Saturday, December 14, 2019

All New ZX81 : A Minstrel Issue 3 Kit

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A long time ago in a land far far away Sinclair Research released unto the world a ZX81 kit computer. This is not that kit, this is a brand new Minstrel Issue 3 computer, that happens to be an enhanced reworked ZX81 clone with 32k RAM.

Part Minstrel Review, Part Not

Over the last couple of years Dave Curran of Tynemouth Software has been busy designing and producing modern recreations of Sinclair's early home computer kit, the ZX80. Although in fairness, to call them recreations is probably a disservice. One of the major goals has always been to take the project to the next level and launch a full ZX81 work alike.

This of course is where the Minstrel Issue 3 comes into the picture, it being the first of Dave's fully functional ZX81 clones-ish computers. There are of course some differences, the most obvious being that there is no ULA, or modern equivalent, and the computer is entirely designed around discrete logic IC's . In a world full of FPGAs this refreshing.

To find out more on the inner working of the Minstrel family and the Minstrel 3 in particular Dave has written a number of exceptional blog posts that deserve a good read through.

See a Kit, Build a Minstrel

Kits Done Right: ICs Layed out as per the Minstrel Circuit Board
One of the first things I noticed when opening the kit is just how much thought and care has gone into producing it. From the PCB design to how the IC parts tray was laid out to match the PCB, all the way down to included documentation. First impressions count, and the overall presentation put me in a very good mood before I dared assemble anything.

With 25 ICs, plenty of resistors and capacitors the Minstrel takes some time to put together. While It's certainly no picnic to build, thanks to the layout and documentation it never seemed an insurmountable chore. In the end I managed to construct my kit in 4 reasonable sittings with a similar amount of coffee (coffee being a very accurate measure of time).

Using the Minstrel

After completion comes the power on, will it work will it not work? It didn't, but that was entirely my fault. A quick inspection latter, seems I'd failed to solder exactly one IC pin leg. Power on two, success! Aside from being quite elated at a fully working Minstrel, I was immediately amazed at just how clear the image emanating from it was. Truly the image quality is better than using an emulator, which in the case of a ZX81 style computer is a brilliant thing.

Of course it's not all about image quality. The Minstrel is designed to fit within a standard UK ZX81 case, as such it makes a pretty perfect replacement for a dead ZX81 board. Note that American ZX81 and Timex 1000 cases would require some modification around the video output holes for the board to fit.  

Minstrel Issue 3 Mostly Assembled
If placed inside a ZX81 case the only real clue to it not being a ZX81 would be the swapping out of the mono phono jack power socket for a barrel style one. This is possibly one of the finest moves possible, at least to the user. Going out on a limb here, but in my experience a wobbly phono jack is far more likely to cause an unexpected reset than that legendary RAM pack wobble ever did.

Like the original ZX81, the Minstrel does lack a of a power button. That's not really the Minstrels fault, it's more of a design limitation brought about by ZX81s case design. There are a number of solutions, the easiest is to just go out a buy an external switch from the 'The Future was 8 Bit'. It might be something that Tynemouth could include as an extra option at purchase time.

How Compatible is Compatible

I've not found any software so far that wouldn't work with the Minstrel, I dare say I won't be able to. The little computer is even compatible with a number of newer games and programs that take advantage of hires graphics modes, modes that required hardware modification on an actual ZX81.

Hardware expansions on the other hand may be a little to harder to guarantee due to both the modern design of the Minstrel and the esoteric nature of ZX81 expansions.

I've only a couple of expansion that I can test with the Minstrel, and I don't any 80s period hardware to throw at it. The best news is that the most required modern add-on, the ZXpand works perfectly, indeed Dave Curran in consultation with Charlie Robson the creator of the ZXpand is planning a special edition of the ZXpand specifically for the Minstrel. 

Also of note, the Zeddynet network interface, a card I've had trouble with on some actual ZX81s  work flawlessly. Internet meet Minstrel, a perfectly modern retro way to connect to the world.

Sadly for me one expansion didn't work, my ZX-Keys Expansion card. After speaking to Dave on the matter I have some leads on as to why, I'll have to see what can be done on a revision 2 of my boards. For the moment the ZX-Keys keyboard works perfectly using the Minstrels internal keyboard connector. 

Adding a ZX-Key Keyboard

I have some future plans for my Minstrel involving a custom case and a full sized keyboard. For the moment though I need a working keyboard (There are keyboard options at kit purchase time). As discovered earlier my ZX-Key Expansion card didn't work so I built a temporary adapter board for the ZX-Keyboard.

Internal ZX-Key Keyboard Adaptor
The resulting kludge is a simple wire up job on some protoboard On the Minstrel I soldered on a Female Header Socket Strip to plug it into. Nothing groundbreaking here then. The next step will be to make up a proper PCB board. On the temporary one I've only wired up the bare essentials, the keys. The keyboards LEDs and reset button don't work and it all looks a little messy. Still I do have a nice modern-ish keyboard to use with a nice modern-ish ZX81 clone.

In Summary

I have to say I've been very pleased with the Minstrel kit. It's fun and rewarding to put together and in all honesty it's a much better computer than ZX81. If you enjoy assembling kits then go get one, if you don't know one end of a soldering iron from another Dave supplies them pre-built too.

Now of to play some games, how about a nice game of Tut-Tut?

Minstrel up and running playing a little bit of Tut-Tut

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