VP-Digi

VP-Digi is a functional, cheap, easy to assemble and configure STM32-based APRS digipeater controller with built-in KISS modem.
Full documentation can be found here.
Dokumentacja po polsku dostępna jest tutaj.

• Multiple modems:
  • 1200 Bd AFSK Bell 202 (VHF standard)
  • 300 Bd AFSK Bell 103 (HF standard)
  • 9600 Bd GFSK G3RUH (UHF standard)
  • 1200 Bd AFSK V.23
• PWM (or deprecated R2R) signal generation
• Analog-digital busy channel detection (data carrier detection)
• AX.25 coder/decoder
• FX.25 (AX.25 with error correction) coder/decoder, fully compatible with Direwolf and UZ7HO Soundmodem
• Digipeater: 4 settable n-N aliases, 4 simple aliases, viscous delay (known from aprx) or direct only, black and white list
• 8 independent beacons
• KISS mode (can be used as an ordinary Packet Radio, Winlink, APRS etc. modem)
• USB and 2 UARTs: independent, running in KISS, monitor or configuration mode

Updating to 2.0.0+ on older hardware

Since version 2.0.0 the component values have changed to provide support for faster modulations (9600 Bd). If you want to use these some components must be replaced. For more informations refer to the manual (polska wersja).

Description, schematic, instructions

The user manual and technical description is available here (polska wersja).

Source code

The firmware was written using System Workbench for STM32 (SW4STM32) and you should be able to import this repository directly to the IDE. You can get the source code using:

git clone https://github.com/sq8vps/vp-digi.git

Since version 2.0.0 you will also need to get appropriate submodule (LwFEC for Reed-Solomon FEC):

git submodule init
git submodule update

Since version 2.0.0 there is also a possibility to build the firmware with or without FX.25 protocol support. The ENABLE_FX25 symbol must be defined to enable FX.25 support. On SW4STM32 (and STM32CubeIDE probably) this can be done under Project->Properties->C/C++ Build->Settings->Preprocessor->Defined symbols.

References

The project took a lot of time to finish, but now it's probably the most effective, publicly available, STM32-based modem and the most customizable microcontroller-based APRS digipeater. I would like to mention some resources I found really useful or inspiring:

• multimon-ng - general demodulator idea (correlation)
• BeRTOS - AX.25 decoder
• Forum thread by SP8EBC - inspiration
• DireWolf - PLL bit recovery idea, FX.25 references
• A High-Performance Sound-Card AX.25 Modem - preemphasis and low pass filtering idea
• UZ7HO Soundmodem - PLL-based DCD idea

Contributing

All contributions are appreciated.

License

The project is licensed under the GNU GPL v3 license (see LICENSE).