Rain affecting signals and sensing rain.

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Hi

I am thinking of making a rain sensor to detect light rain as the BOM
radar is often not accurate at measuring light rain in my local area. I
have an Internet weather station linked to http://weather.org.au .

I heard some wireless transmissions can be affected greatly by rain so
if I set up a transmitter and receiver, the signal would get weaker in
the rain and the strength of it could be measured. The distance between
the transmitter and receiver could be experimented with. Perhaps I
could set up one for the very local area where the distance between the
transmitter and receiver is only about 50 or 100 meters. However,
another one could be set up so that it spans a distance of a kilometer
or more. The signal could extend between my house and someone else's
place in the direction where the prevailing weather comes from. This
would alert us when rain is about to arrive.

It would be good if the sensor detected even light drizzle. Ideally it
would be nice to see or measure the signal reduce as the drizzle or
rain became heavier between the transmitter and receiver.

Is there a simple way to do this, such as by using an infa red
transmitter and receiver? The receiver could be housed in a pipe to
block out as much background interference as possible and so it only
received signals from the direction of the transmitter.

Another alternative could be a low cost radar if one is suitable.

What sort of transmitters and receivers could be used and would the
setup be affordable?
How accurate would the system be?

Your help is appreciated,
Regards Richard.


Re: Rain affecting signals and sensing rain.


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You want sensitive, accurate, cheap and simple. Any other options?

Seriously, if you want a simple way to detect rain, Google rain detector
circuit. Build a sensor (basically just a mesh of tracks on a circuit board
which get a low-resistance path across them when they get wet. Stay away
from the RF stuff, it's cheap/accurate/reliable (pick two). Note I don't
include simple. The other sort of sensor though is easy - however it will
tell you it *is* raining, not that it *will*. Therefore if you have
neighbours who are interested also you could set up a network of these in
the district and maybe use wireless IP or some such to let each other know
what's happening. That'd be a neat community project.

Here's just one page plucked at random from the search result:
http://www.electronics-lab.com/projects/science/015 /

Make the sensor really big with close tracks and it becomes more sensitive
to light rain. Note though that you'll probably detect fog too. Plenty of
room for experimentation! :-)

Cheers.

Ken



Re: Rain affecting signals and sensing rain.


Hi

Thanks for you suggestion. I have thought of the exact thing that you
mention and I was about to get someone to make it up. However, he said
that there would be a fair bit of time and electronics involved as the
resistance of rain water would be very low and difficult to measure and
sense. Also the acidity of rain can vary and this may cause major
inaccuracies. Another way I thought of doing it would be by putting two
bits of fine mesh very close together but not quiet touching. One would
be positive and the other negative. There would be a short when the
raindrop bridged the two pieces of mesh. Also a heater would have to be
going near the system so it would dry out quickly after the rain
stopped so that the system would reset itself for the next lot of rain.


One way I thought of that may make the electronics simpler would be to
use very high voltage like on the bug zappers. This may make changes in
voltage or current larger and this may be more easily be able to be
measured. I am not sure what you think would be the best way to go if I
make up something like this.

However, even if I make the above up I would still like to be able to
try something like a lazar over a distance of about one kilometre to
measure rain that is approaching. I think this could be simpler than
the other suggestion of a network of sensors via the Internet. The
lazar would be pointed at a light dependent resister. The light
dependent resister would be housed in a tube to stop as much other
light entering as possible. When there is rain or drizzle around, it
would partially dim the light from the lazar so that the light
dependent resister would put out a lower voltage.

Another type of lazar or diode may be better than a light lazar. For
example an infa-red diode which could use resisters that respond to
infa-red instead. This may make it more accurate in the day time as
outside light may affect it less. I also thought other types of
radiation could be used such as micro waves etc.

What do you think would be the easiest way to go based on the above
suggestions?

Your help is appreciated
Regards Richard.


Re: Rain affecting signals and sensing rain.


On 15 Mar 2006 02:22:49 -0800, " snipped-for-privacy@yahoo.com"

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How much electronics experience do you have?

I think the what the BOM use is probably the best solution. RADAR.

Laser doppler (as with any optical system) is no good in fog/polution.
PCB based sensors have poor response time, and when the rains stops
you need to wait for the water to evaporate. High volatage is
susceptable to moisture and high humidity.


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Re: Rain affecting signals and sensing rain.


Hi

How much would radar cost? I think it would be very expensive?

We do not get a lot of pollution or fog in our area that obscures
visibility, so lazar may work ok. However, it would be a bit of trouble
to line everything up over a long distance.

I thought there may be some other signal that would also work which
would be easier to line up as they would have a wider beam and would be
less affected by outside radiation . However, I understand no matter
what I would use I would need line of sight

If anyone has any more ideas on this and what I stated in the previous
letter, please let me know.

I do not have a lot of electronics experience, but I know someone who
can help.

Your help is appreciated,
Regards Richard.


Re: Rain affecting signals and sensing rain.


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Note: it helps to include at least some of the post you are replying to
so we have some context for the discussion.

Yes, the radar will cost a lot more than the other simple methods here.
Also, you are unlikely to get it licenced. Or calibrated. The BoM has
pretty strict procedures for cal'ing radar (and everything else) so that
they get meaningful results. I also would hesitate to suggest you use
one when they are actually dangerous when used incorrectly.

A laser or similar beam is susceptible to being interrupted by animals,
birds, people, etc. Can you reliably get around that problem? Also note
that a laser powerful enough to go the distances you are talking about
is likely to be a hazard to eyeballs.

I didn't bother to take you to task earlier on your statement that their
radar is unreliable in your area - what do you mean by this? Are you
outside the area(s) of coverage, or you just feel the radar is unreliable?

Have you considered checking out the satellite coverage? Also available
at BoM's site - not as real-time as the radar though. The reason you are
not seeing the very light drizzle you want is that it is essentially
insignificant so gets averaged out. Do you really care about
precipitation in such small quantities?

Not trying to tell you how to suck eggs or anything but the simple
detector with a large fine mesh should work well enough. A high voltage
won't be of significant use though it may kill the moths.  :-)

Cheers.

Ken


Re: Rain affecting signals and sensing rain.



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Unreliable readings from the rain radars are quite common - there's an
explanation on the BOM site explaining this. The most common issue is the
curvature of the earth and the multiple beam angles used to try and achieve
a consistent sensing altitude across the scan radius, which I think is
something like 3,000 feet. If rain is forming below this it won't be seen.




Re: Rain affecting signals and sensing rain.


Hi

Thanks for the letters.

We get a lot of drizzle in our area which does not get detected by
radar or audiably by sound on a roof. Also the radar covers a large
area and does not detect small amounts of rain. The frames are also
only updated every 10 minutes. However, the drizzle we get is still
enough to wet things. I am on the Atherton Tableland at 737 meters
altitude.

So is there any other signals or radiation apart from lazar light that
would have their strength reduced by such precipitation so that their
strength could be easily measured?

Your help is appreciated,
Regards Richard.


Re: Rain affecting signals and sensing rain.


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The problem with using path loss to detect rain is that other things
will cause path loss as well. It won't be any more dependable than the
radar. Again, why not try out the simple sensor?

Cheers.

Ken

Re: Rain affecting signals and sensing rain.


 > Again, why not try out the simple sensor?

A piece of Veroboard mounted on a steep angle (so most of the rain runs
straight off) might be an easy way to prototype a simple sensor.  Just
connect all the odd tracks together, and then all the even tracks
together, and (depending on the requirements of the OP), check for
continuity or measure the resistance between the pairs of tracks.

I believe Jaycar and Altronics carry Veroboard.  I doubt it'd be
suitable for long-term outdoor use, but it'd be hard to beat for a
"proof of concept".

Peter

Re: Rain affecting signals and sensing rain.


How about a large collector (think *big* funnel, or possibly even the
existing roof drainage system) and in the output pipe, either a flow
sensor (to give a range of outputs depending on actual rainfall), or a
simple continuity test to detect rain/no rain.

Rethinks: perhaps the "dynamic range" of the existing guttering and
downpipes might be just a *little* too large between "barely raining"
and "extreme storm" :-)

Peter

Re: Rain affecting signals and sensing rain.


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If you use too big a collector, light rain (an undefined variable) may
evaporate before getting tot he sensor. But in principle a good idea.

Cheers.

Ken

Re: Rain affecting signals and sensing rain.


Hi

Thanks for your letter.

I plan to get some Veroboard. However, stainless steel mesh would last
longer and may be easier to mount with a very small gap between the two
pieces of mesh. Or do you think fine mesh could have other
disadvantages? I am thinking of using some with holes of about 2mm
across.

The rain I want to detect would often be before there is any runoff so
the idea about the funnel is no good. I have a tipping bucket rain
gauge that measures the intensity of heavier rain and it is graphed out
at http://weather.org.au/tolga /

I would still like to try a signal as well as it would not matter if
other things interrupted it on occasions. It would still give an idea
and would be able to detect lighter rain than the radar. If you know of
any other radiation that would be better than light to use, please let
me know.

Your help is appreciated,
Regards Richard.


Re: Rain affecting signals and sensing rain.


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As others have said, the problem is that pretty much anything in the air
(dust, pollen, haze, smoke) is going to attenuate a beam.

My suggestion is to try the circuit at the bottom of this page:

http://www.emesystems.com/lwet_dat.htm

It's a simple circuit - you can just use a standard 555 and regulator rather
than the specialised versions they use, it is hella-sensitive, the sensor is
a simple grid - you could use veroboard as someone suggested, or maybe make
up something finer, and you can interface the output a number of ways,
voltage, current or frequency - the latter being a very easy way to
interface to a micro.









Re: Rain affecting signals and sensing rain.


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just measure relative humidty,

if it's 100% there's excess moisture in the air. (sleet/hail/rain/drizzle/fog)


--

Bye.
   Jasen

Re: Rain affecting signals and sensing rain.


snipped-for-privacy@yahoo.com says...
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The radar is most likely able to detect the rain.
There is one proviso though, it has to be able to see it from it's point
of view.

The lowest threshold is actually a fair bit higher than light drizzle.
It is also possible that the radar is detecting it, but the signal is
being suppressed.
The level 1 threshold of 12dBz is roughly equivalent to 0.2mm/hour.

Which radar are you using? Cairns?

If it is light drizzle on the hills, it is also possible that the radar
is gating the signal off due to massive permanent echo contamination.

Cheers, Ray



Re: Rain affecting signals and sensing rain.



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You know the noise that rain makes on a tin roof?  Well my suggestion is to
get a tin can or plastic sheet and attach the element of a piezo buzzer to
the inside surface of the end of it or use a moving coil speaker with a
high gain amplifier, and then design some kind of filter (probably high
pass) that feeds a comparator that will trigger off the sound of a rain
drop hitting the diaphragm but not from ordinary noises.

If you can get the signal processing right then it should be very cheap and
the sensitivity could be improved by adding more of them and totalling the
number of pulses per minute.

Chris


Re: Rain affecting signals and sensing rain.



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I will post an image of my data, but I'm using a leaf wetness sensor with a
heater
and it works

Match




Re: Rain affecting signals and sensing rain.


Hi

Thanks for your letter.

I would be interested in getting a leaf wetness sensor made. However, I
do not have much electronics experience or time. Could you or do you
know of anyone who could make one up for me or are there any made up
units for sale. If so, how much would it cost to either buy one or get
one made? How long do they take to make? I am about to make an order
from Electus Distribution so I could purchase the parts.

I have a data logger that collects data so that the weather can be
graphed out. It is then automatically uploaded on to a public site
linked to http://www.weather.org.au/tolga/ The logger requires
between 0 and 5 volts. The voltage values are saved in a text file and
pasted into Microsoft Excel to be converted into the values I need and
graphed out. It would be good if very light drizzle registered at
perhaps the lowest voltage and heavier drizzle was logged at a higher
voltage so that a graph could be created. Also it would be good to put
an alarm on the wetness sensor so it would buzz even when light drizzle
is falling on it. The buzzer could be switched off and separate to the
computer and data logger.

Could you also please contact me by email if possible. The address is
snipped-for-privacy@truesolutions.info or you can go to the website above.

Your help is appreciated,
Regards Richard.


Re: Rain affecting signals and sensing rain.


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I'm not sure whose  you are replying to, but the leaf wetness sensor on this
page
http://www.emesystems.com/lwet_dat.htm
is available from them for US$65
It's listed about 3/4 down on this page:
http://www.emesystems.com/prices.htm

The base unit puts out 0.2-1v but it looks like you can get  one with a more
suitable voltage output for an extra $10. I'd suggest you send them an email
if you're interested.






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