digifiz thoughts

[flaatr@yahoo.com (Euroroc II)]

It can be done... the speed sensor that bolts up to the tranny produces a 
pulse train whose rate corresponds to the speed of the vehicle. The Digifiz 
receives those pulses and counts them vs. time to determine the speed in 
KM/Hr. Since speed in KM and Miles is a simple ratio and zero is zero the 
simplest way to do this is to build a small box that receives the pulses 
from the speed sensor, processes them and outputs pulses at a different 
rate, a rate that corresponds to MPH.

Not putting a lot of thought in it I come up with this idea if speed is 
determined by pulse frequency. It a two part conversion. First take the 
input signal and ignoring the pulse width do a frequency to voltage 
conversion. now take that voltage thru an amplifier with variable gain and 
run the converted voltage into a voltage to frequency converter. You may 
need to use a PWM here instead but I don't know since I have never seen the 
signals... I'm only guessing. Adjusting the gain and possibly the offset 
you should be able to calibrate the display to show MPH.

Now if the Digifiz measures pulse widths for speed, which I seriously doubt 
but is possible, you could do the same thing but you would have to do a PW 
to voltage conversion and defiantly use a PWM at the output.

It really isn't as hard as I made it sound... you are talking about 3 IC 
and a handful of resistors and a potentiometer. All of the parts can be 
purchased thru Jamaco or Digikey or any other on-line electronics parts house.

I'll add this to my list of projects...

-Raffi

At 05:07 PM 3/13/2003 -0500, you wrote:
>In the last year that I've been on the list, I've noticed that we have
>some very skilled people assembled here.  One of the things thaty throws
>me on the digifiz is that it's that the odometer and speedo are in KM.
>Do we have anyone on the list that could re-program the eprom (if it
>uses one) or make some circuit adjustments so that it reads in american
>measurments for some of us dumb folks that hate doing concersions on the
>fly while looking in the rear mirror to see if that cop is going to come
>after us or not?
>
>I'fve often thought about doing the digifiz conversion, I love the way
>it looks, but so far, cost and the metric system have kept me at bay.
>
>So what do we have, anyone that knows enough about it to where they
>could change it?  Or anyone that if they could look at one long enough
>that might be able to make the adjustments?
>
>
>Just thought I'd ask,
>William
>--
>http://www.techography.com/scirocco (s.org forums)
>http://www.techography.net:82/scirocco  (my rocco's site)
>
>88' Scirocco 16v (Crabby 16v)
>89' Cabriolet 8v (pretty bunneh)
>71' Karmann Ghia (air sucker)
>
>
>_______________________________________________
>Scirocco-l mailing list
>Scirocco-l@scirocco.org
>http://neubayern.net/mailman/listinfo/scirocco-l