[Vwdiesel] Tach

[HWY9FERGS@cs.com]

In a message dated 9/20/2005 7:58:52 PM Pacific Daylight Time, Roger Brown  
writes: 
> At least on the units I have looked at, the W terminal signal is way to 
> high a frequency to be used to feed a cruise control. 
> They are usually set up with calibrations for differing number of pulses per 
> mile, as from a Vehicle Speed Sensor (VSS).  The 
> one I used went up to about 8000 pulses per mile.  Assuming you are using a 
> 4-cyl gas engine turning about 3000 RPM at 60 MPH, 
> that equates to about 6000 ignition pulses per mile, so using an 
> ignition/tach signal works well, I think I set mine to around 
> 5000-6000/mile.  Problem with the W-terminal input is that is is about 12-13 
> times as fast since the signal is the unfiltered 
> output of the alternator, so you would be getting 70,000-80,000 pulses per 
> mile and I doubt the standard cruise control units 
> could handle that high a frequency without pre-conditioning the signal.  
> Dakota Digital makes a programmable frequency divider 
> that can generate a more "ignition-like" signal, or the optical pickup unit 
> I designed makes an exact "ignition" signal that 
> requires no calibration.  Mine drives my cruise control and the tachometer 
> with no problem.
> 
> -- 
>     Roger

Are the tachs THAT different between the diesels and the gas cars? I didn't 
know.  This list is fantastic.  I learn something new every day. Thanks for the 
clarification.  Ferg