I've been posting around a lot for a rainfall measuring project. Right now I'm trying to use IR detector / emitters to detect a drop.
This is the setup I'm using:http://imgur.com/mhLtm
and I've got these detectors / emitters, courtesy of sparkfun:http://www.sparkfun.com/products/241
right now, I can't seem to catch a drop. If I drop something big through the PVC pipe, the values change (I'm just reading through the analog port).
I'm not sure if the problem is time-related (I've changed around the internal clock so that my analogRead is fast, at least 10kHz but maybe up to 50kHz), or if these sensors are just picking up infrared from all directions, and it won't work until I add baffles or something to redirect their signals.
Ideas? Drops should be falling around 4-5m/s, and they are 3-5 mm in diameter (but not actually spherical when airborne, more hamburger-shaped). So the time window is probably between 0.1 to 1 ms. Seems like it should work. But I've got a goofy setup.