|In the beginning of the nineteen-eighties
a whole new line of home computers emerged. They had several things in
common, such as:
- BASIC as an easy-to-understand programming language
- a Television set for displaying text and graphics
- a Cassette tape player used for saving and loading computer programs.
Amongst the first of these computers were
the Sinclair ZX80 and improved version ZX81.
My uncle's ZX81 later became my own, so
I continued programming on it a lot. I went on to buying an Atari 600XL
a few years later when I could afford it, and in the years after that I
went on to buy a second hand Commodore 64, a new IBM386 machine, several
second hand Amiga500s and also a new Amiga 1200HD.(and of course the PC
I own right now, a Wintel PII machine)
A few years ago, I subscribed to an internet provider for the first time, and because I somehow got the idea to see what was available about the ZX81 on the internet, I decided to search for internet pages about the ZX81 and actually found quite a few. This renewed my interest for the ZX81, because these pages had lots of information that reminded me of my own ZX81 and the fun I had with it...
Then I somehow came across a small archive
of postings to the ZX81 mailing list of JaRaSoft, and read some articles
about the ZX97, designed by Wilf RIgter, and there were even ASCII schematics
amongst these articles.
I had had some practice during my schooldays
in designing PCBs with CAD, so I decided I wanted to build my own ZX97...
After many months of work in my spare time,
I finally got a prototype ZX97 that worked. It was not quite optimised
from a PCB point of view though, due to my inexperience with PCB designing
at the time.
During my ZX97 design work, I also found the ZX80 Hardware Page, by Grant Searle, on which there were very detailed instructions and schematics to build your own ZX80 and even upgrade it to a ZX81.(!)
I should mention that Sinclair Research used a design technique for their ZX81 called integration. They integrated lots of loose logic chips into one big chip to save space on the ZX81 PCB and also to make the PCB design less complicated and to decrease the costs of building the entire computer. This was a very sound idea of Sinclair Research, but it has one disadvantage: if this integrated logic chip dies, you have to replace it. In the nineteen-eighties this was a lot easier than in present time. The integrated logic chip of the ZX81, also called ULA is no longer manufactured, so in many cases the old ZX81s can't be repaired and remain defective. The ULA would also be a problem when you want to build a ZX81 yourself. (if you can't obtain an original ULA at least)
The concept of a ZX81 made almost according to the original design, and at least functioning exacty as the original did, (by using alternative components that are readily available) was very tempting, and I decided I was going to design PCBs for these ZX81 schematics as well, according to all the instructions of Grant's homepage.
During the work on this prototype I posted
some questions on the newsgroup news:comp.sys.synclair
and came into contact with some helpful people who were willing to help
me by verifying my CAD schematics and ironing out prototype design bugs.
Especially Andreas Rohrbacher from the USA, Edward Patel from Sweden and
also Wilf Rigter were very helpful by double-checking my schematic designs
and pointing out errors as well as discussing several issues. I'm sure
that without their help it would have taken me much longer to build the
first ZX81 prototype... Thanks guys!
A few years ago I came across the homepage
of Peter Liebert-Adelt from Germany. He is a member of the German ZX-Team,
a team of ZX81 enthusiasts who have been active for quite a long time.
Their main activities involve having ZX-Team meetings in Germany, discussing
the possibilities for the ZX81 at the present time, writing software for
it and also developing ZX81 related hardware. Some of the very professional
hardware projects they have produced are a ZX81 3.5" DD Floppy drive interface,
a ZX81 Harddisk interface, a ZX81 LCD interface which interfaces to a notebook
LCD screen and many more. Many of these projects can be combined into a
single ZX81 system contained for example in a 19" case. They call this
assembly the ZX96. Also the ZX-Team has a 'ZX-Team Magazin' in German which
comes out 6 times a year. I myself am subscribed to this Magazin, which
in itself means that I'm considered to be a member of the ZX-Team :-) and
have plans to write several articles for it about some of my prototypes
Please visit the LINKS section for some directions to pages of other ZX-Team members...
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