[DeTomaso] Fuel Gage Linearizer

John Taphorn jtaphorn at kingwoodcable.com
Sun Nov 2 08:42:48 EST 2008 

Ed

Several years back, Thomas Tornblom offered his electrical engineering 
expertise to the group with an alternative solution he called his Gauge 
Corrector.

It is an adjustable eeprom to match the sender to any gauge.  If I recall 
correctly, the eeprom can store 10 data points.  Thus, I was able to adjust 
my fuel gauge to read accurately at 1/8th intervals by filling the tank 2.65 
gals at a time and storing the value.  Of course, it assumes that the 
quantity of fuel used between those data points is linear for a given drop 
in the float arm.  However, accuracy at 1/8th intervals is close enough for 
me.  Obviously, if you are using a data point for every gallon verses 2.65 
gals, your approach will be more accurate between my 1/8th data points.

Although a benefit of Tom's eeprom approach is that I was able to calibrate 
it myself and could easily perform the operation again should I change my 
gauges to a set with a different impedance.  I.E. I am currently using it on 
my Auto Meter, but could have used it on my Veglia initially.

I don't know if Thomas is still offering the product.  It was very 
inexpensive and has the JT Seal of Approval.

I am not trying to discourage your idea or willingness to help, simply 
illuminating the possibilities and the contributions of others.

JT


----- Original Message ----- 
From: "Edward A. Nauman" <enauman at roadrunner.com>
To: "Email Forum Pantera" <detomaso at realbig.com>
Sent: Saturday, November 01, 2008 1:56 PM
Subject: [DeTomaso] Fuel Gage Linearizer


> Hi guys,
>
>        I have been away from the list for a while and was searching 
> through
> the archives.  I came across a message about a circuit I designed a couple
> of years ago.  Being an instrumentation engineer for 3 decades, one of my
> pet peeves developed over the years is the non-linearity of automotive 
> fuel
> gages.  The fuel gage in most cars is really a fuel level gage and not a
> fuel quantity gage.  Since the fuel level transducer is usually a 
> wire-wound
> potentiometer actuated by a float at the end of an arm, the potentiometer
> output is proportional to the angle of the float arm which is a sinusoidal
> function.  Most of the automotive fuel level pots I have examined have a
> linear output with respect to rotation angle of the shaft.  So, the fuel
> level with respect to the output of the potentiometer becomes a function 
> of
> the length of the float arm and the sin of it's angle.  In other words the
> measurement, if uncorrected, is non-linear.  This is sometimes corrected 
> for
> by manufacturing a non-linear pot that linearizes the sinusoidal output in
> the range of interest.  Remember, that is for fuel LEVEL.  When you
> translate level into quantity. The shape of the fuel tank becomes the next
> source of non-linearity.  Obviously if you had a cone shaped tank, one 
> inch
> of fuel level near the top is a lot more than quantity 1 inch at the 
> bottom.
> Depending on the irregularity of the cross-sectional area of the tank as 
> the
> fuel level rises, the equation for quantity Vs. level can get quite
> complicated.  The simplest way to correct the situation and still be
> adaptable to different tank shapes and sizes is to use a micro-controller
> and a calibrated look up table to translate the level into actual 
> quantity.
> The design I came up with for my car uses a PIC microcontroller that has 
> on
> board an EEPROM to store the look-up table.  Operationally, the fuel level
> potentiometer is connected to my circuit which reads the resistance and
> "looks up" the correct corresponding fuel quantity. It then drives the 
> gage
> with the correct voltage to indicate the actual quantity.  The setup
> requires calibrating the tank at 1 gallon intervals which means draining 
> the
> tank and filling it one gallon at a time.  Since I was only building one 
> of
> these circuits for myself, I did not write any code to have the micro
> perform the calibration automatically, meaning, that I recorded ADC output
> on my computer, generated the lookup table with Excel and manually entered
> the lookup table into the micro.  I did the same thing for the one I built
> for Chuck Buthala.  But that meant he had to perform the calibration, 
> email
> me the data, and I programmed his look up table and sent the box to him.
>
>        If you guys are interested in something like this, I can do 1 of 2
> things.  I can put together a kit consisting of a PCB and a parts list 
> with
> a schematic and a wiring diagram.  Or, I can build you one and send it to
> you with installation instructions.  But unless you are familiar with PIC
> microcontrollers and own a programmer, you would have to send me the data
> and I would have to program it and send it back to you.  In order for me 
> to
> write the code for an auto calibration routine, I would have to have 
> enough
> commitments to justify the time spent.  Bear in mind, I'm not trying to 
> make
> money here, just offering this to my Pantera brothers if they are
> interested.  If there is enough interest, I will figure out a price based 
> on
> the responses I get.
>
>
>        Cheers,
>
>               Fast Eddie  (#2100)
>
>
> P.S.  If my explanation is either too complicated or too simple, please 
> let
> me know and I will clarify any questions you may have.
>
>
>
>
>
> Edward A. Nauman\
>
> C.E.O.
>
> Smart Litez Inc
>
>
>
> Palmdale, CA. 93551
>
> (661) 305-7636
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>>The circuit was designed by Ed Nauman.  He built one for me and it works
> great.  The gizmo works with a chip which uses the sending unit 
> resistance,
> compares it to a look up table in the memory and >sends the correct signal
> to the gage.  You have to go though a calibration cycle to set it up. 
> There
> is an article in the POCA news about two years ago on the circuit.  Ed if
> your listening I hope my >description is correct.
>
>>"www.ProvaMo.com" <pantera007 at sbcglobal.net
> <http://list.realbig.com/mailman/listinfo/detomaso> > wrote:   It was not
> "Me" Chuck that Ohm'ed, but I did test one gallon at a time, the
>>ohming was, I think, someone in the Nordic region perhaps.
>
>>Chuck
>
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com
> <http://list.realbig.com/mailman/listinfo/detomaso>
> [mailto:detomaso-bounces at realbig.com
> <http://list.realbig.com/mailman/listinfo/detomaso> ]On
> Behalf Of Mark McWhinney
> Sent: Tuesday, July 24, 2007 10:41 AM
> To: 'Garth Rodericks'; detomaso at realbig.com
> <http://list.realbig.com/mailman/listinfo/detomaso>
> Subject: Re: [DeTomaso] Incorrect gas gauge
>
>
> Some of the fancier aftermarket gauges allow for multiple calibration
> points. I think little Larry has that. If he is lurking, may he can fill
> us in.
>
> As I recall, Chuck did the one-gallon at a time work to record the ohm
> readings.
>
>
> -----Original Message-----
> From: detomaso-bounces at realbig.com
> <http://list.realbig.com/mailman/listinfo/detomaso>
> [mailto:detomaso-bounces at realbig.com
> <http://list.realbig.com/mailman/listinfo/detomaso> ] On
> Behalf Of Garth Rodericks
> Sent: Tuesday, July 24, 2007 10:33 AM
> To: detomaso at realbig.com
> <http://list.realbig.com/mailman/listinfo/detomaso>
> Subject: [DeTomaso] Incorrect gas gauge
>
> Just another reference point for the non-calibrated nature of our gas
> gauges.
>
> When mine is full it registers Full.
> 40 miles after fill up it registers at the 3/4 mark, or slightly below.
> But I can drive for quite a long time between 1/2 tank and Empty.
> And, at Empty the warning light comes on.
>
> I have not tested how far I can go after the warning light comes on,
> however the most I've
> been able to add at a fill up was 19.5 gallons.
>
> Now, I recall a year or two back that someone posted that they made a
> simple electronic
> converter to calibrate the fuel gauge. I think they took ohm readings from
> the sender as they
> filled the tank 1 gallon at a time, then created a mapping table to send
> an accurate reading
> to the gauge. Does anyone remember who that was? I recall they were
> planning to make it
> available for sale, but I never saw anything more on it. Does anyone have
> more info? I'd like
> one.
>
> Cheers!
> Garth
> #4033
>
> YMMV,
> Garth
> #4033
>
>
> ---------------------------------
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