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References: <3DE1426C.4FFE@the-zoo.com> <3DE3397F.953DD657@chariot.net.au> <3DF5DFB0.C7734F12@one.home>
Subject: Re: Electronic Auto Dashboard
X-Newsreader: Microsoft Outlook Express 5.50.4133.2400
NNTP-Posting-Date: Thu, 12 Dec 2002 03:16:36 EST
Organization: Prodigy Internet http://www.prodigy.com
Date: Thu, 12 Dec 2002 08:16:36 GMT
"Ed Price" wrote in message
> "Bob" wrote in message news:3DF5DFB0.C7734F12@one.home...
> > I have some old (early '80s) Radio Electronics magazines with
> > construction articles including schematics and PC boards for
> > speedo, tach and other basic dash instruments. If there's
> > interest, I'll scan and post them. (reply here)
> > -Bob Emery
> Well, the basic instruments are fairly straight forward. Did those speedo
> circuits allow for calibration to a measured mile? And how did they approach
> the odometer design? In that case, I would really like to see the circuits.
The speedo and tach had both bargraph and numeric readouts. The pulses provided
by the sensors are conditioned and then divided by a DIP switch progammed
counter. The article incleded a formula to calculate DIP switch settings, which
alter the timebase of the display counter, so that it counts to the appropriate
number based on your timebase setting. (hope that makes sense). The tach section
just has a 4/6/8 cylinder switch to set it's counter's timebase. The bargraphs
were driven by the original pulse train passed thru F-V convertors into
LM2917(memory?) bargraph drivers. (I used 3 for the speedo, 2 for the tach)
The formula called for parameters including tire diameter and gear ratio if
necessary (depends where the sensors are placed). I planned to measure the tire
by pouring some flour on the ground, driving over it and measuring the distance
between spots, but never made it that far.
The odometer was not approached at all, as in the U.S. (AFAIK, all states) it is
illegal to tamper with the OEM odometer. I planned to leave the original up in
the trunk of the car (remember, old VW beetle) and had an 8 digit LED calculator
display in the center of my cluster, which I had a counter 'designed' for but
never even prototyped. Nowadays I have some old 8-bit computers which might
simplify the design. (Even a Vic-20 could do that job!)
I'll go dig the mags up and post a link when I can.
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