looking for GM smartcoil driver circuit...

[Orin Eman]

> | I have been investigating these...
> | You have to raise the control line over 2.7V to 'arm' the coil.
> | It then fires when the control line falls below 2.5V _OR_
> | 0.1 second later, whichever comes first.

> 0.1 sec later than what?.
> Meaning it fires a 0.1 sec after raising to 2.7v?.

Yes, 0.1 sec after raising to 2.7V.  I fed it a very slow square
wave connected to one channel of the 'scope and an inductive
sensor on the coil wire connected to the other channel.
The spark was 0.1 seconds after the control line went high.

> | So, toggling between 5V and ground works fine.  Input impedance is
> | high, over 10k, so you don't do any harm connecting directly to 5V.
> | I have driven them using an opto isolator (4N35), collector to
> | 5V, emitter to resistor to coil, resistor to ground too.  I also
> | tried forming a darlington with the opto and a generic NPN in a
> | similar config.  Both methods work fine on the bench.
> | Other things that I noticed were that it takes approximately
> | 25 uS between grounding the control line and the spark and
> | you don't get a very good spark with the control line high
> | for only 1mS.

> Just curious was this with a battery type power supply, or an amperage
> limited test bench power supply?.   Could there be a coil "charge" sensor
> item?.

20 amp bench power supply, no current limit.  I have yet to investigate
how much current the coil takes, the power supply's meter is too slow
to respond - shows 5 or 6 amps peak.

Orin.