This Cyberdeck Build Uses the Iconic, Underpowered Sinclair ZX81 as Its Base

With a 3.5MHz Z80 and just 1kB of RAM — expanded to a generous 32kB externally — this is one of the least powerful cyberdecks we've seen.

Gareth Halfacree
1 month agoHW101 / Retro Tech / 3D Printing

Pseudonymous maker "dmitrij" has built what could be a contender for the least powerful cyberdeck build around, based on a Sinclair ZX81/Timex Sinclair 1000 microcomputer from the earlier 1980s — which comes with just 1kB of onboard RAM.

Released in 1981, the Sinclair ZX81 — known as the Timex ZX-81 and later the Timex Sinclair 1000 in North America — was Sinclair Research's even more affordable follow-up to the Sinclair ZX80, based around the same eight-bit Zilog Z80 processor but with a dramatic reduction in component count thanks to heavy use of a single Ferranti uncommitted logic array (ULA) chip.

With a 3.5MHz processor and just 1kB of onboard RAM, the machine wasn't exactly a powerhouse — but it would go on to sell an estimated 1.5 million units worldwide before it was discontinued three years later.

Such a machine, with its iconic but much-derided flat membrane keyboard and low-resolution black-and-white video output, may not seem like the logical basis for a cyberdeck build — but that hasn't stopped dmitrij from building one anyway. At the heart of the build is an original Sinclair ZX81, the RF video modulator of has been replaced by a composite output connected to a 3.5" LCD TV board from Adafruit mounted in a 3D-printed replica of an Apple monitor case.

This tiny CRT-esque display is then mounted on a 3D-printed case housing a ZXpand+ expansion board which offers features missing from the original ZX81 hardware — including Yamaha AY audio, a joystick port, serial port, 32kB of RAM, and an SD Card interface for solid-state storage in place of the cassette deck traditionally used with the system.

"I was toying with an idea of using it as a super restrictive writing machine," dmutrij says of the project. "I even installed a Tasword word processor. Unfortunately, the keyboard and screen are too restrictive. I mainly use it for playing with basic and assembler, coding short arty programs (as the one running on a screen, a black hole simulator)."

It's not just the RF modulator that's been tweaked in the ZX81, either: the keyboard has enjoyed a makeover too. "It [uses] a replacement with sandwiched microswitches," dmitrij explains of the upgraded keyboard. "It gives a slight haptic feedback. Still terrible though."

More information is available in dmitrij's Reddit post.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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