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PICList Thread
'How to measure rainfall (digitally)'
2000\02\16@225043 by Wesley Moore

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I have a friend interested in making his own logging weather station. I
was wondering if anyone had any ideas on how to measure rainfall for such
a project.

___________________________________________
Wesley Moore
RMIT - BEng/BApp.Sc. 2nd Year

spam_OUTwmooreTakeThisOuTspamcs.rmit.edu.au
http://wmoore.tsx.org/

2000\02\16@233523 by Ken Webster

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Wesley Moore wrote:
>I have a friend interested in making his own logging weather station.
>I was wondering if anyone had any ideas on how to measure rainfall
>for such a project.


Tipping bucket rain guages are very common.  These basically have a funnel
of known cross-section which dumps water onto a little teeter-totter like
thingy with two buckets.  Whichever bucket is in the "up" position catches
the water falling from the funnel.  Once it fills with enough water to shift
the center of gravity over the pivot point, the teeter-totter tips the other
way and the bucket that was "up" drops down dumping out its water.  A reed
switch or optical interrupter is used to count each time the bucket tips.
Each tip represents a known amount of rainfall.

... I did a quick search to try and find a diagram.  The site I found
doesn't have a diagram but it does have a picture (the lower picture shows
the tipping bucket mechanism):

http://www.greenspan.com.au/rain.htm


I have code for a PIC16C73 that runs at 76.8kHz (so it can go about 6 months
on a 9V battery), maintains a real-time clock, and records the time of each
bucket tip to the nearest second in an I2C EEPROM.  It communicates with PC
software over an RS232 port to offload the data.  Software on the PC can
analyze the bucket tip times to provide measurements of rainfall intensity
as well as total rainfall amounts for each rainfall event.  We used a whole
bunch of these at work (hence the cheap PIC-based design) to analyze
rainfall patterns over various crops in a study area.  Since I did this work
as part of a government-funded research project, the code and design are in
the public domain.  The code is here if you are interested:

http://kdsl32.dnvr.uswest.net/cgi-bin/tl2.exe/RAIN

I could dig out the schematics and board design too if you like.

Cheers,

Ken

2000\02\16@234124 by Steve Kerrin

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The usual method is by means of a "tipping bucket" device. It is essentially
two chambers either side of a pivot which are a lot easier(for me) to sketch
than describe. A gathering funnel is placed over the pivot point and as one
chamber fills, it upsets the center of gravity and tips. This places the
other chamber under the funnel and empties the first chamber. This repeats
back and forth and the "tips" are counted electronically. Quantitation is
derived from the volume of the chambers and the area of the gathering funnel.
The larger the gathering area and smaller the chamber volume, the more
sensitive the device in terms of tips per unit time.

A search on "rain gauge" AND "tipping bucket" should yield both commercial
versions and, perhaps, a home-brew unit. Email me directly and I'll scan my
sketch if you don't have any luck.

Steve Kerrin (a new lurker and learner)
Escondido, CA



Wesley Moore wrote:

{Quote hidden}

2000\02\16@235143 by Stephen Wright

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You can use a bistable bucket.
This has two compartments and looks a little like this:

         \        |        /
          \       |       /
           \      |      /
            \     |     /
             -----------
                  ^ pivot
                  |


The bucket will start in one state or the other.
The rain input fills the upper bucket until the quantity of water causes the
bucket to tip and empty all its water.  The cycle then repeats for the other
bucket.

If you use a sensor (reed relay, optical etc) you can could the number of
bucket transitions.  All you need to do is calibrate to find out how much
water (mm) it takes to change the state of the bucket.


Steve Wright
vk2kha


> {Original Message removed}

2000\02\17@070846 by Tom Handley
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  Wesley, others have already mentioned the standard tipping bucket rain
collector. I decided to buy a commercial unit from Davis Instruments for my
PIC-based weather station. It's very accurate. You get a switch closure each
time the bucket tips which is equal to 0.01" of rain. They also have a
metric version. I installed mine around 4 years ago. Davis charges $75 but
if you shop around you can probably find it for $60-$65. It's used in
several weather station packages from Radio Shack and others.

  If you want to build one, the October 1993 issue of Electronics Now
has detailed plans. There is also plans for building an anemometer and a
wind vane. The same author, Fascinating Electronics, now sell kits. Their
rain collector kit is around $35 I think. In both cases, you need to
calibrate it.

  Another source is Dallas Semiconductor's weather station using their
IButton 1-wire devices. The basic weather station is around $80 and the rain
collector is around $50 but needs calibration. This is probably the best
overall package for the money. Especially for interfacing to a PIC.

  For more info, take a look at:

     www.davisnet.com/weather/products/sensors.asp
     http://www.gernsback.com/
     www.columbia-center.org/fascinating/obs/observer.html
     http://www.ibutton.com/weather/index.html

  - Tom

At 02:48 PM 2/17/00 +1100, Wesley Moore wrote:
>I have a friend interested in making his own logging weather station. I
>was wondering if anyone had any ideas on how to measure rainfall for such
>a project.
>
>___________________________________________
>Wesley Moore
>RMIT - BEng/BApp.Sc. 2nd Year


------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

2000\02\17@074413 by Rich Clemens

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The Peet station has four wires that almost touch and a drop of rain water
completes the circuit and is tallied.

--
Richard Clemens
clemensspamKILLspamwvwc.edu


{Original Message removed}

2000\02\17@144437 by Terry

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face
Sorry, 1st mail didn't have a "Who" entry....


How would you like to count practically every raindrop?

A piezoelectric disc is connected to a MCU's ADC (PIC of course) through an
interface circuit (peak voltage limiting, variable gain amplifier and a
digitally programmable filter).

What it does is "listen" for raindrops. How will it know it's rain or
birdseed? Heavy rain or a light drizzle? And more importantly how much rain
is falling?

By knowing the "signature" of falling raindrops and the amount. Use a
piezoelectric disc of known area (say 1 inch dia) and calibrate a table of
signatures for a known amount of rainfall. The PIC will set the interface
amplifier to maximum gain and wait for any "hits" to the piezoelectric
element. Once *any* hit is detected (birdseed, sand or rain), the PIC sets
the amplifier gain so that the peak signal to the ADC is at say 3/4 of full
scale. The PIC then sets up the programmable filter for whatever it's
supposed to detect, in this case "RAIN".

So by varying the gain and filters the PIC can be programmed to detect and
count a specified object (sequencial hits) or to determine the approximate
amount of a specified object (averaging hits).

Slanting the piezoelectric disc at an angle is necessary to prevent the
counted object or liquid from accumulating on the sensor. Thin aluminium,
glass, ceramic, steel, teflon, etc can be attached to the piezoelectric
element for wear resistance and/or electrical insulation.

Benefits are, it will have no mechanical moving parts, no corrosion,
adaptable to function as a rain detector, liquid flow detector or count
small falling objects like screws, nuts, ball bearings, etc.

A patent search i did in Dec '98 has a similiar but simple circuit to count
seeds as they were discharged from a farm machine (seed sowing). I offered
my improved idea for a local development grant and nothing came of it. So
if this improved idea is "new", so to speak, and doesn't infringe on any
existing rights. It's free to anybody that wants to use or develope it. I
sure hope the piclist is used for a prior art patent search coz i'm not
going to patent this and it'll be available to any and everybody that
want's it.


Cheers
Terry



At 02:48 PM 2/17/00 +1100, you wrote:
{Quote hidden}

2000\02\17@144858 by Craig Lee

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How would you differentiate, say..... a frog.

Exodus 8:2


-----Original Message-----
From: pic microcontroller discussion list
[EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU]On Behalf Of Terry
Sent: Thursday, February 17, 2000 12:31 PM
To: PICLISTspamspam_OUTMITVMA.MIT.EDU
Subject: Re: How to measure rainfall (digitally)
Importance: High


Sorry, 1st mail didn't have a "Who" entry....


How would you like to count practically every raindrop?

A piezoelectric disc is connected to a MCU's ADC (PIC of course) through an
interface circuit (peak voltage limiting, variable gain amplifier and a
digitally programmable filter).

What it does is "listen" for raindrops. How will it know it's rain or
birdseed? Heavy rain or a light drizzle? And more importantly how much rain
is falling?

By knowing the "signature" of falling raindrops and the amount. Use a
piezoelectric disc of known area (say 1 inch dia) and calibrate a table of
signatures for a known amount of rainfall. The PIC will set the interface
amplifier to maximum gain and wait for any "hits" to the piezoelectric
element. Once *any* hit is detected (birdseed, sand or rain), the PIC sets
the amplifier gain so that the peak signal to the ADC is at say 3/4 of full
scale. The PIC then sets up the programmable filter for whatever it's
supposed to detect, in this case "RAIN".

So by varying the gain and filters the PIC can be programmed to detect and
count a specified object (sequencial hits) or to determine the approximate
amount of a specified object (averaging hits).

Slanting the piezoelectric disc at an angle is necessary to prevent the
counted object or liquid from accumulating on the sensor. Thin aluminium,
glass, ceramic, steel, teflon, etc can be attached to the piezoelectric
element for wear resistance and/or electrical insulation.

Benefits are, it will have no mechanical moving parts, no corrosion,
adaptable to function as a rain detector, liquid flow detector or count
small falling objects like screws, nuts, ball bearings, etc.

A patent search i did in Dec '98 has a similiar but simple circuit to count
seeds as they were discharged from a farm machine (seed sowing). I offered
my improved idea for a local development grant and nothing came of it. So
if this improved idea is "new", so to speak, and doesn't infringe on any
existing rights. It's free to anybody that wants to use or develope it. I
sure hope the piclist is used for a prior art patent search coz i'm not
going to patent this and it'll be available to any and everybody that
want's it.


Cheers
Terry



At 02:48 PM 2/17/00 +1100, you wrote:
{Quote hidden}

2000\02\17@150321 by l.allen

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>
> How would you like to count practically every raindrop?
>

>
> What it does is "listen" for raindrops. How will it know it's rain or
> birdseed? Heavy rain or a light drizzle? And more importantly how much rain
> is falling?
>.....
> Benefits are, it will have no mechanical moving parts, no corrosion,
> adaptable to function as a rain detector, liquid flow detector or count
> small falling objects like screws, nuts, ball bearings, etc.
>
There are devices that measure rain by shaping every drop into the
same size and the Frequency of the drops coming off the bottom of
this plumb-bob looking device is proportional to the actual rainfall.
I know this because the chap who taught me to programme
microcontrollers was working on the controller for such a device
and I have found the units for sale on the web..cant remember
where though.
_____________________________

Lance Allen
Technical Officer
Uni of Auckland
Psych Dept
New Zealand

http://www.psych.auckland.ac.nz

_____________________________

2000\02\17@155637 by paulb

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Craig Lee wrote:

> How would you differentiate, say..... a frog.

 That would be tricky, but it would be a much larger signal in general.
It depends on how many feet land and in what sequence of course.  I
think it would be part of a general algorithm to say "something *BIG*
has landed".

> Exodus 8:2

 What *may* damage the PIC might be the hail (Exodus 9:25) and I think
the grasshoppers (Exodus 10:15) would give a quite large "kick" on take-
off.
--
 Cheers,
       Paul B.

2000\02\17@162750 by Terry

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erm... listen for a Thump! and a Gribbit?!


At 12:51 PM 2/17/00 -0700, you wrote:
{Quote hidden}

2000\02\18@105749 by M. Adam Davis

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Not only that, but you could pipe the sound into your bedroom, put it through a
chorus effects processor, and listen to the rain outside...

-Adam

Terry wrote:
{Quote hidden}

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