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LED petrol gauge

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jasonbondi

New Member
hey guys, new to here and joined for the reason that i want to make a fuel gauge for my car using like 10 LEDS

basically my car has a sender which is 0 Ohms empty 90 Ohms full

looking for any advice, any guidence to help me turn these LEDS all on with 90 Ohms and one at a time go off all the way down to bout 5 Ohms

Thanx

Jason
 

birdman0_o

Active Member
This is pretty simple, a lm3915 is a 10 part voltage comparotor, this means it will will take in an analog voltage and turn on 1-10 of its pins based on how larger the voltage is compared to reference. This means that if you use the "sender" and a 100 ohm resistor in series (I dont think 90 exists, try to get closest to 90 you can) and your car battery voltage divided by 2 ( use a resistor voltage divider here to) as a source, it will divide it up 10 times based on the voltage accross the resistor. Larger the resistance of the "sender" bigger the voltage drop accross the 100ohm resistor and the lm3915 will turn on one pin at a time. To make it "count down" use pnp transistors such as (2n2222) at every out put pin and you'll get your desired effect :)
 

ccurtis

Well-Known Member
One potential problem is the sloshing of fuel in the tank resulting in a display that wanders or flickers. That could be annoying if something is not in place to dampen it. Maybe the sensor already has dampening. If not, the LM3914 has very little hysteresis and it would be advisable to refer to the datasheet to add some.
 
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jasonbondi

New Member
thanx for the reply!
i pretty much understand it all... for voltage divider do u mean like a 6v regulator such as a Z6549?

any chance some1 could do a quick sketch of how the components should go together? just something quick

thanx
 

jasonbondi

New Member
also wondered bout sloshing, could something be used to maybe hold the leds on for couple seconds after? that way if it does slosh and is re enegised again withing couple seconds you wont notice?
 

ccurtis

Well-Known Member
The datasheet for the LM3914 goes into a good amount of detail and explaination, with examples. If you work up a draft schematic based on it, I am confident you will find reviewers here, on this thread. I would check the fuel sender output with an ohmmeter while the fuel is sloshing first to see if dampening is needed.
 

crutschow

Well-Known Member
Most Helpful Member
thanx for the reply!
i pretty much understand it all... for voltage divider do u mean like a 6v regulator such as a Z6549?
A voltage divider is simply two resistors in series.
 

crutschow

Well-Known Member
Most Helpful Member
This is pretty simple, a lm3915 is a 10 part voltage comparotor, this means it will will take in an analog voltage and turn on 1-10 of its pins based on how larger the voltage is compared to reference. This means that if you use the "sender" and a 100 ohm resistor in series (I dont think 90 exists, try to get closest to 90 you can) and your car battery voltage divided by 2 ( use a resistor voltage divider here to) as a source, it will divide it up 10 times based on the voltage accross the resistor. Larger the resistance of the "sender" bigger the voltage drop accross the 100ohm resistor and the lm3915 will turn on one pin at a time. To make it "count down" use pnp transistors such as (2n2222) at every out put pin and you'll get your desired effect :)
Since the sender is zero ohms when the tank is empty, the voltage will be zero and the LM3915 will have not LEDs lit, which is what you want, so I don't understand your comment about using pnp transistors to "count down".
 

Hero999

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