signal from coil and back emf......

[Simon Quested]

Hi All

> I think you guys are reading this all wrong - he is popping his INPUT
> from what I read. 

Yep

> This is due exclusively to the fact that the primary
> of the ignition system does NOT run on 12 volts, but something closer to
> 400 volts due to the self generated EMF in the coil

Thats what I guessed the problem is.....

> You MUST use a high value resistor

Duh!!! Here's the solution I think.....I only have the zener

> - something in the order of
> 470K should do the job, to limit the current, then a varister or zener
> rated somewhere about 5 volts to keep the trigger voltage low enough it
> will not blow holes through the junctions in the 555. You could use  up
> to 12 volts with a 555c.

I'm using a 555c and a 12v zener

> The coil back-emf from a 2 ohm injector is
> negligible - I would use the low impedence units with a limitting
> resistor to start with, then go to a peak and hold driver if necessary.

That's what I'm doing....

> just my $.02 worth - and .02 of a $.70 dollat at that!!

The cheque is in the mail ;-)

Thanks guys for all the help.

Simon 
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  Simon Quested (E-mail questeds at lincoln.ac.nz)
  Computer Technician, Silicon Graphics & Windows NT Support
  Centre for Computing and Biometrics
  LINCOLN UNIVERSITY OF NEW ZEALAND
  Phone (64)(03) 3252811 Ext. 8087
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http://www.lincoln.ac.nz/ccb/techs/simon/default.htm
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I drive way too fast to worry about cholesterol
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