Hello after some break with blog updates, I got a case to arrange mailbox alarm to prevent unnecessary visits to the mailbox. Site already had RuuviTag based measurement system with gateway, so next step was to install one additional sensor inside mailbox.

The sensor was installed on the inside of the mailbox cover using adhesive tape. The main idea is to use movement counter to create needed alarms. Almost immediately after installation it became clear that other sensor data gathered was valuable for upcoming mail detections.

Humidity measurement early morning hours gave clear indication about dry newspaper arrival. See picture below. Few percent drop after paper arrival is measured. After paper is taken away humidity values will start to rise again.

Signal level measurement gave also significant indication. It could be probably possible to use estimate amount and type of arrived mail. Typically few dBm drop is seen when mailbox have stuff inside. Some more data is still need to be gathered to get proper idea about possible correlation with different type of mail.

In this case first drop is from Helsingin Sanomat delivered in the morning and later is weekly mail including separate mail items.

To get more interesting measurements it was clear that mailbox was acting now also as a rain sensor. Water droplets will create small drumming effect causing counter to create ghost movements and false alarms.

During heavy rain it was also possible to measure small drop in received signal strength like in this example below. 2-3 dBm drop in 2.4 GHz signal was detected during one very heavy thunder cell rain event.

And finally, when the summer sun shines, temperatures will go pretty high inside box.

Future studies will be done when I have more data about different scenarios.