Replacing a board in an old keyboard with teensy++2.0

[vuckale]

I saw a project on a blog post where someone replaced board in an old Compaq keyboard with a teensy++2.0 (https://hackaday.com/2020/06/19/vintage-keyboard-gets-the-qmk-treatment/), but there is no much info on how it was done.

I noticed that the board on that keyboard is similar to one in my old Compaq keyboard.

One from linked project:

Mine:


My keyboard is Compaq Internet Keyboard - model sdm4540ul and there is a set of keys that doesn't work in any OS I have tried it and thought that being able to attach a teensy there would allow me to flash a qmk firmware and make those keys work again.

My guess is that I would desolder my chip and solder teensy++2.0 on the place of it since all leads from ribbon cable socket lead there?

Another guess is since there are 2 ribbon cables that I could somehow solder only the smaller one (that is the one that controls the set of keys that don't work) to teensy and then only write a firmware for those?

Do you have any guide where something similar is done that I could follow or could you tell me if my guesses are correct?

Thank you all!

 

[PaulStoffregen]

My guess is that I would desolder my chip and solder teensy++2.0 on the place of it since all leads from ribbon cable socket lead there?
....
or could you tell me if my guesses are correct?

Impossible to say for sure without knowing the layout of that circuit board. But since the board wasn't specifically designed for Teensy, having it all line up by chance would be a pretty amazing coincidence. Seems pretty unlikely.

The power wires are the most important thing to check first. If the other stuff is wrong, odds of hardware damage are low. But hooking up the power wrong will very likely kill hardware. Probably best to use a voltmeter or just follow the traces and explore where the power connects, before you try connecting Teensy to that board.

 

[manicksan]

here is a pinout your keyboard ic (it's a KS86C6404) and the teensy 2.0++


you could probably fit it you you rotate the teensy around

scrape/cut the tracing leading to the KS86 pins 10 11 12 13 14 15 18 21 22 37(if it connected) 38 39 40

and then do some rerouting to the (if required) KS86 pins 1 10 21 22 42

to for example teensy pins (which is now free because of the cuts above):
PB4 PB1 PB0 PE7 PE6 or PC6 PC5 PC4 PC3

the teensy GND pin should also be routed to the keyboard-pcb as it's probably needed for the leds to work
or if the leds are driving by having the anode connected to the vcc then the teensy VCC is also needed.



found the pinout by googling sdm4540
and found a better picture of the same board
where I could read out the part number.


I can not find any pinout of the ic XC409410P used
in the Compaq MX11800 keyboard
and the github page
https://github.com/jkutianski/qmk_compaq_mx-11800
contain no schematic or further explanations either.

 

[pictographer]

I guess this is possible

there is a set of keys that doesn't work in any OS I have tried it and thought that being able to attach a teensy there would allow me to flash a qmk firmware and make those keys work again.

What makes you think the keyboard controller is the problem and not the switches or a trace in common between the failing switches?

 

[vuckale]

Thank you for detailed answer! I am going to buy a spare of a same keyboard and attempt to do that. Do you maybe have some guide I can follow to be absolutely sure where to connect what to be absolutely sure? I have never done anything similar.

 

[vuckale]

I have recorded HID signals in wireshark and I am getting some response back when I press those buttons. There was a special driver for those buttons for windows 98 and I guess that I would need to write a driver for it to if I want to use them. I think that replacing the old chip with teensy is way easier and I can then flash a QMK firmware and some other stuff that I wouldn't be able to do with current board.

 

[vuckale]

I am surely going to buy a spare keyboard of the same model and attempt this. But since I have never done anything similar I will first see If I can understand what I am doing exactly.