Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sun-barr!olivea!mintaka!think.com!zaphod.mps.ohio-state.edu!n8emr!colnet!sppy00!jwm
From: jwm@sppy00.UUCP (Jeffrey W. May)
Newsgroups: sci.electronics
Subject: Re: measuring vehicle speed
Keywords: car speed
Message-ID: <1254@sppy00.UUCP>
Date: 20 Jun 91 15:52:21 GMT
References: <31487@hydra.gatech.EDU> <1991Jun18.003032.18571@mulga.cs.mu.OZ.AU> <31529@hydra.gatech.EDU> <1991Jun20.024446.18473@en.ecn.purdue.edu>
Reply-To: jwm@sppy00.UUCP (Jeffrey W. May)
Organization: Online Computer Library Center, Dublin, Ohio.
Lines: 35


Two ideas on this one:

1).  Put a 'mark' (either with white paint, or attach a small magnet) on
the driveshaft and mount a sensor next to it to count the revolutions.
This number could then be scaled with a multiplier circuit, depending on
the tire size and the gearing in the differential, to yield the car speed.
Since the driveshaft-rotation-to-tire-rotation is a fixed proportion this
would give a reasonable result.  Be careful if you do this because the
driveshaft is balanced and if you throw it too far off balance you will
cause excessive wear in the universal joints and seals.

2).  See if one of the electronic speedometer sensors will fit your car.
My car has one of those digital dashboards and I looked up in the technical
manual how the speedometer works.  On the side of the transmision there is
a mount where the speedometer cable bolts in, for the electronic
speedometer there is a sensor that goes there instead.  It has a
gear/fitting similar to a spedometer cable so it will fit right in.  This
sensor does essentially what #1 above does, it monitors the rotation of the
output gears and produces voltage pulses on a wire.  The dashboard
controller has a counter/multiplier that translates this to decimal digits
for display.


You will have to do some road tests and math to figure out what multiplier
values to use for your car.

Hope this spawns some more ideas!

-Jeff
-- 
______________________________________________________________________________
 Jeffrey May             UUCP: jwm@sppy00.UUCP     Internet: jwm@rsch.oclc.org
 OCLC - Online Computer Library Center             
        Dublin, Ohio          "Heavens they're tasty and expeditious."