Amongst the first of these computers were the Sinclair ZX80 and improved version ZX81. 
I learned how to program BASIC on the ZX81, owned by my uncle. I spent many hours typing in BASIC programs and trying them out to see what happened. Of course, since before that I had never worked on any computer at all, this concept of thinking up programs and letting the computer run them was entirely new to me and also very exciting as well. The program was something I thought up myself and the computer carried out the instructions on its own. In fact the ZX81 introduced me to the world of computers, and to this day I still have a weak spot for the 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) 
Also I am a very big Nintendo fan (I own several generations of Nintendo consoles) and also of the concept of game consoles that use cartridges itself.(from a technical interest point of view) 

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. 
This ZX97 actually is a well-designed computer using off-the-shelf components that can do everything the ZX81 could, with the same BASIC commands, and even more. It additionally has a so-called RAMDISK, a big RAM chip that can contain several programs, and also a parallel port with which it is possible to exchange programs with a PC. This ZX97 was very appealing to my imagination, I must say! 

I had had some practice during my schooldays in designing PCBs with CAD, so I decided I wanted to build my own ZX97... 
I contacted Wilf Rigter who to my surprise was quite willing to assist me in 'building the second ZX97 in the world'. :-) 
I hereby would like to thank Wilf Rigter for all the help he has given me with my designs! Wilf is in my opinion a very valuable person in the ZX81 discussion groups of the present time and he has had several quite unique and refreshing ideas in the past few years, one of which of course is the 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. 
For example, this first prototype was actually on three PCBs slightly bigger than a CD box and these PCBs were connected to each other with two flatcables, a 40 pin flatcable and a 50 pin flatcable that contained all the ZX81 expansion port signals. I did use single-sided PCB design by making good use of a large number of wire jumpers to fill in the connections that couldn't be made on the bottom. 
Since this first prototype worked, this was a big happening for me, the first computer I built myself and that actually worked! 
This motivated me to improve the designs more and more, and since I have built a new prototype, the ZX97 Lite. 
The ZX97 Lite is a ZX97 computer without the RAMDISK and parallel port, which I am going to add later in a ZX97 Full Expansion PCB with some other extra options. I have designed this ZX97 computer also with Wilf Rigter's help because the ZX97 schematic and concept are his design and I contacted him to give him the chance to also make the source schematics for this new version, which he kindly agreed to do. 

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 very soon. 
I myself have the following ZX-Team projects combined and working in a 19" case: ZX81 floppy drive interface, ZX81 harddisk interface, ZX81 AT Keyboard interface and Poke board. I have also designed and built my own version of a line buffer and integrated Poke board from ZX-Team schematics which can interface my ZX-prototypes to the ZX96 system bus. I must say that the ZX81 interfaces I got from the ZX-Team work perfectly and are very user-friendly because the integrated operating systems are very easy to understand and work with... 

Please visit the LINKS section for some directions to pages of other ZX-Team members... 

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