Arduino LED with Button Tutorial - Control an LED with a Push Button

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Introduction

In this beginner Arduino LED with button project, you will learn how to control an LED using a push button. The circuit will allow you to turn an LED on or off by simply pressing a button connected to your Arduino board.

How read the output from a LDR light sensor with an Arduino Uno

Controlling outputs with user inputs is a fundamental and extremely important concept in electronics and embedded systems because you'll use inputs and output in every system you design.

This simple LED button circuit is a great way to get started with Arduino as it introduces fundamental topics like digital input/output, if-else logic and button presses as events that trigger code.

By the end of this tutorial, you will understand how to build the circuit on a breadboard, write the code to sense button presses and drive the LED accordingly.

Let's get started on our first introductory project!


Required Components

  • Arduino Uno board
  • LED (any color)
  • 1k ohm resistor
  • Push button
  • Breadboard
  • Jumper wires

Circuit Diagram :Arduino LED with button

The layout diagram shows how to place components on the breadboard. Note that you have to place the LED the right way round -the flat side of the LED (cathode - or negative side) connects to ground (GND or 0V).

Ground (0V) and supply voltage (5V) are connected from pins in the lower pin header of the Arduino Uno, while control pins 2 and 7 are connected from the top connector.

arduino led with button layout with breadboard
Diagram using fritzing

The schematic shows the pin connections and components.
arduino led with button schematic
Diagram using fritzing

Example Sketch : Arduino LED with button

You can copy and paste the code below into the Arduino IDE (in a new sketch) replacing everything that is in the new sketch window (See "Uploading the code" below).

// LED pin
int ledPin = 7;

// Button pin  
int buttonPin = 2;

void setup() {

  // Set LED pin as output
  pinMode(ledPin, OUTPUT);

  // Set button pin as input with internal pull-up resistor
  pinMode(buttonPin, INPUT_PULLUP);

}

void loop() {

  // Read the state of the button pin
  int buttonState = digitalRead(buttonPin);

  // Check if button is pressed
  if (buttonState == LOW) {
 
    // Button pressed, turn LED on
    digitalWrite(ledPin, HIGH);

  } else {

    // Button not pressed, turn LED off
    digitalWrite(ledPin, LOW);

  }

}

Short Code Explanation

The following bullet points explain how the code works in short form.

  • LED is connected to pin 7 and set as OUTPUT
  • Button is connected to pin 2 and set as INPUT_PULLUP
  • Read button state and check if LOW (pressed)
  • If pressed, turn LED ON by writing HIGH to pin 7
  • If not pressed, turn LED OFF by writing LOW
  • This will turn the LED on when the button is pressed and off when released.

Detailed Code Explanation

This is a more detailed explanation of the code operation, explaining all the code used in the Arduino with LED Button tutorial.

The code is divided into two main parts - setup() and loop().

setup() runs once at the start to initialize pins.

  • ledPin and buttonPin variables declare the pin numbers used.
  • pinMode() sets the mode of each pin - ledPin as OUTPUT to control the LED, buttonPin as INPUT_PULLUP to read the button.

The loop() function runs continuously after setup().

  • digitalRead(buttonPin) reads the state of the button pin - HIGH or LOW.
  • The code check if the reading is LOW (if (buttonState == LOW))  which means the button is pressed.
  • If pressed, digitalWrite(ledPin, HIGH) turns the LED on by writing HIGH to the pin.
  • If not pressed, LED is turned off with digitalWrite(ledPin, LOW).

Setting the button pin as INPUT_PULLUP means there is an internal resistor pulling the pin HIGH. Pressing the button connects it to ground, pulling the pin LOW.

So each time the loop runs, it checks the button state and toggles the LED accordingly.

This provides a simple switch to turn the LED on/off by pressing/releasing the button.

Explaining the button press.

The only thing that can cause confusion is that when you press the button the input to the microcontroller goes to 0V. This is counter-intuative as you expect a button to produce a high voltage for on.

The reason for this is the internal pull-up resistor in the microcontroller. You don't get pull-downs (at least not in most chip designs). When the pin is left alone the pull-up pulls the pin voltage to 5V (hence the name pull-up). This sets the inactive state of the input pin to 5V (high).

Note: You could add your own pull-down resistor (100kOhms), so that the button input reads "1" for a button press. You would turn off the internal pullup (change INPUT_PULLUP to INPUT), and change the code to turn on the LED when the input signal is high (5V), and change the circuit so that the button connects to 5V (not GND).

But, because it is more work, it is easier to just change the sense of the input value in software!

When the pin is shorted to ground - by you pressing the button, the voltage at the pin is pulled to 0V - the input voltage at the microcontroller pin is 0V representing "0". So a press = "0".

The other end of the internal resistor is still at 5V, but because the internal pull-up resistor is of high value 50k~100kOhms only a small current flows (while you press the button) so it is safe. Small current = low heating therefore does not blow up.

Inverting the input logic for the button

In the code, when you press the button, and the input is set to 0V, the code interprets this to mean turn on the LED i.e. it inverts the value of the button - the Zero input value is translated to a "One" (or 5V) at the output pin.

The relevant part of the code is this:

// Check if button is pressed
 
if (buttonState == LOW) {

    // Button pressed, turn LED on
   
digitalWrite(ledPin, HIGH);

Uploading the Code

There are a few steps to uploading the code using the Arduino IDE:

  • Connect the Arduino Uno to the PC with a USB cable.
  • Select the Arduino Uno hardware.
  • Open a new sketch.
  • Paste the code above into the new page (overwrite everything).
  • Press the upload button (right arrow at top).

You can find a more detailed tutorial on the Arduino IDE page.

Testing the Circuit

Just push the button OK!

  • When pushed the LED lights up.
  • When released the LED is off.

Troubleshooting Arduino LED with button

Even though this is a simple circuit there are two things that can go wrong.

  1. Putting the LED the wrong way.
  2. Putting the switch button the wrong way.

The LED

If LED doesn't light its probably the wrong way round  - an LED has polarity - it is actually a diode (Light Emitting Diode) so current will flow when positive voltage connects to the positive terminal, and negative voltage connects to the negative terminal.

If you get the LED round the wrong way it won't light up so you have to be able to tell which side is positive and which is negative.

There are two ways to do this:

  1. The flat side of the LED is negative (look from the top to see which is the flat and round side).
  2. The short lead is negative (not much if you've chopped the legs off - hence why 1. is available).

The switch

I can never remember which way round the switch is placed! Even though there are 4 connections two pairs are connected together. Usually I use a multimeter to check but this is not crucial - you want the pins that are not connected (unless the button is pressed) to be left and right in the above layout diagram. If your switch is the wrong way round (after programming - the LED will always be on) then turn it by 90 degrees.


Note: These types of switches do not naturally fit into a breadboard so I use a pair of flat-nosed pliers to flatten the legs so they will go into the breadboard.

Conclusion

Even though it is a simple circuit it demonstrates the fundamental operation when you use microcontrollers:

Reading inputs using the function digitalRead().
Setting outputs using the function digitalWrite().

It also shows that you need to wire up circuits careful as you can easily get components the wrong way round. In this case, no damage will occur. But for more expensive chips you want to get it right (putting the power supply the wrong way around will blow up any chip). So, always double check before powering the board i.e. before plugging in the USB cable. This helps avoid accidental damage.



Written by John Main who has a degree in Electronic Engineering.

Note: Parts of this page were written using claude-instant as a research assistant.







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