This information can be used to build a LORA-based mailbox receiver and a sender, using the same PCB.

Many projects like this use WiFi, but if the distance is beyond that reach, like in an apartment building, you can't use it.

LORA technology should solve that issue, so I experimented with that and after many trials and testing, build a sender that is located in the mailbox itself, and runs on a LiPo cell. It sends a message to the receiver that is located in the apartment, and upon receipt will beep a few times and turn on an LED.

Although the sender can last a long time on a full LiPo charge, it needs to be exchanged with a fully charged one every once in a while. When the sender has a mail message, it also sends the voltage of the cell, so the receiver can turn on another LED when the voltage is too low.

Unfortunately, I don't get mail that much, so the risk was that the cell would be depleted before the low capacity was noticed. To circumvent that, I used a voltage supervisor in the sender that would trigger on a critical cell voltage level, and send a distress signal to the receiver.

I also spent a lot of time on selecting the right sensor to signal arriving mail. At this moment I'm using a mechanical vibration sensor, but that also depends on the mailbox construction you have.

All these details can be found on my Blog here:

https://www.paulvdiyblogs.net/2024/12/mail-letterbox-notification.html

The required software and hardware files and pictures are also on my Github project here:

https://github.com/paulvee/LORA-Mailbox-Alarm