Progress1: Software Dyno

[Bartz, Jamison]

What does the VSS signal look like?  If you are sampling through the
parallel port and your software isnt too complex, you shouldn't have a
problem capturing each pulse. Depending on the format of the VSS signal, you
could possibly be able to just use a comparator to adjust the voltages and
do the timing stuff in your program, or if you want to be able to read in a
value, a freq to volt converter will do the work in hardware.

As far as the parallel port's sampling rate goes, the bus behind it inside
your box usually runs at 8Mhz.  Newer boxes may have that changed.  If you
read a sample on every clock you get a sample time of 125 nanoseconds.  Your
software could hinder you from sampling every clock.  It depends on the
complexity (and possibly language) of your software.  If the VSS sender
spits out 2002 pulses every mile then at 100mph you get roughly 56 pulses
per second.  In computer terms, this is an eternity.  You should have no
problem catching every one of them.

-----Original Message-----
From: Dave Zug [mailto:dzug at delanet.com]
Sent: Friday, August 20, 1999 8:54 AM
To: gmecm at efi332.eng.ohio-state.edu
Subject: Progress1: Software Dyno


Okay I've been working and I have the software reading the parallel 
port bits directly and logging them. I'm not sure of how quick the 
sample rate is.. still a test to do. What I need now is a very simple 
circuit to turn vss into what the parallel port considers a 0 and 1. 

another circuit could turn ABS signal or even the spikes from 
the ground noise from the distrib (another responder idea) into 
parallel voltage transitions it does not matter to the software. 1 
setting maybe.

If a more complex circuit is used.. all 8 bits can be read 
representing the number of transitions sensed in a 0.1 second period 
or something (the basis for this idea is from one of the responces-- 
thanks). 

I think "simple" is a good way to start.. if the electronics portion 
can be left simple and very cheap all the better IMO.

The circuit can be made more complex later.. my goal is to see data 
with the PC as simply as possible as a first step

more to come.
~~~
Dave Z. www.delanet.com/~tgp