Mez Forums

Eliot · Posted: Fri Oct 27, 2006 10:08 am Post subject: New Dakar Fuel tank

Finally got my fuel tank made, it was done by allyfab.

Interestingly, even he had problems with warpage - which makes me feel better.
Larger photos:
www.mez.co.uk/ms13.html
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Eliot
www.mez.co.uk

mevrocket · Honda C90 Joined: 16 Jun 2007 Posts: 4

hello there.
ive just been searching the web for a led fuel guage for my kit car and came across your petrol tank build.
i love the idea of the led guage you have built and i would like to build one for my own kit.
i dont think i would have a problem building one although not from the schematic you have posted ( im not quite that much of a electronic wizard)
do you have any more detailed wiring schematic with a parts list that i could use.
cheers in advance

and if you want to check out my build you can find it here www.mevrocket.talktalk.net alothough updating the site has been a little slow at the minute ( i would give yourself and this site full credit for the help)

paul

Eliot · Posted: Thu Jun 21, 2007 5:51 pm Post subject:

Hi,

It uses two LM339 quad compator's. They are simple devices that give a postive output if the two inputs are the same or more.

So, the fuel gauge forms a simple voltage divider - as the arm moves up and down, the voltage varies accordingly - that voltage is fed into all 8 negative sides of the comparitor.

We then setup a further 8 voltage dividers using 8 "trimpots" - varible resistors - by twiddling the pot you very the voltage.

So all you do then is fill the tank up 1 gallon (or whatever division you want) and twiddle the pot until the first led comes on, then put another gallon in and twiddle the next one - so on and so forth.

my tank holds 16 gallons, so each led is 2 gallons - you can add or reduce the number accordingly.

the datasheet and pinout the the LM339 can be found here:
http://www.national.com/pf/LM/LM339.html

The parts are from maplin:
D220R 2W Res 220R £0.18

UH31J LM339N 0.69

UK15R LED Clip Concave 5mm £3.60

WL27E 5mm Red LED £0.34

WL28F 5mm Green LED £1.02

WL29G 5mm Orange LED £0.17

WR49D 18-Turn Cermet 10k £6.77

You may need to adjust the value of the 220 ohm resistor that goes to the level sender - it depends on the resistance of the actual sender. You could just by a few of the 220ohm ones and experiment with series and paralel to get the desired voltage swing.

hope that helps,
Eliot.
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Eliot
www.mez.co.uk

mevrocket · Honda C90 Joined: 16 Jun 2007 Posts: 4

hi eliot thanks for the fast reply..
i think it helps a lot ...but this is my first electronic project ever so please bear with me...

i think i may have decifered the plan with your help could you have a read and tell me if im on the right lines..

1. using the Lm339 i connect all the negative inputs to the positive side of the fuel sender

2. then i connect the Positive inputs of the lm339 to each seperate comparitor

3. the comparitors are connected to the positive supply and ground acordingly

4. and the outputs of the lm339 are connected the the leds then to the positive supply

5. there is a 220 ohm resistor between the 12v supply and the fuel guage

6. this only leaves the ground and voltage connectors on the lm339.. do these need to be wired tho the supply and ground respectively or are the left unconnected

just one more thing.. in your schematic there is a 1k resistor between the lm339 and the LED.. is this an extra component or is it part of the lm339 ...

thank again

paul

Eliot · Posted: Fri Jun 22, 2007 9:58 pm Post subject:

Nearly..
You connect all the postive sides of the comparitors to the fuel sender.
Each negative side goes to each trimpot. Trimpot has three legs, middle leg is the "wiper" which leads to the comparitor.

> this only leaves the ground and voltage connectors on the lm339.. do these need to be wired tho the supply and ground respectively or are the left unconnected

Indeed, I didn't show them as wired. You must connect these to 12v and Gnd respectivley.

>just one more thing.. in your schematic there is a 1k resistor between the lm339 and the LED.. is this an extra component or is it part of the lm339 ...

Well spotted- thats an external component - it limits the current through the LED. An led is effectivey a short circuit - putting a voltage straight through it would burn it out in seconds.You can buy led's with internal current limit resistors, if so - you can omit the external one.
Its missing from my parts list, the maplin part number is M1K

Perhaps get yourself a breadboard from maplins, it allows you to build the whole circuit without even turning a soldering iron on - just press the components in. (thats how i built the prototype)
http://www.maplin.co.uk/Search.aspx?criteria=breadboard&source=15&SD=Y
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Eliot
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mevrocket · Honda C90 Joined: 16 Jun 2007 Posts: 4

thanks for the reply again..
i think i have it now..
spent a few hours planning the circuit on paper to use a strip board.. but i will take your advice and build it first using the breadboard..im off to maplins today to buy the stuff.

ive just measured the resistance of the fuel sender and it is 25 ohms with a full tank and 250 ohms when the sedenr reads empty.. i have no idea if this makes a difference.. i will just wait til i can test it...

i will let you know how i get on later in the week..paul

Eliot · Posted: Sun Jul 01, 2007 8:08 pm Post subject:

mevrocket · Honda C90 Joined: 16 Jun 2007 Posts: 4

finaly sorted.
didnt buy the breadboard. i just thought i would build it to the plans a drew. soldered everthing on as is i expected it didnt work.

i left this project for a few weeks as i had other stuff to be getting on with
though last night i had an easy time on night shift last night so i decided to sort out the guage.

desoldered all the components and used a new board. this time i decided to ditch the drawing as i have looked at the schematic and component sheets so much thy were burnt into my brain.
and my new plan was to solder the chip in and build up the rest of the circuit one LED at a time. testing as i went.
this method worked a treat.
only decided to use 4 LEDs as the tank only holds 6.5 gallons. hopefully i should be fitting the modified fuel pump and sender to the tank tonight.

not sure how to attach pics so the link is here
http://www.picturehosting.com/images/paulhaze/22july07015.jpg

thanks for your help Eliot

Paul

Eliot · Posted: Mon Jul 23, 2007 9:19 pm Post subject:

good-o, glad it worked out for you!
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Eliot
www.mez.co.uk

archebald23 · Honda C90 Joined: 17 Dec 2009 Posts: 1

nice Fuel Tank, what was it made of? and how much? Im planning on ordering a custom made Fuel Tank myself to fit in my car modification.

Eliot · Posted: Thu Dec 17, 2009 6:32 am Post subject:

HI,
Tank is sheet aluminium. It was made by Ally Fab and cost about £150
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Eliot
www.mez.co.uk