How-To: Keyboard Breakout Board

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 Responses to How-To: Keyboard Breakout Board

Dave Bell on January 9th, 2012 at 1:39 pm said:

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…

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- Sean Michael Ragan on January 9th, 2012 at 1:47 pm said:
  
  Yes, thank you! Fixed!
  
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Anonymous on January 9th, 2012 at 7:36 pm said:

A teensy is $16 and is USB. It can be programmed to act like a keyboard very easily. Why not just use that?

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- Sean Michael Ragan on January 11th, 2012 at 8:18 am said:
  
  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.
  
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Keith From Canada on January 14th, 2012 at 8:55 pm said:

FWIW, if that doesn’t do it for you, there are always the U-HID, I-PAC and the (appropriately named) EPIC interface modules.

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jamesskaar on October 24th, 2012 at 6:26 pm said:

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.

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