Digital fluid level display project help.

Discussion in 'Programmer's Corner' started by zorbzz, Apr 20, 2010.

  1. zorbzz

    Thread Starter Member

    Jun 16, 2008
    20
    0
    Can anyone help with the program that would allow me to use an existing tank sender unit to read the fluid level from a generator fuel tank so I know how much fuel was in the tank.

    The tank is from an old car and the gauge sender unit reads 10 ohms empty and 150 ohms full.

    The tank has a maximum capacity of 68 litres so it would be ideal if I could either have a 3 digit readout of 0 - 100% or even better 0 to 68 litres with the 3rd digit being in 100 ml incriments like 63.5 etc.
    Because we live away from fuel stations this project would be great for us as we would know when to get more fuel.

    I dont have a clue about programming pics to this degree but I have all the equipment to do it and can buy whatever pic I need.

    Im only new to pics and am trying to learn about multiplexing and adc so I think this would be an excellent project that with guidance I can learn a lot from.

    I have pic16f684 pic16f628a pic16f88 and pic16f57 pics to use if that helps.


    I can do step by step pictures and post the whole project here if someone can help me complete it.
    Thanks alot this is my last resort.
     
  2. johndoe45

    Member

    Jan 30, 2010
    364
    1
    this is matlab code

    here is what i got
    decrease dx for more accuracy.
    all do is change meter reading in ohms and it gives you level of tank in liters
    however. sometimes the program doesn't have answer. for example 52.3.

    dx=0.01;

    tank=0:dx*0.485714:68; %liters
    gauge=10:dx:150; %ohms

    meter_reading=150; %ohms

    tank_level=tank(find(gauge==meter_reading)) %liters
     
    Last edited: Apr 21, 2010
  3. t06afre

    AAC Fanatic!

    May 11, 2009
    5,939
    1,222
    Hi Zorbzz
    What kind of program language do you use. I also do not think someone have a project matching your needs 100% But break your task into small sub tasks. We can not do the project for you. But we will be happy to discuss any problem you will meet during your project work
     
  4. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    How about a simple constant current circuit feeding from 5V through the sender, then an off-the-shelf digital panel meter reading the voltage across the sender.

    Adjust the current to get 0.68V across the sender when it's full and you will get a display in litres on the meter.

    If linearity is not important (and the sender may not be linear anyway), a 470 Ohm fixed resistor plus a 1K preset for calibration may do as the current source.

    Example meter (find one useable with 2V scale):
    http://www.web-tronics.com/panelmeter.html
     
  5. John P

    AAC Fanatic!

    Oct 14, 2008
    1,634
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    I wonder if an A-D approach is right, given the very low resistance that you have there. Maybe the thing to do is get a capacitor charged up to the power supply voltage (give it a good long time to charge, so it's at a steady state voltage) then have an output from the PIC connect it to ground via the level sensor, and use the PIC to determine how long the voltage takes to drop. I've had very good success doing this to read a manually adjusted potentiometer, and I could imagine it working OK for your tank sensor.

    Presumably you don't need this thing to give readings very frequently, so if the charge-discharge time is say, several seconds, it should be OK.
     
  6. zorbzz

    Thread Starter Member

    Jun 16, 2008
    20
    0
    Thanks for the replies so far.
    I Only just started reading the picbasic manual. Ive never programed anything before but would like to learn. The picbasic pot command wont read my fuel sender its out of range I think the smallest is 5 k to 50k??
    I really need to be steered in the right direction to either a project I can modify or someone that can write me some code to try.

    John P I think your idea sounds pretty good but I dont know where to start with it.
    I was even thinking about trying a project that is a vlotmeter and trying to modify that somehow but I cant get a pic16f676 where I am.

    Would I be able to substitute a pic I have?
    I have pic16f684 pic16f628a pic16f88 and pic16f57 would any of them work?

    heres the diagram
    [​IMG]

    If I made this how could I make it to read the input from the sender and maybe convert the ohms into milivolts like 0 to 680 mv.
    Then half a tank would be 340mv whutch would mean 34 litres of fuel 285 mv would mean 28.5 litres etc. Possible ??
     
  7. t06afre

    AAC Fanatic!

    May 11, 2009
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    Do you have some basic electronics skills? Like you have used opamps before?
     
  8. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    I explained above how to get a scaled voltage from the sender.

    I was thinking of displaying it with a simple digital voltmeter, but you could equally well measure it with a PIC ADC and do what you like with the measurement from there.
     
  9. zorbzz

    Thread Starter Member

    Jun 16, 2008
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    0
    Yeh but will that give me a 3 digit reading if I used a panel meter or just the voltage like 068 etc ?
    Maybe a millivolt panel meter then reduce the voltage to suit?


    t06afre yes I have built many projects before just never designed a pic one yet.
     
  10. rjenkins

    AAC Fanatic!

    Nov 6, 2005
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    If you adjust the current source (or resistor + preset pot) so you get 0.68V across the 150 Ohms of the sender, it should display as 680 on a 2V digital panel meter.

    Add the appropriate decimal point link and you get 68.0
     
  11. zorbzz

    Thread Starter Member

    Jun 16, 2008
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    Last edited: Apr 25, 2010
  12. t06afre

    AAC Fanatic!

    May 11, 2009
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    This is the car basic fuel gauge. You will burn the resistor inside the "sender" if you do not have some serial resistor. I also think you can do something with your panel meter. But check if it need a battery in order to work. Some measurement modules must have a separate power supply in order to work. They do not work if they use the same power source as the measurement target
    [​IMG]
     
  13. zorbzz

    Thread Starter Member

    Jun 16, 2008
    20
    0
    Yep this meter uses either.
    It can use common ground or seperate power and grounds FOR ONLY $9
     
    Last edited: Apr 26, 2010
  14. zorbzz

    Thread Starter Member

    Jun 16, 2008
    20
    0
    Bought the meter today will wait to see if it works when it comes from thailand.
    Its just a pity that with all of the experienced people here that no body could help me to make it myself with 7 segment displays. I had the schematic just needed help programming which I never got. I had to buy from overseas. I would have paid 5 times the amount to buy the parts locally and build it myself but I guess the overseas market really does own us.
    I got the panel meter for AU$ 13 delivered from thailand. How can we beat that when people dont help eachother with the knowledge thay already have.
    GO CHINA!!
     
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