Supplier: William Stuart Systems
Price: £25.50

An input/output port is similar to the junction box at a railway siding. It takes the mess of signals going into and out of the Spectrum and brings a semblance of order to them.

The Spectrum can only do one action at a time. It can, for instance, send a piece of information out through its edge connector or listen for a piece of information which is expected from an external device. Your computer can't do both jobs at once so the input/ output (I/O) interface time sequences the signals which are transmitted to the Spectrum or vice versa.

That's clever and useful but no I/O interface would be worth much if it had just one channel, or port, through which data could flow. Many hardware devices, such as mechanical arms need at least two channels, one of which sends out information while the other monitors the arm's movement. The WSS I/O port has two 8-bit ports which you can program individually to accept input or output - the ports are, therefore, bi-directional.

The instruction booklet includes circuit diagrams which will allow you to connect switches, photo cells, light emitting diodes, relays, organ keyboards and stepper motors. Diagrams are hand drawn but simple enough to understand.

The WSS I/O system is an inexpensive way of turning your Spectrum into a control console. It may not look terrific and the instruction booklet does not suffer fools gladly, but it is all you need to step into the world of robotics, home security or even entertainment.