Fuel Gauge Redux

Posted: Wed May 11, 2022 3:56 pm

Some time ago I began working on a fuel gauge option to go with my ComboMeter which already includes a voltmeter and optional ammeter and oil temperature displays. (I don't really need a fuel gauge mind you, so don't ask me why I did this. I thought it would be nifty). I now have something I think is ready for primetime.

Initially I didn't think any method of measuring fuel that relied on the height of the fuel in the tank would work very well. The odd shape of the tank meant that there was no simple relationship between the volume of fuel and the height it comes to in the tank. I began working on a method to weigh the tank instead. My plan was to display the results on a 10-segment LED bar-graph more or less in keeping with my ammeter display. I actually came up with a couple of bizarre but elegant sensors that replaced one of the fuel tank mount rubbers. They definitely responded to the weight of the tank, but were too variable, difficult to build and tricky to install.

Thinking about it some more convinced me that since I was considering what was essentially a digital display, I really didn't need a tremendously accurate correlation between the display and the true level of fuel. After all, every automotive fuel gauge I've ever seen shows distinctly non-linear responses such as taking weeks to get down to half a tank and then fuel level plummets over days. Also, I thought that a display showing 10 levels was overkill, and I decided that a smaller display showing approximate 1/4 tank intervals was plenty. That made potential inaccuracies less significant.

Along about this time another member indicated he was working along the same lines and had already developed a pressure sensor based fuel gauge, so I stopped work on my project to get out of his way. But not having heard anything new on his work for two years, I resumed my efforts. Here's what I came up with:

This is a pressure sensor that plumbs into the fuel line using a tee provided in the kit. It is therefore very reversible and makes it easy to transfer the unit to a different bike. For the display, I decided on a 4-segment green LED bar-graph. It displays:
4 bars when there are 4 or more gallons in the tank,
3 bars with more than 3 (but less than 4),
2 bars with more than 2 (but less than 3),
1 bar with more than 1 (but less than 2),
1 blinking bar with less than 1 gallon which is about when you would be switching to reserve.

This kit is an add-on to my ComboMeter, but I could consider making it a standalone item.

I chose to install my display inside my instrument cluster just between the neutral light and the ammeter display:

So now I can use my trip odometer for something other than a fuel gauge like maybe showing trip mileage?! What a concept.

Posted: Thu May 12, 2022 10:18 am

Nice work Peter! Your ingenuity is impressive!

Cheers!
Chris