The circuit shown in the figure can be used on the car with motors that use conventional contact breakers to indicate rotation on a 50uA moving coil instrument. The only adjustment is made in the trimpot in series with the instrument. The circuit works as a frequency / voltage converter whose scale is basically determined by the time network connected to pins 6 and 7 of the integrated circuit. The zener diodes are 1 W and the circuit can be used in other applications involving the indication of frequency or engine speed with the use of an appropriate transducer.
