A Mailbox Notifier with Laser Rangefinder

As Gary Watts explains, smart mailbox notifiers are fun and challenging projects that have become more popular due to wireless hardware like ESP8266 and ESP32. Such devices could normally use the opening and closing of the mailbox door as a “mail’s here” indicator, but in this case the letterbox has no door. It’s simply a gap in an arrangement of bricks.

Watts' answer to this unusual situation was to implement a VL53L0X time-of-flight (ToF) sensor to detect the presence of letters in the box, facilitated by the fact that the opening is thin enough that letters generally have to be stuck in vertically. The sensor is fastened in place via a 3D-printed mounting bracket, plus liquid nails.

Processor-wise, the notifier is based on a Wemos D1 mini ESP8266 dev board, which relays sensor information to a Home Assistant installation via MQTT. Home Assistant then uses this information to determine whether a letter is indeed present.

Watts' notifier, as with many such devices, is located in an area without a readily available power supply. It employs an 18650 cell, along with a pair of solar panels and a charging board to provide juice. The ESP8266 is normally kept in sleep mode in order to conserve power, waking up every 25 minutes to take measurements. Circuitry, including the solar panels, is stuffed into a waterproof housing with a clear top, offering protection from the elements while still allowing it to charge.

A full build guide, complete with configuration files and schematic, is available on Watts' website.