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mahjongg
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Re: My new ZX81 clone, built from discrete pin-through hole components

Thu Jan 30, 2020 12:49 pm

rpdom wrote:
Thu Jan 30, 2020 10:08 am
Maybe some 0Ohm resistors to jump over tracks, or even wire links?

It looks like a fun problem.
For some definitions of "fun" perhaps. :mrgreen:

Don't worry, I know all the layout tricks, and I'm not yet desperate.

I will do all the layout changes necessary to create a working ZX81 clone first, then concentrate on connecting the expansion port, if wire-bridges are the solution I will use them.

I already considered supporting "fly wires" that can be used when someone is in desperate need to have one or more esoteric (never used) signals connected to the expansion port. But I consider this more or less a cop-out.

Currently I aim to at least have enough signals connected to at least support the printer.

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Re: My new ZX81 clone, built from discrete pin-through hole components

Wed Feb 12, 2020 12:06 am

Current status (February 12, 2020)
temporarily removed much of the expansion connector wiring, for a better overview.
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Re: My new ZX81 clone, built from discrete pin-through hole components

Wed Feb 19, 2020 10:12 am

Finished routing (100% connectivity). And added enough signals to the expansion port so that I/O based (not memory map based) expansion should work. So printer, PSG, joystick port and any other I/O driven devices should work fine, but memory expansion devices will not.
Which should not be problematic as the ZX81+38 already has expanded RAM to the max.

Next step is to thoroughly check all design rules are met, and add copper fill (on both sides, connected to GND).

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Re: My new ZX81 clone, built from discrete pin-through hole components

Wed Feb 26, 2020 11:00 am

I wasn't satisfied with incomplete wiring to the expansion connector, so I tried to complete the remaining wiring.
I did all but two signals, nBUSACK and nWAIT, but I expect to finish those two next week.
The layout is now impressively "busy". most wiring is done in 0.15mm, and almost everywhere I have to route two wires between pins, especially on the right hand side.
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Re: My new ZX81 clone, built from discrete pin-through hole components

Thu Mar 05, 2020 12:40 pm

Connectivity now is 100%, also did a DRC, (design rule check) and added copperfills (connected to GND). next to do is to complete solder mask and silk screen.

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Re: My new ZX81 clone, built from discrete pin-through hole components

Wed Mar 11, 2020 10:46 am

PCB (Rev 1.4) is now finished, this is how it will look like:

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rpdom
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Re: My new ZX81 clone, built from discrete pin-through hole components

Wed Mar 11, 2020 11:14 am

Very neat. Nice work!

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Re: My new ZX81 clone, built from discrete pin-through hole components

Wed Mar 11, 2020 12:29 pm

well done, it looks great
Tony


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Re: My new ZX81 clone, built from discrete pin-through hole components

Wed Mar 11, 2020 11:46 pm

Stunning Work!

Dave

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Re: My new ZX81 clone, built from discrete pin-through hole components

Thu Mar 26, 2020 3:22 pm

The PCB is finished, (done some tiny tweaks and improvements) such as all the default jumper connections are now all on the back where they can be cut and modified if you want to use a real ZX-81 ROM, or switch to 32K RAM (instead of 16K) among other things:
Image
Image

PCB production files are published here:
https://github.com/mahjongg2/ZX81plus38 ... LICENSE.md

I'm working on a BOM (Bill of materials) file, which will also be published on GitHub, as well as a final schematic (in black and white). and probably other files as well.

The keyboard PCB I designed for my older ZX81+35 can be used with this version too, or you could use a real keyboard foil, which you can still buy. This PCB should fit in the original case nicely.

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Re: My new ZX81 clone, built from discrete pin-through hole components

Thu Mar 26, 2020 3:25 pm

It certainly looks impressive :D

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Re: My new ZX81 clone, built from discrete pin-through hole components

Fri Mar 27, 2020 2:53 pm

well done. it looks great
Tony

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Re: My new ZX81 clone, built from discrete pin-through hole components

Fri Mar 27, 2020 3:26 pm

Thanks all, still a lot to do. Bill of materials, construction manual, user manual, building the prototype and testing it. etc etc, will keep me busy for months to come...

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