I developed one by the use of the back of a CD case such as the impact target. I will try other different materials in the future, but for the moment it is enough to test.
But my first question now is: how to connect it to arduino? I think that something similar to the knock sensor explained in the arduino webpage could be a starting point. Take a look: http://www.arduino.cc/en/Tutorial/Knock. But other possibility is to capture the sound itselft. May be this option is more complex (?), and theauthor of the instructable already recognize that it is not able to measure the rain from the record of the drops. so may be the use of the knock idea could be a better option... (?)
The second question is how to measure the intensity of the rain? i don´t want to have a yes/no rain detector, but also a intensity measurement. I suppose that it could be related to measure the number of impact per area (the area of the CD case, in my case) per time unit (30 seconds or one minute or something like that).
Any idea about this topics (how to interface it with arduino, and how to measure intensity -i suppose that depends on how it is interfaced to arduino)??
This is just a wild stab in the dark here, so keep that in mind. Couldn't you use a small microphone to detect a single drop, estimate the size of an average rain drop, and count the number of the drops. That way you could extrapolate to inches of rain per hour?
The only problem that I can foresee with this plan would be the speed that you would need to monitor the microphone. I think that you would need a pretty speedy ADC, and I don't know if the Arduino would be fast enough.
This is just a wild stab in the dark here, so keep that in mind.
:-/
I don´t want to overlap the work of the author. I made it just for fun. I know that they want to publish it (i suppose than in a scientific or technical journal). So i don´t want to copy or stole their work because i will not publish it anywhere.
Just only i saw this project, and find it interesting. Since they didn´t provide information about how to read it (in fact they say that they record the sound to process it later), i think that it could be cool try to do it with arduino, but without record the sound, and just only using something similar to the knock idea.
About your comment, i think that you are right. May be arduino is not enough fast, at least for an important rain, because a lot of drops at the same time could be impossible to recognize such as different drops, more than one very "fat"... So may be it could be interesting to think about to have different intensity levels , also depending of for how long we have knocks and how important they are... what do you think?
So, this post was only to take and discuss ideas, but for fun!
Thanks!
Inspired in this design, i developed something similar cutting the lower base of a coke can (ok, in my case a beer can!) I will take some pictures this weekend and post them here to illustrate, and coming soon... the code!