This project is a mail box notifier for indicating the presence of letters and other post items in my mail box at the street access to my garden. It is a standard "Swiss Post" specification mailbox, but the ideas and design could be adaptable for other types. This document describes the design and construction of this device.
It consists of a battery operated transmitter part and a receiver part.
The transmitter uses an ATmega328P and an NRF24L01 2.5GHz transceiver module together with an infrared sensor array embedded in a mat on the base of the mailbox. The sensor array uses a reflection and beam break principle to detect objects in the mailbox. It periodically scans (every 32 seconds) and transmits status data including the detection status and battery condition to the receiver. It is optimized for very low power consumption.
The receiver part also uses an ATmega328P and an NRF24L01 together with a sounder and LEDs to indicate the presence of post items and the battery condition of the transmitter. The receiver is permanently active and is powered via a USB power supply.
This is a development of a project I started over 5 years ago. It had a fundamental rework 4 years ago but still on prototype boards. The version here is new and differs only from the previous version in that it is now on printed circuit boards but the electronics and program design is the same. This design proved very reliable and had a battery life of at least 2.5 years.
The attached PDF file contains a full description of the development, including schematics, and all the software is in the attached .ino files
TX .ino upgraded to V1_06P (27.07.2020)
MailboxMonitor_V1_00.pdf (1.2 MB)
MailboxMonitor_RX.ino (5.92 KB)
MailBoxMonitor_TX.ino (12.6 KB)