Sinclair I/O Board Completed Over 30 Years Later

In the early 1980s when the 8-bit microcomputer boom was well under way, [Alan Faulds] was a student, and an owner of a Sinclair ZX81. He had ambitions to use it, in his words, “to control the world“, but since the Sinclair lacked an I/O port he was thwarted. He bought an expander board and a couple of I/O card PCBs from the British electronic supplier Maplin in the days when they were a mail order parts stockist rather than a chain of stores chasing Radio Shack’s vacated retail position.

Sadly for [Alan], he didn’t have the cash to buy all the parts to populate the boards, then the pressures of a final year at university intervened, and he never built those Maplin kits. They sat forgotten in their padded envelope for over three decades until a chance conversation with a friend reminded him of his unfinished student project. He sought it out, and set about recreating the board.

zx-io-thumbnailThe ZX81 had a single port: a PCB edge connector at its rear that exposed all the Z80 processor’s lines. It was notorious for unreliability, as the tiniest vibration when a peripheral was connected would crash the machine. Maplin’s expansion system featured a backplane with a series of edge connector sockets, and cards with bare PCB edge connectors. Back in the 1980s it was easy to find edge connectors of the right size with the appropriate key installed, but not these days. [Alan] had to make one himself for his build.

The I/O card with its 8255 and brace of 74 series chips was a double-sided affair with vias made through the use of little snap-off hand-soldered pins. [Alan] put his ICs in sockets, a sensible choice given that when he powered it up he found he’d put a couple of the 74 chips in the wrong positions. With that error rectified the board worked exactly as it should, giving the little ZX three I/O ports, albeit with one of them a buffered output.

We haven’t featured the little Sinclair micro as often as we should have here at Hackaday, it seems to have been overshadowed by its ZX Spectrum successor. We did show you a VGA ZX81 emulated on an mbed though, and a rather neat color video hack for its Brazilian cousin.

Hackaday Links: June 26, 2016

Solar Freaking Roadways. What is it? It’s technology that replaces all roadways with a smooth sheet of glass and solar panels. You know how asphalt is soooo easy to repair and soooooo cheap? Yes, this is the exact opposite of that. They’re coming to freaking Missouri. A parking lot for the Route 66 Welcome Center in Conway, MO will be paved with the solar freaking roadways that netted $2 Million in an Indiegogo campaign two years ago.

There is a National Potato Expo. As far as I can tell, this is a trade show for potatoes and potato-related paraphernalia. As with all trade shows you need a great demo, in this case one involving potatoes. How about a phone charging station powered by potatoes? It’s a bunch of potatoes, copper pipe, galvanized nails (neat design, btw), and a USB socket. Yes, it works, but not well.

The travelling hacker box is a USPS flat rate box filled to the brim with random bits and bobs of electronics, shipped back and forth between dozens of electron enthusiasts. It’s making one last trip around the US, and now the travelling hacker box needs destinations from Idaho to Michigan. Idaho, of course, is a fictional state created in 2004 for Napoleon Dynamite, but that still leaves Montana, the Dakotas, Wisconsin, Minnesota, and the UP. If you live in one of these states, there’s a travelling hacker box with your name on it. Request to join the project and PM me on

It’s election year in the US, and that means half of the population hates one candidate, half of the population hates another candidate, and half of the population will vote. Don’t think about that for too long. Here’s an Arduino doing something topical with Twitter.

Hotends for 3D printers are getting more and more robust, but thermistors are fiddly little things. E3D just came up with the solution. It’s a standard, modular temperature ‘cartridge’ that fits in E3D’s heater blocks. You can already change out the heater cartridge on a 3D printer for a higher wattage model, and now you can change out a thermistor for a thermocouple just as easily. E3D sells their stuff in GBP, so considering recent events it might be a good time to pick up a new hotend for that Monoprice 3D printer you picked up

The 8-Bit Generation recently released their documentary The Commodore Warschronicling the stupendous rise and meteoric fall of Commodore. Now they’re working on the Atari version and they’re funding it with a Kickstarter. Rumor has it Hackaday’s own [Bil Herd] has been asked to narrate.

Here’s another Hackaday Retro Edition success story @KetturiFox pulled up the Hackaday Retro Edition on a Texas Instruments TravelMate 5000 laptop. That’s a relatively modern laptop with a 75MHz Pentium, PCMCIA slots, and a nub mouse.