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Flexible PCB rewiring Answered


  I'm working on a project where I want to strip a 'roll up piano' down and take the rubber keyboard innards which feed into the electronic sound unit and get rid of the floppy rubber roll up piano keyboard and replace it with a standard PC qwerty keyboad. I got used to using a qwerty keyboard for playing tunes already and want tomake one that is stand alone that I don't need to connect to the PC to play music with. That means I need to take all the connections that you can see in the photos I uploaded and re connected each one to a key on the keyboard.

 First of all, I don't know if pressing the rubber key on the roll up keyboad 'completes a circuit' and therefore prompts the electronic unit at the end of it to play the sound or if it 'breaks the circuit'. These units have two flexible pcb sheets as you an see in the second photo so when the rubber key is pressed they touch (although they all seem to be pretty much touching anyway). In an old casio solid keyboard I have there is a hard pcb and the piano keys touch a small rubber disk (much like is what under qwerty keys) to the pcb.

  would it be better for me to take a razor and painstakingly slice up the flexible plastic which the pcb is printed on then lead them to the innards of the qwerty keyboard I'm going to modify or would it be better for me to just chop the flexible pcb off and use some kind of very thin coppe wire to feed dirctly into the unit and to the underside of the qwerty keys?

  Any guidence would be appreciated.


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9 years ago

LMB thank's very much, I really appreciate the input.

If you look at the pictures I uploaded of the flexible thing thenyou can see that it seems to make a loop with each key so I wonder if a straight connection will work.
Also, I don't know for sure but I heard that a PC keyboard doesn't have a straight key to input corresponding config as it uses some kind of pulse. For example when we press down shift it changes the signal going through the same connection. All together there are over one hundred signals going to the qwerty pcb so I think I can't do a straight re route wire job. That's why I suspect that I'll have to cut out the qwerty pcb and just wire the individual key pressure points to the roll up piano pcb.

I'll check the other posts though as you suggest. I'm sure it will be a big help, Thank's again.


9 years ago

There must be a PCB inside the piano unit that contains the actual circuits used to read the switches and generate the right notes. I would expect those components to be on a rigid pcb, along with some kind of connector where the flexible keypad makes contact.

If that is the case, I would identify the row and column connections of the piano keyboard to the PCB. (I am also assuming that the keys are arranged in a matrix configuration). I would then determine which row and column connections correspond to each of the piano keys, and record it for later. The flexible keyboard of the piano could then be discarded.

Now you will need to open up a computer keyboard and go through a similar process. There should be a small PCB inside the PC keyboard where the rows and columns of the switch matrix connect. Map out which keys on the keyboard you want to use to play the musical notes.

Now you'll need to solder wires from the rows and columns on the piano electronics PCB to the desired row and columns on the PCB inside the PC keyboard.

You'll want to make sure the wires leading from the PC keyboard to the piano electronics PCB are mechanically strong and protected with strain releif.

I know that seems like a complicated mouthful, but if I understand you correctly, that is the approach I would take. Search this site and the web in general for "keyboard hack" type of projects to learn more about the inards of the PC keyboard and how to map it out for use in other applications.