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"Flicker Filter" for low fuel warning float switches?

 
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BigD(at)DaveMorris.com
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PostPosted: Mon Jan 23, 2006 7:21 am    Post subject: "Flicker Filter" for low fuel warning float switches? Reply with quote

Bob, I have a switch float in my header tank that I use to control the pump
that feeds the header. (Other Dragonfly builders manually switch the pump
on and off, watching a big red light, and install a huger overflow tube.)

I was planning to install a 1 minute timer, so that when the float
indicates a full tank, the pump switches off for 1 solid minute, before
being allowed to come on again (if the float indicates it's time to run
again). Basically a kind of debounce circuit. I think that can be done
with a simple 555 circuit or even some of the off-the-shelf timer kits from
QKits.

Dave Morris
At 12:00 AM 1/23/2006, you wrote:
Quote:

<nuckollsr(at)cox.net>

Some months ago, someone was asking about a circuit to
make the float-switches in their airplane be a bit more
definitive as to when the low fuel warning light was
illuminated.

I have hardware in hand that can be programmed to accomplish
this task. We can watch for switch behavior to exhibit
some characteristic like "switch closed more than 50% of the time
over a 1 minute period" before the warning light is latched
on. Given the flexibility of software, we can probably address
any other low-fuel trip protocol. Does anyone have a need for
this capability?
Bob . . .
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
http://www.aeroelectric.com




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nuckollsr(at)cox.net
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PostPosted: Mon Jan 23, 2006 1:17 pm    Post subject: "Flicker Filter" for low fuel warning float switches? Reply with quote

At 03:45 PM 1/23/2006 -0500, you wrote:

Quote:

<Dr.Laurence(at)mbdi.org>

> Some months ago, someone was asking about a circuit to
> make the float-switches in their airplane be a bit more
> definitive as to when the low fuel warning light was
> illuminated.
>
> I have hardware in hand that can be programmed to accomplish
> this task. We can watch for switch behavior to exhibit
> some characteristic like "switch closed more than 50% of the time
> over a 1 minute period" before the warning light is latched
> on. Given the flexibility of software, we can probably address
> any other low-fuel trip protocol. Does anyone have a need for
> this capability?>
>
> Bob . . .

Do I understand correctly that a LOW FUEL condition is detected
by a CLOSING switch? Is there any problem with having the flicker
filter pulling lamps to ground to illuminate them?

The way the hardware is currently configured, float switches will
pull an input to ground as the fuel level goes down. The present
control algorithm I'm considering is to ignore the "flickering
switch" until it has been closed for more than 50% of the last
minute. When this condition is reached, the output pin for that
channel latches low (pulls annunicator light to ground).

The light will go out when the fuel level switch has been open
continuously for some period of time . . . say one minute.

If this sounds like something you could use, I'll put it in the
hopper that holds my software manager's tasks . . .

Another question, what kind of switches are you using? Hall
effect sensors would be ideal, totally enclosed reed switches
would be second best.
Bob . . .
< What is so wonderful about scientific truth...is that >
< the authority which determines whether there can be >
< debate or not does not reside in some fraternity of >
< scientists; nor is it divine. The authority rests >
< with experiment. >
< --Lawrence M. Krauss >
http://www.aeroelectric.com


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