Tutorial 10 : Input Pullup Serial

This example demonstrates the use of INPUT_PULLUP with pinMode(). It monitors the state of a switch by establishing serial communication between your Arduino and your computer over USB.

Additionally, when the input is HIGH, the onboard LED attached to pin 13 will turn on; when LOW, the LED will turn off.

 


 
 

/*
 Input Pullup Serial
 
 This example demonstrates the use of pinMode(INPUT_PULLUP). It reads a
 digital input on pin 2 and prints the results to the serial monitor.
 
 The circuit:
 * Momentary switch attached from pin 2 to ground
 * Built-in LED on pin 13
 
 Unlike pinMode(INPUT), there is no pull-down resistor necessary. An internal
 20K-ohm resistor is pulled to 5V. This configuration causes the input to
 read HIGH when the switch is open, and LOW when it is closed.
 
 */

void setup(){
  //start serial connection
  Serial.begin(9600);
  //configure pin2 as an input and enable the internal pull-up resistor
  pinMode(2, INPUT_PULLUP);
  pinMode(13, OUTPUT);

}

void loop(){
  //read the pushbutton value into a variable
  int sensorVal = digitalRead(2);
  //print out the value of the pushbutton
  Serial.println(sensorVal);
 
  // Keep in mind the pullup means the pushbutton's
  // logic is inverted. It goes HIGH when it's open,
  // and LOW when it's pressed. Turn on pin 13 when the
  // button's pressed, and off when it's not:
  if (sensorVal == HIGH) {
    digitalWrite(13, LOW);
  }
  else {
    digitalWrite(13, HIGH);
  }
}

Download this sketch :