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Simple automotive tachometer which is schematically shown in the figure, designed to measure the rotational speed of the crankshaft carburetor engines with electrical system that has a minus battery the battery is connected to the case.

The basis of the scheme is a single pulse shaper, collected on the CD4007 chip (domestic analogue - CLP). The driver starts positive pulses occurring at the moment of contact opening the breaker.

The instrument PA1 connected to the output of generator via the limiting resistor R5, measures the voltage across the measuring capacitor C1, which proportion to the frequency of the input pulses with an accuracy not worse than 1...2%.

Frequency pulse 30 times less than the frequency of rotation of the crankshaft four-stroke engine.

Author: T. Tikhomirov, Chita