Peripherals & 'Add-ons' for the ZX Spectrum

The ZX Spectrum's design was primarily driven by price, and at £125, the Spectrum was a lot cheaper than most of its contempories. To keep the price down, the Spectrum had to do without some of the 'luxuries' that were fitted as standard on its competitors. These 'luxuries' included things like 3-channel sound, typewriter-style keyboards, printer and joystick interfaces, digital-to-analogue interfaces, and disk drive interfaces.  This led to a large number of peripheral manufacturers building and selling 'add-ons' with features that matched and often surpassed those of other computers.

Keyboards

The original ZX Spectrum's keyboard was a forty-switch touch-sensitive membrane similar to that used on the ZX81. The forty switches were arranged in a 10 x 4 matrix, and a one-piece rubber keyboard was placed over the top of the membrane. Each key had a maximum of six functions, and these could be accessed by pressing the required key on its own, in conjunction with the CAP SHIFT or SYMBOL SHIFT keys, or both together to obtain extended mode.

Since some keys were used more than others, naturally some keys would wear out quicker than others, especially the BREAK/SPACE, SHIFT, and number keys. Faults mostly occurred in the keyboard membrane; usually, one of the data or address lines would have a break in the circuit around the key that failed, but they could also fail on one of the ribbon cable connectors that connected to the Spectrum's PCB.

Once a membrane failure occurs, it is almost impossible to repair, and it was this and the Spectrum's lack of a full-size typewriter-style keyboard that led many manufacturers of peripherals to design their own keyboards.


Third-party keyboards came in many shapes and sizes, but most had a typewriter-style keyboard, and many had extras like function keys, extra shift keys, numeric keypads, and even sound amplifiers.

Joystick Interfaces (also ROM cartridge interfaces)

Sinclair did not originally market the ZX Spectrum as a games machine, but with its reasonable price tag, its popularity grew, and the Spectrum gained a young audience with an appetite for video games. The Spectrum was, however, lacking in the joystick department. Unlike machines such as the Commodore 64 and Atari 800, the Spectrum did not have a built-in joystick port.

Interfaces from manufacturers like Kempston, AGF, and Protek soon became industry standards and before long the market was flooded with joystick interfaces, from simple one-port devices, to joystick ports with built-in sound amplifiers.

Sinclair Research even released its own joystick interface, the ZX Interface 2. The Interface 2 has two joystick ports and a ROM cartridge slot for a very limited range of software, and it is for this reason I also include ROM cartridge interfaces in this section.

Light Pens  Light Guns  Graphics & Touch Pads  Digital Tracers


The standard way to move a cursor or a pointer on the ZX Spectrum, would be to use the cursor keys, 5 to 8, shifted. Less cumbersome input methods are available, and these would be able to directly translate the input of a light pen or a stylus, to a movement of a cursor, or the selection of a menu item.

I have placed Light Pens, Light Guns, Graphics/Touch Pads, and Digital Tracers in one category, 'Input Devices', as they all perform similar functions. Light Pens and Light Guns work similarly, detecting a point of light on a screen by way of the timing of the TV scan. Graphics Pads, Digital Tracers, and Lights Pens are commonly used with graphic design software, or C.A.D. software.

Joysticks & Mice will have their own dedicated sections.

MIDI Interfaces  MIDI Keyboards


MIDI, or Musical Instrument Digital Interface, is an industry standard for connecting compatible musical instruments to computers and other devices. A few interfaces were produced for the ZX Spectrum so it could be used a sequencer for MIDI devices and some of these are listed on the MIDI Devices page.

MIDI keyboards were also produced, although not specifically for the Spectrum, and are also listed on the MIDI Devices page as they were originally advertised in ZX Spectrum magazines.

The ZX Spectrum+ 128K models had built in MIDI ports which could be controlled with the PLAY statement.

Sound Amplifiers  Sound Synthesizers


The original ZX Spectrum only came with an internal buzzer, which could be made to produce 'beeps' of low volume and questionable quality. Many manufacturers of peripherals produced devices to improve on the Spectrum's BEEP, some of these amplified sound from the Spectrum's EAR or MIC sockets to a loudspeaker, while others amplified the sound using the TV output. Sound synthesizers^* were also available. These utilised a sound chip, usually with 3 or 4 sound channels, and produced cleaner, crisper, sounds than the Spectrum's own 'beeper' could produce.

Some of devices produced combined both amplifiers and synthesizers, and some also included other features such as joystick ports.

The ZX Spectrum+ 128K models included a 3-channel sound synthesizer, and amplified sound through the television set.

^*In Britain the correct spelling is synthesisers with an 's'. Synthesizers, as spelt with a 'z', is the american spelling and was more commonly used in the UK computer press of the 1980s. The american spelling with a 'z' is the one which is used throughout this website.

Speech Synthesizers  Speech Recognition


Humans have always been fascinated by the idea of computers that talk. Film and television have portrayed computers as electronic intelligences with the ability to learn, listen, and be heard. Computers like HAL-9000 from Stanley Kubrick's 2001: A Space Odyssey, K.I.T.T. from TV's Knight Rider, and C-3PO from George Lucas' Star Wars give the impression of conscious intelligence, a creation of an artificial mind. Speech synthesis in the 1980s was still in its infancy, and most speech add-ons did tend to have a robotic, metallic sort of voice. BBC Micro users could hear the dulcet tones of newsreader Kenneth Kendall coming through their computer's speaker, whereas Spectrum users had something that sounded more like Metal Mickey. But that was part of the charm of speech synthesizers - that they did sound robotic.

Of course, we cannot discuss speech synthesis without mentioning speech recognition. Speech recognition on the ZX Spectrum, like most microcomputers of the 1980s, was crude. Usually only a maximum of ten or twenty words could be recognised, but this was just enough to whet the appetite of computer hobbyists wishing for a taste of the future promised by TV shows and movies.

Only a few speech recognition systems were available for the Spectrum, but they did give a glimpse of the future that was to come. Today, mobile phones and televisions can recognise whole spoken sentences, not just single words. But it was the microcomputers of the 1980s, like the Spectrum, which laid the foundations for modern speech recognition and its integration into our devices and everyday lives.

This page, last revision : 24/08/2024