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.

Pocket Calculator Emulates Pocket Calculator

msp430 Calc Emu

[Chris] has built a pocket calculator that emulates… a pocket calculator. Two pocket calculators, in fact. Inspired by [Ken Shirriff’s] incredible reverse engineering of the Sinclair scientific calculator, [Chris] decided to bring [Ken’s] Sinclair and TI Datamath 2500II simulators to the physical world.

Both of these classic 70’s calculators are based on the TMS0805 processor. The 0805 ran with 320 11-bit words of ROM and only three storage registers. Sinclair’s [Nigel Searle] performed the real hack by implementing scientific calculator operations on a chip designed to be a four function calculator.

[Chris] decided to keep everything in the family by using a Texas Instruments msp430 microcontroller for emulation. He adapted [Ken’s] simulator code to run on a MSP430G2452. 256 bytes of RAM and a whopping 8KB of flash made things almost too easy.[Chris’] includes ROMs for both the TI and the Sinclair calculators. The TI Datamath ROM is default, but by holding the 7 key down during boot, the Sinclair ROM is loaded. The silk screen includes key icons for both calculators, as well as some Doge-inspired wisdom on the back.

All joking aside, these really are amazing little calculators. Children of the 60’s and 70’s will be taken back when they see the LEDs flash as the emulated TMS0805 performs algorithmic arithmetic. [Chris’] code is up on Github. While he hasn’t released gerbers yet, he does have images of his PCB layout on the 43oh.com forums.

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Sinclair ZX Spectrum +2A Slims Down

sinclair

[Carl] got his hands on a dead Sinclair ZX Spectrum +2A. He decided he wasn’t just going to fix it, he was going to improve it! The ZX Spectrum Compact is literally a “sawn-off” Spectrum +2A. [Carl’s] inspiration came from a similar mod at the Old Machinery blog.

Amstrad seems to have had a habit of bolting on additions to their products. In the case of the Spectrum +2A, it was a tape drive. Tapes weren’t a great storage method in the 80’s, and today they’re downright annoying. [Carl] didn’t need the tape interface, as he’s using a DiVide ATA interface.

The modification is rather straight forward. [Carl] broke out the hacksaw and cut the right end cap away from the tape drive. He then cut the entire tape drive away. The motherboard wasn’t safe from the saw treatment either, as the printer interface was cut off. Thankfully there were no components on the printer interface. Apparently [Carl] didn’t short any traces as he went to town with his saw.

With the motherboard modified to fit the abbreviated case, [Carl] was ready to begin reconstruction. He glued the cap onto the sawn-off case with Grip Fill glue, which also served to fill any gaps. Some sanding, priming, and painting later, The ZX Spectrum Compact was finished. This isn’t a perfect mod, as the gap is still slightly visible under the paint – but it’s good enough for [Carl]. Hey, it’s good enough for us, too – we can’t all be [Ben Heck]!

 

Obsolete technology band


Radiohead held a contest for fans to remix the single Nude from their album In Rainbows. Frontman Thom Yorke mentioned on NPR that the contest was essentially a joke, since the Nude track is recorded at 6/8 timing and 63bpm, much slower than traditionally mixed music. The above video from [James Houston] is one of the most creative entries. Using old computer hardware he has recreated the track in a very unique way. He uses a Sinclair ZX Spectrum for the guitar track, a dot matrix printer for the drums, a scanner for bass, and a hard drive array for vocals.

Want to make your own band with obsolete technology? Click through for a few pointers to get you started.

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