MikeR
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| posted on 25/9/05 at 02:25 PM |
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Budget Fuel Gauge idea
For ages i've been looking at a set of gauges and not buying them cause they don't have a fuel gauge. then i had this idea ........
Fuel gauge sender is based on resistance, has anyone got a simple wiring diagram on how i can get 10 leds to light up at different resistances (and
set each light to a fixed value).
Thinking of making a line of LED's to go under my bright 6 to indicate fuel level.
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rayward
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| posted on 25/9/05 at 03:00 PM |
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i will have a look at work, see what i can knock up, do you know the resistances of your fuel gauge sender(or a standard one) at full and empty?.
Ray
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MonkeyHunter
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| posted on 25/9/05 at 03:19 PM |
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Hi MikeR,
Sounds like you want a LM3916 LINK
should do what you want with minimum fuss, free smaples as well 
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rayward
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| posted on 25/9/05 at 04:08 PM |
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thats what i was thinking, would also possibly give the option of having LED flashing when fuel is low/near empty.
we use these at work, so will have a play, may even be able to knock up some PCB's
Ray
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MikeR
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| posted on 25/9/05 at 05:24 PM |
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seem to remember you can buy flashing LED's thought i'd just get the last one as a flasher.
As for resistance - not off the top of my head. Planning on using two gauges so depending on price it would be two gauges or adjustable.
The first is a standard ford one, the second a standard MGF one for when i go fuel injected. Seem to remember the MGF one was something like 5 to 105
ohms (can't remember which was full / empty tho)
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wilkingj
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| posted on 25/9/05 at 07:30 PM |
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Please be very very careful here... You are designing an electrical device that is NOT SEALED, and are dropping it into a tank full of Petrol or worse
still a nearly empty tank of fumes and some petrol.
What ever you do... just make sure you do it right.
Worst case you could do a good imitation of a Terrorist Attack without a Target
I have seen quite a few inexperienced postings in the Electrical section, and a few equally ill-informed replies.
Electrics on a car is an area where a lot of people do not properly understand the subject or the effects of getting it wrong.
A Car fire is one thing,, but Starting it in the Fuel Tank is another.
You are taking an unusual step of designing a fuel gauge.. no problem there... but the consequences of getting it wrong are Life threatening, are
worse. ie a Major Burns to your soft tissues.
Just make sure you get it 110% right.
I dont want to read about you being in a hospital burns unit with half your skin missing, and your hands tied up in those Roasta bag things.
Signed:
Scared of Cambridge (Scared for you)
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skydivepaul
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| posted on 25/9/05 at 08:20 PM |
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Monkeyhunter..
That is the funniest avatar I have seen, especially when is eyeball is flailing around before it snaps off the cord..........fantastic
Where'd you get it?
Paul
http://www.smartideasuk.com
http://www.smartmapping.co.uk
HD CCTV
3D design solutions and integration
IP security systems
access control systems
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rayward
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| posted on 25/9/05 at 08:45 PM |
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wilkingj, i think you've misunderstood, we are not designing a fuel sender unit, only the gauge(which will be sat in the dash well away from
any source of fuel)
the piece sat in the tank, will be a standard fuel sander, be it from donor car or new.
Ray
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MikeR
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| posted on 26/9/05 at 07:46 AM |
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yep - totally correct, this is the fuel gauge that connects to the signal the standard car sender is giving us.
As a side point, my mate who does Fuel Injection systems for a living (BMW / Toyota / ROVER etc) still thinks i'm going to burn with a standard
locost as we don't go through 10% of the hoops he has to.
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Kissy
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| posted on 26/9/05 at 10:08 AM |
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I have a piece of translucent green tube connecting between two outlets on the tank, one top, one bottom. Seems to work ok
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MonkeyHunter
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| posted on 26/9/05 at 10:15 AM |
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quote:
Originally posted by skydivepaul
Monkeyhunter..
That is the funniest avatar I have seen, especially when is eyeball is flailing around before it snaps off the cord..........fantastic
Where'd you get it?
Paul
Hi Paul,
Glad you find it amusing, it was on an email i got sent, im not sure of the original source.
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smart51
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| posted on 26/9/05 at 11:10 AM |
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You only want the last LED to flash if it's the only one lit. It will get annoying otherwise. Use a minature adjustable pot on your PCB to
trim the "full" level light on your display. Easier than using fixed resistors.
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Peteff
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| posted on 26/9/05 at 02:18 PM |
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That is the funniest avatar I have seen.
You'll like happy tree friends and
joe cartoon then. Itchy and Scratchy for real people.
National want 10 dollars for the free sample . Anybody else find this contradictory?
[Edited on 27/9/05 by Peteff]
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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MikeR
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| posted on 27/9/05 at 09:36 AM |
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National want 10 dollars for the free sample of the little bit of electronics. I've got no issue with paying the money but can smoeone confirm,
does the chip take volts or resistance as its trigger signal & how do i adjust the signal to fit into my range?
(i last did electronics as a 1/3rd of a GCSE 17 years ago)
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rayward
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| posted on 27/9/05 at 01:24 PM |
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had a quick look at it last night, an LM3914 would be better suited, as it has hysterisis functions(will stop the lights going up and down as the fuel
sloshes about in the tank), you will also need a voltage reulator(LM317 or the like) to make sure theres no fulctuation in supply voltage, the LM3914
can work from a 0 to 5v input, so it sjust a case of some fiddling with resistors to adapt the output from your sender.
Ray
[Edited on 27/9/05 by rayward]
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wilkingj
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| posted on 27/9/05 at 07:45 PM |
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quote:
Originally posted by rayward
wilkingj, i think you've misunderstood, we are not designing a fuel sender unit, only the gauge(which will be sat in the dash well away from
any source of fuel)
the piece sat in the tank, will be a standard fuel sander, be it from donor car or new.
Ray
Ray,
I have understood perfectly what you are proposing. Namely a redesign the gauge end of the fuel level circuit.
The design of your gauge needs to be very carefully considered. The Tank unit is basically a variable resistor. IF you make a gauge that has a
different resistance to the original design, you could increase the voltage (subject to a max of the cars system) across the variable resistor in the
tank. It could then spark and thus cause a fire / explosion.
Using the Std tank sender is fine.
You say above you are only changing the Gauge end... BUT you will almost certainly end up changing the current and voltage distribution in the WHOLE
circuit. This is the danger area. You cannot change one part of a circuit without it having an effect on the other part (electrically speaking).
Effectively you have two resistors in series (gauge and sender) with 12V applied across the circuit. Altering ONE (Gauge end) will alter the current
in the circuit AND thus voltage distribution across the two parts of the circuit.
If you understand Ohms law and resistors in series and parallel you can work it all out, and understand what I am trying to say.
My main concern, is simply if you get it wrong, you could be putting your life and others at risk. This especially the case with electrical and wiring
functions on cars. You are adding petrol to the equasion which makes it especially dangerous.
Please Take care. If you do not understand what I have said above. I seriously recomend you consult a Qualified Auto Electrician, or better still an
Electronics Engineer (due to your redesign).
I can see the possibility of danger as plain as day. I am not so sure you can see it too.
No offence intended, but this is a dangerous area to play with if you do not fully inderstand it. Please take care.
Best Regards
Geoff
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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MikeR
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| posted on 27/9/05 at 07:57 PM |
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Point made very loud and clearly now ........ thanks 
What ever is designed will be pushed past my mate (who i've probably bored everyone to death saying designs fuel tanks / pumps / lines for a
living)
As you seem to know something about this, how do third party gauge manufactures get away with this? They can't know what level sender is going
to be used.
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iank
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| posted on 27/9/05 at 08:58 PM |
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The key to safety is NOT passing a big current through the fuel sensor, ie. make the guage high impedance.
There is some information here:
http://www.westol.com/~beaurega/gas.htm
Under "How the simple circuit works."
Be careful !
As for LED dash displays I really like the one on 'Bob C's locost which does fuel on a bargraph amongst everything else:
http://freespace.virgin.net/bob.carter/locost_build.htm
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wilkingj
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| posted on 27/9/05 at 09:31 PM |
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quote:
Originally posted by iank
The key to safety is NOT passing a big current through the fuel sensor, ie. make the guage high impedance.
Absolutely... Too much current could heat the sender...
But also to make it so you NEVER get a high voltage across the sender thus avoiding sparks which are just as dangerous.
I was not trying to upset anyone... just trying to make you think it through, and above all to be safe..
Which is one of the Main points of the Forum... Its dead easy to do it dangerously, eg not using hi-tensile bolts on stressed components like
suspension etc. We are all here to help and to learn from each other.
Good luck with it.
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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wilkingj
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| posted on 27/9/05 at 09:42 PM |
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quote:
Originally posted by MikeR
Point made very loud and clearly now ........ thanks
How do third party gauge manufactures get away with this? They can't know what level sender is going to be used.
I know what I mean, but am not always best at putting it down in writing!
I believe there are standards / guides.
Like a lot of senders are 30-180 ohms, and the USA ones are 180-30 Ohms.. simmilar but different.
I dont really know the exact answer, but you can bet that there are UK or EU standards at work behind almost every aspect of a vehicle.
Just as we have to adhere to the SVA Manual. Large Companies, do exactly the same, but probably on a slightly different basis.
They have professional designers etc, we arent in the same league, hence the SVA manual / test to ensure our builds meet a minimum safety spec.
Personally speaking you can never be too safe.. especially on the roads.
lets face it... none of us want to smash up our builds especially after working so hard to get them built and on the road.
Thats why this Website is SO important, and so very useful. for all of us. We ALL bring different skills, and experience(s).
If you boiled us down into One person... you would be a Chief Designer / Engineer / Production Manager all rolled into one!
1. The point of a journey is not to arrive.
2. Never take life seriously. Nobody gets out alive anyway.
Best Regards
Geoff
http://www.v8viento.co.uk
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rayward
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| posted on 27/9/05 at 10:54 PM |
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OK,
just a bit of background info,
I am a time served electrical technician, have ONC's in electrical and electronic engineering,and an HNC in electronics.
from the info on sender units i have found , the current at the sender would be approx 50mA at 12volts.
the circuit i have designed(all but calibration to appropriate sender) will run 5volts at a MAX of 30mA through the sender unit.
however, from the comments posted here, i do think that it would be best not to bother making this info available, then i can't be blaimed for
anything that may or may not happen if the people building and/or using this circuit don't fully understand the principles involved.
Ray
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NS Dev
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| posted on 28/9/05 at 07:16 AM |
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quote:
Originally posted by rayward
the circuit i have designed(all but calibration to appropriate sender) will run 5volts at a MAX of 30mA through the sender unit.
Ray
........I don't think there is any problem with that then!
................................On the other hand, I am keeping my car simple, not because I am scared of technology!!! but because everything adds
weight. (ok, a TINY amount in this case!)
I can live without a fuel gauge, in fact I can live without any gauges apart from a speedo (bike one) and it all saves weight in the simplest possible
way, by not fitting it to start with!!!
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MikeR
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| posted on 28/9/05 at 10:20 AM |
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quote:
Originally posted by rayward
however, from the comments posted here, i do think that it would be best not to bother making this info available, then i can't be blaimed for
anything that may or may not happen if the people building and/or using this circuit don't fully understand the principles involved.
Ray
Ray could you send me the design privately. I'll do my best to get my mate to look at it and evaluate it for you.
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