This is a copy of the recreation that used to be hosted at http://projectspeccy.com/projects/ with permission from Steve SmithI reverse-engineered this interface as a reaction to prices I saw online for the original Mikro-Gen hardware. It’s not a very complicated piece, just an EPROM and an IC with a joystick connector at the top with a few diodes. The original is a single-sided PCB and is routed for convenience (more of that later).
I then laid out the components in a KiCad schematic and started to trace each connection. I tend to do the edge connector first and any point-to-point connections later. This builds up a complete schematic. Then it is a simple process to lay out a PCB. I stayed pretty close to the original in this case, but I did cheat and use a few second-layer connections for my own convenience. I also wanted to line the diodes up to make the board neater than the original too.
I also took the opportunity to recreate the original logo to add to the board. KiCad makes it easy to make graphics for the silk screen layer. KiCad include an application where you can import one bit BMPs and turn them into library parts.
I had the boards made by JLCPCB.com as usual and they arrived in a few weeks as is normal. I built one up and programmed an EPROM up from the ROM image at World Of Spectrum. But, the interface failed to work. This was when a lot happened personally, and I thought I’d made a mistake. I shelved the interface for a while in frustration.
I came back to it recently and re-checked the tracing. As you can see in the first image, it’s not too complicated and I was puzzled why it wouldn’t work. I then showed it to my friend Russ and it dawned on us that because the address lines were scrambled, then the ROM would be too. This explained the ‘convenient’ routing on the PCB. The ROM image on WOS must have been descrambled for use with emulators!
I posted this info on Facebook in the Spectrum Forever and Spectrum For Everyone groups and several people lent a hand in re-scrambling the ROM. Many thanks go to everyone on the two Facebook pages – but especially Russ, Jerzy and Matthew Logue who supplied a ready-to-run scrambled ROM image which you will find below.
On my own copy of the interface, I have used an Atmel 27C128 one-time programmable EEPROM, but you can use a UV Erasable EPROM in its place like the original interface. You can find all the instructions for the game and other documents on WOS. Please remember that the ROM image on WOS is not the one you should use with this interface. Use the file posted below.
All the files necessary for fabricating the Shadow of the Unicorn Interface can be found here: https://github.com/lostretrotapes/Shadow-of-the-Unicorn-Interface-Re-Creation
I have included the TZX files of the game for convenience and also a .MDR file for those lucky enough to have a vDrive ZX.
I hope this project enables those who could never obtain the original or refuse to pay the ‘Retro’ prices demanded these days to play the game as originally intended.