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;
}
