Abstract: An electronic timer is provided of the type used for producing command signals to initiate and discontinue the operation of external devices such as pool pumps, lights, and the like. The timer is organized to adapt it to a modular arrangement whereby modules are easily added to increase the number of different command signals provided. The timer includes a common bus to which there are applied a plurality of parallel pulse signals that in combination define a timing interval divided into a sequence of time slots. A plurality of independently operable decoders are connected to the common bus so that all the decoders continuously monitor the parallel pulse signals. Preferably, the plurality of parallel pulse signals are generated in a control center module and applied to the common bus which propagates them to one or more other modules each of which contains at least a pair of the independently operable decoders.