My office frequently hosts many guests. Restrooms are shared with other businesses on the floor and require a key to access which guests are given and quite often forget to return. We are not allowed to duplicate the keys and the landlord charges a fee when they go missing. Attaching a bigger key chain like a hubcap was frowned upon by management so I came up with a Bluetooth solution using the Adafruit Feather nRF52840 Express board.

The Feather nRF52840 Express has many great features that this project leverages:

• Support for Bluetooth Low Energy
• Built-in NeoPixel RGB LED
• I^²S digital audio interface
• 21 GPIO pins
• Code can be written in CircuitPython
• Built-in LiPo battery port with charging circuit

Key fobs powered by the nRF52840 will reside in wireless charging cradles in the office lobby.  The fobs will determine their proximity by scanning Bluetooth BLE beacons placed throughout the office.  The Feather's built-in NeoPixel color will indicate location and battery status.  If the fobs are removed from the vicinity then a warning tone and message will be played.

Parts List