#5 · Control LED with pushbutton on Arduino

Introduction

In this Arduino tutorial for beginners I teach you how to read a push button the right way. For example, did you know that it is useful to use a pull-down resistor? New? Then read on 😃

Course material

At the bottom of this page you'll find the course material button. This button allows you to download the code, circuit diagram and other files relevant to this Arduino tutorial.

Push button

A push button has different names such as push button, switch and tactile switch. They come in all shapes and sizes. We are going to use a 4-pin push button .

On the right you see a schematic representation of the push button. Pin 1 and 2 are connected to each other, just like pins 3 and 4. As soon as we press the button, all pins are connected to each other.

Normally open / normally closed.

This push button is a so-called Normally Open button. This is often abbreviated to NO. This means that the button is open by default and therefore does not connect the pins. A Normally Closed switch is the mirror image. Here all pins are connected to each other. This connection is not broken until the button is pressed.

The circuit

Press the push button exactly over the center gutter in the breadboard. Connect the following jumper wires

• The 5V on the Arduino -> the pin lower left of the push button
• The 12 on the Arduino -> the pin top right of the push button

Pulldown resistor

In principle, the push button should now be able to do all its work. As soon as we press the button, the 5V is connected to pin 12 and the Arduino sees this as HIGH. The problem now is that you have a "floating" state if you don't press the button. It may be that the push button does not block 100% current. This small current can prevent the Arduino from reading the state of the push button properly.

Therefore, in this circuit we use a pull-down resistor. This resistor ensures that the state of the push button is really 0 Volt when the button is not pressed. We put the resistor between the pin lower right of the push button and the GND of the Arduino. The resistor now "pulls" the current to the GND.

Arduino Code

We start the code by defining three variables:

1 int switchPin = 12;
2 int ledPin = LED_BUILTIN;
3 int switchState = LOW;

• switchPin is the pin to which we connected the push button
• We set ledPin to LED_BUILTIN with which we automatically get the correct LED pin back
• In switchState we store what the current state of the push button is

setup()

1 void setup() {
2     Serial.begin(9600);
3     pinMode(ledPin, OUTPUT);
4     pinMode(switchPin, INPUT);
5 }

First, we initialize the serial monitor. Then we set the ledPin as the output and the switchPin as the input.

loop()

1 // repeat infinitely
2 void loop() {
3     switchState = digitalRead(switchPin);
4 
5     Serial.println(switchState);
6 
7     if (switchState == HIGH) {
8         digitalWrite(ledPin, HIGH);
9     } else {
10         digitalWrite(ledPin, LOW);
11     }    
12 }

The loop() function consists of 3 parts:

• Read out push button
• Print to serial monitor
• Switch LED on/off

Explanation code

First we read the state of the push button with digialRead. After this use Serial.println to send the read value to the serial monitor.

In the if statement we determine whether the state of the push button is HIGH or LOW. Once it is HIGH, we turn on the built-in LED and vice versa.

Upload code to Arduino

Our program is now ready to be sent to the Arduino . Then open the serial monitor:

Tools ▸ Serial Monitor

You should see the number change from 0 to 1 as soon as you press the button and the built-in LED turns on or off.