The Arduino will trigger each transistor individually through a 1Kohm resistor. The collector of each transistor connects to a ground line from the keypad.

9) The Keypad/PIR Sensor Connector – This three pin header allows for you to connect to a resistor based keypad, or a PIR motion sensor module. We will be using these for many of our projects.

As explained by Arduino to Go, each color band on the resistor corresponds to a number but this can differ depending on the band's placement. It's not complicated, but the sheer number of colors ...

Running out of GPIO pins? Learn how to connect multiple buttons to just one Arduino pin using clever wiring and resistor techniques. Perfect for compact projects, keyboards, or when using small boards ...

The Arduino will trigger each transistor individually through a 1Kohm resistor. The collector of each transistor connects to a ground line from the keypad.