RE: How to measure a state of a battery by using saadc example with NRF52832?

BelvitaSoft — Tue, 23 Jul 2019 13:10:38 GMT

Ok guys, thank you for your support. Pin Analog A0 is defined as P02 on the development kit, although on the bottom of the board is written that pin P3 in A0.

Thank you, for all answers. Big love!

RE: How to measure a state of a battery by using saadc example with NRF52832?

Igor — Tue, 23 Jul 2019 12:08:21 GMT

Try something like this:

#include "app_timer.h"
#include "nrf_log.h"
#include "nrf_log_ctrl.h"
#include "nrfx_saadc.h"

#define INPUTS 1
#define TIMER  1000 // ms
#define AIN_BATTERY 0 

APP_TIMER_DEF(saadc_timer);

static nrf_saadc_value_t buffer[2][INPUTS];
static uint8_t battery_level = 0xFF;

static inline uint16_t adc_to_mv(nrf_saadc_value_t adc_result) {
    // http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.nrf52840.ps/saadc.html?cp=2_0_0_5_22_2#saadc_digital_output
    // Vresult[mV] = (adc_result * Vref[mV]) / (2^resolution * gain) = (adc_result * 600) / (2^10 * 1/6)
    return (adc_result * 3600) >> 10;
}

uint8_t get_battery_level() {
    return battery_level;
}

static void saadc_timeout_handler(void *p_context) {
    UNUSED_PARAMETER(p_context);
    APP_ERROR_CHECK(nrfx_saadc_sample());
}

void saadc_event_handler(nrfx_saadc_evt_t const *p_event) {
    if (p_event->type != NRFX_SAADC_EVT_DONE)
        return;
    nrf_saadc_value_t *adc_result = p_event->data.done.p_buffer;
    battery_level = battery_level_in_percent(adc_to_mv(adc_result[AIN_BATTERY]));
    APP_ERROR_CHECK(nrfx_saadc_buffer_convert(adc_result, INPUTS));
}

void saadc_init(void) {
    //  SAADC config & calibrate
    nrfx_saadc_config_t saadc_config = NRFX_SAADC_DEFAULT_CONFIG;
    APP_ERROR_CHECK(nrfx_saadc_init(&saadc_config, saadc_event_handler));
    APP_ERROR_CHECK(nrfx_saadc_calibrate_offset());
    while (nrfx_saadc_is_busy())
        sd_app_evt_wait();

    // Channels config
    nrf_saadc_channel_config_t battery_config = NRFX_SAADC_DEFAULT_CHANNEL_CONFIG_SE(NRF_SAADC_INPUT_VDD);
    APP_ERROR_CHECK(nrfx_saadc_channel_init(AIN_BATTERY, &battery_config));

    // double buffering
    APP_ERROR_CHECK(nrfx_saadc_buffer_convert(buffer[0], INPUTS));
    APP_ERROR_CHECK(nrfx_saadc_buffer_convert(buffer[1], INPUTS));

    // start SAADC timer
    APP_ERROR_CHECK(app_timer_create(&saadc_timer, APP_TIMER_MODE_REPEATED, saadc_timeout_handler));
    APP_ERROR_CHECK(app_timer_start(saadc_timer, APP_TIMER_TICKS(TIMER), NULL));
}

Use saadc_init() (only once!) to start measuring. Then use get_battery_level() to get battery level in percents (0x64 = 100%).

RE: How to measure a state of a battery by using saadc example with NRF52832?

Jørgen Holmefjord — Tue, 23 Jul 2019 11:58:11 GMT

Hi,

It looks like you are confusing the analog input number with the Arduino Pin naming on top of the board. Please have a look at this post, and follow the pin assignments in the product specifications.

Best regards,
Jørgen