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Old 05-06-2003, 10:45 PM
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ZAGNUT
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Default Scratch Built Ignition???

http://perso.wanadoo.fr/transmic/gbfixe2.htm here you can see a very simple CDI circuit. this does not include the high voltage circuit needed for uor applications but a search of diy electronics sites will find lots of dc-dc converters based on small ferrite E cores.
iv'e made an ignition using the tiny module found in the distributor of a suzuki swift, worked great but with all the coils i tried the lowest current draw i got was a little over 2 amps at 6 volts, not so great. CDI is the only way to go imo.
CDI only uses the coil as a step-up transformer and doesn't rely on the inductance of the coil, so you don't need the big mega-wind coils with the heavy iron core. look at the tiny coils on zenoah engines, these are the same as the trigger-coils used for strobe lights, flashes, stun-guns....and are readily available from electronics suppliers for a fraction of the cost of dedicated model engine coils.
ignition advance/retard:
our engines aren't too picky about timing so a simple solution is to use two ignition sensors, one retarded for idle and start-up and one for high speed, a microswitch operated by a cam an the throttle shaft can switch between the two at about 1/3 throttle. i've been thinking about a simple ignition delay circuit that would vary timing depending on voltage recieved from the pick-up coil (not hall effect sensor) at different engine speeds. i don't know squat about electronics though, so any help would be welcome.

dave