Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser EarthX Batteries Garmin G3X Touch
Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 39

Thread: New Low Fuel Alarm Sensor

  1. #21
    Senior Member Eric Page's Avatar
    Join Date
    Jun 2020
    Location
    Toledo, WA
    Posts
    863

    Default Re: New Low Fuel Alarm Sensor

    My apologies to anyone who was following this little side project. I posted something about this a month ago, immediately realized I had made an error in the schematic, took it down and immediately got distracted building an airplane! The schematic error has been corrected, so I'll try again.



    First, here's the interface for using the DS1603NF ultrasonic liquid sensor with an EFIS alarm input:

    Schematic: [Obsolete file removed; please see post #36, below, for final version.]

    Circuit board:
    EFIS PCB.jpg

    As you can see, it's dead simple: just a couple of capacitors to clean up the supply voltage to the sensor, a 4.7kΩ pull-up resistor on the active low output, and a transistor to provide a self-test of the system.

    The 4-pin connector (J1) on the end of the board mates with the one that comes installed on the sensor pigtail. This circuit will pull the EFIS alarm pin to ground when fuel is present and apply 12V when fuel is absent.

    Since it takes some time for an EFIS to boot and it won't show an alarm until that's done, I incorporated a press-to-test function. This is simply a normally open pushbutton switch that, when pressed, turns off a transistor to interrupt power to the fuel sensor, causing it to restart. If you do this after the EFIS is booted up you should see the low fuel alarm while the button is pressed, and for 2.5 seconds after you release it. If the alarm then goes away, the sensor is working properly.



    Next, here's the interface for use in non-EFIS equipped airplanes:

    Schematic: [Obsolete file removed; please see post #36, below, for final version.]

    Circuit board:
    Flasher PCB.jpg

    This circuit flashes an indicator LED when the sensor does not detect fuel. It's a simple 555 timer based oscillator running at ~2Hz, with the output driving a 20mA LED driver IC (Microchip CL520N3-G). The LED driver may seem like overkill, but it has a few advantages:

    • It simplifies installation when users choose their own indicator by automatically providing 20mA to drive any LED, regardless of the compliance voltage required, up to the supply.
    • It protects the output of the 555 timer from overload if the installer tries to use an incandescent bulb or accidentally shorts the output to ground.
    • It costs $0.45.

    I found an illuminated switch that I think would make a nice indicator for the sensor, and would allow the pilot to shut off the flashing to reduce distraction, or test the system by briefly interrupting power. It has a bright red LED inside, and you can install your choice of diffusers and actuator caps in various colors. The cap is meant to have a legend printed on transparency film behind it, which is visible when the LED is turned on. The face of the switch is 0.622" x 0.866" and it will mount in panels from 0.039" to 0.157" thick (my Series 5 panel is 0.070" thick). I'll order a switch, as well as diffusers and caps in white, clear and red to experiment with, to see which combination looks best. The image below shows a narrow-end view of the switch with the diffuser and cap removed.


    Switch.jpg

    This is my quick first-pass attempt at how an indicator legend might look:

    Switch Legend.jpg



    I'm asking that anyone with electronics experience please take a look at the schematics and feel free to critique my work. I'm not an engineer, so I'm looking for feedback on basic function, robustness and any ideas for simplification.

    You could probably reduce parts count by using a microcontroller (and likely the cost, given how cheap they are), but I think that would represent a high barrier for builders who don't have the capability to flash firmware. You could likewise reduce board size by using surface-mount components, but again, it would be a barrier to builders who lack the equipment or skill to solder SMD.

    I'll wait a few days to see if anyone has any suggestions. If there are, we can hash that out, then I'll order boards and parts. It'll take about two weeks to get everything, then I'll stuff some boards and give them a test. If they work, I'll wrap this up with instructions on where to get everything and how to assemble the boards.
    Last edited by Eric Page; 03-02-2021 at 06:18 PM. Reason: Remove obsolete schematic files.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  2. #22

    Join Date
    May 2019
    Location
    Ithaca, NY
    Posts
    68

    Default Re: New Low Fuel Alarm Sensor

    Eric, sorry I dropped the ball on this. I like your idea of an illuminated switch so that you can turn off the alarm. The danger is that you leave it off but that can be a checklist item.

  3. #23
    Senior Member Eric Page's Avatar
    Join Date
    Jun 2020
    Location
    Toledo, WA
    Posts
    863

    Default Re: New Low Fuel Alarm Sensor

    No worries! If you see anything that could be done better, let me know. We'll get this thing sorted out...
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  4. #24
    Senior Member Eric Page's Avatar
    Join Date
    Jun 2020
    Location
    Toledo, WA
    Posts
    863

    Default Re: New Low Fuel Alarm Sensor

    Circuit boards have arrived. Components should be here next Wed.

    PCBs.jpg
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  5. #25
    Senior Member Kitfox Pilot's Avatar
    Join Date
    Aug 2019
    Location
    Spring Garden Illinois
    Posts
    859

    Default Re: New Low Fuel Alarm Sensor

    Thanks Eric for your time to do all this research and development on this project. This could save a life someday.
    Harlan and Susan Payne
    Sold Piper Archer
    Flying FarmFox STI Kitfox N61HP
    Rotax 915is, Airmaster prop
    https://www.youtube.com/channel/UC5A...oCVUP15G0uB-Yw

  6. #26
    Senior Member Eric Page's Avatar
    Join Date
    Jun 2020
    Location
    Toledo, WA
    Posts
    863

    Default Re: New Low Fuel Alarm Sensor

    I finally got around to populating the circuit boards and doing some tests. I'm making some small changes to the design of one of them and moving to v2.0. New boards and parts are on order.

    It doesn't look like the illuminated switch that I found is going to be a good solution. It's not nearly bright enough, and the bezel isn't big enough to make a legend that says both "LOW FUEL" and "PRESS OFF" in text large enough to be readable for anyone over the age of 20. This image doesn't do a good job showing the brightness, but it's not great. It certainly wouldn't be adequate in bright sunlight; it's not very impressive in a well-lit room. I've ordered a discrete LED instead that should be much more attention-getting.

    Switch_Lit.jpg

    Watch this space...
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  7. #27
    Senior Member
    Join Date
    Nov 2008
    Location
    KDKB (Dekalb, Illinois)
    Posts
    644

    Default Re: New Low Fuel Alarm Sensor

    I am replacing my header Tank, and lacking a port for the optical sensor (Thanks for that change Kitfox )
    I am considering the non-contact liquid sensor you are using. It seems from at least a quick look at Amazon
    reviews for variants of that sensor the failure rate of the sensor is about 50%, as well beneath the sticker is
    supposedly a trim pot for adjusting sensitivity.

    I do not have a sensor at present so I can't say if any of that is true, but you might want to look at how well
    sealed, and assembled is the back side of that sensor. There seems some comments that they are sensitive
    to environmental change on the backside (when for example used as outdoor Tank sensors).

    Just some thoughts

    Jeff

  8. #28
    Senior Member
    Join Date
    Nov 2008
    Location
    KDKB (Dekalb, Illinois)
    Posts
    644

    Default Re: New Low Fuel Alarm Sensor

    I can't find the comments which I read earlier, but it seems there is concern about sensitivity
    drifting, and due to the trim pot on the back, it's sensitive to environment.

    41vDkQRwmRL._SL1024_.jpg

  9. #29
    Senior Member Eric Page's Avatar
    Join Date
    Jun 2020
    Location
    Toledo, WA
    Posts
    863

    Default Re: New Low Fuel Alarm Sensor

    Can you post a link to the Amazon listing that you're looking at? I'd like to take a look at the product info and the reviews.

    The image you posted above does not look like the sensor that I'm using. The DS1603NF has a gray plastic 2-piece enclosure with no flange on the edge, which is ultrasonically welded at the seam. There's a very shallow depression in the back where the sticker is located, but there's nothing underneath it.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
    Member: EAA Lifetime, AOPA, ALPA
    ATP: AMEL | Comm: ASEL, Glider | ATCS: CTO
    Map of Landings

  10. #30
    Senior Member
    Join Date
    Nov 2008
    Location
    KDKB (Dekalb, Illinois)
    Posts
    644

    Default Re: New Low Fuel Alarm Sensor

    There's a bunch of essentially the same sensor on Amazon, this is the one with the image
    and multiple output types, I'm looking at the high/low output sensor. Your original link is
    discontinued. But I believe they are all the same, just sold by different vendors. I do a lot
    of Arduino based hobby stuff, and my experience is that between Amazon, and Ebay the
    same device is almost always available from a multitude of sources with different names.


    Taidacent Non-Contact Liquid Level Sensor Externally Attached Liquid Induction Level Switch Water Level Switch (PNP Output(24V)): Amazon.com: Industrial & Scientific


    Your idea is a good idea, but I may end up doing a two sensor, with mini Arduino
    with high/low, and a comparator logic for determining a fault condition. This way if for
    example you had a continuous high on one, and low on the other it could be flagged
    as a fault condition.

    So - LED/ON - Low fuel. LED/OFF have fuel. LED/Blinking - Fault condition.

    Or maybe use a tricolor LED, and make it Green=good, Red=low fuel, blinking amber = fault.
    Something like this ...





    Jeff

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •