My knowledge of electronics is minimal but I hope someone can help. My principal interest is in old motorcycles, and I am looking for some way to build a device to tell me when the points open on a magneto. For those who don't know, the magneto is a self contained ignition system containing primary and secondary windings, both rotated with respect to a permanent magnet. There are points across the primary winding which are opened at a specific time by means of a cam, collapsing the primary current and inducing a high voltage in the secondary windings.
When the points are closed, there is essentially a zero resistance between them and earth; when they open the resistance seen is that of the primary winding which is of the order of 3Ω. So I need something which can detect this change in order to time the magneto accurately, preferably sounding a buzzer when the points open.
The old-fashioned way is by putting a cigarette paper between the points and checking when it becomes free, but I'm convinced this should be easy using electronics.
Any help would be very gratefully received.
When the points are closed, there is essentially a zero resistance between them and earth; when they open the resistance seen is that of the primary winding which is of the order of 3Ω. So I need something which can detect this change in order to time the magneto accurately, preferably sounding a buzzer when the points open.
The old-fashioned way is by putting a cigarette paper between the points and checking when it becomes free, but I'm convinced this should be easy using electronics.
Any help would be very gratefully received.