Hi Converse and NormK,
Yes it's much cheaper to buy a ready made module than building one. The parts plus time will cost more than $20. At least we understand what's possibly inside the black box and how it could possibly works.
To explain how it works, normally with contact point, the contact stays open 98% of the time and it only close when pushed by the cam. The condenser is used to absorb any arching and store the energy for the next contact cycle. Contact arching can ignite the fuel so we don't want this to happen. Now the circuit works the same thing. The TRIAC stays open 98% of the time while the energy or voltage is stored in the capacitor. That voltage also bias the hall effect sensor through a voltage divider resistor R1 & R2. Assuming the potential voltage is 100V, the supply voltage to the hall effect is 5V. Limiting resistor R3 is used for the TRIAC gate drive current limiting. The hall effect with Schmitt trigger output magnetic sensor turns on when the flywheel magnet pass through it which drives the gate which caused the TRIAC to conduct or short circuit. This cycle will repeat energising the primary winding and discharge to the secondary winding which produce high voltage spark. Next time I would like to design and prototype an inline LED spark tester to detect shorted spark plug, weak spark or no spark or can be represented with inline digital high voltage meter.
Cheers,
TheCarbyMaster
