Android PTT Bluetooth Speaker

Pair of Android apps:

1. sender
   • captures audio from the microphone and sends it to the receiver
2. receiver
   • receives audio from the sender and plays it through the speaker

Background:

• there are many other apps that use bluetooth to enable two-way communication between users
  • WalkieTalkie is an excellent example because its mechanics are very similar under the hood
• the use-case I had in mind is a little unusual..
  • communication needs to be one-way
  • on the receiver side, the app should run as a server within a foreground Service
    • there is no visible UI
    • make bluetooth adapter discoverable
    • start a bluetooth socket server
    • listen for a connection from a sender
      • when a sender connects:
        • stop listening for a sender connection
        • read audio stream from connected socket
        • play audio
      • when a sender disconnects:
        • resume listening for a new sender connection
  • on the sender side, the app should run as a client within an Activity
    • display a list of all paired devices
      • click the one that identifies the desired receiver
      • wait for connection
    • touch a PTT toggle button in the UI to stream audio from the microphone through the connected socket
      • touch the PTT toggle button again to temporarily interrupt the audio stream
    • move a slider to adjust the volume of the audio stream
      • the receiver plays the audio stream at its maximum volume
      • the sender can apply a gain factor to change the loudness of the microphone's normal volume before it is sent through the socket
        • the default gain is 25%
        • the maximum gain is 200%

Notes:

• receiver:
  • bluetooth adapter is only discoverable for 60 seconds after the service is started
    • Android displays a prompt to ask for permission to do so
    • if the intended sender has already been paired, then this step isn't necessary
      • there's no harm to decline Android's prompt
• sender:
  • if not already paired to the receiver
    • can become paired during the 60 seconds that the receiver is discoverable
  • after a persistent pairing is established to the receiver
    • can (re)connect at any time

Misc:

• PTT is short for: Push To Talk
  • which is a term that describes how the button on a Walkie-Talkie is used:
    • push to broadcast
    • release to listen
  • the sender was originally designed to follow this usage pattern
    • which explains why this term is included in the name of the app
    • however, I subsequently chose that a toggle button would be easier to use

Screenshots

Legal:

• copyright: Warren Bank
• license: GPL-2.0