pwm for speaker

[Cindy]

Hi

I'm using this simple_pwm code to drive my speaker, I use this as a buzzer but I want to change the frequency.

In this code ".base_clock   = NRF_PWM_CLK_125kHz", the clock can only go as low as 125kHz, I want to have like 2kHz frequency. 

I don't know how I can achieve it, please correct me if I was wrong.

thanks,

Cindy

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/** @file
 * @defgroup pwm_example_main main.c
 * @{
 * @ingroup pwm_example
 *
 * @brief PWM Example Application main file.
 *
 * This file contains the source code for a sample application using PWM.
 */

#include <stdio.h>
#include <string.h>
#include "nrf_drv_pwm.h"
#include "app_util_platform.h"
#include "app_error.h"
#include "boards.h"
#include "bsp.h"
#include "nrf_drv_clock.h"
#include "nrf_delay.h"


#define OUTPUT_PIN 8

static nrf_drv_pwm_t m_pwm0 = NRF_DRV_PWM_INSTANCE(0);

// Declare variables holding PWM sequence values. In this example only one channel is used 
nrf_pwm_values_individual_t seq_values[] = {0, 0, 0, 0};
nrf_pwm_sequence_t const seq =
{
    .values.p_individual = seq_values,
    .length          = NRF_PWM_VALUES_LENGTH(seq_values),
    .repeats         = 0,
    .end_delay       = 0
};


// Set duty cycle between 0 and 100%
void pwm_update_duty_cycle(uint8_t duty_cycle)
{
    duty_cycle = 70;
    // Check if value is outside of range. If so, set to 100%
    if(duty_cycle >= 100)
    {
        seq_values->channel_0 = 100;
    }
    else
    {
        seq_values->channel_0 = duty_cycle;
    }
    
    nrf_drv_pwm_simple_playback(&m_pwm0, &seq, 1, NRF_DRV_PWM_FLAG_LOOP);
}

static void pwm_init(void)
{
    nrf_drv_pwm_config_t const config0 =
    {
        .output_pins =
        {
            OUTPUT_PIN, // channel 0
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 1
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 2
            NRF_DRV_PWM_PIN_NOT_USED,             // channel 3
        },
        .irq_priority = APP_IRQ_PRIORITY_LOWEST,
        .base_clock   = NRF_PWM_CLK_125kHz,
        .count_mode   = NRF_PWM_MODE_UP,
        .top_value    = 100,
        .load_mode    = NRF_PWM_LOAD_INDIVIDUAL,
        .step_mode    = NRF_PWM_STEP_AUTO
    };
    // Init PWM without error handler
    APP_ERROR_CHECK(nrf_drv_pwm_init(&m_pwm0, &config0, NULL));
    
}


int main(void)
{

    // Start clock for accurate frequencies
    NRF_CLOCK->TASKS_HFCLKSTART = 1; 
    // Wait for clock to start
    while(NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) 
        ;
    
    pwm_init();

    for (;;)
    {
        for(int i = 0; i <= 100; i++)
        {
            nrf_delay_ms(10);
            pwm_update_duty_cycle(i);
        }
    }
}


/** @} */

[Edvin]

The pwm_library set the period in:

app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_2CH(5000L, BSP_LED_0, BSP_LED_1);

5000L (L for long integer) is the period in µs. If this is set to 5000 this equals a frequency of 200hz.

So if you want a certain frequency, you must set it to:

APP_PWM_DEFAULT_CONFIG_2CH(XL, BSP_LED_0, BSP_LED1);

where X = 1/desired frequency

[Cindy]

thanks, I tried this. now I'm kind of confused. I thought the buzzer isn't loud is because the frequency.

now, it's still not very loud even after I change the frequency.   

https://www.mouser.ca/datasheet/2/670/cui%20inc._ccv-084b16-smt-1216976.pdf

this the buzzer I'm currently using.

/** @file
 * @defgroup pwm_example_main main.c
 * @{
 * @ingroup pwm_example
 *
 * @brief  PWM Example Application main file.
 *
 * This file contains the source code for a sample application using PWM.
 *
 *
 */

#include <stdbool.h>
#include <stdint.h>
#include "nrf.h"
#include "app_error.h"
#include "bsp.h"
#include "nrf_delay.h"
#include "app_pwm.h"

APP_PWM_INSTANCE(PWM1,1);                   // Create the instance "PWM1" using TIMER1.

static volatile bool ready_flag;            // A flag indicating PWM status.

void pwm_ready_callback(uint32_t pwm_id)    // PWM callback function
{
    ready_flag = true;
}

int main(void)
{
    ret_code_t err_code;

    /* 1-channel PWM, 100000 microseconds period = 0.1 second , output on pin 28. */
    app_pwm_config_t pwm1_cfg = APP_PWM_DEFAULT_CONFIG_1CH(1000L, 28);

    /* 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);
    
    //DUTY CYCLE SET TO 50%
    while (app_pwm_channel_duty_set(&PWM1, 0, 50) == NRF_ERROR_BUSY);


    while (true)
    {

    // Configure pin 5 as output
    nrf_gpio_cfg_output(4);
    // Set pin 5 high
    nrf_gpio_pin_set(4);
    nrf_delay_ms(1000);
    // Set pin 5 low
    nrf_gpio_pin_clear(4);
    nrf_delay_ms(1000);

    }

}


/** @} */

this is the code I'm currently trying. 

I also tested this sensor on Arduino, it can be very loud with 1kHz, I'm not sure what went wrong. 

this is a very simple code I tried on Arduino.

const int buzzer = 9; //buzzer to arduino pin 9


void setup(){
 
  pinMode(buzzer, OUTPUT); // Set buzzer - pin 9 as an output

}

void loop(){
 
  tone(buzzer, 1000); // Send 1KHz sound signal...
  delay(1000);        // ...for 1 sec
  noTone(buzzer);     // Stop sound...
  delay(1000);        // ...for 1sec
   
}

will it because of the current?

[hmolesworth]

Have a look at nrf52-midi-piano which I posted; it explains in some detail how to generate more pleasing audio tones and might be useful