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-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Wesley Moore
> Sent: Thursday, 17 February 2000 14:48
> To: PICLIST@MITVMA.MIT.EDU
> Subject: How to measure rainfall (digitally)
>
>
> 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
>
> wmoore@cs.rmit.edu.au
> http://wmoore.tsx.org/
>