I also did the placement, and checked it against my keyboard overlay:
details on my revspace pages.
and the solder side
the PCB works with a real ZX-81, or my clone, and its dimensions are such that it will fit in the keyboard recess (if you round of the PCB corners somewhat) of a real ZX-81, as it is 6.2 inch wide, and 2,5 inch deep.
you can solder 5-wire and an 8-wire flat-flex cables to the PCB, and stick those trough the opening in the case and connect the flat-flex to the ZX-81 as you would with the normal foil keyboard.
The keyboard uses forty 6 x 6 mm buttons ( MCDTS6-2N or equivalent ) keys with a 6.5 mm x 4.5mm pad pitch, these are industry standard keys and about the most cost effective keys you can buy.
But the reaction I got the most was, its (mostly) SMT and that's way too difficult for me.
I can see that now, I saw it from the start, but because soldering is part of my job I have no problem with SMT, but I do understand why it scares off many people.
also, PCB's have become much less expensive lately, so I'm not restricted to the scrap size of 10 x 10cm to keep things affordable.
So I think I will start over, and design a much easier to build simplified version, but one that is still 100% compatible with the real ZX-81, will drive modern TV's well, and load tapes with ease from the sound output of a laptop.
I will start by examining if every part in my design is still available in PTH, I think that shouldn't be a problem (knocks on wood).
hopefully there are still people alive when I finish with it that remember the ZX-81 (i'm joking, I guess it will take me only a couple of months to get a prototype ready) and hopefully there will still be interest in it. I'm gambling there will be, as RETRO computing interest seems to be on the rise again.
I'd also say the silence regarding most projects is quite normal, don't expect too much cheers or you'll end up disappointed. I know I was.
There’s already Grant Searle’s version, and ZX96, ZX97, ZX2000.
If I would build my custom ZX81 it will probably be ZXNU from ZXTeam. It also uses standard components and has build-in flash drive.
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube
Most of these projects are personal challenges with mods and improvements that are documented then (hopefully) released to the public, I really enjoyed Mahjongg’s blog on the design of this one over a long period of time and it’s great that it’s been released - I’ll probably choose this one as a project to have a go in order to learn better how it all works - after a Gigatron, Ben Eater’s 8-bit computer and the PiDP-11 I’ve got waiting...
Doesn't matter, as I said this is a hobby project, my goal is not to create money, its to create what is in my eyes my perfect ZX-81 clone that anybody can build.
I see now that I have made some choices in my previous attempts that seem wrong now, so Ill just try again, just for fun.
Don't know much about the ZXNU, but what I heard its not really a ZX-81 copy, just inspired on it.
Using built in Storage device, or other "extras" doesn't seem to be in the spirit of building something that people are interested in because of nostalgia, building in the 16K ram pack, and a slightly better keyboard, are my only planned concessions to building a ZX-81 clone kit for nostalgic reasons. That and a few practical features because it has to be usable with 2019 equipment, like a modern TV and replacement for a cassette recorder.
martin de jong.
I made an adapter for my earlier prototype keyboard, and tested it, and its fully working! with very good picture quality.
He patched it for 16K ROM, and included a small assembly code monitor in the free 8K.
This is the result of the following small BASIC program, I used to check out the video quality of the character alignment, note that this ROM also has the character 6 patched, so it looks less like an 8.
I'm happy, the characters are sharp and align perfectly, see the checkerboard pattern characters.
Thomas also reported that saving and loading using the cassette interface works very well, my cassette input circuit is doing its job.
I will order a keyboard PCB for this board, and continue testing it, for one thing I want to try if I can simply implement loading bars.
In any case this confirms my ULA replacement is working, so I can be confident when continuing with my new easy to build version ZX81+38.
P.S. my new keyboard PCB has been reported to work fine too!