Make a custom button pad for Raspberry Pi [Pt II]

Categories Interaction, RMIT

In my previous post I was using a testing cable with an alligator clip on one end and a probe on the other, shorting the circuit board that I took out of a cheap USB Keyboard. The small distance between each contact point made using the alligator clip awkward and prone to bridging nearby contacts. I decided that I would use a section of jumper ribbon cable that I salvaged from an old computer to form a sort of breakout board that I could use as a more robust, exploratory interface.

Firstly, I started stripping two sets of 13 wires for each bank of contacts on the USB circuit.

From there I started soldering each wire to the circuit board. Initially, creating a successful solder joint was difficult and I found that a light sanding of the contact points (to remove some surface coating and presumably add texture) made soldering much easier.

After all the contact points (in actuality, only those that were necessary) were soldered to the ribbon cable, I used jumper cables to open out the pins onto a small breadboard, allowing me to hook multiple jumpers up between points. I used this setup to create a document that outlines which connections produced a useable keystroke within the context of my project (in this case letters, numbers and symbols – no function or conditional keys). In total, I needed at least 25 different keystrokes for use in my 5 x 5 button matrix, with 8 additional keys to account for function keys.

In a later post I’ll show the process of creating the actual 25-key button matrix, solder it all up and test it to make sure that every button on the custom pad triggers a unique keystroke. It’s been a while since I’ve done a great deal of soldering, and my connections on the USB circuit – though functional – aren’t very clean looking, so I’m worried about soldering up 25+ buttons. Ultimately all the ugly electronics will be hidden inside a 3D Printed housing anyway, so no one will ever need to know.

 to be continued