Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!wuarchive!rex!ukma!tindle
From: tindle@ms.uky.edu (Ken Tindle)
Newsgroups: sci.electronics
Subject: Re: Digital dash (was: Inductive pickups.)
Message-ID: <1991May31.143333.16729@ms.uky.edu>
Date: 31 May 91 14:33:33 GMT
References: <1970@ole.UUCP> <1991May30.151040.50@cmkrnl.uucp>
Organization: University Of Kentucky, Dept. of Math Sciences
Lines: 49

In article <12974@mentor.cc.purdue.edu>, wilker@gauss.math.purdue.edu
(Clarence Wilkerson) writes:
}I used to have an add-on cruise control for a Plymouth.
}The pickup was activated by 2 small magnets taped and glued
}to the drive shaft, fairly near the transmission. The weight
}was small, and fairly balanced anyway.

In article <54642@rphroy.UUCP>, vbreault@gmr.com (Val Breault) writes:

}There's a lot of stuff happening under your car.  Stones, water, vibration,
}dust. Then too, the driveshaft will wobble several thousandths on it's spline.
}Rather than attempt to make something that will work in that rather hostile
}environment, why not try this idea?
 
}In the days before automotive computerization, a cruise control setup 
}consisted of a mechanical device that was attached via flexible cable
}between the transmission and speedometer.  You should be able to get one
}of these pretty cheap at a nearby junk yard (oops, 'Automotive Recycler').

An interesting idea- how did this mechanical setup work?

It seems to me that an encoder wheel attached to the speedometer cable, with
an interrupter IR diode/ phototransistor pair is the way to go.  You have to
rig the cable drive to pass through, since it is illegal under Federal law to
disable the odometer on purpose.  This has the benefit of being more universal
as well, since one can find the speedometer cable on older cars without too
much hassle (fiddling with it in such a way that it doesn't break in two later
is the hard part).

This will get you away from the driveshaft, and provide pulses you can count
in a digital circuit.  With these pulses, you can use the circuit provided
by Dakota Digital in Radio-Electronics.  That speedometer circuit also has a
twenty-step LED bar driven from two LM3914N's for an "analog" display, acknow-
ledging the need for such.  You have to change their input conditioning stage,
since they use an inductive driveshaft sensor.  

It's interesting to note that most aftermarket cruise controls now use a 
connection to the ignition system instead of the driveshaft, which works IF
you don't have an "overdrive" transmission and this transmission is in its
highest gear (1:1) all the time the cruise is on.

So, can one of these older in-line mechanical devices be made to output a
pulse train?

--------------------------\ /-----------------------------------------------
INTERNET:tindle@ms.uky.edu | "Could you please continue the petty bickering?
BITNET: tindle@ukma.bitnet |  I find it most intriguing."   ---    Data, 
Ken Tindle - Lexington, KY |  Star Trek, The Next Generation, "Haven"
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