Digital Tach and Newbie!

[Ludis Langens]

Shane Moseley wrote:
> 
> If pulling the data from the coil negative.  List - could someone describe the
> voltage characteristics there.  I assume the negative side will go to zero volts
> when collapsing and then what?  Float high?  What kind of spikes and current
> shunts to expect?  Is opto-isolation absolutely necessary?  Thoughts on sample
> rate?

GM runs their electronic tachs by pulling a signal from this side of the
coil.  Near the coil they wire a small cylinder.  This device contains
an RC filter feeding a second RC filter.  The output from the second
filter then goes to the IP which contains a series diode feeding yet
another RC filter.  The filter output goes to a voltage divider that
goes to the base of a transistor.  The transistor's E is grounded and C
has a pullup resistor and is where the final tach signal is found.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/


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