Page 269 - ARM Based Microcontroller Projects Using MBED

8.37 PROJECT 31—VARYING THE LED BRIGHTNESS 255
/***************************************************************************

ELECTRONIC ORGAN
================
In this project a buzzer is connected to PWM port PA_8. The program is an
electronic organ that can play the notes for one octave. The following keys
are used on the keyboard for the notes:
a:C5, s:D5 d:E5 f:F5 g:G5 h:A5 j:B5 k:C6
Pressing a key plays the corresponding note for 200ms.

Author: Dogan Ibrahim
Date : September 2018
File : EOrgan
****************************************************************************/
#include "mbed.h"
Serial MyPC(USBTX, USBRX);
PwmOut pwm(PA_8);
#define MaxNotes 8

//
// Define the musical note (C5 - C6) frequencies
//
float Notes[MaxNotes] = {523.25,587.33,659.25,698.46,783.99,880.0,
987.77,1046.5};

float Periods[MaxNotes];
float DutyCycle[MaxNotes];

//
// Serial interrupt service routine. The program jumps here when
// a key is pressed on the keyboard
//
void ISR()
{
char c;
int k;

c=MyPC.getc(); // Get a key from keyboard

switch (c)
{
case 'a': // Is it 'a' ?
k = 0;
break;
case 's': // Is it 's' ?
k = 1;
break;
case 'd': // Is it 'd' ?
k = 2;
break;
case 'f': // Is it 'f' ?
FIG. 8.124 Program listing.
(Continued)