Every facility has a conference room or other meeting space. And when the door is closed, it is always a guessing game whether the room is occupied or not. This inevitably leads to someone opening the door and disturbing what is happening inside. It could interrupt a meeting or spoil an important experiment.
Commercial sensor/indicator combinations can cost over $400 dollars. If you have many rooms, the cost could be prohibitive.
This project started as an inquiry by the Indiana University IT Department who wrote to Adafruit asking if there was a less expensive alternative to commercial units by using Adafruit’s Trinket mini-microcontroller. This project is inspired by that inquiry.