Car Service Module

A compact unit that measures speed of a petrol engine in revolutions per minute, and the dwell angle of the ignition. by. A. Rig by The car service module is composed of two units: a circuit for measuring dwell angle and engine speed on one printed circuit board, and an associated liquid crystal display (LCD) read-out on another board. The units are connected by a cable terminated in 9-pin D-type connectors. The compact LCD readout is purposely kept separate to enable it to be used in other applications also. Electronics and the petrol engine Engine speed and the ignition dwell angle are both physical quantities which are to be converted to a voltage that can be shown on a display. Figure la shows the basic elements of an ignition system in a petrol engine. The primary of the ig- nition coil is connected between the positive pole of the car battery and the contact breaker, which is shunted by a capacitor and indirectly operated by the camshaft. When the camshaft revolves, the cont...