special-issue-x/basics/simple-osc-explained/simple-osc-explained.ino

/*
 * 
 * Simple (PWM) Oscillator Explained
 * 
  Instead of using the Tone() function, you can create a square wave oscillator by 
  turning the digital pin 11 (speakerpin) on (HIGH) and off (LOW) very fast:
  

        |
   HIGH |       ___      ___
        |      |   |    |   |     50% duty cycle
   LOW  |  ____|   |____|   |     (50% on, 50 off) Determined by delayMicroseconds()
        |
        |____________________
                TIME

 * 
 * 
 * 
 * 
 * 
 */

 
#define SPEAKER_PIN 11 

void setup() {
  // set pin 11 as output
  pinMode(SPEAKER_PIN, OUTPUT);
}

void loop() {

    //in simple-osc.ino we use tone(outputpin, 1000); to make a 1000Hz tone
    //1000Hz means 1000x on and off in one second.
    //instead of using tone(), we can write out what happens:
    //turn on a pin on and of on/off 1000x per second:

    digitalWrite( SPEAKER_PIN, LOW ); //turn pin off
    delayMicroseconds( 500 ); // wait 
    digitalWrite( SPEAKER_PIN, HIGH );//tunr pin on
    delayMicroseconds( 500 ); // wait 

    //the wait period determains how long it takes to loop through the
    //code, and thus how fast the code runs, and thus how fast
    //the pin turns on and off and thus at what frequency this happens:
    //we get an oscillation (on-off)!
    //Maths:
    //  for 1Hz, the pin goes on and off in one second. So the delay should be 0.5 second
    //  for 1000Hz the pin goes on/off 1000x in 1 sec. So the delay should be 1000x smaller: 0.0005 seconds
    //  wich is 500 micro seconds (dont confuse milliseconds with microseconds).

    //To control the frequency with a knob we can use analogRead, uncomment the code below (and comment out the one above):

//    digitalWrite( SPEAKER_PIN, LOW ); //turn pin off
//    delayMicroseconds( analogRead(A2) ); // wait 
//    digitalWrite( SPEAKER_PIN, HIGH );//tunr pin on
//    delayMicroseconds( analogRead(A2) ); // wait 
    
  
}