Midi controller from commercial PCB - tapping into switches on a calculator

HI, I recently got an Arduino and made a basic midi controller from a guide.

Now I would like to make another one but instead of using individual parts I would like to connect the Arduino to pre-existing switches and LEDs on a PCB I have.

I have an old calculator and I want to use the switches that are printed on the PCB, i see on the PCB there are lines going to and from theses switches. They end up as little holes in the board. If I connect a wire to each of these holes for each button and wire it to the Arduino, will it work? If the calculator is on, will it interrupt the signal at all?

Here is an image of the holes I am talking about:

I also have another PCB with leds on it and one with a rotary encoder and I want to do the same thing.

Hacked calculator prank

This Hacked Calculator Prank on YouTube seems to be along similar lines. is that any help?

Siddy: I have an old calculator and I want to use the switches that are printed on the PCB, i see on the PCB there are lines going to and from theses switches. They end up as little holes in the board. If I connect a wire to each of these holes for each button and wire it to the Arduino, will it work?

Well, you could try that, but it may or may not work correctly.

I noticed that the keyboard of this calculator seems "separate" from the rest of the calculator via that ribbon cable connector (18 lines). Likely the keyboard is a matrix schema of some sort (6 x 3?), or it is some other form; I would remove the keyboard portion, and start tracing lines and such with a meter, making notes and a switch arrangement "schematic" for a column -and- row of keys - that should give enough to try a "guess" at how another row/column is connected, so make that guess, then do another check to see if your guess was right. If it isn't, then it might be easier to just continue the mapping and drawing until you know what goes where.

Then connect your wires to where the ribbon cable went. You might find it easiest to remove the ribbon cable connector, and possibly use some sandpaper to remove any of the PCB mask to get to the copper to solder to (if the connector doesn't use tinned pads). Use fine-pitch wire-wrap wire, and a fine point soldering iron to do this.

This of course means the calculator portion won't work again; I am not sure if you are expecting the calculator to continue to work (ie, you want that/need that as a part of your project), or if you just want to use the keypad "standalone" and trashing the calculator isn't an issue...?

:)

Thanks guys, so it should work but I might have to trace the lines a bit :slight_smile:
Will try it tonght

They end up as little holes in the board.

No that is only something they go through on there journey from key pad to chip. These are called vias and are plated through holes that connect the traces on one side of the board to another.

However these could be places to break the track or solder wires onto.