# Digital Input

#### Circuitry

We will now understand the basic working of taking input through pins with the help of ‘push buttons’. Get hold of one (these are pretty cheap) and connect it like the following circuit.

Note the use of a pull-down resistor (150 ohms) in conjunction with the push button. To understand how pull-down and pull-up resistors work, refer to (this)2.

#### Code

Now enter the code:

Plug in the Arduino, click Verify, then Upload if no errors are found. The breadboard LED should be turned off by default and should glow as long as the button is depressed.

#### Understanding the Code

• Most of the code should be easy to figure out once you have understood the previous examples.
• Note the pins from which output has to be gathered are set to the INPUT pinMode in the setup block.
• digitalRead(pin) This** function returns a boolean value - HIGH if the pin is high and LOW if the pin is low**.

#### Internal Pull-Up Resistors

Conveniently, the Arduino contains pull-up resistors that are connected to the pins (the analog pins have pull-up resistors also). These have a value of 20K ohms and need to be activated within software to use them. To activate an internal pull-up resistor on a pin, you first need to change the pinMode of the pin to an INPUT and then write a HIGH to that pin using a digitalWrite command. Make sure that your button is connected across the pin and the ground in this case:

pinMode(pin, INPUT);
digitalWrite(pin, HIGH);


Note that now pressing the button will cause the state variable to read LOW and otherwise HIGH by default. The wire connecting the push button to +5V is no longer needed. The circuit should be like this: