What is it?

Open Modem Firmware is an open source AFSK modem platform for ATmega microcontrollers. The base implementation targets the ATmega1284p. The firmware supports 300-baud, 1200-baud and 2400-baud operation, suitable for communication over a wide variety of analogue mediums, both radio and wired.

In it's default configuration will provide a fully KISS-compatible packet radio TNC. The firmware is designed for and compatible with OpenModem, but can be used on any similar build.

The firmware is modular and flexible, and while the default configuration implements a host-controlled TNC, it can also support applications running in-modem, such as digipeaters, APRS-trackers, message exchange and much more.

The source-code is available on GitHub.


  • AFSK operation at 300, 1200 or 2400 baud.
  • KISS-compatible TNC implementation
  • SD-card with exFAT support
  • AES-128 encryption support
  • GPS driver
  • Bluetooth driver
  • Packet logging in PCAP format (WireShark compatible)
  • Digitally adjustable input and output gain control
  • P-persistent CSMA