With the basic wiring of my Psion Bluetooth keyboard locked in, I set about the process of designing the keyboard case.

The Psion Series 5 keyboard component is a fully self-contained external part that forms part of the Series 5 case. This introduces some interesting design constraints as it’s not a simple internal part I can reuse. There are no convenient mounting points, excepting the hinges, sliding rails, and the little hook that depresses the sleep switch when the keyboard is closed.

keyboard component picture, perhaps highlighting the existing points

In my earlier iteration of the PsiBoard, I had planned to use these existing brackets, but they’re awkward and not nearly as robust as I’d like—these are often cracked in donor systems making them a poor choice for mounting.

(I very briefly experimented with designing my own mounting bracket for the keys in an attempt to replace the whole case, but after a number of test prints, I concluded I couldn’t replicate it with sufficiently high tolerance using my X1C.)

With these limitations, and a desire to establish my own design language for the case, I decided too fully enclose the keyboard component in my own case. This necessarily increases the size of the resulting device a little but gives me a lot more design freedom. This also gives me a little more leeway when it comes to modeling the Series 5’s keyboard shape—I don’t have to perfectly match those 90s curves.

sketch of basic design

Having locked in the basic approach to mounting the keyboard, my remaining constraints come from the remaining components: the nice!nano, battery, reset button, and ribbon cable placement on the keyboard component.

layout diagrams or photos

Of all the components, the battery is the thickest at 4mm for the controller. After that, it’s the PCB which clocks in at ~3.6mm so long as I mount the nice!nano upside down in a cutout on the main PCB. These are all so similar in dimensions that I can further simplify the design process by simply opting for a layered design: the keyboard forms one layer; the electronics another; sandwiched together by two halves of a case.

layer diagram

With the basic approach in mind, the remaining process was one of iteration; all-told. I went through 20 different test prints as I nailed down the design. I started out printing only small slices of the design checking I’d got the dimensions of the keyboard component correct, and that the lip I was using to secure the keyboard worked well, and then graduated to more component components, finally installing thermal inserts and screwing together the later designs.

animated gif or automatic slideshow for all the different designs

Perhaps most challenging aspect of the design was working out what to do with the hinges on the keyboard component—these sit proud of the keyboard itself by a few millimeters, making it hard to design a flat top to the keyboard. I hard originally planned to try to have them fully enclosed by the top half of the keyboard case, but it significantly increases the thickness of the case. I ultimately settled on designing a couple of inserts to ‘complete’ the hinges on the case, filling in the gaps, and allowing them to sit proud of the case. After living with this design for a little while, I have found I quickly stop noticing the hinges and, when I do, it feels like a nice nod to the origins of the keyboard.

hinge details

Buttons remain one of my least favourite design elements; the PsiBoard’s reset button is no exception. As I ease my way into the world of industrial design for electronics design, I realise that buttons, along with ports, are some of the constraining elements. Buttons, especially, require you to select suitable microswithces, and source, or design button caps, and tracks for those caps. They constrain the shape of the PCB, define points where it must sit near the edge of the case, and necessarily introduce an opening in a case that invites dust and liquid damage. I’ve previously avoided many of these challenges by using PCB-mounted switches with long actuators, but with the PsiBoard I wanted to make something that felt a little more polished.