If you’re building a standalone project with an embedded PC (say, a CNC rig or a MAME cabinet) one of the easiest ways to get instructions to the software is using the PC’s baked-in keyboard interface. But if you don’t want to actually use a keyboard to control the thing, you need some way to convert button presses and/or joystick movements from your custom control panel into signals that look like keyboard input.
In this offering, UK hacker Rupert Hirst shows us how to reverse-engineer the key matrix on a scrap keyboard and attach a breakout board, ready to wire straight to the switches in your custom control panel. Sure, manually mapping the membrane switches with a multimeter may be a bit tedious when compared to using a drop-in keyboard simulator like PoLabs’ PoKeys, but it’s also a lot cheaper, and a lot more instructive.
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6 thoughts on “How-To: Keyboard Breakout Board”
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Nice hack, but a minor point that that doesn’t really affect the utility of the project:
That sure looks like a PS2 connector, not USB…
Yes, thank you! Fixed!
A teensy is $16 and is USB. It can be programmed to act like a keyboard very easily. Why not just use that?
I don’t know Rupert personally, but from what I’ve seen of his work I’d say it would gall him to buy a teensy when he’s got a scrap keyboard on-hand. If he were getting paid to do this, one might argue that he’s undervalued his time. But it’s a hobby for him, he does it for pleasure, and I get the sense that he likes to spend his hobby hours soldering, not programming. Others may feel the same way.
FWIW, if that doesn’t do it for you, there are always the U-HID, I-PAC and the (appropriately named) EPIC interface modules.
without a multimeter, it’s possible to use coloured pens to draw on the membranes, it’s how i used to do it, the column conductors would do ushaped paths, it’s not that hard, and membranes are transparent to see the colours through them.