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mondshine Samba Member

Joined: October 27, 2006 Posts: 2798 Location: The World's Motor Capital
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Posted: Fri Nov 11, 2022 3:06 pm Post subject: MeterMatch |
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Here is something that I posted on my local VW club's facebook page.
I won't complete this project until next spring, when I fill the Thing's fuel tank with fresh gas, but it might interest some people here.
Yes, he is crazy!
Here’s a little project that I have considered for years.
The non-linear behavior of the fuel gauges on every ACVW that I have ever owned was always mildly annoying, but never enough to make me try to fix it.
I am convinced that this characteristic of the fuel gauge operation is based on the irregular shape of the fuel tank, where the bottom half of the tank holds considerably less volume than the top half.
So, with some time to kill this winter, I took on a project with an electronic device called a MeterMatch.
The MeterMatch interpolates output from resistive senders, and outputs a calibrated resistance averaged between four set points.
To start, I set up a “test rig” with a power supply, a fuel sender from my old 1302, and the fuel gauge from my old 181.
The 1302 sender reads 79Ω with the float at its lowest point, and 9Ω at the upper limit.
I expect to see some variation from these readings when the actual “in the car” sender and gauge are in substituted, but this “test rig” is a good starting point.
The testing went just as expected, so I am ready to do the actual installation.
So anyway, my plan is to do the actual “in the car” installation and calibration next spring, when I am ready to fill the fuel tank with fresh gas.
First, I will drain the fuel tank. My Thing’s fuel tank is said to hold 40L. Making my measurements in metric will keep the arithmetic simple.
Next, I will add measured amounts of fuel for each set point.
My four set points will be 5L, 10L, 20L, and 40L.
I will pour in 5L of fuel, and using the MeterMatch, set the fuel gauge to read “top of the red”.
Then pour in another 5L, and use the MeterMatch to set the fuel gauge to read 1/4 tank.
Another 10L for 1/2 tank, and another 20L for full.
The MeterMatch unit has a provision for a low set point alarm, which I intend to set at 7.5L.
The alarm provision will flash an existing LED indicator already in place on the dashboard.
As an explanation of the wiring diagram…
My Accusump has an additional oil pressure sender which provides a path to ground when engine oil pressure is being provided by the Accusump (rather than by the oil pump). There is also a piezo buzzer which will sound under the same conditions. System voltage is sent to the piezo buzzer through a low voltage cutoff device, so that the buzzer can only sound when the engine is running (and therefor, system voltage is at or above 13.2V). All of this is already in place (before the MeterMatch installation).
The MeterMatch device can be set to provide a pulsing (or steady if desired) path to ground for a low fuel warning light. My intention is to set the MeterMatch device to pulse the Accusump warning light when the fuel level drops to ~7.5L (2 Gal.). The diode will prevent the piezo buzzer from sounding with the "low fuel" warning.
So, in use, when the Accusump warning light is flashing, it indicates low fuel.
When the Accusump warning light is on steady, and the piezo buzzer is sounding, it indicates that engine oil pressure is being provided by the Accusump (rather than by the oil pump).
Just 133 days to go until the first day of spring 2023, and Springtime is Thingtime!
Here's the manufacturer's video:
Link
Good luck, Mondshine |
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Joe 20 Samba Member

Joined: August 27, 2005 Posts: 655 Location: Ohio
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Posted: Fri Nov 11, 2022 8:27 pm Post subject: Re: MeterMatch |
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you're not crazy...just way smarter than me! _________________ "Someday the world is gonna be populated by nothing but Volkswagens'" Corporal Klairvoy |
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Semper_Dad Samba Member

Joined: May 14, 2005 Posts: 3525 Location: Indiana
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KAmes Samba Member

Joined: February 16, 2014 Posts: 896 Location: Illinois
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Posted: Sun Nov 13, 2022 9:15 pm Post subject: Re: MeterMatch |
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And here I've been pondering leaving the fuel gauge out of my dune buggy project altogether.  |
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SilverThing  Samba Member

Joined: July 19, 2004 Posts: 833 Location: Everett
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Posted: Sun Dec 04, 2022 5:27 pm Post subject: Re: MeterMatch |
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I'm interested to see how that works.
My VW gas gauges have generally been pretty accurate in terms of half, quarter, and reserve. I've only had issues with my 1973 Thing when it has suddenly stopped going below half. Both times this happened I ran out of gas on the same block as a gas station, thankfully. _________________ "I like how everyone likes talking about Zeke's Thing yet he's the only one that's ever seen it." - Katie
"I've seen pictures..." - Jeremy |
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mondshine Samba Member

Joined: October 27, 2006 Posts: 2798 Location: The World's Motor Capital
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Posted: Sun Dec 04, 2022 6:41 pm Post subject: Re: MeterMatch |
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As I understand it...
The voltage to the fuel gauge is un-regulated.
System voltage can range from 12.6V with a fully charged battery and engine off, to ~14V with the engine running (depending on other loads; lights, wipers, etc.).
The stock fuel gauge vibrator is not a true voltage regulator, but rather a thermally actuated switching device which toggles system voltage to the gauge on-off-on-off two or three times per second.
So, over time, the average voltage to the gauge is about 5V. Later model (1980’s water cooled) VW’s used a solid state regulator chip to power a very similar type of fuel gauge (and water temp gauge) at 5V.
The gauge itself is also thermally actuated; where a heating element deflects a bi-metallic strip to move the needle.
All of this serves as sort of a damping mechanism so that the gauge needle isn’t flopping around on bumpy roads with a partially filled fuel tank.
On the ground side, the fuel sender provides a path to ground with varying resistance based on the fuel level; from about 80Ω empty to about 10Ω full.
The Ohm readings that I observed from a (1302) fuel sender indicate that over distance of float travel, the resistance is fairly linear, but the float travel in inches does not reflect fuel volume, based on the shape of the fuel tank.
In other words, with an oddly shaped fuel tank, fuel level and fuel volume are not congruous, in that one inch of float travel at the top of the tank might represent two gallons of fuel, but that same inch of float travel at the bottom of the tank might represent less than a gallon.
So, I have good reason to believe that this MeterMatch thing will allow me to calibrate the fuel gauge based on fuel volume, rather than by fuel level.
Meanwhile, I have sketched a revised wiring diagram which includes a 5VDC regulated power supply to the fuel gauge. There's some extra stuff in the diagram, but it should be understandable.
Not much more to add; it will be at least four months until it's time for fresh gas and top-down motoring.
All of this, just to solve a problem which is only mildly annoying, but it's good clean fun. |
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KAmes Samba Member

Joined: February 16, 2014 Posts: 896 Location: Illinois
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Posted: Mon Dec 05, 2022 8:20 am Post subject: Re: MeterMatch |
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So are you planning to use the mentioned later vw 5 volt regulator or something else? Despite my earlier comment I'm also interested in seeing how this turns out, I can think of several uses for such a thing. |
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mondshine Samba Member

Joined: October 27, 2006 Posts: 2798 Location: The World's Motor Capital
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Posted: Mon Dec 05, 2022 8:36 am Post subject: Re: MeterMatch |
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Kevin-
This is the buck converter I intend to use:
https://www.amazon.com/dp/B07P663XJV?psc=1&ref=ppx_yo2ov_dt_b_product_details
It's about the same size as the standard vibrator, and could be mounted on the back of the speedometer case like the original.
I probably could use a smaller capacity converter (it would have been physically smaller too), but this one worked nicely on my "test rig".
These inexpensive buck converters are more efficient than a single regulator chip (like VW used in the '80's), so heat from the chip is not an issue.
Another potentially useful item is the low voltage cutoff gizmo.
This is an easy and inexpensive way to power a device only when the engine is actually running.
Anyway, I will post again when this project is finished. |
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mondshine Samba Member

Joined: October 27, 2006 Posts: 2798 Location: The World's Motor Capital
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Posted: Sat Mar 18, 2023 12:44 pm Post subject: Re: MeterMatch |
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Maybe if I start getting the Thing ready for spring, it will hasten springs arrival
When I started this project this noon, it was 22º outside, and pouring down snow.
Starting with a drained fuel tank, I added measured amounts of gasoline and set the gauge to read "red", 1/4, 1/2, and full.
Anyway, the Meter Match installation is done.
It seems to have worked perfectly, just as it was designed.
My car has an additional LED warning light and piezo buzzer for the Accusump, which I was able to integrate into this electronic marvel; the envy of the civilized world.
Two more sketches:
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germansupplyscott Samba Member

Joined: May 22, 2004 Posts: 7187 Location: toronto
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Posted: Sun Mar 19, 2023 12:28 pm Post subject: Re: MeterMatch |
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Amazing illustrations. The content is, if not over my head, kind of outside of how I'd ever look at any of this stuff, but your ability to explain complicated stuff in a graphic format is really something. Well done and I hope you get all these widgets working exactly how you want them to work. _________________ SL |
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mondshine Samba Member

Joined: October 27, 2006 Posts: 2798 Location: The World's Motor Capital
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Posted: Sun Mar 19, 2023 12:51 pm Post subject: Re: MeterMatch |
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germansupplyscott wrote: |
Amazing illustrations. The content is, if not over my head, kind of outside of how I'd ever look at any of this stuff, but your ability to explain complicated stuff in a graphic format is really something. Well done and I hope you get all these widgets working exactly how you want them to work. |
Thanks for that. I was a photographer/graphic arts guy when I was a working stiff.
I need to do my best to document the modifications I made made to the Thing, especially the electrical system, because by next week, I will have forgotten what I have done; let alone how or why.
Fun stuff! |
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germansupplyscott Samba Member

Joined: May 22, 2004 Posts: 7187 Location: toronto
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Posted: Sun Mar 19, 2023 6:13 pm Post subject: Re: MeterMatch |
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mondshine wrote: |
I was a photographer/graphic arts guy when I was a working stiff.
Fun stuff! |
Not a surprise! I am still a stiff and I also do a fair bit of regular work in Illustrator (which appears to me to be what you're using) but it's all related to my business, not ‘pure’ design if you will. In a previous life I was all day designing, mostly for graphics and print. Before that 3D design. Your skill shows. _________________ SL |
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Semper_Dad Samba Member

Joined: May 14, 2005 Posts: 3525 Location: Indiana
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Posted: Sun Mar 19, 2023 7:15 pm Post subject: Re: MeterMatch |
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mondshine wrote: |
I need to do my best to document the modifications I made made to the Thing, especially the electrical system, because by next week, I will have forgotten what I have done; let alone how or why.
Fun stuff! |
I feel your pain. Sometimes I feel like I can hide my own Easter eggs  _________________ Walküre Restoration Thread: https://www.thesamba.com/vw/forum/viewtopic.php?t=737492 |
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mondshine Samba Member

Joined: October 27, 2006 Posts: 2798 Location: The World's Motor Capital
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Posted: Tue Mar 21, 2023 6:53 am Post subject: Re: MeterMatch |
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Semper_Dad wrote: |
I feel your pain. Sometimes I feel like I can hide my own Easter eggs  |
I love to work on my old VW, but two things I hate are:
Getting up off of the ground.
Putting down a part or tool, and not being able to find it 30 seconds later.
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Deckard Samba Member

Joined: April 07, 2012 Posts: 296 Location: Knoxville, TN
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Posted: Tue Mar 21, 2023 3:36 pm Post subject: Re: MeterMatch |
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I love to work on my old VW, but two things I hate are:
Getting up off of the ground.
Putting down a part or tool, and not being able to find it 30 seconds later.
:?[/quote]
I solved the second problem by laying down a silver tarp every time I work near the car. I also keep small boxes where I put everything I take off.
I can't help you with getting it off the ground, which I've actually enjoyed since I was a skinny kid changing tires on my mom's 1976 Ford LTD, which weighed about 6 tons. |
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Joe 20 Samba Member

Joined: August 27, 2005 Posts: 655 Location: Ohio
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Posted: Tue Mar 21, 2023 7:31 pm Post subject: Re: MeterMatch |
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Deckard....he's talking about getting HIMSELF off the ground!! This gets harder and harder with age. _________________ "Someday the world is gonna be populated by nothing but Volkswagens'" Corporal Klairvoy |
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ST Dog Samba Member
Joined: March 06, 2018 Posts: 81 Location: Rocket City USA
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Posted: Wed Sep 27, 2023 2:27 pm Post subject: Re: MeterMatch |
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mondshine wrote: |
Starting with a drained fuel tank, I added measured amounts of gasoline and set the gauge to read "red", 1/4, 1/2, and full.
Anyway, the Meter Match installation is done.
It seems to have worked perfectly, just as it was designed.
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Nice, but dang that unit ain't cheap. |
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