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Starting with arduino: button clicks, states, LEDs.

Updated on September 3, 2012

Things you are going to need

  • 10k resistor (for button)
  • 220 ohms resistor (for LED)
  • button
  • LED
  • breadboard

In this project we are going to use button to turn on LED. Although it can be done without programming, with this example you can learn how to code button presses in arduino. When the button is pressed it sends HIGH value to arduino, when the button is in off state arduino reads it as LOW. Knowing that we can create variety of projects that rely on button presses. Firstly, you should connect everything as it is shown below.

Programming

const short int ButtonPin = 5; //Button is connected to pin 5.
int CurrentState;              //Holds the current state of the button
int LastState = 0;             //Holds the last state of the button
int short count = 0;           //Holds number of button presses.
void setup() 
{
  Serial.begin(9600);          //Begins communication with computer
  pinMode(ButtonPin,INPUT);    //Sets ButtonPin as input.
}
void loop()
{
   Serial.println(count);      //Prints current number of button clicks
   CurrentState = digitalRead(ButtonPin); //reads state of the button.
   if(CurrentState != LastState)
   {
     if(CurrentState == HIGH)  //if button is pressed count is
                               //increased by one
     {
       count++;
     }
   }
   LastState = digitalRead(ButtonPin);
}

At the end of the loop program reads state of the button again and puts it in LastState. Therefore next time the loop begins CurrentState will be compared to LastState(which happened in the loop before)

Modifying the circuit

Now we can add LED and several lines of code to make the button turn it on. Modified circuit is shown below.

Modified code

const short int ButtonPin = 5; 
const short int LedPin = 2; //set LED pin.
int CurrentState; 
boolean LedOn = false; //create statemen that tells
                       //if Led is on
void setup() 
{  
  pinMode(ButtonPin,INPUT);
  pinMode(LedPin,OUTPUT);  //set LedPin as output.    
}
void loop()
{     
   CurrentState = digitalRead(ButtonPin); 
   if(CurrentState == HIGH)                            
    {
      LedOn = true;   //If button is pressed
                      //LedOn turns to true.
      if(LedOn == true)
      {
        digitalWrite(LedPin, HIGH); //Turn on the led
      }
    }
}

As you can the code to turn LED looks a bit simpler then counting number of button presses. Because the action itself is simpler. That is it for this time. You can try modify the circuit and code yourself, creating more complex programs. Some things you might want to try:

  • Program it so that after button press LED starts blinking.
  • Code it so if you press the button X number of times only then LED turns on.
  • Try to program that if u press the button same time as the LED blinks. LED stops blinking at all.

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