The Timex Sinclair 1000 (ZX81) is a charmingly limited computer from 1982. It has one of the worst keyboards of all time, and it begs for you to DIY something better. Many people have have already created improved keyboards and cases, but I wanted to try my hand. I figured there are enough chunky, old computers out there though; I want to make something thin and sleek.
Video
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| RF modulator |
The RF modulator is the tallest part of the board, and needed to go. It can be replaced with a simple transistor buffer to get composite video. Some ULAs require a more advanced mod to get usable video. One option is this Ginger Electronic board. It has the bonus feature of allowing you to invert the screen "colors".
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| Channel switch |
The channel switch on the bottom of the PCB also adds to the height, and needed to be removed.
Power
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| Heatsink |
The heatsink isn't thick, but it is quite large. It's meant to extend under the keyboard, but this would add to the thickness of our new keyboard. Out it went. The regulator can't run without it though, so that had to be replaced. I found these generic buck converters that are drop in replacements, and don't require heatsinks.
Keyboard
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| Redragon K603 |
The original keyboard is as thin as it is unpleasant to use. To keep the new one thin, I looked for low-profile switches and especially short keycaps. I found the Redragon K603 keyboard to be a cheap source of both. The switches are even socketed, so they can be easily removed. The switches can be found separately though, and there are many options for keycaps.
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| Keycap stickers (image from 4keyboard.com) |
The next issue was the key legends. They're unique to this computer. Luckily I found these stickers from 4keyboard.com. They have all the information of the original keys, and they fit on a standard keycap.
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| Keyboard membrane connector |
It's easy enough to design a mounting plate and board for a custom keyboard, but it has to connect to the motherboard's strange connector. It's expecting the mylar sheets of the original button matrix. I could have bypassed or replaced the connector, but that felt like cheating. Instead, I designed a flat flex cable that fits into the original connector, and a standard flat flex connector on the new keyboard PCB.
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| New flex cable |
Case
I don't have any experience with 3D printing, and I'm not always impressed with the results I see. I stuck with 2D and designed a laser cut case. To keep things simple, I used all right angles, and dovetail joints. I settled for using super glue to join the majority of pieces (these nozzles helped immensely). The rest are held with screws and m2 nylon standoffs. Many of these are recessed into the bottom of the case as a way of achieving non-standard heights.
A few standoffs go through the case lid also. This requires a screw with a head larger than the standoff to secure the lid. I found this pack that includes "large head" m2 screws.
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| M2 case screws |
Jacks
The power, video, ear & mic jacks need to be brought to the outside of the new case. One option is to butt the motherboard against the left side, and expose the original jacks. This offsets things strangely due to the width of the new keyboard. The expansion edge connector ends up in the middle of the case, and the mounting holes off to the left. So, I placed it at the far right, and used new panel mount connectors instead.
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| Motherboard placement |
I took the opportunity to remove the headphone-style connector that's misused for power, and replace it with a normal 2.1mm barrel jack. I also added the conspicuously missing power switch. Lastly, I included a small toggle switch that can be used to invert the video signal.
Lettering
The case needed some lettering to differentiate the "Ear" jack from the "Mic" jack, and to add some character. These letters can be etched in, but you get very little contrast with acrylic. Paint is pretty much required. Luckily, laser etching usually gets you a free stencil because they etch through the protective film that comes on the acrylic. This makes it very easy to paint the parts, and then remove the film. I found that model spray paint works well for this.
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| Lettering on the new case |
Putting it all together
After all the gluing, painting, soldering, and desoldering, I had a finished case.
The design files are on my github.
