Re: Different approach to VSS question

[Ludis Langens <ludis@cruzers.com>]

TK wrote:
> 
>What does the ECM expect to see? 0-12V? A zero crossing?

Here's what the "magnetic VSS" interface chip of a P4 ECM expects:

  if ((vsshi > magic) || (vsshi < -magic))
    output = 0;
  else
    output = 1;

The magic constant is something like 0.001 volts.  The above logic
creates a pulse as the VSS signal crosses zero.  This pulse clocks a
toggle type flip flop.  The output of this flip flop is thus the same
frequency as the raw VSS signal.

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


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