Abstract: An ignition coil primary winding signal processing system that is suitable for use with cathode ray tube based instruments used in the troubleshooting, diagnosing, and servicing of spark ignition internal combustion engines. A primary trigger signal gnerator (4) processes the waveform obtained from the primary winding of the ignition coil of an internal combustion engine, V.sub.S, and produces a logical signal, V.sub.L, which drives a bistable circuit. The bistable circuit includes a D flip-flop FF1 that produces a square wave trigger signal, V.sub.T, whose rising edge corresponds to the point in time of the ignition points break, or the equivalent occurs in an electronic or transistorized ignition system. A dwell angle-to-voltage converter (8) also processes the complex waveform obtained from the ignition coil primary winding of an internal combustion engine, V.sub.S, and produces a nonfluctuating waveform, V.sub.C4, that is compared to a reference voltage.

Abstract: An advance reference cylinder trigger generator that provides a more effective trigger signal to synchronize the horizontal sweep of a cathode ray tube based instrument used for troubleshooting, diagnosing and servicing of spark ignition internal combustion engines. The trigger pulses, V.sub.pt, derived from the primary winding of an ignition coil are applied to a cylinder position counter (5) and, after being delayed by a delay circuit (4), to a cylinder count counter (8). When the value of cylinder position counter (5) equals or exceeds the value of cylinder count counter (8), an output from comparator (6) enables a monostable multivibrator (10) to produce an advance reference cylinder trigger V.sub.at upon receipt of the next ignition coil derived trigger pulse, V.sub.pt. Because the V.sub.pt pulses lead spark plug discharge derived pulses, the V.sub.pt pulses lead the spark plug discharge pulse associated with the V.sub.pt pulse causing the firing of the monostable multivibrator.