That's why you need a pull-up or pull-down resistor in the circuit. This is because the input is "floating" - that is, it will randomly return either HIGH or LOW. If you disconnect the digital I/O pin from everything, the LED may blink erratically. If so, the behavior of the sketch will be reversed, with the LED normally on and turning off when you press the button. You can also wire this circuit the opposite way, with a pullup resistor keeping the input HIGH, and going LOW when the button is pressed. When the button is closed (pressed), it makes a connection between its two legs, connecting the pin to 5 volts, so that we read a HIGH. When the pushbutton is open (unpressed) there is no connection between the two legs of the pushbutton, so the pin is connected to ground (through the pull-down resistor) and we read a LOW. The other leg of the button connects to the 5 volt supply. That same leg of the button connects through a pull-down resistor (here 10K ohm) to ground. The third wire goes from digital pin 2 to one leg of the pushbutton. The first two, red and black, connect to the two long vertical rows on the side of the breadboard to provide access to the 5 volt supply and ground. HardwareĬonnect three wires to the board. This example turns on the built-in LED on pin 13 when you press the button. Pushbuttons or switches connect two points in a circuit when you press them.
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