ZX14


4 posts
by mahjongg » Sat May 17, 2014 2:47 pm
The ZX14 is my (mahjongg's) clone of the Sinclair ZX81, which design is still ongoing, but this is a 3D rendered preview of it:
Preview_ZX14_with_keyboard.jpg
zx14 full system preview
Preview_ZX14_with_keyboard.jpg (417.83 KiB) Viewed 825 times


its latest schematic can be found here:
https://revspace.nl/File:ZX14_schematic.pdf

As the Revspace wiki is private, there was no public comment section before, so I made this thread instead.

more information, background story, schematics, keyboard layout and schematic etc etc, can be found on the Revspace site, in the "projects" section, https://revspace.nl/Main_Page
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by TonyD » Mon May 19, 2014 12:56 pm
Nice :-)

Going OT for a bit, I found Chris Smiths ZX Spectrum clone a great site.

http://www.zxdesign.info/
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by Ravenous » Mon May 19, 2014 1:38 pm
mahjongg wrote:The ZX14 is my (mahjongg's) clone of the Sinclair ZX81, which design is still ongoing, but this is a 3D rendered preview of it:

Can it run Windows?

ONLY KIDDING :o

The joystick port looks a good idea - does it duplicate keys on the keyboard?
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by mahjongg » Mon May 19, 2014 6:59 pm
Ravenous wrote:The joystick port looks a good idea - does it duplicate keys on the keyboard?

Yes, it "presses" the 5 6 7 and 8 "arrow keys" and the 0 key for "fire", (jump etc) those are the keys most often used for action games. although 4 of the 5 keys (three arrows and the 0 key) share a common wire, the fifth (left arrow) unfortunately does not, so directly connecting just wires to the switches in the joystick isn't possible, the easiest solution was to use 5 n-FET's mounted in parallel with the buttons. the ZX14 schematic shows the details.

I redesigned (I have redrawn) the ZX81 keyboard layout, so that you can use a keyboard overlay with 6x6mm buttons of which 3.5mm diameter "plungers" will go through holes in the overlay.
buttons like these:
tactile-1024x768.jpg
6x6 mm button
tactile-1024x768.jpg (152.98 KiB) Viewed 656 times

Placed on a standard 1/10" grid perfboard, the button pins will fit with a bit of bending, in an arrangement that you can see in the picture of the ZX14 above, open the picture in a new windows to see the necessary details.
Simply putting the original overlay over buttons would not have worked, as these buttons have too much stroke, so I in may redrawing I re-arranged the texts inside the "button areas" to make place for 3.5mm round holes.
The redesigned overlay looks like this, the brown circles represent the holes for the buttons:
Nieuw_keyboard_overlay.png
zx14 keyboard overlay
Nieuw_keyboard_overlay.png (56.52 KiB) Viewed 665 times


You can compare it with the original:
zx81keyboard original.jpg
ORIGINAL ZX81 KEYBOARD OVERLAY
zx81keyboard original.jpg (178.76 KiB) Viewed 660 times


a .PDF of it can be downloaded from the revspace site if you want to print your own overlay. It should print correctly scaled when printed on A4 paper. I recommend laminating the paper afterward.

ZX81 keyboard replacement.
So now you can also add a keyboard with real keys to a real ZX81, by soldering up 40 buttons to a normal 1/10" grid perfboard (wiring layout schematic is available on the site) of at least 160cm wide (eurocard), and by using this overlay. My keyboard should be compatible with a real ZX81. So its also useable as a replacement keyboard, if the original has disintegrated, as many have.

P.S.
The power of a ZX81 like device lies in the possibility to completely understand it, and that is the antithesis of Windows. As only with full understanding can there be full control. 8-)
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