Phone Keypad Hacking: Part 4

So when part 3 of this series turned out to be a bit uneventful, I wasn’t expecting a grand finale with fireworks. I was right about it being more difficult though.

Through numerous failed attempts I was running into trouble isolating the signals between the rows and columns. Everything was getting connected in one big circuit. Then I realized it was a perfect place to use diodes! Each button needed 2 though; one for its connection to the row and one to the column. I have a bunch of 1N4148 signal diodes so I wired everything up.


Although the Fritzing is using a different board than in the implementation pictured above, it’s much easier to follow the wiring…

2x3-custom-keypad-wiring.png

This obviously is a lot more complicated circuit than the examples in part 3 of this series. It was a success at what I set out to do though and it works great with my custom keypad code. I’ve also added the actual Fritzing file for this circuit to the repo.

I’m glad I continued down this path with keypad experimentation. I learned a lot. In the beginning I was wondering why the keypads you can buy these days work the way they do and not how I had wired up the old phone keypad to function. Turns out what ended up being a simple solution for me was due to how the old phone keypad made its connections mechanically inside the device. The keypad solutions I showed in part 3 are much easier to create as I’ve now proven by recreating the circuit above.

I’m still curious if I could wire up the old phone keypad to work with the Arduino Keypad library. I guess if I ever get my hands on another old phone, I’ll have to continue with a part 5 of this series.

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