DIY LED/Digital Fuel gauge

My bike is a 650 maxim which I am putting a 750 tank on. I wanted to make use of the fuel sender but not add another gauge so I did some research.

I found this website: http://www.mez.co.uk/ms13.html and found a schematic for an 8 LED fuel gauge using simple components. I decided 8 LED's is overkill for my bike. 4 is more than enough for an approximately 5 gallon tank. One light goes out for each gallon gone is the plan. I chose 3 green and 1 red LED. I plan to mount them in the face of my tach though they could be mounted anywhere.

I cut one of the comparitors out and reworked the schematic:



I ordered all the parts:



First step for me, I laid it out on a breadboard:



Then determined my sender was bad. It had no reading. I checked it over and over. Cleaned it several times. Unwound it and found the wire was bad. Then found this on Summit. The working end of it fits almost perfectly on the original sender which will have it's resistor portion cut off. The tank mounting plate will remain the Maxim original.



Then alot of soldering later it's on the board:



The wires on the right run off to a 12V source, the sender, a ground, and the 4 LED's. I plan to hook it up to the tail light circuit since the box will be under the seat next to the fuse box and my tail/brake/blinker box when I get it on the bike. This will also let it come on with just the key on. The LED's can be powered from inside the gauges with the gauge lights.

The gauge is completely adjustable to any fuel levels you want and any size tank. Basically, pour in the amount of fuel you want to have the first LED come on at and adjust the multiturn resistor to make it come on. Then repeat until all your LED's are lit. I set mine on the bench so far since I need to paint my tank. I set each for 1/4 of the sender travel. It'll be close and I'll adjust as I fuel up the first time.

Hopefully this helps someone else with a fuel gauge. If you want better quality schematics I have PDF's I can e-mail just shoot me a PM.

 

Well done, it would be good to see a surface mount version - there are some
generic SMT boards similar to veroboard. Would be a nice small solution.

I noticed in your original diagram you have treated the sender as a 3 wire potentiometer. You may want to update the diagram to reflect the fact it only has 2.

 

Good catch on that. I'll get it fixed and update the diagram. The power goes through the 200 ohm resistor then the sender wire is connected then to the comparitor. It creates a voltage divider.

I was hoping to get this all on half of that board. It's just not big enough. This way it's still about the same size as the aftermarket 6 fuse box I have.

 

So how did you mount the LED's?

Also, related to This Post About Fuel Tanks I was wondering if and how this could be adapted to activate a relay to turn a fuel pump on and off.

Thanks and I'll take my answer off the air.

 

I opened my tach and drilled, carefully, thought the face for the 4 LEDS across the bottom. Though I've now changed gauges, again. Because I can't seem to decide what I like best and haven't remounted the LEDs.

It cuts the ground for each LED below a certain (variable based on the resistors) voltage. You could tap the wire coming to the board from the LED for a duble pull single throw relay and then wire it so your pump would come on when that LED goes out.

Third LED goes out, pump comes on.

 

Can you please send me the better schematics? I think I might try something like this. I would love to do lots of neat electrical work on my bike, but lack a lot of knowledge. Fortunately, I work with a bunch of electricians.

I probably won't every add a supplemental tank like that, but I like knowing that it can be done!

 

sure thing. Shoot me a pm or e-mail with your address and I'll dig them up. I don't remember if it got updated as pointed out above.

 

pm sent, thanks!

 

Should be in you email box.

 

hey can you do me a favour and post the schematics of 8led version i seem to have problem understanding the other guys schematic

 

The 8 LED gauge is linked in my original post.

8 LED's would just be double my schematic.

 

I have been thinking about going to a 750 tank for my bike also. It sure would be good to take advantage of the sending unit. Do you happen to have any pictures of your tach with the led's in it? I might want to do this also. Thanks

 

I don't have that tach anymore. So no pics.

 

I have a 96 xj600S would this work on my bike? I don't think my take as a sender. Would it be hard to install one?

 

With a fuel level sender it would work on any bike, car, plane or boat.

If you don't have a sender you would have to cut your tank to install one. Depening on your tanks shape, the sender you choose and your skill level that could be easy or not.

 

Hi,

Would you be able to send me the better drawings as i want to put this onto a PCB.

Thanks

 

That's awesome. Something I definitely have to do for my koso kit.

 

new link for led fuel guage
http://www.mez.co.uk/ms13-new.html