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Minstrel ZX80 Clone (tynemouthsoftware.co.uk)
113 points by sohkamyung on Jan 4, 2017 | hide | past | web | favorite | 31 comments

No 3D Monster Maze - well, that is a disappointment!!! That was my favourite game on the ZX81 and it actually was terrifying to bump into him even though the screen was very blocky pixels with a very slow refresh rate. We are talking seconds per frame.

I am also amazed that you can buy a replacement ZX80 keyboard. This required someone out there to know what it was and to bother to put it on ebay etc. for someone else to find. This is trade at its most obscure, yet this is also our key survival skill - trade. It is what enabled our variation of the human form to survive ice ages where other human varieties perished. We could trade, they could not. Once we traded in things like salt, nowadays it can be in anything including a ZX80 keyboard.

The UHF modulator was replaced in this article, the original modulator was ubiquitous and found in all computers of the era that needed a TV for the monitor. At the time this part was taken for granted, however, it was the component that enabled the home computing revolution, without it and screens would have been an extra £400 or so (as per BBC/Acorn monitor). There must be more information out there on how these UHF modulators came into being.

> I am also amazed that you can buy a replacement ZX80 keyboard

There's a thriving scene for retro computing in the UK - looks like that is the primary business of the creator. I assume that the (non-test) keyboard, ULA and case all came from a donor machine. After all, there's the link to "Send me something interesting to repair / review / reuse / recycle"


Just for the record, and for those not familiar with these, the original ZX80 and ZX81's had only 1 Kb memory.

The "expansion" to 16 Kb (and later to a whopping 64 Kb!) was an extremely costly "add on", it was a small "vertical box" attached to the rear end connector (and the connection was - to say the least - flaky):


An image of a ZX81 with the expansion box mounted is here:


Thanks for the pic. I had a 16K expansion pack for my ZX81, but it was third party, so a little cheaper than the official Sinclair product. Perhaps 30GBP rather than 50? I remember there being much chat at the time about the dreaded "RAM pack wobble". The ZX81 keyboard claimed to be touch sensitive, but was really thump sensitive! This could easily jiggle the bus connection from the motherboard to the RAM pack, causing the ZX to crash, possibly losing hours of work before it could be saved to tape. For me the solution was yet another third party peripheral: a real keyboard.

Static electricity was also a problem. Touching the ZX81 after walking over a carpet in winter resulted often in a crash.

That would be kB (kilobyte) and not kb (kilobit) or Kb (kelvinbit).

Yes, actually to be strict it would be kibibytes, KiB.

But in 1980/1981 kibibytes didn't exist, all we had was good ol' fat Kilobytes made out of 1024 bytes, and WE LIKED IT.


What's a "kelvinbit"?

Now I want to see someone derive a nice formula that results in a kelvinbit. Offhand, I'd guess something to do with information entropy in temperature sensitive media. (Entropy rather than density as that would be more along the lines of bits/kelvin I'd assume. Or heat output would be kelvins/bit.)

Exactly. ;)

This might be a cool project to build at Seeed. I think they could populate a board with sockets, SMD resistors, jacks and switches, leaving just the chip insertion for the end-user.

Caveat: I've only ever had them build an unpopulated through-hole board for my one hardware project.

Doesn't look like there's any surface mount involved - in other words, the construction aspect shouldn't be hard. Remember the original ZX80 was available to buy in kit form!

I realize that. What I'm saying is that he/she could produce a second board with SMD components to replace the thru-hole passives, leaving only the insertion of the chips to the end-user.

I have an EE degree myself, but soldering has never been terribly enjoyable.

Parts availability might be a serious problem, especially the ULA.

That's the point of this clone, it's based on the ZX80 which uses only standard TTL chips, all of which are still available today. The original 1K RAM chips and mask ROM are not, but modern parts have been substituted. The next version will incorporate an NMI slow mode circuit which will make it fully ZX81 compatible, still only using standard TTL parts.

The ZX80 used TTLs, only the '81 and Spectrum used ULAs.

The ZX80 was the first computer I touched and used and it was bloody awful.

I mean really, you press a key and the screen blanked out as I recall.

Didn't stop me from getting the far superior Vic-20 the following xmas.

The ZX81 had the revolutionary ability to support both screen refresh, and keyboard input simultaneously! Well - as long as you didn't engage 'FAST' mode - which made your FOR NEXT loops go super-fast, at the expense of blanking the screen.

I seem to remember mine would crash every time the fridge turned on.

Can anyone explain what he means by "I have replaced [the UHF modulator] with the single transistor composite video buffer" ?

On the original ZX80 it produced modulated RF to connect to your TV aerial socket as it wasn't common then to have any other inputs on TVs.

More modern TVs have a composite video input which makes the RF modulator redundant. The quality of the picture is much better via composite video.

In fact that is how I used to use my ZX80 back in the day with a wire clipped onto the input to the RF modulator connected to a 9 inch monitor my dad liberated from work!

"transistor buffer" is a single transistor amplifier - or impedance adapter depending on the way you look at it

Articles like this one makes me wonder if dad's ZX81 clone is still sitting in the basement.

Your dad cloned a ZX81 or he has another company's clone of a ZX81?

Tangentially related: The Jupiter Ace was a relative of the ZX81 (same designers, different company) which ran FORTH instead of BASIC. If anyone has one they are worth a lot of money because it seems fairly few were made and/or survived.

The Jupiter Ace inspired me to port the Forth Interest Group's 8080 Forth implementation to the Camputers Lynx back in summer 83. There was no assembler for the Lynx, but there was a hex editor, so I hand assembled the 8080 ASM listing to Z80, and stitched in some calls to the Lynx BIOS for IO and graphics. Since Z80 was a superset of 8080 much of the code worked without mods. Happy daze!

If digi_owl's dad is/was resident in the US or Canada it could have been a Timex branded version of the ZX-81. There were also quite a few clones back in the day:


Timex clones were also sold in the Iberian peninsula.

I had a 2068.

Just one he bought at some point. May well have been the first computer i had the "fortune" of interacting with.

after having perused the big wiki and old-computers.com, i have come to the conclusion that it was most likely the Lambda PC 8300...


This web-based emulator (http://www.zx81stuff.org.uk/zx81/jtyone.html) is pretty decent. It even simulates the display wobbles if you put it into 'fast' mode.

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