The simplest and most direct way of measuring rainfall is to use a tipping bucket rain gauge. The mechanism of this device (shown left) collects rain in the collector and directs it to drip through a small hole into the "top" bucket. As the bucket fills, it gets heavier. At a certain point, the weight causes the bucket to fall. As the bucket assembly moves,
the magnet mounted near the bottom swings past the reed switch, which momentarily closes,triggering the counter circuit.
After the bucket falls, the water spills out and the other bucket is now in the "top" position to
catch the dripping water. When it gets full, it falls, triggering the reed switch as the tipping
bucket assembly swings back. This process repeats as long as water is dripping from the collector.
Many of the tipping bucket rain gauges are designed to tip at 0.01 inches of rain. The first
tip usually takes a little more than this, because some of the first few raindrops "stick" to the
A pair of adjustment screws usually provides calibration. By shortening the screws so that the
bucket assembly is tipped further, it takes more weight to tip it. This has the effect of reducing
the counts for the same amount of water. Conversely, by lengthening the screws, there is less
travel and buckets tip more often.
The reed switch is connected to a DS2423 l-Wire counter. For each switch closure the counter
increments by one. Looking at the schematic below, the counter input is pulled low via
resistor Rl. When the reed switch closes, the counter input is pulled high momentarily, producing
a count. The DS2423 incorporates internal filtering on the counter inputs to minimize
In order to maintain the rain count during one-Wire bus power outages, battery BATl provides
power to the counter via D3. Using a CR2035, the battery should last at least 5 years. With
the counter always powered, there is no way to reset the counts and so you must zero the counter in your software.