My mailbox is ~5 meters away from my flat, so I thought it’d be fun to install hardware into the mailbox that a) automatically detects when a letter has been thrown in, b) detects when the mailbox is being emptied and c) notifies me via push notification, Alexa and an LED signal in my flat when the mailbox is full.
Hardware / Sensors:
My outdoor mailbox is a rather challenging enviroment (-10°C - +40°C, up to 90% humidity plus actual moisture in the mailbox during heavy rain).
My first attempt to solve this three years ago was using two Homematic’s HmIP-SWDO. Knowing that the enviroment is somewhat challenging, I sealed the entire PCB with an insulation spray (non-conductive coating). One year in, one of the two sensors stopped working, and the other one heavily drained the battery. My interpretation was: Even if you seal the PCB with the coating, the battery (and the battery contacts) are still exposed to humidity, which led to corrosion and eventually sensor failure.
My second (and so far reliable) attempt was using two IKEA Parasolls. They have one big advantage: The battery compartment, and with it the entire sensor, is sealed with a rubber gasket. So no need to apply a custom coating, as the battery and its contacts are sealed at the same time.
I’ve seen letterbox-automations based on with vibration sensors. But I felt that using window sensors (and using two sensors of the same type) is just a nicer way of doing it. So I opted for one sensor at the lid, and one sensor at the door.
The Parasoll’s are magnetic contact sensors, which means that they require a magnet on the opposide side to tell them when something is open or closed. In the case of the main door, the doing was easy: Just place the magnet on the main door, and the sensor at the base of the mailbox (see bottom of the mailbox: left: sensor, right: magnet).
Equipping lid with a sensor was a bit trickier: Probably as part of a rain detection (or “grab-in-prevention”), there’s a metal rim below the lid that prevented me placing magnet that comes with it next above the sensor. The solution was to just just use a stronger magnet (in my case: the magnet of a conference-name tag) to overcome the greater distance and metal rim in between. See picture below: Sensor at the bottom, stronger magnet (plastic piece with three round magnets) at the top). Important: Since mailmen often don’t fully open the lid to throw in mail (and thus only open the lid slightly), some trial and error was needed to find the optimal position of sensor and magnet.
With this hardware now in place, there are four states:
- Main door closed
- Main door open
- Lid closed
- Lid open
Sensor / Wireless connection:
My mailbox is not only a metal case, but also incapsulated in a block of concrete (so not the ideal setting for a wireless connection).
The solution was to place an IKEA Tretakt as a zigbee node in between the mailbox and the nearest indoor Zigbee node at my porch. Only in that setting, the connection was stable.
Software / rule:
The rule tha tinterprets what’s going on should be executed if either the lid or the door are being opened. Therefore, the rule trigger looks like this:
The rule itself looks like this and is pretty straight forward.
In addition to the notifications executed by the rule itself, the variable Variable_Briefkasten is monitored constantly to signal a full mailbox with a yellow light on my Homematic HmIP-BSL
I can highly recommend this LED signal being placed at a central location of the flat, as it’s a convenient way to signal important messages (full mailbox, rain, alarm status, etc) in an easy and suble way.
Feel free to post thoughts and comments below.