Here is some additional info regarding that RuuviTag based mailbox alarm system explained earlier post which quite quickly leads to advanced meteorological measuring device. The basic idea of current RuuviTag installation is shown in picture below.

Sensor is located just below the tiltable metal cover. Water droplets create small detectable vibration, like drumming effect, which is then displayed as a movement counts.

More intense rain is, more counts are coming, very simple. RuuviTag counter values are by the way reset at 254, so in this example below during some heavy rain, values start again from zero.

After some experiments, looks like current mechanical design leads surprisingly sensitive detections even in quite light rain events. There is no any trees or other objects too close which could lead additional droplet generation. All counts are based pure rain coming from the sky.

When continous rain was present, there is small increased “noise” also measured using accelerometer data. See the last part of measurements right side of this graph seen below. Higher spikes are from cover openings.

In summary, the mailbox now functions as an advanced weather observation device, only lacking of wind measurements. Wind can be definitely also measured using mailbox RuuviTag setup, but looks like its sensitivity begins starting from hurricane or trombi level wind speeds.