PWM with a piezo buzzer,How can I change the PWM frequency?

RE: PWM with a piezo buzzer,How can I change the PWM frequency?

Ole Bauck — Tue, 31 May 2016 12:11:29 GMT

Looks good, maybe you should also change uin16_t freq to uint16_t period_us for better readability ;)

You actually don't have to call app_pwm_disable() either as this is done in app_pwm_uninit().

RE: PWM with a piezo buzzer,How can I change the PWM frequency?

Mahesh Venkitachalam — Tue, 31 May 2016 12:05:41 GMT

app_pwm_disenable() should be app_pwm_disable() ?

RE: PWM with a piezo buzzer,How can I change the PWM frequency?

Mahesh Venkitachalam — Tue, 31 May 2016 12:01:54 GMT

Here's a previous discussion on this topic: devzone.nordicsemi.com/.../

RE: PWM with a piezo buzzer,How can I change the PWM frequency?

Mike — Tue, 31 May 2016 11:13:23 GMT

Is this OK?

 /*
 init, Once executed
 */

 void pwm_init(void)  
 {
    /* 1-channel PWM, 200Hz, output on DK LED pins. */
    app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_1CH(5000L, BSP_LED_0);
    
    /* Switch the polarity of the second channel. */
    pwm1_cfg.pin_polarity[1] = APP_PWM_POLARITY_ACTIVE_HIGH;
    
    /* Initialize and enable PWM. */
    err_code = app_pwm_init(&PWM1,&pwm1_cfg,pwm_ready_callback);
    APP_ERROR_CHECK(err_code);
    app_pwm_enable(&PWM1);
  }
  

  
 /*
 pwm_change_frequency,Can be executed multiple times
 */
   void pwm_change_frequency(uint16_t freq)  
 {
 
  app_pwm_disenable(&PWM1);
  app_pwm_uninit(&PWM1);  
     /* 1-channel PWM, 200Hz, output on DK LED pins. */
    app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_1CH(freq, BSP_LED_0);
    
    /* Switch the polarity of the second channel. */
    pwm1_cfg.pin_polarity[1] = APP_PWM_POLARITY_ACTIVE_HIGH;
    
    /* Initialize and enable PWM. */
    err_code = app_pwm_init(&PWM1,&pwm1_cfg,pwm_ready_callback);
    APP_ERROR_CHECK(err_code);
    app_pwm_enable(&PWM1);
    
    }

RE: PWM with a piezo buzzer,How can I change the PWM frequency?

Mike — Tue, 31 May 2016 11:06:07 GMT

please offer a detailed example that can change the PWM frenuency.

RE: PWM with a piezo buzzer,How can I change the PWM frequency?

Ole Bauck — Tue, 31 May 2016 10:47:35 GMT

You cannot change the PWM frequency without un-initializing and then initialize the PWM instance again.

RE: PWM with a piezo buzzer,How can I change the PWM frequency?

Mike — Tue, 31 May 2016 09:13:33 GMT

I need change the PWM is from 1KHz, to ,1.5KHz,then 2.0KHz,then 2.7KHz. I can not reset the NRF51822 CHIP. How can i realtime change the PWM frequency at the 51822 is run?

RE: PWM with a piezo buzzer,How can I change the PWM frequency?

Mahesh Venkitachalam — Tue, 31 May 2016 09:06:59 GMT

The first parameter of APP_PWM_DEFAULT_CONFIG_2CH is the PWM period in microseconds.

So in the above code, 5000 us => 1000000/5000 Hz == 200 Hz. So to set the buzzer frequency to f, set the value as 1000000/f.

Also, if you just need PWM on one pin, you can use APP_PWM_DEFAULT_CONFIG_1CH.