RE: Power consumption using PWM powering a Piezo buzzer

Einar Thorsrud — Wed, 31 Oct 2018 13:25:45 GMT

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.

RE: Power consumption using PWM powering a Piezo buzzer

Jason Anderssen — Wed, 31 Oct 2018 02:44:02 GMT

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

RE: Power consumption using PWM powering a Piezo buzzer

Einar Thorsrud — Tue, 30 Oct 2018 12:48:56 GMT

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?