On 09/04/2020 18:43, Paul wrote:

CDI Capacitor Discharge Ignition Circuit Demo

https://www.youtube.com/watch?v=0yK3Opq_i0M

Primary side V
|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___
|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___|Â*Â* |
|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___|Â*Â*Â*Â*Â*Â* |
|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* |Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* ___
|Â*Â*Â*Â*Â*Â*Â* ___|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* \Â*Â*Â*Â*Â*Â* ___|
|Â*Â*Â* ___|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* |Â*Â* ___|
| __|Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â * \_|
+-------------------------------------------- Time
Â* excitor charges C,Â*Â*Â*Â*Â*Â*Â*Â* ^
Â* SCR dumps to coilÂ*Â*Â*Â*Â*Â*Â*Â*Â* |
Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â*Â* Â* spark on

Thanks Paul, this system is a bit later than that I think, I would have
to pull the flywheel to see, the magnets are on the inside of the
flywheel and it rotates round the excitor coil, Difference is the
exciter and sensor are all in one. I think the trailing edge current
from the discharge is what should cause the spark but because the
magnets are weak the current generated in the primary isn't high
enough to cause the voltage in the secondary to creat the spark.

Hence I was looking for something to switch the current in the coil
primary from a 12V battery off when it senses that trailing edge.

I was hoping someone would know of a simple circuit where the present
live feed from the CD was taken to ground by a suitable resistor and the
voltage across the resistor would cause a current to flow therough the
base of a transistor which would switch the current through the coil
off and reset.