NEW
Specialist Input Devices
Specialist input devices offered ways of interacting
with the ZX Spectrum beyond conventional keyboards,
joysticks and light pens. Some were intended for graphics
work, tracing or transferring information from physical
drawings, while others used unusual methods of input.
This section documents specialist input hardware for the Sinclair ZX Spectrum, including its operation, advertised features and contemporary descriptions where these can be established from surviving sources.
This section documents specialist input hardware for the Sinclair ZX Spectrum, including its operation, advertised features and contemporary descriptions where these can be established from surviving sources.
Features
Original Price
RD Digital Tracer
R D Laboratories
The RD Digital Tracer is a graphics input device designed to transfer the outlines of drawings and other images to the ZX Spectrum's display file, avoiding the need to enter individual screen coordinates manually. The resulting image can be displayed on screen, printed using the ZX Printer or saved to cassette. The supplied software includes fast colour fill, audible keystroke acknowledgement, fast PAPER colour change and fast loading of saved display files.1
Notes
Supplied with a tracing sheet, software cassette and full instructions. Designed for the ZX Spectrum, it was also compatible with the ZX81, although the ZX81 could not provide the Spectrum's high-resolution colour graphics. The advertisement promoted the device for engineers, architects, technicians, education and computer training.1
£55.50
1
price included VAT and p&p
Spec Switch
FLET.ELEC
Advertised by Flet-Elec for the 16K/48K ZX Spectrum and ZX81, the Spec Switch was presented as an input system for graphics, measurement and technical applications. The advertised package included an interface, pen, measuring wheel and software utility.2
A patent filed by Martin Geoffrey Fletcher in September 1983 describes a computer-input system using a mechanically operated pen switch and a toothed measuring wheel that generates electrical signals as it rotates. This is a strong technical match for the unusual combination of components advertised with the Spec Switch, although the patent does not explicitly name the product.
The advertisement quoted £49.50 and announced availability from mid-January 1984. No independent evidence of commercial release has yet been established.2
A patent filed by Martin Geoffrey Fletcher in September 1983 describes a computer-input system using a mechanically operated pen switch and a toothed measuring wheel that generates electrical signals as it rotates. This is a strong technical match for the unusual combination of components advertised with the Spec Switch, although the patent does not explicitly name the product.
The advertisement quoted £49.50 and announced availability from mid-January 1984. No independent evidence of commercial release has yet been established.2
Notes
The advertisement describes the Spec Switch as a new type of input device rather than another light pen. It refers to patent application number 8325406. The advertised measurement functions include working to scales ranging from 1:1 to 1:5000. The product was announced as available from mid-January 1984.2
£49.50
2
Advertised price, inclusive. Availability was announced for mid-January 1984, but independent evidence of commercial release has not been found
References
1.
"INSTANT IMAGE TRANSFER TO ZX SPECTRUM RD DIGITAL TRACER £55.50" - Contemporary advertisement for the RD Digital Tracer, describing its operation, software features, compatibility, applications and £55.50 price., Personal Computer News (PCN), No. 34 (OCT 27 - NOV 2 1983), p. 86
↩
2.
"SPEC SWITCH" - FLET.ELEC Spec Switch advertisement, Your Spectrum, No. 1, p. 76
↩
External Links
GB2146845A — Switch Assembly for Computer Input
— Published patent describing a switch assembly for providing computer input, potentially explaining the operating principle of the Spec Switch.
GB8325406D0 - Spec Switch Patent Application
— Patent application record associated with the Spec Switch advertised by Flet-Elec.
Page Revised: 16/10/2026