How to Read a Switch Input with digitalRead() on Arduino

This guide explains how to connect a switch to Arduino and write code to detect whether the switch is pressed or not. You’ll practice using digitalRead(), a fundamental command for almost every Arduino project that accepts user input.

How digitalRead() Works

Arduino digital pins can be configured as inputs or outputs. When set as input, use digitalRead(pin) to check if that pin has voltage present.

The command returns one of two values:

• HIGH → Voltage present (around 5V)
• LOW → No voltage (0V)

Basic Pull-down Circuit

A normally-open (NO) pushbutton doesn’t hold a stable state when not pressed. This leaves the input pin floating with no defined voltage, leading to erratic readings. The solution is to add a pull-down resistor as shown below:

Wiring steps:

1. Connect one leg of the switch to 5V
2. Connect the other leg to an Arduino digital pin (e.g., D2)
3. Connect a 10kΩ resistor between that Arduino pin and GND (this is the pull-down)

Operation:

• Switch open → current flows through resistor to GND → reading is LOW
• Switch pressed → 5V flows into Arduino pin → reading is HIGH

Code: Read Switch Input to Control LED

// Pin definitions
const int buttonPin = 2;   // Switch connected to pin 2
const int ledPin = 9;      // LED connected to pin 9

// Variable to store switch state
int buttonState = 0;

void setup() {
  // Start Serial Monitor for debugging
  Serial.begin(9600);
  
  // Set LED pin as output
  pinMode(ledPin, OUTPUT);
  
  // Set switch pin as input
  pinMode(buttonPin, INPUT);
}

void loop() {
  // Read the state of the switch pin
  buttonState = digitalRead(buttonPin);

  // Check if switch is pressed (HIGH)
  if (buttonState == HIGH) {
    // Switch pressed → LED turns on
    Serial.println("LED ON");
    digitalWrite(ledPin, HIGH);
  } else {
    // Switch released → LED turns off
    Serial.println("LED OFF");
    digitalWrite(ledPin, LOW);
  }
}

What this code does:

• Continuously reads pin D2 using digitalRead()
• If it reads HIGH (switch pressed) → turns the LED on
• If it reads LOW (switch released) → turns the LED off
• Prints the state to Serial Monitor for verification

Customization Points

Adjustment	Default	How to change
Switch pin	2	Use any available digital pin
LED pin	9	Change to another pin or swap LED for Relay, Buzzer, etc.
Resistor config	Pull-down	Switch to Pull-up to invert logic

Test Using Serial Monitor

After uploading the code, open Serial Monitor (baud rate 115200). You should see the text change every time you press or release the switch. This confirms Arduino is reading the input correctly.

Key Takeaways

digitalRead() is a core command you need to master before building Arduino projects that accept input from switches, sensors, or other devices. Understanding pull-down and pull-up resistor logic lets you connect a wide variety of input devices reliably.

Reference Video

Video demonstrating Arduino switch input wiring and testing