Push Buttons/Contact Switch

The pushbutton is a component that
connects two points in a circuit when
you press it. The example turns on an
LED when you press the button. We
connect three wires to the Arduino
board. The first goes from one leg of the
pushbutton through a pull-up resistor
(here 2.2 KOhms) to the 5 volt supply. The second goes from the
corresponding leg of the pushbutton to
ground. The third connects to a digital
i/o pin (here pin 7) which reads the
button’s state