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Toggle an LED with a Button

Turn a red LED on and off with a button: every press flips the LED, and the press count and the LED's state are written to the Serial Monitor. It teaches reading a button with digitalRead, the Arduino's built-in pull-up resistor (INPUT_PULLUP), catching the moment a button is pressed and waiting out contact bounce (debounce). The button needs no extra resistor, and no extra library is needed.

What you need

• 1 × Arduino Uno R3
• 1 × Breadboard 830 Points (MB-102)
• 1 × 12x12 mm Push Button
• 1 × LED - Red (5mm)
• 1 × Resistor 220 Ω (1/4W)
• 4 × Jumper Wire - Male/Male

Wiring steps

1. 1

   Connect the common ground (GND)

   

   Plug a black jumper wire into the GND pin next to pin 13 on the Arduino's digital header. Connect its other end to the breadboard's top blue (−) rail. Both the LED's resistor and the button's ground wire will go into this rail.

   • Arduino GND → the top blue (−) rail (black wire)
2. 2

   Add the LED and its resistor

   

   Plug the red LED's long leg (+) into column 10 in the top half of the breadboard and its short leg (−) into column 11. Put one end of the 220 Ω resistor in column 11 and the other end in the top (−) rail. Then connect the Arduino's pin 8 to column 10 with an orange jumper wire (LED_PIN 8). The resistor limits the current through the LED; without it both the LED and the Arduino's pin can be damaged.

   • red LED long leg (+) → column 10, top half
   • red LED short leg (−) → column 11, top half
   • 220 Ω resistor (leg 1) → column 11, top half
   • 220 Ω resistor (leg 2) → the top blue (−) rail
   • Arduino pin 8 → column 10, top half (orange wire)
3. 3

   Add and wire the button

   

   Seat the button over the middle gap of the breadboard: two legs in the top half and two in the bottom half, in columns 5 and 7. Connect the Arduino's pin 2 to column 5 in the bottom half with a green jumper wire (BUTTON_PIN 2). Then connect column 7 in the top half to the top (−) rail with a short black wire. Because you use two diagonal legs of the button, it works whichever way round it sits. The button needs no resistor of its own: the Arduino's built-in one (INPUT_PULLUP) keeps it HIGH when released, and pressing it reads LOW.

   • push button → across the middle gap, columns 5 and 7
   • Arduino pin 2 → column 5, bottom half (green wire)
   • column 7, top half → the top blue (−) rail (black wire)

Arduino sketch

// The button's and the LED's pins
const int BUTTON_PIN = 2;
const int LED_PIN = 8;

// Time to let the contacts settle (ms)
const unsigned long BOUNCE_TIME = 50;

bool ledOn = false;
int lastReading = HIGH;
int presses = 0;

void setup() {
  // Pull-up: a released button reads HIGH
  pinMode(BUTTON_PIN, INPUT_PULLUP);
  pinMode(LED_PIN, OUTPUT);
  Serial.begin(9600);
  Serial.println("Press the button to turn the LED on or off");
}

void loop() {
  int reading = digitalRead(BUTTON_PIN);

  // Act only when the button changes
  if (reading != lastReading) {
    // LOW: the button was just pressed
    if (reading == LOW) {
      ledOn = !ledOn;
      digitalWrite(LED_PIN, ledOn ? HIGH : LOW);
      presses++;
      Serial.print("Press ");
      Serial.print(presses);
      Serial.println(ledOn ? ": LED on" : ": LED off");
    }
    lastReading = reading;
    // Wait while the contacts bounce
    delay(BOUNCE_TIME);
  }
}

What the Serial Monitor shows

Press the button to turn the LED on or off
Press 1: LED on
Press 2: LED off
Press 3: LED on

What you will see

Every press flips the LED: it lights on the first press, goes out on the second and lights again on the third. Holding the button down changes nothing; what counts is the moment it is pressed. If nothing happens when you press the button, check that it sits over the middle gap, the green wire is in column 5 and the black wire in column 7. If the LED never lights, check that its long leg is in column 10 (the same column as pin 8's wire).