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Digital Fuel Gauge

Discussion in 'Electronic Projects Design/Ideas/Reviews' started by Stuee123, Jul 10, 2017.

  1. Stuee123

    Stuee123 New Member

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    Hi, want to add a temp digital fuel gauge to my boat, i have an analog one at the moment. Is there any schematics i can use to make one, i need to accurately read my fuel sender on a few trips to work out usage.
    Thanks in advance.
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    Welcome to ETO!
    Does the boat have a fuel-injected engine, or an engine with a carburetter?
     
  3. Stuee123

    Stuee123 New Member

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  4. dave

    Dave New Member

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  5. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Quick and dirty. Just use an ohmmeter for a few trips.

    You should probably do a calibration anyway. Start with an empty tank (easier said then done). then add gas in increments to get resistance to gallons.
     
  6. Stuee123

    Stuee123 New Member

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    was thinking that but i want to know the litres per 5%. so i can get a better reading of the underground 160L tank and remaning fuel when out.
    I have a digital inclinmeter which when flat in the water will put take the reading, then when home ill tilt to boat to the same angle then keep adding fuel and see work out home many liters per 5% graduations.
     
  7. Stuee123

    Stuee123 New Member

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    is there any of them ebay china module things that you just plug in to the signal and power. I tried looking but couldn't find, probably calling the wrong name
     
  8. Les Jones

    Les Jones Well-Known Member

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    Have you read the data on these sensors ? The output changes in steps every 13mm. (0.5 inch) It is not a smooth change from empty to full. They will make customised sensors with the steps every 4.5mm. The output will only be linear if the cross sectional area of the tank is constant over it's depth.

    Les.
     
  9. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Moreover, if you buy the 18" rod, and there is one step every 1/2", that is only 36 steps of resistance. 36 steps means that if you convert that to a per-cent digital display, you will have a 3% smallest change, so like 0%, 3%, 6%, ..., 94%, 97%, 100%.

    If your tank is more or less than 18" deep, you will loose resolution. If your tank is deeper than 18", you will loose resolution because the step pitch goes to 1", so a 19" deep tank would have only 19 steps. If your tank is less than 18" deep, you will have less than 36 steps.

    More than two numeric digits in the readout display is wasted. I would use one of these as the readout. Put the sender in a Wheatstone bridge circuit that scales the output voltage from the sender to 0.00V empty to 10.0V full. There will only be a few steps (~18 to ~30) in between, but that is the best you can do with that type of sender.

    I predict that you will need a "slosh" filter, too. Otherwise, the display will be unusable while in motion. That is why fuel gauges use analog meters; it is much easier to interpret a swinging analog meter needle than it is to average rapidly changing numerical digits (it is a human factors thing).
     
    Last edited: Jul 10, 2017
  10. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    Usually with a silicone fluid to damp the motion.

    I suppose you can fill in reverse too and work out the linearity. Fill to the same spot each time, Maybe drain a smidge to get the same resistance, Subtract out what you drained.

    The "One of these" only measures from 6 to 32 volts.

    This Bar display (20 dots) http://www.rammeter.com/texmate-am-20-led-bargraph-meter-200mv-2v-20v-200v-1200v.php might work for you. In any event some signal conditioning will be necessary.
     
    Last edited: Jul 10, 2017
  11. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Not anymore. I fixed the link in post #8.
     
  12. KeepItSimpleStupid

    KeepItSimpleStupid Well-Known Member Most Helpful Member

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    The 1/2" increments would act as a slosh filter. If the tank dimensions are "nice", you could calculate volume at each level.
     
  13. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Not really. As with any digital readout, the system can be poised to toggle between two adjacent steps, like 59% and 62%. A bit of slosh or noise, and the display will look like 88 instead of 59 or 62!
     
  14. Stuee123

    Stuee123 New Member

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    Thanks everyone for the input, that escalated quickly :)
    MikeMl i already have a volt meter like that, how do i make a Wheatstone bridge circuit, i did google it and saw some but see they are variable with resistors and not sure what resistors i would need.

    Thanks again
     
  15. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Before I launch into it, let's get some things on the table.

    1. Which, specifically, sender do you intend to use?

    2. What will be its resistance tank empty?

    3. What will be its resistance tank full? You cant answer these 'till you actually mount a sender in your tank!

    4. How many steps will it make full-to-empty? A float-arm sender has continuous varying resistance.

    5. The power source is an 12V alternator/battery system? ~12V parked? 14.2V engine running?

    6. I presume you want to make the fuel gauge immune to voltage changes engine stopped vs engine running? You want to average out sloshing in a moving boat?

    7. You are hell-bent on having a digital readout instead of an analog meter?

    8. You are willing to mentally move the decimal point if the digital meter reads 10.0 for 100% full?

    9. You are willing to build a circuit which uses some 1% resistors, a couple of electrolytic capacitors, a voltage regulator, a dual opamp, and one of those Ebay voltmeters?

    10. You are willing to settle for two point calibration (Full and Empty)?

    11. What have I forgotten?
     
    Last edited: Jul 11, 2017
  16. dr pepper

    dr pepper Well-Known Member Most Helpful Member

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    How about a set of weighing scales with a tare function.
     

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