This invention relates to a speed responsive system for a motor vehicle whereby the vehicle may be kept at a predetermined speed, or the driver may be warned when a predetermined speed is reached. In one embodiment, the system includes an inductive pick-up or transducer, which senses rotation of a ferrous-toothed disc rotatable with a shaft to generate a voltage dependent upon the rotational speed of the shaft. Means, comprising a potential divider or a memory circuit, are provided for generating a reference voltage, and a comparator circuit is provided for comparing the voltages, the comparator being arranged to emit or change its output signal when the speed responsive voltage, or a voltage derived therefrom, reaches the reference voltage.
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