The programmable controller has a microprocessor (CPU) with a clock (28) and a read-only memory (5). An electrical connection allows external electric supply to be connected through a switch controlled by the programmable unit. A variety of detectors or switches can be mounted as modules on the printed circuit board (2) supporting the processor. The controller has a key pad (4) to allow entry of programming instruction, and a display screen (3) to show entered data or for checking programming. The printed circuit and the modules attached to it are housed in a casing (1). The programme can be stored on a plug-in card. An interface circuit can be provided to allow connection to other devices or computers. Optical coupling can also be used.
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