When cleaning out my fuel tanks before starting putting Thunder Bird (26' Overnighter) back together a couple of years back I came up with the idea of doing away with those Rochester manual read gauges and wanted to get something on the dash so I could better monitor my fuel. I became intrigued with the gauge itself and how it allowed for a completely sealed gauge by using a little magnet inside the tank that would rotate with the fuel floats position. The manual gauge itself that was on the ouside of the tank just above the magnet was nothing more than a cheap compass indicating F & E instead of NSEW.

After scratching my head for a bit I thought of these field effect compasses you find in just about every vechicle now-a-days. So I found a Dinsmore Sensor for doing just that. It provided 4 outputs indicating N, E, S, & W. NE, SE, SW, and NW could be interpeted when two sensors outputs were on simutaniously.

I guess I could have been content just wiring up 4 LED's and interpeting how much fuel was in my tanks BUT how would I tell which LED's were being lit at night if all the others were off? So I determined to make a bar graph display with 8 LED's indicating the magnets position with the bottom 2 being red, middle, 3 yellow and the top 3 green. As I have had some expirence with logic circuits I set out to design a system that would light the bottom 2 red LED's when compass sensor reads west, then light the 2 reds and 3 yellows when the magnet is pointing SE relative to the sensor, and all LED's when magnet is pointing N. So N would indicate full, S would be a 1/2 tank and so forth.

Anyway I will attach my logic diagrams and pictures of what I have so far. The N,E,S,W are the outputs from the compass sensor, triangles reverse the logic and would make a +5volt 0 and 0 +5 volts. The other two type of gates I used are AND and OR. OR gates have the arc and AND gate a straight line for their base. AND gates need both inputs to be positive before the output goes positive, with an OR gate either input being positive will produce a positive output.

I should be able to pull this off with 4 logic chips, 8 LED's, a driver for the LED's and the compass sensor. We will see.

No can find "Button" gauge at boatfix.com

Do you have more info?\

Found it Moeller part # MOE 03576010 $66.67
Dam...Rochester want $300 something for theirs.

Thanks

Went to order it and their price was $44 each! Alot better than $300

centroid products makes a nice digital gauge with features that are not necessary on a Marinette, since the tanks are rectangular. Still, they make a nice capacitive sender that I have had good luck with.

Years ago I manufactured stuff for the electroplating industry. One of the most popular items was simply a vertical plastic pipe with a series of reed switches inside. Around the pipe was a floating "donut" with a magnet in it. It closed the switches as it floated up and down with the fluid level. You could put in a switch for every 10 gallons, perhaps. We had a panel with a series of lights (no leds then) in different colors - red for low level, green for OK, and so on. Easy to build and profitable, those were the days.

I made one once with a resistor array and reed switches that worked with a standard automotive gauge, not digital.

My experience with boats leads me to avoid electronic stuff over reliability concerns. The some old airplanes had a clear tube sticking down below the wing, housing a rod with a float at the top and a red ball at the bottom. A glance out the window told you how long you'd be flying. I miss that.

Hi Joe,

I couldn't view your diagram for some reason but I just thought I'd mention that you could replace the 4 logic chips with a cheap PLD (programmable logic device - a couple of bucks max. I think it is likely that you'll need (or do better with) an LED driver chip whether you use the programmable choice or not. If needed, I could write a simple little program for the chip and program it for you.

With either the discrete logic approach or the programmable logic approach, removing power to the circuit will not be a problem. Having 2 bargraphs active at the same time could be an issue unless provisions were made for it. To deal with that, you could have a switch at each station to turn it on there and off at the other station - similar for port/stbd tank. I would recommend "active low" logic where a logic zero from the gate turns the LED on.

Having said all of that, if my guage no longer worked, I think my preferred approach would be to replace the sender or the guage.

QUESTION: I only have fuel guages at my lower station which is a bit of a problem since I ONLY pilot from the upper station. Does anyone know if I would need to do anything special if I were to add a second guage at the upper station? Logic tells me the second guage would change the reading unless some adjustment were made but .....

The centroid products capacitive senders that I use are only around 50-60 bux, it's been a while since I bought one, but they are very slick and seem to be reliable. I know that we fool with our boats for FUN, so go at it with the electronics, sounds neat.

A sender will drive two gauges, simply connect the "S" terminal of both gauges to the sender. However, the gauges will read half when the tank is full. To get it to work correctly, you will need a sender designed to work with two gauges.