What about this:

Use an IR led and a lens to spread the beam out so it is an inch wide. Then
have a second lens to focus this beam back onto an IR phototrans which is
somewhat sheilded from visible light (one of the ones with a dark filter on
it). Modulate the IR beam and use synchronous detection on the other end.
Position the emitter/lens system opposite the detector/lens system,with an
inch between them. Have a large funnel to collect rain and channel it
between the two lenses. Look at the output of the synchronous detector and
look for high frequency changes (> a few Hz). If you see such noise, it has
to be something falling in between the sensors, most likely rain. You might
also want to angle the optical axis with respect to the vertical so that
not only would water change the transmission,but the refraction of the
air/water/air path would divert some of the IR away from the detector.

Its just a guess :-)

Sean


At 10:54 AM 4/17/99 +0800, you wrote:
>At 12:59 PM 16/04/99 -0500, you wrote:
>>     Put the board in 60¡ angle so that the water pours down from the 
>>     board. Also, the distance between the tracks should be less than the 
>>     size of a water drop.
>>     
>>     Juan Jimenez
>>     
>>Water conducts electricity. Make a sensor with a PC board that has two 
>>tracks in a Zig-Zag fashion about the size of a match box. Connect the 
>>one track to +V and measure the Vdrop on the other. The lower the Vdrop, 
>>the more water is on the sensor.
>>Of course, you will have to keep this clean and you also have to wait 
>>for the sensor to dry before you can make another measurement.
>>Just a nutshell, I have not done this yet, but thought about it one time 
>>or another.
>>     
>>Quentin
>Try this and you will find water droplets sticking between the tracks. You
>can use some form of spinning to centrifuge the water away but this brings
>in other problems.
>
>Peter 
>
|
| Sean Breheny                   
| Amateur Radio Callsign: KA3YXM 
| Electrical Engineering Student  
\--------------=----------------
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
mailto:shb7@cornell.edu ICQ #: 3329174