System to control the on-off time of a pulse train of variable frequency, particularly the dwell time of ignition signals for an internal combustion engine

摘要

A pulse train of a first frequency is generated, for example representative of speed of an internal combustion engine, and counted in a counter in a first counting cycle until the counter reaches a predetermined count number, the counter then being reset; a second frequency signal, for example a multiplied frequency derived from the first is then applied to the counter during a second count cycle, the counter stopping to count when current flow through the ignition coil of a predetermined level is sensed, and establishing a count number from which the counter can start counting at the next subsequent first cycle. The ON time of ignition current flow is controlled to commence at the beginning of the second count cycle, terminating at the ignition instant, as controlled by an ignition time control arrangement.