Sensing and Control for hobbyists and schools: Weather: Rain
The "easy" way to measure rainfall electronically is with a "tipper" device.
Rain from a known horizontal area is collected with a funnel. It falls in a tiny waterfall onto something like a little see-saw with a piece of roof gutter on it's upper side. The "roof gutter is divided in the middle by a vertical septum. As the rain dribbles into the gutter, it begins to collect on the uphill side of the see-saw. When enough has collected, the see-saw tips. Now the septum has moved, and newly fallen rain collects in the other, now upper, side of the see-saw. When enough has collected... and so on.
Connected to the see-saw is a magnet. As the see-saw tips, the magnet passes by a reed switch. The openings and closing of the reed switch reveal the rainfall to whatever you connect it to.
I have tried making the tippers... and it isn't easy to get the geometries just right. Go ahead... treat yourself... buy one ready made. The big boys can afford to have the necessary bits made out of plastic.
The best I've seen is available from AAG. It is the one once sold by Dallas, as a demo to promote its 1-Wire chips.
They also have a "Torrent" rain gauge for $59.95 that appears to be a more
standard size. Same URL, search for RG-3029
This may not be a tipping bucket design though since it doesn't have any
moving parts and is freeze proof. Someone remembered seeing a rain gauge awhile back that used a medical iv drip type setup with gold plated contacts to
count each drop of water. Perhaps this is of the same design.
I'm told that the "standard" collecting funnel, as mandated by the US Weather Service has an 8" diameter.
Colder climes: If you have below freezing periods, it is an interesting challenge to fit your "rain" fall collector with something to warm it, turn snow to rain, and find out how much has fallen that way. See my page on miscellaneous weather sensors if you are interested in measuring depth of snow fallen.
Rainfall collectors are especially vulnerable to problems arising from debris (leaves, etc) and the activities of arthropods. If you put a screen over the top, you will, in each rainstorm, "miss" some of the rainfall.
This page is meant for hobbyists. A lot of pleasure (or inspiration to improve your design!) can be had from comparing the results your electronic rainfall monitors record with the results of a simple traditional rain gauge.
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