Sorry I know the title's a little rough, but hopefully some pictures will help

I have this keypadenter image description here

Here it is the front panel removed (note that each metal node is a button in itself, you can press them, and I think this is what will make this not possible or very difficult) enter image description here

Here is the back of the keypad: enter image description here

Now I want to try to replace the buttons on this keypad, with this old phone numberpad: enter image description here

Here is the front off: enter image description here

Here is the back: enter image description here

So basically 2 concerns:
1) The phone keypad has 13 buttons, but only 8 wires, so no idea how to deal with that
2) The security keypad has buttons embedded into it

So what do you guys think? Is this project possible with what I have? What are some of the things I need to know, or need to try?


  • \$\begingroup\$ Given the potential for mismatch between the key matricies of the two parts, consider reverse engineering the target keyboard to see if you can figure out what it does - that's an ATmega168 after all, with great data sheets, and you can use a cheap USB fifo logic analyzer to watch it in action. Then you can potentially make a replacement from a mini Arduino clone that works with the keymatrix of your replacement. \$\endgroup\$ Jul 24, 2017 at 1:39
  • \$\begingroup\$ unfortunately that sounds like it's beyond my current skill, and not something i can budget for time-wise for this project :\ \$\endgroup\$
    – A O
    Jul 24, 2017 at 2:21

2 Answers 2


The buttons on the round pad are in a matrix. The ones ok the remote door lock interface is also in a matrix, but I can't be sure based on just the picture.

Since a button is nothing more than two nodes that are connected when pressed, you can easily extend it.

Cut all the traces from the round pad so that each button is independent. Remove the metal discs from the buttons on the square pad. Now extend them by soldering wires between one and the other. A bit messy if each of the buttons on the square pad do not use common grounds, but doable. 26 wires at most. I recommend wire like 24 or 26 awg just to make the bulk less difficult. I use IDE/PATA cables.

This is the same thing that game console modders do all the time to swap one remote for another.

enter image description here

Ben heck put a Xbox 360 wireless controller inside an original Xbox "duke" controller. Same exact procedure.

  • \$\begingroup\$ Thanks for the answer! What is the trace, and how can I cut it? \$\endgroup\$
    – A O
    Jul 24, 2017 at 2:23
  • \$\begingroup\$ @AO a trace is a piece of copper between two points... \$\endgroup\$
    – Passerby
    Jul 24, 2017 at 2:26
  • \$\begingroup\$ So before I commented, I had googled "electronics board trace", and "how to cut trace electronics" and didn't find much material. most youtube videos have low like ratios (youtube.com/watch?v=H-IXcfnH_Rs), and looking at my board, it isn't quite clear what I'm supposed to be cutting, or with what/how. I see the lines, but they don't look like copper, and so I assume I just run a box-cutter across them, but I'm not 100% \$\endgroup\$
    – A O
    Jul 24, 2017 at 8:17

I started to make a wiring list on the round keypad and then ran into a problem for #5 & #6

  • Pin Button ( arbitrarily choosing sides as +,- on switch)
  • J1-1 1+,2+,3+,4+,7+
  • J1-2 2-,8-
  • J1-3
  • J1-4
  • J1-5
  • J1-6
  • J1-7
  • J1-8

here there are two carbon tracks printed over an insulator over copper tracks, but the tracks are not joined to key #5 they are just floating in parallel.

You can learn more with a DMM ohmeter.

So good luck matching up the matrix row/column muxing of the contacts. If you are able to match the number of rows and columns but not the pad labels, those can be swapped. Otherwise, it's a PITA. ;)

enter image description here

Note, the top has no tracks and the bottom has 2 layers, copper and carbon with a clear insulator.

Ah @Passerby solved my blindness, enter image description here Your wiring lists will tell you if it is easy to match.

  • 1
    \$\begingroup\$ I'm sure the top one connects to the other side, it's just hidden by the carbon layer. \$\endgroup\$
    – Passerby
    Jul 24, 2017 at 2:39
  • \$\begingroup\$ THe other side is shown in photo without any copper. ie. single sided 2 layer board Cu + C. p.s. I have done something similar to this project when I started as a EE in '75 when LED calculators 1st came out for $10 and I interfaces external switches, logic and 1" LED's to display counts from a switch to "=" while a Johnson counter sequenced the formula for calories or just +1 or -1 step counts from an initial value for a primitive exercise calorie/step counter. \$\endgroup\$ Jul 24, 2017 at 2:54
  • \$\begingroup\$ Yes. I am referring to your red question marks. What i am saying is that the top right circle connects to the rightmost trace. The bottom left circle connects to the leftmost trace. It's a simple jumper setup. \$\endgroup\$
    – Passerby
    Jul 24, 2017 at 2:58
  • 1
    \$\begingroup\$ ah now I see the connection to a copper pad. good bridge. and you have better eyes. \$\endgroup\$ Jul 24, 2017 at 3:01

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