The disdrometer presented here is better for "listening", since this instructable competes in the "Art of Sound" contest. In a future instructable, a version that is optimized for measuring rain will be presented.
Acknowledgements: This instructable is based on the work of Coen Degen, student at Delft University of Technology, whom I had the privilege to supervise.
Example file: the example file is a recording of a rainstorm in Tanzania, made by Coen Degen.
Step 1: The components
-a piezo electric element. These can be bought at radioshack. They should cost you next to nothing. The one used in this setup is also used in alarm buzzers. When deformed, a small voltage difference forms between the poles of the element. This will be used to turn the rain into en electric signal.
-a vertical piece of glass (ceiling windows are great) or
-a smell piece of glass mounted on a picture frame (see first picture)
-an audio cable with a mini-jack connector. (old earphones form old i-pods will do the trick)
-soldering gear (carefull: HOT, only use when you know how to!)
-superglue (carefull: superglue is irritating to the skin. Be very carefull!)
-a computer with a microphone input, or a sound system with a mini jack input (or any input, but you'll have to use a different connector above, of course)
Step 2: Assembly and listen
Be careful not to get any superglue on your skin (never, like I once did, try to open it with your mouth), if you do, get it off directly.
Stick the minijack in the microphone input of your computer and put your speakers on: now you can listen to the rain.
The file attached to this step is a wave file of a minute recording of rain (quite a heavy storm).
Good luck and enjoy!