This circuit is a tester for flywheel based ignition systems in small aeroplane engines. Basically the same ignition coils are also seen in other small combustion engines used in/on mopeds and lawn mowers in brief, engines without a battery. The part to be tested comprises a primary coil in parallel with the contact breaker. The timing of this contact breaker has to be adjusted correctly. Since the coil’s primary has a very low resistance it is difficult to determine whether the contact breaker is open or closed. However, you can determine that reliably with this circuit, using an LED and a beeper. The circuit is implemented twice because aviation engines (Cessna, Piper and similar) always have two ignitions in parallel to increase reliability. For two-cylinder engines, well the purpose is obvious. Ignition Timer Circuit Diagram The circuit consists of a 555 and a few transistors. The 555 supplies a square wave of about 3000 Hz. This signal goes to power transistors...