In this tutorial you will learn how to read the status of a digital pin of Arduino. I hope that you already go through our first tutorial, Getting Started with Arduino Uno – LED Blinking. In this example, a push button switch and an LED is connected to Arduino Uno. When we press the switch, LED will glow for 3 seconds. A pin is configured as Input Pin to connect switch and another pin is configured as Output Pin to connect LED. You need to connect PULL-UP or PULL-DOWN resistors while interfacing switch.

If we haven’t use PULL-UP or PULL-DOWN resistors, there will be an UNDETERMINED STATE (neither LOW nor HIGH) when the switch is OPEN. In this tutorial we will follow PULL-UP resistors.

Digital Pins of Arduino can be configured as OUTPUT, INPUT or INPUT_PULLUP mode using pinMode() function. INPUT_PULLUP mode is used to enable the Internal PULL-UP Resistor. The value of Internal PULL-UP resistor of Arduino Uno is about 20-50KΩ.

Now we have two options to interface switches with Arduino :

 

1. Using External PULL-UP Resistor
2. Using Internal PULL-UP Resistor

The simple solution is to using Internal PULL-UP resistor but in some cases you may have to use External PULL-UP resistors.

Using External PULL-UP Resistor

This method is not recommended, but it is explained first just because it is easy to understand. In some cases you may forced to use External PULL-UP resistor.

Circuit Diagram

Here the switch is connected to digital pin 4 (D4) and LED is connected to digital pin 8 (D8) of Arduino Uno. Thus pin D4 should be declared as INPUT and pin D8 as OUTPUT in the sketch (program). 10KΩ resistor is used as PULL-UP resistor and a 680Ω resistor is used to limit the current through the LED.

Arduino Sketch

const int switchPin = 4; //Switch Connected to PIN 4
const int ledPin = 8; //LED Connected to PIN 8
int switchState = 0; // Variable for reading Switch status
void setup()
{
    pinMode(ledPin, OUTPUT); //LED PIN is Output
    pinMode(switchPin, INPUT);//Switch PIN is input with PULLUP
}
void loop()
{
    switchState = digitalRead(switchPin); //Reads the status of the switch.
    if (switchState == LOW) //If the switch is pressed
    {
        digitalWrite(ledPin, HIGH); //LED ON
        delay(3000); //3 Second Delay
        digitalWrite(ledPin, LOW); //LED OFF
    }
}

 

Read more Using Push Button Switch with Arduino Uno