Opto-electronic version of high energy ignition

SILICON CHIP regularly receives requests for modifications to published circuits and the High Energy Ignition System for cars – described in the June 1998 issue – is a popular example.

Readers often want to use it with an opto-electronic distributor and most of these requests are met by a simple modification that was published in the August 1998 issue (page 91). However, this present version is aimed at a different opto-electronic pickup which has a common negative connection and has been implemented for the original version of the ignition circuit which was published in May 1988.

Zener diode ZD1 and transistor Q1 make up a simple voltage regulator which delivers 7.5V at the emitter. This is used to supply the opto-electronic pickup which consists of an infrared LED and photo-transistor. This is used in conjunction with a light chopper disc on the shaft of the distributor.

The current pulses produced by the photo-transistor are inverted by Q2 and fed via the 0.1µF capacitor and 22k resistor to pin 5 of IC1. In other respects, the circuit remains the same as published in May 1988 but it can be adapted to the later version in June 1998.

SILICON CHIP.