Weather station - Rainfall sensor

Alright, as I am an electrical engineering student, I just have to submit my designs I used for 'successful' projects. You can be inspired by them or alter it to suit your needs but please mention me.

This circuit:
It was part of an rainfall sensor. When it rains, a transparent tube fills with water. Inside this tube is a floating cylinder that blocks light. A number of LEDs and photo diodes are glued at the side of the tube. When some rain has fallen, the cylinder will block the light of a LED and the photo diode won't give of a current. This schematic shows how to connect the LED (left) and the photo diode (right) to an OP-amp which gives an high or low voltage. This signal could be sent to a microprocessor or a DAC. This circuit could be easily used for other projects. An automatic doorbell could be implemented by replacing the LED by an Laser.