
}


/**@brief Function for handling the idle state (main loop).
 *
 * @details If there is no pending log operation, then sleep until next the next event occurs.
 */
static void idle_state_handle(void)
{
    if (NRF_LOG_PROCESS() == false)
    {
        nrf_pwr_mgmt_run();
    }
}

/**@brief Function for handling bsp events.
 */
void bsp_evt_handler(bsp_event_t evt)
{ 
    switch (evt)
    {
          case BSP_EVENT_KEY_0:
          packet_buf = BSP_EVENT_KEY_0;
          break;

          case BSP_EVENT_KEY_1:
          packet_buf = BSP_EVENT_KEY_1;
          break;

          case BSP_EVENT_KEY_2:
          packet_buf = BSP_EVENT_KEY_2;
          break;

          case BSP_EVENT_KEY_3:
          packet_buf = BSP_EVENT_KEY_3;
          break;

          case BSP_EVENT_KEY_4:
          packet_buf = BSP_EVENT_KEY_4;
          break;
           
          case BSP_EVENT_KEY_5:
          packet_buf = BSP_EVENT_KEY_5;
          break;
   
          case BSP_EVENT_KEY_6:
          packet_buf = BSP_EVENT_KEY_6;
          break;
      
          case BSP_EVENT_KEY_7:
          packet_buf = BSP_EVENT_KEY_7;
          break;

          case BSP_EVENT_KEY_8:
          packet_buf = BSP_EVENT_KEY_8;
          break;
   
          case BSP_EVENT_KEY_9:
          packet_buf = BSP_EVENT_KEY_9;
          break;
      
          case BSP_EVENT_KEY_10:
          packet_buf = BSP_EVENT_KEY_10;
          break;  
    }
   
    NRF_LOG_INFO("%u", packet_buf);
    (void)sd_ble_gap_adv_stop(m_adv_handle);
    advertising_data_update();
    advertising_start();
}


/**
 * @brief Function for application main entry.
 */
int main(void)
{
    NRF_POWER->DCDCEN = 1;    
    uint32_t err_code = NRF_SUCCESS; 
 
    // Initialize.
    nrf_pwr_mgmt_init();
    //log_init();
    timers_init();
    //leds_init();
    //power_management_init();
    ble_stack_init();
    gap_params_init();
    //advertising_init();
    advertising_data_update();
    
    
    err_code = bsp_init(BSP_INIT_LEDS | BSP_INIT_BUTTONS, bsp_evt_handler);
    APP_ERROR_CHECK(err_code);

    saadc_init();
    saadc_sampling_event_init();
    saadc_sampling_event_enable();


    // Start execution.
    NRF_LOG_INFO("Beacon example started.");
    advertising_start();

    // Enter main loop.
    for(;;)
    {
        idle_state_handle();
    }
}


/**
 * @}
 */

I would appreciate any help!!!

Thanks!!!

Vidar Berg · Accepted Answer

I'm glad to hear that it worked on your custom board as well. 
 techietech said: Now the thing is it is consuming ~ 22 uA (fluctuating) on idle state but I want to measure the battery level when the broadcasting is happening and stop else so that it will not consume any current. 
 22 uA may be the average current consumption if you have increased the default advertising interval (100 ms by default). You can try out our online power profiler ( https://devzone.nordicsemi.com/nordic/power/w/opp/2/online-power-profiler-for-ble ) if you want to estimate current with other configurations. 
 You can comment the advertising_start(); function in main() to measure the System ON idle current with the RTC running. 
 techietech said: Also what should be interval for measuring the voltage to keep track of battery level? 
 Not very frequent if the battery is expected to last for months/years. One time per hour is probably sufficient.

Vidar Berg · Answer

Hi, 
 The chip is powered down in System OFF mode and a wake-up from this mode will lead to a system reset. Is this what you want, or should the chip always stay in System ON mode and do periodic advertising?

techietech · Answer

Hi! 
 
 I just want to system should be on while advertising on button press and else it should be either on system on sleep mode or system off sleep mode as it's not that much concern as per my requirements. 
 Also system should be always wake up immediately on each button press. If you could review the above code so that you could provide yours suggestions whether if I missed something.

Vidar Berg · Answer

Hi, 
 It makes sense to use System OFF if the device is expected to stay inactive (i.e. no advertising) for longer periods of time, and that you only rely on the button press as the wake-up source. 
 Before entering system OFF you should also make that there is no ongoing SAADC sampling. From the PS: 
 Before entering System OFF mode, the user must make sure that all on-going EasyDMA transactions have been completed. This is usually accomplished by making sure that the EasyDMA enabled peripheral is not active when entering System OFF.

Vidar Berg · Answer

Hello, 
 1. Do you plan to use the System OFF mode or not? You were enabling the NRF_PWR_MGMT_CONFIG_STANDBY_TIMEOUT_ENABLED option earlier which will cause the device to enter system OFF if you let it time out. 
 2. Try to define 'remote_led_indication' as 'volatile' : volatile uint8_t remote_led_indication 
 3. 1.3 mA indicates that the i2c peripheral on the nRF might be staying in receive mode all the time. Or are you utilzing the 'attention/sleep' signal from the Cypress IC to only enable i2c when needed? And I guess the 4 mA is because the CPU is kept running 
 4. It's likely caused by an assertion in your code (e.g. when an error code is passed to the APP_ERROR_CHECK() macro, please see the " Error module " documentation for more on this.

Low Power Mode using SAADC with ble_app_beacon

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