Let’s start by uncommenting our button code, sending a serial message when it is pressed and commenting out our potentiometer code.

/*
* 6.2.1 State Changes
* roguescience.org
*
* Turns a LED connected to digital pin 13 on based from input on digital pin 2
* and sends a message using serial communication.
*/

int ledPin = 11;                //choose the pin for the LED - needs to be (3,5,6,9,10, or 11)
int buttonPin = 2;               //choose the input pin for a pushbutton
int potPin = 0;                  //choose the input pin for a potentometer
int buttonVal = 0;                    //variable for reading the button status
int buttonState = 0;            //variable to hold the buttons curr
int bounceCheck = 0;            //variable for debouncing
int potVal = 0;                //variable for reading potentiometer value
int mappedPotVal = 0;          //variable for remapping pot data to 0-255

void setup() {
  pinMode(ledPin, OUTPUT);      //declare LED as output
  pinMode(buttonPin, INPUT);     //declare pushbutton as input
  Serial.begin(9600);            //begin serial communication at 9600 baud
}

void loop(){

  buttonVal = digitalRead(buttonPin);     //read input value from button
  delay(10);                              //wait 10ms
  bounceCheck = digitalRead(buttonPin);   //check again
  if(buttonVal == bounceCheck){           //if val is the same then not a bounce
    if (buttonVal == HIGH) {              //check if the input is HIGH
      digitalWrite(ledPin, LOW);         //turn LED OFF
      Serial.println("OFF");
    } else {
      digitalWrite(ledPin, HIGH);       //turn LED ON
      Serial.println("ON");
    }
  }

  /*
   potVal = analogRead(potPin);         //read input from potentiometer
   mappedPotVal = map(potVal, 0, 1023, 0, 255);  //map value to 0-255
   Serial.println(mappedPotVal);                   //send potVal via serial
   analogWrite(ledPin, mappedPotVal);        //use PWM to set LED brightness
  */
}

Notice how the message is getting sent over and over again - this might be appropriate for some applications but in our case if we want to trigger a single MIDI event with a button press we only want it to send the message once. To do this we want to send a message only when the STATE of the button CHANGES.

/*
 * 6.2.2 State Changes
 * roguescience.org
 *
 * Turns a LED connected to digital pin 13 on based from input on digital pin 2
 * and sends a message using serial communication - only sends a message when the
 * state of the button changes.
 */

int ledPin = 11;                //choose the pin for the LED - needs to be (3,5,6,9,10, or 11)
int buttonPin = 2;               //choose the input pin for a pushbutton
int potPin = 0;                  //choose the input pin for a potentometer
int buttonVal = 0;                    //variable for reading the button status
int buttonState = 0;            //variable to hold the buttons current state
int bounceCheck = 0;            //variable for debouncing
int potVal = 0;                //variable for reading potentiometer value
int mappedPotVal = 0;          //variable for remapping pot data to 0-255

void setup() {
  pinMode(ledPin, OUTPUT);      //declare LED as output
  pinMode(buttonPin, INPUT);     //declare pushbutton as input
  Serial.begin(9600);            //begin serial communication at 9600 baud
}

void loop(){

  buttonVal = digitalRead(buttonPin);     //read input value from button
  delay(10);                              //wait 10ms
  bounceCheck = digitalRead(buttonPin);   //check again
  if(buttonVal == bounceCheck){           //if val is the same then not a bounce
    if (buttonVal == HIGH && buttonState == 1) {   //check if the input is HIGH
      digitalWrite(ledPin, LOW);         //turn LED OFF
      Serial.println("OFF");
      buttonState = 0;
    }
    if(buttonVal == LOW && buttonState == 0){
      digitalWrite(ledPin, HIGH);       //turn LED ON
      Serial.println("ON");
      buttonState = 1;
    }

  }

  /*
   potVal = analogRead(potPin);         //read input from potentiometer
   mappedPotVal = map(potVal, 0, 1023, 0, 255);  //map value to 0-255
   Serial.println(mappedPotVal);                   //send potVal via serial
   analogWrite(ledPin, mappedPotVal);        //use PWM to set LED brightness
   */
}