I'm investigating an idea for low cost, non-contact low fuel level sensing.

After pondering this thread for a couple of days, I started searching for fuel level sensors. Most of the results were float switches, but I also found some optical sensors like the one Jerry showed. Many of them aren't cheap and all of them require contact with fuel, which means a hole in the tank and the possibility of plastic deterioration.

Then I got to thinking... some time ago I built a project using an ultrasonic distance sensor. I recalled that while searching for that sensor I also found liquid sensors, but I couldn't remember any details. It took some online sleuthing, but I finally came up with the sensor manufacturer's website (Chinese).

There are basically four versions of this company's sensor:

  • DS1603L - RS-232 output
  • DS1603DA - RS-485 output
  • DS1603AQ - analog voltage output
  • DS1603NF - "switch" output (pulls to 12V or to ground)

The first three are of little use to us, primarily because interfacing them to an EFIS or panel indicator would be a bit of a hassle. However, the last version is more interesting. It has a simple high-low output, which will talk to a digital or alarm input on an EFIS, or it could drive an LED indicator directly (like one of these flashing LEDs, perhaps).

I ordered one of the DS1603NF sensors, and I have a new aluminum header tank on order from Kitfox. When those items arrive I'll run some tests and report back here. Stay tuned...

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P.S. For anyone who's interested in how these sensors work, this Texas Instruments application note gives a useful overview.