A simple, low-cost device is described, which the authors have developed for prototyping industrial machine vision systems. The unit provides facilities for controlling the following devices, via a single serial (RS232) port, connected to a host computer: (a) Twelve ON/OFF mains devices (lamps, laser stripe generator, pattern projector, etc) (b) Four ON/OFF pneumatic valves (These are mounted on board the hardware module.) (c) One 8-way video multiplexor (d) Six programmable-speed serial (RS232) communication ports (e) Six opto- isolated 8-way parallel I/O ports. Using this unit, it is possible for software, running on the host computer and which contains only the most rudimentary I/O facilities, to operate a range of electro- mechanical devices. For example, a HyperCard program can switch lamps and pneumatic air lines ON/OFF, control the movements of an (X,Y,(theta) )-table and select different video cameras. These electro-mechanical devices form part of a flexible inspection cell, which the authors have built recently. This cell is being used to study the inspection of low-volume batch products, without the need for detailed instructions. The interface module has also been used to connect an image processing package, based on the Prolog programming language, to a gantry robot. This system plays dominoes against a human opponent.