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
  • I²S 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

Adafruit Feather nRF52840 Express

PRODUCT ID: 4062
The Adafruit Feather nRF52840 Express is the new Feather family member with Bluetooth Low Energy and native USB support featuring the nRF52840!  It's...
$24.95
IN STOCK

Adafruit I2S 3W Class D Amplifier Breakout - MAX98357A

PRODUCT ID: 3006
Listen to this good news - we now have an all in one digital audio amp breakout board that works incredibly well with the 
$5.95
IN STOCK

Inductive Charging Set - 5V @ 500mA max

PRODUCT ID: 1407
The squarish board with two chips on it is the transmitter (power with 9V).  The longer board is the output and you can connect that to the part of your project that...
OUT OF STOCK

Lithium Ion Polymer Battery - 3.7v 500mAh

PRODUCT ID: 1578
Lithium ion polymer (also known as 'lipo' or 'lipoly') batteries are thin, light and powerful. The output ranges from 4.2V when completely charged to 3.7V. This battery...
$7.95
IN STOCK

Compact Switching Power Supply - Selectable Output 3-12VDC

PRODUCT ID: 1448
Wow, is this not the most useful thing you did not know existed or what? Its a switching wall adapter where you can easily change the voltage! It's like a benchtop supply you can...
$14.95
IN STOCK
2 x Waterproof Speakers
DB 67 Series Waterproof Speaker 8 Ohms 1.5 W (SW390608-1)
3 x Ibeacons
USB Ibeacon BLE 4.0 Module
2 x Cooling Fans
60 mm 1600 RPM 11 dba Fan
2 x Reed Switches
Reed Switch 14mm Plastic Anti-Interference Normally Open
2 x Micro USB Plugs
Micro USB Male Type B, 5 Pin Solder Plug
1 x DC Power Jack
DC Power Jack 5.5 mm x 2.1 mm
2 x Bangles
Silicone Bangle Key Ring Wrist Keychains
2 x Magnets
10 X 4 mm N35 Magnets
8 x Threaded Brass Inserts
M2.5-0.4 Threaded Heat Set Inserts for 3D Printing
8 x Screws
M2.5 x 10 mm Stainless Steel Hex Head Screws
8 x Bumpers
Adhesive Rubber Bumpers 12 mm x 7.5 mm
This guide was first published on Jul 22, 2020. It was last updated on Jul 22, 2020.
This page (Overview) was last updated on Aug 02, 2020.