Project Description

BlueBox is a Bluetooth-based audio management system developed for one of our clients.
It was designed as a central hub for wireless audio connectivity and analog audio routing, enabling seamless communication between mobile phones, Bluetooth earphones, and desktop audio systems.

The system provides advanced features such as hands-free calling, phonebook synchronization, SMS access, and audio stream switching, all controlled through a dedicated Windows utility application. BlueBox ensures flexibility by routing microphone and speaker signals intelligently between different connected devices.

Working

The design integrates two Bluetooth audio modules:

  • One module connects to the mobile phone, handling calling, phonebook, SMS, and music playback.
  • The second module connects to the Bluetooth earphones, providing wireless audio and microphone support.

For communication and control, the system implements multiple Bluetooth Audio Profiles:

  • A2DP (Advanced Audio Distribution Profile) – Streams audio from mobile phones to speakers or earphones.
  • AVRCP (Audio/Video Remote Control Profile) – Provides music control (play, pause, track navigation).
  • HFP (Hands-Free Profile) – Enables microphone and speaker switching for phone calls.
  • HSP (Headset Profile) – Manages call functions such as ringing, answering, hanging up, and volume control.
  • MAP (Message Access Profile) – Transfers SMS messages to the BlueBox Windows utility.
  • PBAP (Phone Book Access Profile) – Synchronizes the phonebook and retrieves call history (missed, incoming, outgoing).

The audio switching is managed by analog MUX ICs that route signals between Bluetooth modules, desktop audio I/O ports, and earphones.
A microcontroller controls the modules using UART commands and drives the MUX with GPIO logic.

For PC integration, BlueBox connects via USB-to-TTL bridge (CP2102) and communicates with the Windows-based utility.
The utility software, developed using PyQt, provides a GUI for pairing, device monitoring, call control, SMS viewing, and audio routing.

BlueBox Features

  • Connect up to two mobile devices simultaneously
  • Answer and make calls using desktop speakers or Bluetooth earphones
  • Stream audio from PC or mobile phones directly to Bluetooth earphones
  • Receive/end calls using the earphone button
  • Automatic disconnection of PC audio streams during calls
  • Switch audio streams between earphones and desktop speakers
  • Download call history (incoming, outgoing, missed) for both connected mobiles
  • Noise cancellation (CVC technology) for clear voice calls
  • Download and synchronize phonebooks from both mobiles
  • Read incoming SMS via Windows utility
  • Automatic reconnection when paired mobiles are in range
  • Automatic or manual switching of PC audio streams to Bluetooth earphones
  • Stream mobile audio to desktop speakers with auto PC audio disconnect
  • Simple pairing with any modern Bluetooth earphones and smartphones
  • Status notifications for connections, calls, and device pairing

Main Components

  • Bluetooth 4.0 Module BC127
  • Microcontroller: Atmega644P
  • USB to TTL Interface IC: CP2102
  • Quad SPDT Audio Switch IC: MAX4740

BlueBox Windows Utility


BlueBox Demo Video