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'[EE]: Cheap light level sensor'
2001\10\02@030435 by Dave VanEe

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Hey,
I'm still thinking about how to sense fuel levels in a fuel tank I'm
building.  I'm leaning toward the idea of a clear shaft tapered at several
lengths.  Can anyone suggest a cheap way of sensing the reflected light?
The only cheap sensors I can find appear to have a sensing distance of only
a few mm at best (I'd be using a ~12" shaft).  Am I looking at the wrong
type of sensor for this purpose?

Thanks,
Dave

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2001\10\02@081111 by Tsvetan Usunov

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>Hey,
>I'm still thinking about how to sense fuel levels in a fuel tank I'm
>building.  I'm leaning toward the idea of a clear shaft tapered at several
>lengths.  Can anyone suggest a cheap way of sensing the reflected light?
>The only cheap sensors I can find appear to have a sensing distance of only
>a few mm at best (I'd be using a ~12" shaft).  Am I looking at the wrong
>type of sensor for this purpose?
>
>Thanks,
>Dave

I would try two approaches:

1. ultrasonic distance measurement - put sender and received on the top of
your fuel tank. send chirps and listen the echo to calc the distance
2. capacitive (may be dangerous if not well isolated) - if your tank is with
metal walls (it should be if it's fuel tank) put well isolated metal rod
inside the tank and make high approx.200kHz frequency generator - the fuel
level will change the capacitance of your rod-tank wall system with 10 to
100 pf depend on your tank volume - then all you have to do is to measure
the frequency on the output

Best regards
Tsvetan
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2001\10\02@101903 by Douglas Butler

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Range of a light sensor depends almost entirely on the optics of the
situation.  If your shaft makes a good light pipe (the outside should be
polished) you may well get the range you need.  Simple amplitude sensing
will be cheap and may be good enough.  For a little more cost you could
flash the light source and measure reflection vs. time.  Each step in
diameter would produce a reflected pulse of different amplitude
depending on whether it is wet or not.  I am afraid the timing will be
faster than a PIC can handle without hardware help.

My suggestion is to build a sensor and try it.  Even if it doesn't quite
work you will learn a lot.

Sherpa Doug

> {Original Message removed}

2001\10\02@104613 by M. Adam Davis

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Since what you are really looking for is the level of reflected light,
then you can simply use an LED to provide light and a [cds cell,
photodiode, LED, etc] to sense the amount of light returning.

Any sensor that outputs light and returns information on how much light
is returning should work.  The few mm sensor should work well, since the
light will travel much better and further inside the tube.

-Adam

Dave VanEe wrote:

{Quote hidden}

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2001\10\02@110128 by Alan B. Pearce

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The trick that has not been mentioned is to switch the transmitting LED of
and on at a suitable frequency, and then use the photodiode with an
amplifier. Because you are sensing an AC signal it is a lot easier to get
decent gain if you need it. with the right settings this should enable you
to sense accurately with minimal component count.

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2001\10\02@211258 by Anthony Bussan

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Go capacitive.  I think it will be easier in the long run.  Here is my
favorite book on capacitive sensors of all types: Capacitive Sensors :
Design and Applications, by Larry K. Baxter, ISBN: 078035351X.  I actually
own a copy.  LOTS of ideas for different applications in this book.

Have fun,
Tony

{Original Message removed}

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