This circuit was found in American documentation from the 1980s. The integrated circuit used is a voltage comparator of the time. Modern equivalents can be tested.
This circuit is from 1990 documentation. It uses a bridge with LEDs and the potentiometer must be...
This circuit has the spark duration controlled by a 555 timer. The circuit was found in the 1990...
Taking Raytheon's 3900 integrated circuits as an example, uncommon today, this circuit can be used...