Using internal pull-up resistor in arduino

In this post, we will discuss how to use internal pull-up resistor in arduino uno. It's quite simple.

No need of using external pull-up resistor.

What is pull-up resistor?

First, we will find what pull-up resistor is and why it is used.

In many microcontroller, there are no internal pull-up resistor. For example: In 8051, there are four IO ports. Port0 has no internal pull-up resistor. Therefore, it requires external pull-up resistor.

In arduino, the moment we define any pin as input it will attain tri-state. Tri-state is  a state between logic low and logic high. We must remove this condition. Some microcontrollers have built-in internal pull up resistor while some has not.


Pull-up resistor basically ties the voltaage level to logic high (+5Volts) whereas pull-down tie it to logic low (0 volt). Using pull-up or pull-down is one's choice.

Let's consider the case of arduino:

/*
Program starts here
*/

void setup() {
pinMode(9,INPUT);    // configure this pin as input (internal pull-up disabled)
}

void loop() {

}

/*
Program ends here
*/

Arduino simulation in proteus

/*
Program starts here
*/

boolean state=LOW;

void setup() {
pinMode(9,INPUT);    // comfigure this pin as input (internal pull-up disabled)
digitalWrite(9,HIGH);  // internal pull-up enabled
}

void loop() {

}

/*
Program ends here
*/

This is how we can enable/ disable internal pull-up resistor

Hope you had enjoyed the post.

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