To make provision for expanding the keyboard, the computer's keyboard Data and Address lines have been made available at 2 DIL sockets. As well as key switches, any switching device can be connected and mapped onto the keyboard, including Joysticks. To take advantage of this, 2 adaptors are provided which convert the sockets into 9-pin Sinclair Joystick Ports. Any joystick can be simply converted to return a particular set of key inputs and we have a prototype Joystick which can be completely redefined using a small plug-in board.
The problem of providing extra, shifted key functions has taxed many manufacturers, who have either not attempted it (DKtronics), confined themselves to those particular functions that can be' obtained using diodes on shared Data or Address lines (Transform) or used logic circuitry to simulate the double keypresses (Fuller). The latter course entails a power supply to the keyboard, a larger PCB and increased costs. The double-layer membrane used in the Saga Crusader appears to have been unsuccessful as it has not been advertised for some months.
The Kappa unit employs a unique and simple' circuit that permits any number of shifted keys to be added to the keyboard. It is located below the Caps Shift key, and needs no power supply. This small size means that all the space an the PCB can be occupied by extra keys, resulting in the most comprehensive collection of single key functions available from any Spectrum keyboard.
When the keyboard is fitted to the computer, the case locates on the base, forming a robust unit that allows any peripherals to be connected without interference. The keys have clear tops and we ask users to fit the legends themselves. We recognise that this job, and the unpolished look of the unit compared to same other keyboards, will be unattractive to many purchasers, but we have found that those who recognise the need for more facilities an the keyboard have been extremely pleased with the greatly increased ease of programming. The Joystick Interface is a bonus.
I would draw your attention to the information sheet and instructions for further details of the unit.