Mahjongg

I am Mahjongg (M.C.J. de Jong), an electronic engineer, (of Dutch descend) specialized in designing PCB's for Analog, Digital and to a lesser degree RF systems. I am fond of retro computing, and own a collection of retro computers, and literature about retro computing.

my first computer was a nameless home-brew system based on a 6502, I designed in 1978 but it never got finished because I bought a KIM-1 and later a LMW-80.

after my study, I started working for a small hobby computer company, that among many other things sold Apple ]['s, ABC80's and Olivetti M80 systems, but also many kits. Like the Junior Computer (a KIM-1 clone), the Acorn Atom and also ZX80 kits. dozens of those kits I assembled for customers who wanted them assembled. And for owners of ZX80's I would also built in ZX81 ROM's, so they gained the batter basic of the ZX81 (but not "slow" video mode). I also built 48K RAM and our own Floppy disc controller and Centronics printer interface into TRS-80 model I base systems, which was much cheaper in the Netherlands than buying an official expansion interface.

Later I designed amy own Z80 computer, the Aster CT80, a much improved Tandy TRS-80 model 1 clone that also ran CP/M perfectly, and could be used as a Videotex terminal, about 10.000 of them were sold, mostly to schools. It bore a remarkable visual resemblance to the IBM-PC-XT which came out a few years later.

Through the later years, (1984 and later) I designed MSX hardware, many-many modems and audio and FAX recorders, to name just a few things, and also worked as a programmer for the game software house "Aackosoft", and later helped programming the "memo vision" application built into the sony F9P MSX2 computers, the last few years I am learning to layout Integrated Circuits, and am designing and building space related hardware, and other high end electronics for third parties, on-demand Lately I'm programming again in C (for an Arduino MEGA 2560), and in Python 3.5 for a chip tester I designed.

here I designed a few simple computers, for people who want to built their own 8-bit simple to understand computers, I designed two versions of a ZX-81 clone that doesn't need a ULA (I designed my own ULA replacement). the first was the ZX-81+34, because it was designed 34 years after 1980, so 2014 was the year is started designing my ZX-81 clone built using SMT (surface mount) components, on the smallest and thus cheapest, PCB possible. the second (simpler, with Pin Through hole components instead of SMT, which was too hard for most people, and a PCB that is a replacement for a real ZX-81, and can be fitted in a ZX-81 case.

In the meantime I found out about a remarkable, but barely known computer designed in the former Yugoslavia the Galaxia, a cross between a ZX80 and a TRS-80 with just a dozen TTL chips, I wanted to built my own version but soon found out that was no longer possible, and gave up the idea.

So instead I designed my own 8-bit color computer with capabilities comparable to 80's home computers, but with a very minimalistic design based on a Z80 CPU combined with 128K SRAM and for everything else a cheap 8X32A multi cpu in a 40 PIN dip chip parallax propeller that with a few tricks can do everything else that my RhoCoCo needs to make it a functioning computer, again on a minimal 10 x 10 cm dual sided PCB. I have built one prototype, and tested it, it was able to get it to generate 64 colour VGA screen, but was hindered by the fact that my idea to get mass storage from an SD-Card wasn't possible the way I intended it, so I stopped to make a re-design that solved this problem.

I also created a game system in the form of a joypad with a built in Raspberry PI Zero running retropie. I did not release this one because of possible legal action against doing so, but it works, and it works well.

links to my computer project pages are here:

1. a story about why I wanted to build a ZX-81 clone (A simple home built computer you can know completely) . https://revspace.nl/index.php?title=Zx81plus34
2. the complete design stages explained from beginning to working end and several intermediate versions. https://revspace.nl/ZX81PLUS34_ZX81_clone#28_February_2016_It.27s_alive.21
3. I also designed a ZON compatible sound board (PSG based) for my ZX-81+34, which I wrote about here:https://revspace.nl/Zon_ZX-81_Programmable_Sound_Generator_expansion_for_ZX81PLUS35
4. because of complaints agains the use of SMT in a beginners project I started over, and with the experience gained from designing and testing the ZX81+34 I designed my ZX81+38 https://revspace.nl/ZX81plus38_simple_to_build_ZX-81_clone
5. I wrote about the Galaksija here: https://revspace.nl/Galaksija I translated what little was know from the original Yugoslavian texts, so I could understand better how it worked. I also recovered the Schematics.
6. in between both versions in 2017 I started on my own colour capable home computer the RhoCoCo, Z80 based system with 128K RAM and 64-color VGA output. https://revspace.nl/Designing_the_RhoCoCo_Retro_Home_COlor_COmputer_hardware
7. I wrote about the tribulations of ordering PCB's from China here: https://revspace.nl/Ordering_PCBs_for_rhococo but I ended up with 5 nice PCB's of the Rhococo main PCB and the single sided but larger keyboard PCB, it seems it makes hardly any difference anymore price wise between single sided and dual sided, its only the size that determines the price.
8. In april the same year I had built up my first prototype, and had successfully got it to work I wrote about bringing up (first boot) the hardware of the Rhococo here: https://revspace.nl/Bringing_up_Rhococo_(first_boot,_and_firmware_development) and found the first hardware bugs which I wrote about here: https://revspace.nl/Rhococo_prototype_hardware_debugging

other stuff:

1. I repaired a Space invaders console, space invaders was one of the first game consoles that used a CPU, an intel 8080, the same hardware was first used by a cowboy fighting game, but that wan't very successful, it was Space invaders that first took of (after Atari's pong of course, but pong didn't use a CPU) I wrote about it here: https://revspace.nl/Space_invaders_repair Later I took a course in repairing Arcade systems in the Dutch national videogame computer museum in zoetermeer lead by the famous Randy Fromm https://revspace.nl/Arcade_repair_course