Arduino Programming – State change

How to program a state change functionality. ‘State change detection’ is a method to see when a button is pressed or released. You can use it to fire a different action each press of a button.

For example the “Play/Pause” button on a cd-player behaves like that. The first press is play, the next press is pause, the next play again etc. Depending the state the action is different ( play > pause, pause > play ).

In this tutorial I explain also the basic code structure ( setup, loop ) of Arduino script.

Level : beginner with Arduino. ( Basic knowledge of programming principles like if/else and variables ).

Download the Arduino ( .pde ) files : arduino_tutorial_statechange.zip

OnOff.pde :

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/*

  LED on when you press a button.

  LED off when you release a button.  

  

  created 01-12-2009 by kasperkamperman.com

*/



const int buttonPin = 2;      // the pin that the pushbutton is attached to

const int ledPin    = 13;     // the pin that the LED is attached to



int buttonState     = 0;      // current state of the button



void setup() {

  pinMode(buttonPin, INPUT);  // initialize the button pin as a input

  pinMode(ledPin, OUTPUT);    // initialize the button pin as a output

}



void loop() {

  // read the pushbutton input pin

  buttonState = digitalRead(buttonPin);



  // turns LED on if the buttonState=HIGH or off if the buttonState=LOW

  digitalWrite(ledPin, buttonState);

}

State_change.pde :

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/*

  Set a state of a variable when you press a pushbutton ( the 

  button went from off to on ). 

  

  created 01-12-2009 by kasperkamperman.com

  based on example 'State change detection' by Tom Igoe

*/



const int buttonPin  = 2;     // the pin that the pushbutton is attached to

const int ledPin     = 13;    // the pin that the LED is attached to



int buttonState      = 0;     // current state of the button

int lastButtonState  = 0;     // previous state of the button

int ledState         = 0;     // remember current led state



void setup() {

  pinMode(buttonPin, INPUT);  // initialize the button pin as a input

  pinMode(ledPin, OUTPUT);    // initialize the button pin as a output

}



void loop() {

  // read the pushbutton input pin

  buttonState = digitalRead(buttonPin);



  // check if the button is pressed or released

  // by comparing the buttonState to its previous state 

  if (buttonState != lastButtonState) {

    

    // change the state of the led when someone pressed the button

    if (buttonState == 1) { 

      if(ledState==1) ledState=0;

      else            ledState=1;         

    }

    

    // remember the current state of the button

    lastButtonState = buttonState;

  }

  

  // turns LED on if the ledState=1 or off if the ledState=0

  digitalWrite(ledPin, ledState);

  

  // adding a small delay prevents reading the buttonState to fast

  // ( debouncing )

  delay(20);

}

If you like to work with more than two states, do something like below. And use a switch or if statement later to perform some action on a certain stateNum value.

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if (buttonState == 1) { 

      stateNum++; 

      if(stateNum>2) stateNum=0;      

}