Kempston-USB adapter for The Spectrum

What's wrong, or right, in this picture?

After using it for a while, Retro Games' The Spectrum is a rather nice Speccy-tribute. But it's not an authentic hardware replica, and old 9-pin joysticks and peripherals won't work with it.

But what if... I was to purchase a vintage joystick adapter and disguise it as a Speccy peripheral? Delightfully devilish!

I already have an Arduino-based adapter for attaching classic 9-pin joysticks to USB, and it works with The Spectrum. An Arduino Micro or Leonardo can pretend to be a HID device, essentially becoming a gamepad without buttons. On Retro Games' The C64, I had problems possibly because it's a type of controller not "whitelisted" in the firmware.

The USB ports at the back of The Spectrum are where the edge connector is supposed to be. This got me thinking I could build an adapter to look more in line with The Spectrum's appearance.

I happened to have some Speccy joystick adapters, and one Timex Joystick-Sound Unit has had its guts removed already before. Not sure why, but at least I don't have to feel too bad about breaking one now.

Apologies to all Portuguese Spectrum fans to whom the sound unit is a matter of national pride. (Timex manufactured these units in Portugal, among other things).

All the parts

I started by fitting the Arduino Micro inside, using 3x1 protoboard as a replacement for the original circuit board.

There's more room inside than in my compact adapter, but because of how the board fits inside, it's not all in use. Also, I wanted the Arduino to sit on a socket, which eats up quite a lot of space.

But it all fits inside, I then soldered ready-tinned wires to connect everything. Maybe the Arduino would have fit better horizontally, but what's done is done.

The new problem was finding a short USB-cable or some kind of adapter, that would work as a connector and keep in place.

I did look for L-shaped adapters and cables, but there didn't seem to be a ready-made configuration for a USB-A in L-shape that would configure into a micro-USB.

So I just bluntly took the least useful Micro-USB cable I could find, cut it and soldered it into a really short USB-A-to-Micro cable. I found the space was not quite enough for the Micro end, so I whittled the rubber out to bare minimum to make it fit.

The Micro-end has been whittled bare.

I wanted to make the adapter so it could be meaningfully pulled apart, if I need the Arduino again in some distant future.

At this point I could test it already works and fits into its place. I uploaded the same Arduino sketch as with my earlier adapter, and soldered the cables same way. That's it.

The remaining problem was how to make the USB-A end stick to the box firmly enough and still be able to dismantle the whole thing. Of course I could just glue gun it all to oblivion, but it might be tricky to get apart.

The USB sticks into place

I fit a piece of MDF snugly and put two screws through. This looks like enough to keep the USB connector in place and it won't fall apart when I gently remove the adapter from The Spectrum.

Another dummy connector, or something in similar shape, could be added just to keep the unit more firmly in position. I'll do it if I'm in the mood for fine-tuning this box.

I already know the Arduino joystick adapter feels lagless enough, and in practice this unit doesn't add that much to the Speccy experience. The old adapter I built is more practical. But this was a fun project idea and at least The Spectrum has its own adapter.

One future idea is to implement the "sound unit" function promised on the tin. This is not too far-fetched, as I could pull the audio out of the HDMI->VGA adapter's audio splitter and add a tiny speaker with an amplifier circuit. This would add some value to the box, replicating all the glorious 5 octaves from a tinny speaker as it's supposed to be.