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codec2_talkie/README.md

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Table of contents

Introduction

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This minimalistic Android application is a Walkie-Talkie style digital voice frontend for your radio by using open source Codec2.

It connects to your radio KISS Bluetooth/USB modem, records speech from the phone microphone on transmit, encodes audio into codec2 format, encapsulates into KISS frames and sends to your modem.

On receive, modem sends KISS packets to the phone with codec2 speech, application decodes codec2 frames and plays them through phone speaker.

It does not deal with radio management, modulation, etc, it is up to your modem and radio, it could be just AFSK1200, GMSK 9600, LoRa, FSK, FreeDV or any other modulation scheme. Radio just needs to expose KISS Bluetooth interface for speech frames.

It is mainly intended for ultra low cost (under 10$) radio modems (such as LoRa), but could also be used with custom modems + external transceivers.

Requirements

  • Android 6.0 (API 23) or higher
    • Application could also be used with your Android network radio, such as Inrico TM-7, apk just needs to be installed over USB, see Discussion
  • Modem, radio module or transceiver which supports KISS protocol over Bluetooth or USB
    • KISS support is not 100% necesssary for experiments, usually radio module needs to decide on protocol, but KISS frames could be sent over aether, there are plans to add support for other selectable frame structures, protocols or raw audio frames

Features

  • PTT UI button, push and talk, Codec2 speech frames will be transmitted to the modem
  • PTT hardware button, KEYCODE_TV_DATA SERVICE (230 key code) hardware button is used for PTT (used on some Android network radios)
  • USB serial connectivity (default 115200 bps, 8 data bits, 1 stop bit, no parity), just select this app after connecting to USB and it will use given connection, baud rate could be changed from Preferences
  • Bluetooth connectivity on startup, lists paired devices, so you can choose your modem and connect, you need to pair with your Bluetooth device first from Android Bluetooth Settings, default Bluetooth device could be set from Preferences
  • Voice codec2 mode selection, which allows you to select various codec2 modes from 450 up to 3200 bps on the fly, sender and receiver should agree on the codec mode and use the same codec mode on both ends as codec2 mode negotiation between clients is not implemented at the moment
  • Codec2 loopback mode, which records and plays your recorded voice back to test and evaluate different Codec2 modes and speech quality, could be enabled or disabled from Preferences, this mode is activated if no USB or Bluetooth connection were made
  • Voice level indicators, which display levels of transmitted and received audio
  • Preferences, allow to modify default parameters
    • Codec2
      • Set Codec2 mode/speed from 450 up to 3200 bps
      • Enable/disable loopback test mode
    • TNC parameters
      • Change default baud rate for USB port
      • Set default Bluetooth device for automatic connectivity on startup

Suitable radios and modems

Related Projects

FAQ

  • Gaps in received audio, indicator often changes between RX/IDLE on the receiver side when sender and recipient are close by then
    • most likely you do not have enough bandwidth, use higher throughput modem mode, for LoRa modems you need approximately 170% of data rate for the given codec2 bitrate, AFSK1200 modems should work at 450 bps codec2 mode, 700 bps might work, but not on all modems, higher speed codec2 modes won't work on AFSK1200
    • modem goes into RX state too fast after sending first packet, increase TxTail parameter for your modem if it does not handle corresponding KISS command, so it will stay longer in TX before switching to RX
      • if you are using LibAPRS based modem, set TxTail and TxPreamble programatically by using APRS_setPreamble and APRS_setTail methods as it does not seem to set these values from CMD_TXDELAY and CMD_TXTAIL KISS commands
  • Receiving audio on PC/Raspberry
    • For raw audio frames sudo cat /dev/ttyUSB0 | c2dec 700 - - | play -t raw -r 8000 -e signed-integer -b 16 -c 1 -
    • For KISS encapsulated audio frames command above could be used, but instead of cat use https://pypi.org/project/kiss/

TODO

  • Parrot mode, so speech coming from aether will be transmitted back as is (testing or digirepeating)
  • Modem profiles, so different modems could be controlled from the UI with KISS command extensions, so that user can change frequency/channel, modulation scheme, modem speed or other modem parameters on the fly from the application Preferences
    • Rig/radio module control and signal level reports by using KISS command extensions
    • HC-12 module control by using AT commands
  • Investigate support for other non-KISS frame formats and protocols, switcheable from the UI
    • Raw speech frames without KISS
    • AX.25 packets over existing KISS
  • QSO log, voicemail style recording of incoming speech so that incoming transmissions are not missed