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