Stewart Warner fuel senders....idea

So last night I started a thread about what folks were using as a standalone low fuel indicator. I might have come up with a solution while driving home from work today. My past life as an avionics tech thought of this:

According to the specs on the SW fuel sending units (from memory) I think there is about a 20 ohm resistance reading at "full" and 240 ohm at "empty". It seems to me that I could build a circuit, using the output from the SW unit, to "trip a light" at some predetermined resistance threshold. For example, at 3 gallons (whatever ohm reading that turns out to be) using only the SW unit.

I don't even know if this is an original idea or not, but it DID pique my interest.
Ideas? Thought? Has this been tried?

If you have an Arduino, it would be very easy to do that.

An Arduino is a small microcontroller that's inexpensive and relatively straight-forward to program.

Dave

Low Fuel Warning Lt

It's a good idea. Later model Mooneys use this system in some fashion. I believe there is a time delay in the system so the "low fuel qty" lights don't blink all the time in turbulence with less than 1/2 tank.

Don B

RV 9. Rebuild in Progress

An analog comparator with a user adjustable potentiometer to set the threshold voltage (or fixed resistors to make it a bit more reliable). A bit of hysteresis and a big honking low-pass RC filter on the input to smooth out the sloshies. With a qual op-amp you could do an active LP filter and the comparator in one chip. Either way, pretty simple for an Analog Man (Joe Walsh) or an Analog Kid (Rush). Use the output to drive a transistor and LED indicator.

The late, great Bob Pease will be rolling in his grave if you commit this to a micro!

Or, you could use a submerged thermistor like the automobile low fuel lights do. That gives you a nice time constant and super simple circuit.

fl-mike said:

An analog comparator with a user adjustable potentiometer to set the threshold voltage (or fixed resistors to make it a bit more reliable). A bit of hysteresis and a big honking low-pass RC filter on the input to smooth out the sloshies. With a qual op-amp you could do an active LP filter and the comparator in one chip. Either way, pretty simple for an Analog Man (Joe Walsh) or an Analog Kid (Rush). Use the output to drive a transistor and LED indicator.

The late, great Bob Pease will be rolling in his grave if you commit this to a micro!

Or, you could use a submerged thermistor like the automobile low fuel lights do. That gives you a nice time constant and super simple circuit.

Click to expand...

So, build us both one.

I'd appreciate it if you'd draw a circuit diagram and make a list of parts. It's a good idea. Thanks.
John

Time delay is critical...

Yep. Can't have a light "crying wolf". A filter and time delay should combat sloshing and prevent false readings. By adding something with resistance, to a resistance dependent circuit, it will behave like a parallel circuit. Perhaps the effect can be achieved without sacrificing accuracy to the fuel gauge. I have enough parts laying around that I am tempted to give this a go, for a science experiment if nothing else.

Of course, if I go with a glass cockpit, it's gonna do all this for me.

GLPalinkas said:

So, build us both one.

Click to expand...

Too much like work. I build airplanes to relax! Besides, I already have a fuel totalizer.

For a ready to go NTC sensor (for an incandescent indicator). Google: Panasonic ERTLG

My 1960 Mercedes had a low fuel light as part of the gage. When it blinked (no fancy circuit) it got my attention and when it was on solid, it meant business. Why not just a switch and consider the blinking a warning stage!