The brainy Letterbox?

An overview of our concept for a smart letterbox.

We are nearing the completion of our Smart Letterbox prototype, one of our initial projects, and we thought it might be of interest for you to get a coarse overview of the basic concept.

Basically, the concept is very simple: We want an indication at the letterbox itself if there is something inside or not. In a second step, we also want to get notified by mail/SMS or within an app (openhab, webapp). Also we wanted to create a concept, that can be fitted in any standard letterbox in Switzerland. The solution we came up with is shortly described in the following paragraphs.

Hardware

We have chosen an Arduino Uno as the main processing unit, since it allows for easy and fast prototyping. Five scale sensors mounted under a plate do the letter recognition by sensing the weight change. An RGB LED glows in red if the letterbox is empty, and in green otherwise. For triggering the notification, it is planned to transfer the information over a LoRa network to a server.

coarse hardware overview

coarse hardware overview

Software

The software is designed in a modular way, such that features can be added/removed very easily. At the moment, three basic modules are being designed: A control module, a module to handle the sensors (scale, LED) and a module to connect to the LoRa network.

software design

software design

Further Extensions

In a next step, we want to use photodiodes next to the lid to detect if letters are stuck in the slot. Furthermore, some security features could be added to letterbox, e.g. the removal of a letter.

Market Survey

While building the prototype, we also conducted a market survey in parallel. The main conclusion is that people prefer a push notification to an app.

We are aware that the smartness of our letterbox is kept to a low level at the moment, but we wanted to add features step by step, based on the feedback we get from potential customers.

first prototype with the parts to be installed within the letterbox

first prototype with the parts to be fitted within the letterbox