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'[EE]:rain Sensors, was Infra-red Opto help'
2002\11\04@053031 by Alan B. Pearce

face picon face
>which is where the piezo idea came from.

What happens if you have a piezo speaker as the resonant element in an
oscillator? When a rain drop lands on it will the resonant frequency or
amplitude change enough to detect? The only problem I see with this method
is that the electrodes would need protecting against the moisture.

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2002\11\04@054316 by cdb

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Possible, what I thought was get one of those Piezo's that are in a
coin holder looking affair - about $3.00 here, fix it into a
waterproof box with a bolt glued to its backside - this would make
the Piezo very sensitive to vibration -ergo when rain falls on it
vibration happens voltage occurs. I think I've seen water proof Piezo
tweeters somewhere so they might work.

Just disappointed that I can't get the Opto bit to work - must try
some crazed glass see if that makes a difference.

colin
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2002\11\04@060206 by Alan B. Pearce

face picon face
>this would make the Piezo very sensitive to vibration -ergo
>when rain falls on it vibration happens voltage occurs. I
>think I've seen water proof Piezo tweeters somewhere so they
>might work.

I was not thinking of having it like that, I was figuring on having the
piezo unit driven at low level by being the tuned element in an oscillator,
and a PLL to look for frequency shift, or some form of amplitude detection
to look for amplitude damping. It may be that if the level of oscillation is
controlled at a low enough level, then a drop of rain may be enough to make
the piezo element go low enough in Q, or be damped enough to cause it to
drop out of oscillation.

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2002\11\04@061024 by cdb

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Yes, that would probably work - I'll try that one - as a separate
project. otherwise I'll have to rewrite my software - the present
problem is intended as a retro-fit using the least amount of add on
components - though I'll probably still have to use a comparator as
the detectors doesn't 'snap' between voltage levels as I had hoped it
would.

Mind you I could perhaps have it as an arm in the timing chain of a
555  hmm

Colin
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2002\11\04@123216 by Peter L. Peres

picon face
On Mon, 4 Nov 2002, Alan B. Pearce wrote:

*>>this would make the Piezo very sensitive to vibration -ergo
*>>when rain falls on it vibration happens voltage occurs. I
*>>think I've seen water proof Piezo tweeters somewhere so they
*>>might work.
*>
*>I was not thinking of having it like that, I was figuring on having the
*>piezo unit driven at low level by being the tuned element in an oscillator,
*>and a PLL to look for frequency shift, or some form of amplitude detection
*>to look for amplitude damping. It may be that if the level of oscillation is
*>controlled at a low enough level, then a drop of rain may be enough to make
*>the piezo element go low enough in Q, or be damped enough to cause it to
*>drop out of oscillation.

Spent too much time in aerospace ? ;-) A raindrop falls from at least 500
meters of height and has a minimum size. I'd use a simple microphone
attached to a drum-like structure (with saran wrap skin I think). This may
react to other things besides rain.

I still favor the idea of measuring just soil humidity.

Peter

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2002\11\04@133842 by Francisco Ares

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Take a look at Bosch's rain sensor at

http://app3.internetwork-bosch.com/webapp/kea/k/en/start/product.jsp?mfacKey=BE_5_REGENS

and also

http://www.schott.com/magazine/english/info96/si096_12_sensor.html

hope this helps
Francisco


Peter L. Peres wrote:

{Quote hidden}

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2002\11\04@151645 by Bill & Pookie

picon face
Looks like the question might be "How do I tell
how well the wipers are keeping the windshield
clear?"

This could require a device looking through the
windshield.   A simple IR system used for remote
controls, with the transmitter just outputting
pulses and the receiver detecting the lack of
pulses might work if the rain on the windshield
would scatter the IR enuff.

I will test this theory first rain I get.  Can
strap my BoomBox on the hood and see how well the
remote control works in the rain.  And will start
looking for a IR transmitting hood ornament.

Bill


{Original Message removed}

2002\11\05@055307 by Alan B. Pearce

face picon face
>Spent too much time in aerospace ? ;-)

Yeah possibly :)))

>A raindrop falls from at least 500 meters of height and has
>a minimum size. I'd use a simple microphone attached to a
>drum-like structure (with saran wrap skin I think). This may
>react to other things besides rain.

Well yeah, if it is actually raining, in a "cats and dogs" sense. But often
when I'm driving my car, the road is wet, and there is misty water landing
on the wind screen, so there is some precipitation of moisture out of the
atmosphere. It certainly does not land on the windscreen with enough energy
to make any noise.

I guess if all your trying to do is determine if the lawn needs watering,
then this will not be enough moisture to count :)

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2002\11\05@060725 by Russell McMahon

face
flavicon
face
> >A raindrop falls from at least 500 meters of height and has
> >a minimum size. I'd use a simple microphone attached to a
> >drum-like structure (with saran wrap skin I think). This may
> >react to other things besides rain.
>
> Well yeah, if it is actually raining, in a "cats and dogs" sense. But
often
> when I'm driving my car, the road is wet, and there is misty water landing
> on the wind screen, so there is some precipitation of moisture out of the
> atmosphere. It certainly does not land on the windscreen with enough
energy
> to make any noise.

FWIW - a raindrop has a terminal velocity of a few tens of kilometres per
second. Actual velocity depends on drop size but in free fall is never vast.
I imagine that wind blown drops assume a speed approaching that of the wind
gust they are carried by.



       RM

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2002\11\05@062837 by Jan-Erik Soderholm

face picon face
Well, ait depends.

*You* (as standing formly on the ground) beleive that the raindrop
is moving horizontaly. But the *raindrop* itself don't understand that
there is a wind, since it moves along with the wind itself. It thinks that
it's the earth below it that has begun rotating in the opposit direction.

So, it depends how you messure, as always.

And when it commes to the "speed" of the raindrop, the speed trought
the air has, as you said, a terminal velocity, and that speed is always
straigt verticaly, as seen from the surounding air ! Now,  if messured from
the ground, and if there's a "wind" the raindrop will have a horizontal speed
as well as the (constant) vertical speed. The speed-through-air, is constant,
but by doing some vector mathematics, one can calculate the speed-over-ground,
that, with any wind > 0, always will be higher then when it's calm.

So, when driving you car, it's not the raindrop that hits you, it's you
that hits the raindrop...

Anyway, there is a book that describes this better written by someone
called Albert Einstein...

:-)

Jan-Erik Svderholm.

>FWIW - a raindrop has a terminal velocity of a few tens of kilometres per
>second. Actual velocity depends on drop size but in free fall is never vast.
>I imagine that wind blown drops assume a speed approaching that of the wind
>gust they are carried by.
>
>
>
>       RM


Jan-Erik Svderholm
S:t Anna Data
tel : +46 121 42161
mob : +46 70 5241690

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2002\11\05@080021 by cdb

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>FWIW - a raindrop has a terminal velocity of a few tens of
>kilometres per second

So I should abandon my opto attempt and try a microwave radar gun
instead perhaps :) ?


colin
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2002\11\05@080842 by Olin Lathrop

face picon face
> FWIW - a raindrop has a terminal velocity of a few tens of kilometres
per
> second.

Around here they go *much* slower.  At mach 30 or so the sonic booms must
get rather annoying.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com

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2002\11\05@081503 by Michael Rigby-Jones

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{Quote hidden}

Surely tens of *meters* rather than kilometers?

Mike

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2002\11\05@092403 by Mike Singer

picon face
Olin Lathrop wrote:
> > Peter L. Peres wrote:
> > FWIW - a raindrop has a terminal velocity of a few tens
> > of kilometres per second.
>
> Around here they go *much* slower.  At mach 30 or so the
> sonic booms must get rather annoying.


Peter L. Peres COULD reply with Olin's words:
> Yes, you are absolutely right.  I noticed that my statement
> was a bit misleading right after I sent it and wondered if
> some wiseass would bother point it out <g>.


  Congratulations.
  Mike.

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2002\11\05@161151 by Jinx

face picon face
> FWIW - a raindrop has a terminal velocity of a few tens of kilometres
> per second.
>
>         RM

WOW !!!! Is that how hard it rains inTe Atatu ? You must all have council-
issue armour-plated hats

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2002\11\05@164313 by Russell McMahon

face
flavicon
face
> > FWIW - a raindrop has a terminal velocity of a few tens of kilometres
per
> > second. Actual velocity depends on drop size but in free fall is never
> > vast.

> Surely tens of *meters* rather than kilometers?

Whoops - yes
Tens of kilometres per hour that should have said.
Tens of kilometres per second gets you into space :-)



       RM

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2002\11\05@171759 by Peter L. Peres

picon face
On Tue, 5 Nov 2002, Mike Singer wrote:

*>> > Peter L. Peres wrote:
*>> > FWIW - a raindrop has a terminal velocity of a few tens
*>> > of kilometres per second.
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I did not write that. Please clip carefully next time.

Peter

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2002\11\05@234101 by Mike Singer

picon face
Sorry.

> On Tue, 5 Nov 2002, Mike Singer wrote:
>
> *>> > Peter L. Peres wrote:
> *>> > FWIW - a raindrop has a terminal velocity of a few tens
> *>> > of kilometres per second.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> I did not write that. Please clip carefully next time.
>
> Peter

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2002\11\06@005736 by Mike Singer

picon face
  What do spoil the view of a road?  Drops on the
glass, refracting light beams. Let's us use the
refraction.
  1. Let some opto-emitter illuminate the glass at
an angle of about 30 degrees
  2. Then let a set (matrix) of opto-receivers receive
the resulting picture (90 degrees maybe). When the
glass is clear, store in memory the receivers' outputs.
  3. When drops have spoiled the picture, receivers'
outputs should got different from stored in memory,
provided they have proper focus (curved inwards,
may be) to catch drops' refraction.
  Get the standard deviation or what the heck is
appropriate in this case and decide if the view got
spoiled enough to start cleaning.

Mike.

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