Power consumption using PWM powering a Piezo buzzer

[Jason Anderssen]

Hi,

Currently I am sounding a simple beep on and off sound with a Piezo Buzzer on the nRF52832 and using the power profiler, it is consuming approx 713.323 μA, I was wondering it that sound a bit on the high side, and if so, what kind of recommendations I should be following to try and lower this output.

Thanks in advance for your help.

Jason Anderssen

[Einar Thorsrud]

Hi,

It is difficult to say weather that is high or not without knowing more about the buzzer and how you drive it. Can you provide a bit more info?  Also, what is the current consumption of your device if you disconnect the buzzer but keeps everything else the same?

[Jason Anderssen]

Hi Einar,

Thanks for your reply, my code is as follows, basically I create a timer, so every 1/2 a second, it calls play_buzzer_alert, but before the timer starts, I call the start_buzzer_alert() once.  Before the sounds, I am running at approx 14μA, hope that clarifies things a bit better.  I am always happy to hear a better way to do the following if you have one.

static void start_buzzer_alert()

{   

    if (buzzer_emergency_active)

        return;

#ifdef DEVELOPMENT_BOARD

    app_pwm_config_t pwm_alert_cfg = APP_PWM_DEFAULT_CONFIG_1CH(1000L, 31);

    uint8_t pwm_alert_channel = 0;

#else

    app_pwm_config_t pwm_alert_cfg = APP_PWM_DEFAULT_CONFIG_2CH(1000L, SPEAKER_HZ, SPEAKER_2);

    uint8_t pwm_alert_channel = 1;

#endif

    

    pwm_alert_cfg.pin_polarity[1] = APP_PWM_POLARITY_ACTIVE_HIGH;

    

    app_pwm_init(&PWM1, &pwm_alert_cfg, pwm_ready_callback);

    app_pwm_enable(&PWM1);

    

    alert_buzzer_value = 50;

    buzzer_play_count = 10;

    buzzer_emergency_active = true;

    while (app_pwm_channel_duty_set(&PWM1, pwm_alert_channel, alert_buzzer_value) == NRF_ERROR_BUSY);

}

static void play_buzzer_alert()

{

    if (beacon_state != MODE_EMERGENCY)

        return;

    if (alert_buzzer_value == 0) {

        alert_buzzer_value = 50;

    } else {

        alert_buzzer_value = 0;

    }

    if (buzzer_play_count == 0) {

        alert_buzzer_value = 0;

    } else {

        // for now we do continuing beeps, as if we try and uninit here, it seems to cause issues in the beacon.

        //buzzer_play_count--;

    }   

#ifdef DEVELOPMENT_BOARD

    uint8_t pwm_alert_channel = 0;

#else

    uint8_t pwm_alert_channel = 1;

#endif

    while (app_pwm_channel_duty_set(&PWM1, pwm_alert_channel, alert_buzzer_value) == NRF_ERROR_BUSY);

}

static void stop_buzzer_alert()

{

    if (buzzer_emergency_active == false)

        return;

    if (beacon_state == MODE_EMERGENCY)

        return;

    app_pwm_disable(&PWM1);

    app_pwm_uninit(&PWM1);

    buzzer_play_count = 0;

    buzzer_emergency_active = false;

}

Thanks

Jason

[Einar Thorsrud]

I see. The current consumption does not seem high to me. The clock is running, and you have one timer running (app_pwm) and that two alone should give you about 500 μA. Then you have the current consumption of the buzzer itself. That can vary greatly, but 200 μA is not a strange number, so all in all a current consumption of about 700 μA seems reasonable.