Buzzer Test with Edison

This is a rapid sketch where I make sound using a buzzer connected to the PWM pin 9 of the Intel Edison. In the part “Test 5” of the code, the sound is like a siren that I am going to add to my WiFi_Car.

The buzzer is connected to the pin SERVO_2 (which is internally connected to the Intel Edison pin 9) through a 680 ohms resistor.

 

Testing the Buzzer with Intel Edison.

/* Info:https://developer.mbed.org/users/4180_1/notebook/using-a-speaker-for-audio-output/

 *

 * Using PWM hardware to generate a simple audio tone

 *

 * The simplest way to generate an audio signal to play on the speaker is to use a hardware PWM output.

 * Set the PWM period to 1/frequency of the desired sound. The PWM duty cycle is set to 0.5.

 * A lower duty cycle setting produces lower volume, but keep in mind that since square waves or

 * pulses are generated there will also be a lot of higher frequency harmonics produced.

 * Not quite a pure tone, but then again most instruments also generate some harmonics.

 * The advantage of using the PWM hardware is that it takes minimal memory and no processor

 * time to output an audio tone. If only a beep, click, or siren alarm sound is needed this may be the appropriate choice.

*/

//Makefile: g++ -lmraa -o SPEAKER_EDISON SPEAKER_EDISON.CPP

#include <iostream>

#include <stdio.h>

#include <signal.h>

#include <unistd.h>

#include <mraa.h>

#include <mraa/pwm.h>

#define ON  1

#define OFF 0

using namespace std;

sig_atomic_t volatile isrunning = 1;

void sig_handler(int signum);

int main()

{

       signal(SIGINT, &sig_handler);

       float    duty = 0.5;     //50% duty cycle - max volume

       mraa_init();

       mraa_pwm_context PWM_9_pin;

       PWM_9_pin = mraa_pwm_init(9);

       if (PWM_9_pin == NULL)            cout << "Error in PWM_9_pin...\n";

             int i;

             cout << "test 1" << endl;

             // generate a 500Hz tone using PWM hardware output

             mraa_pwm_period_us(PWM_9_pin, 2000);//500hz period, 2ms

             mraa_pwm_write(PWM_9_pin, duty);//50% duty cycle - max volume     

             mraa_pwm_enable(PWM_9_pin, ON);// turn on audio

             sleep(3);

             mraa_pwm_enable(PWM_9_pin, OFF);// turn off audio

             sleep(2);//little pause

             cout << "test 2:";

             // generate a short 150Hz tone using PWM hardware output

             // something like this can be used for a button click effect for feedback

             duty = 0.25;

             for (i = 0; i<10; i++)

             {           

                    mraa_pwm_period_us(PWM_9_pin, 6);//6ms period

                    mraa_pwm_write(PWM_9_pin, duty);//25% duty cycle - mid range volume

                    mraa_pwm_enable(PWM_9_pin, ON);// turn on audio

                    usleep(20000);//20ms

                    mraa_pwm_enable(PWM_9_pin, OFF);// turn off audio

                    usleep(50000);//500ms

                    cout << " ";

                    cout <<i;

             }

             sleep(2);//little pause

             cout << "\ntest 3" << endl;

             duty = 0.25;

             // sweep up in frequency by changing the PWM period

             for (i = 0; i<8000; i = i + 100)

             {

                    mraa_pwm_period_us(PWM_9_pin, (1.0 / float(i)) * 1000);

                    mraa_pwm_enable(PWM_9_pin, ON);// turn on audio

                    usleep(10000);

             }

             mraa_pwm_enable(PWM_9_pin, OFF);

             sleep(2);

             cout << "test 4"<<endl;

             // two tone police siren effect -  two periods or two frequencies

             // increase volume - by changing the PWM duty cycle

             mraa_pwm_enable(PWM_9_pin, ON);// turn on audio

             for (i = 0; i < 26; i = i + 2)

             {

                    mraa_pwm_period_us(PWM_9_pin, 1031);//(1.0 / 969.0)

                    duty = (float(i) / 50.0);

                    mraa_pwm_write(PWM_9_pin, duty);

                    usleep(500000);

                    mraa_pwm_period_us(PWM_9_pin, 1250);//(1.0 / 800.0)

                    usleep(500000);

             }

             // decrease volume

             for (i = 25; i >= 0; i = i - 2)

             {

                    mraa_pwm_period_us(PWM_9_pin, 1031);

                    duty = (float(i) / 50.0);

                    mraa_pwm_write(PWM_9_pin, duty);

                    usleep(500000);

                    mraa_pwm_period_us(PWM_9_pin, 1250);

                    usleep(500000);

             }

             mraa_pwm_enable(PWM_9_pin, OFF);

             sleep(2);

      

       mraa_pwm_enable(PWM_9_pin, ON);

       cout << "test 5" << endl;

       while (isrunning)

       {

             mraa_pwm_period_us(PWM_9_pin, 1031);//(1.0 / 969.0)

             duty = 0.05;

             mraa_pwm_write(PWM_9_pin, duty);

             usleep(500000);

             mraa_pwm_period_us(PWM_9_pin, 1250);//(1.0 / 800.0)

             usleep(500000);

       }

       mraa_pwm_write(PWM_9_pin, 0);

       mraa_pwm_enable(PWM_9_pin, OFF);

       cout << "\nClosing application..." << endl;

       sleep(1);

       return MRAA_SUCCESS;

}

void sig_handler(int signum)

{

       if (signum == SIGINT) isrunning = 0;

}