#13 Matrix Membrane Switch (12-key 4x3) an Arduino PLUS a LED MAX7219 Display

Digital key pads are commonplace, from your cash machine to the entry device to where you work but how they are connected up without using up all the pins on your Arduino is to some a mystery.

After all, if the keypad has 0-9 plus # and * (12 keys) and some even have A-D for good measure, that is surely, at the very least, 12 pins plus one for ground, right? Not so, as this video demonstrates the art of reducing that number by using a key matrix - a design used by your home phone, your computer keyboard and those cash machine pin number pads too.

The theory is quite straightforward once you see how it's done and is useful once you exceed about 3 keys as you start saving valuable input-output connections.

Not only that, but we also cover how such a keypress might be displayed on a 7-segment digital display, using some of the techniques described in my earlier videos on the MAX7219. So much better than displaying stuff on the Serial Monitor window!

All code is found under the video in the comments section, but I'll included it here too for completeness:

Sample code

Thanks for watching and I hope you'll learn something new.