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

[Simon Quested]

Hi All

I'm using a 555 timer set up as a one shot firing an injector. To trigger it I want to 
use the negative of the coil. The circuit works great on the bench 
but the once I connect it it fries the input.... I think this is 
because of the back emf from the coil so I put a 12v zener across the 
input.
Can anyone help me with a filter/clipper to stop this.

Cheers

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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