cyberdyne speed calibration box

[Joe Boucher]

Andris wrote:
> 
> I'm planning on putting a T-56 tranny into my IROC as part of the twin
> turbo project, and would need to calibrate the VSS signal for my
> speedometer. As far as I know, it works on pulses per mile. I know the
> cyberdyne box lets you adjust this, but costs $100. Is there a circuit
> that I could build that will do this? Thanks everyone :)
> 
> ********************Skulte Performance Designs********************
> Andris Skulte askulte at tufts.edu http://www.eecs.tufts.edu/~askulte
> (617)627-1601   89 IROC M5 305 TPI  320 hp / 470 ft-lbs
> 
> Leave late, drive faster, still get there first. ;)

If there is I'd like to know it also.

I ran into the speedometer wall when I did my conversion on the
Suburban.

VSS signal into the ecu is either 2000 pulses per mile or 4000.  The
trannies with the reluctor wheel and sensor coil are the 4000 and the
trannies that output through a mechanical speedo cable are the basis for
the 2000 pulse systems.  

The speedo system is a led bouncing light off a shiny arm in the back of
the speedometer.  

The 4000 pulse system takes the reluctor and coil ac signal and converts
it to a pulsed or on/off 12 volt DC signal.  One of the sparkies here
said $20 at Rat Shack could buy enough parts to make a circuit to do
that.  But he didn't offer to help.  With forty teeth, that would mean
40 peaks every turn of the tranny output shaft. Right?  Getting from
there to an on/off signal is beyond me.

Joe Boucher
'70 RS/SS Camaro  '81 TBI Suburban