Converting an ADB SMK-22 numpad to USB (56k warning)

[Pylon]

So I bought this SMK-22 numpad at a thrift store for $2 the other day. It's a no-name Mac keypad, with ADB.





But hey, clicky white Alps. Disassembly proved that they were complicateds. The keys are pad printed.



The thing's got diodes too. It probably has NKRO as a result.



Controller:



Sadly, the thing's ADB, and I never use my G3 desktop anyways. So my plan is to basically convert it to USB, by using a USB controller from a  rubber dome board. I could use a numpad for my laptop.

I bought this cheap-o rubber dome keyboard at Micro Center for $4 around 2 years ago for my laptop.
http://www.amazon.com/Inland-70008-Pro-USB-Keyboard/dp/B001NACBSA

I've since ruined the above keyboard with failed paint jobs and what not, and I lost a bunch of its domes after repeated take-aparts. It was junky anyways, but the controller still works.

My basic plan is to slice all the traces on the SMK-22 and then wire over the matrices for the USB controller onto the switches, and then use the USB controlller to make it work with a normal PC. I'd lose NKRO sadly because I'll be using a blocking controller, but hey, beats paying good money for an ADB-> USB adapter. The "clear" key will be remapped to "delete", and I'll ignore the brackets and other functions. It'll function mostly like a standard numpad.

Objectives:
1. Convert the thing to USB, where it'll serve as a normal numpad. No 000 functions, no funny brackets, no copy, no undo. Those would
2. Reversibility. I want it possible to convert it back to ADB.  Therefore no chopping off controllers or what not. Also, in the future, I might use a Teensy or something to regain some of the functions like the cut and copy functions on some of the keys.
3. Cheapness. This will not be an expensive mod. At the moment, I'll be using only parts and tools I have on hand.

Progress will be in the discussions.

[Pylon]

Progress so far (as of 12/27):

PCB traces severed:


I also analyzed the rubber dome board's matrices to find the right matrix combos for the keys I want. It's hard on the eyes.


And I finished wiring and soldering the top layer matrices. (I'm too cheap for multi-colored wire)


Pick your Alps (white complicateds on the left, simplified real blacks from my TP-110JIS board on the right)


Note the destroyed black switch next to the 1 key. The actuation mechanism is pretty fragile on the simplified switch, and I broke it due to slight misalignment while trying to reassemble the switch.

And my messy workbench:

[msiegel]

heat sink sahddering iron stand ftw

i love seeing stuff get turned into other stuff

[bladamson]

Grooviness!

Did the insulation on your jumper wires melt back while you were soldering?  Always happens to me too unless I can scrounge up something with teflon insulation. :<

That'll be a neat little board when you get it done!

[Pylon]

I think that was hot glue, but I think a couple underwent that.

[Pylon]

Progress update.


Finished wiring the bottom layer matrices. I used some multicolored stranded wire I salvaged from an old Compaq tower.



I routed them through the holes for the ADB ports. Top layer matrices through the left hole, bottom through the right hole. They look like tentacles.



And soldered them to strip board to neaten it up.


Now I need to figure out a way to attach the wires to the controller. The thing has carbon contacts. Big obstacle. They don't take solder, and the spacing's way too tight to use clips.

[Pylon]

Electrically finished, more or less. I decided to use an SK-8125 controller instead .

Currently Esc and Tab don't work but I don't really use those on a numpad much, and I can't currently find the reason why (wiring seems sound), other than some weak looking traces on the controller board which I may have severed while desoldering the connectors.

I'll also probably add volume controls later, and build a case for it.

[microsoft windows]

I've heard of some pens that can deposit conductive material so you can fix any traces you severed by accident. Forgot what they were called though.

[Pylon]

They're expensive.

[microsoft windows]

Well, there's always good old solder.

[bladamson]

If the connector that you desoldered was through-hole and the board is double-sided, make sure that there's enough solder in the hole that the front and back are electrically connected properly?  Iunno!