← Back to all projects

Kempston joystick interface

26 August 2026

InterfacePCBWay buildMemoir

Difficulty: Beginner-friendly soldering · Fits: All ZX Spectrum models with an expansion bus

The Kempston Joystick interface was what you needed if you wanted to use a joystick on an original ZX Spectrum. It maps two fire buttons and four directions onto a single input port (port 31), which is why it became the de facto standard — almost every Spectrum game with joystick support reads Kempston first. The later Amstrad-manufactured +2/+3 machines had two built-in Sinclair joystick ports, but that was several years away for the average Speccy owner in the mid-1980s, and this is the story of getting one the hard way.

Christmas without a joystick

We received our Speccy on Christmas Day 1984. It was second hand, but still a major purchase for my parents. Unfortunately it didn't come with a joystick or an interface, so we were stuck using the rubber keys for playing games.

Dominic's, October 1985

October 1985, birthday time, and a joystick and interface were on the list. Our parents took us to Dominic's (it began with Dom, owned by the Co-op) on the Warwick Road in Acocks Green. We'd been in there several times before — they had one of those wire baskets full of cassette tape games, and we'd search through it for what felt like hours until we found what we thought was a hidden gem, but would actually make Mastertronic look like gold.

This time, our parents were going to buy us a joystick and interface. We chose the interface (there was only the one) and a pair of wireless joysticks with a telescopic aerial. It didn't list the ZX Spectrum as a compatible system, but it did list the Atari and the Commodore 64, so we figured close enough. On the way home, we wondered whether throwing the wireless joystick down the stairs would let us win Daley Thompson's Decathlon.

The wireless joystick that never worked

We never managed to get the wireless joystick working, so it was back to Dominic's to swap it for a Cheetah joystick instead. My parents didn't want to drive back, so I had to walk. My parents had paid for the wireless joystick, but I'd bought the square 9-volt battery for it out of my paper round money — and forgot to take it out before I handed the joystick back. We had endless fun with the Cheetah joystick and Kempston interface, however despite the warning on the box, one day we accidently removed the interface whilst the speccy was still powered on, that was the end of our Joystick escapades for a while.

What actually grinds now

Forty-plus years later, what grinds me the most isn't forgetting to remove that battery, which cost about £1.50 at the time against the £3.75 a week I was paid for my paper round. It isn't the long walk back either. It's that the joystick interface itself cost £10 — equivalent to around £39 in 2026 money, using the ONS composite price index. It's only started to grind recently, because I found out just how few components are actually inside a Kempston interface, and how cheap and simple it is to build one. I appreciate there are other costs involved in bringing a product to a shop shelf in 1985, and a homebrew interface today can still be built for a fraction of that price. Putting all that aside, though, I genuinely had fun assembling the interface card.

Building your own, forty years on

The PCB used for this build is a community design by MurTek RetroTek (building on an earlier design by Yarek), shared on PCBWay under a CC BY-SA 3.0 licence — free to order and build under those terms with attribution. Five boards cost $5 plus shipping. Unlike the original 1985 interface, which used a 74LS244 buffer and dedicated port decoding logic, this board keeps things to two cheap, common 74-series chips and a handful of resistors:

The 74LS32 (quad OR gate) and 74LS240 (octal buffer) are the only parts worth taking care over — socket them rather than soldering directly, so a dead chip is a five-second swap rather than a rework job. Double-check the edge connector's orientation before it goes anywhere near the Spectrum's expansion bus. Test with literally any Kempston-compatible game once assembled — coverage is close to universal.

Build video

Component list

More like this