DK1DA

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FreeTRX

Firmware DMR OpenGD77 fork Open Source

FreeTRX is a fork of the OpenGD77 firmware for DMR transceivers built around the STM32F405VGT MCU. It adds UI improvements and quality-of-life features on top of the original firmware.

Source code on git.dk1da.de

Programming on the Mac: CPS77 is the recommended codeplug software for FreeTRX — the codeplug format and serial protocol are compatible.

What FreeTRX adds

UI & operation

  • Segmented S-meter — one block per S-level (S1–S9 green, S9+ red)
  • 7-segment frequency font on the VFO
  • Screen dimming after inactivity (100 / 50 / 30 / 15 %)
  • Audio mute with a short tap of SK2; while muted the red LED flashes
  • Theme presets on the radio: Custom, BASIC 80s, Terminal, Vertexic, Red, Neon 80s, Pride
  • CRT-style shut-off animation when powering off

DMR text messages

  • Send & receive SMS — compatible with BrandMeister, hotspots and OEM radios
  • Compose on the keypad (multi-tap, up to 160 characters); pick the recipient from your contacts
  • Inbox & sent (8 messages each, kept across power cycles)
  • 10 editable quick-text templates, an incoming popup with chime and one-key reply
  • Delivery confirmation (ETSI ACK) with a resend prompt on timeout

Channels on the radio

Channels can be created and deleted without a PC — from the channel quick menu via the orange key. New channels start as 145.500 MHz FM and drop straight into the current zone; deleted ones are removed from every zone.

Hardware

Tested devices

TYT
MD-UV380
Retevis
RT-3S

Other OpenGD77-compatible devices (Baofeng DM-1701, Retevis RT-84, MD-9600, MD-380, MD-2017) are not yet tested — testers are very welcome.

Tech

MCU
STM32F405VGT
RF chip
AT1846S
DMR
HR-C6000
Base
OpenGD77 R20260131

Screenshots

DMR call with talkgroup, repeater and the segmented S-meter
VFO with the 7-segment frequency font
Main menu with the Messages entry
Messages menu: quick text, options, inbox and sent
A received message — weather report from a BrandMeister service

Screenshots shown with the Neon 80s theme.

License

FreeTRX inherits the OpenGD77 license — a modified BSD 3-Clause license with an additional non-commercial clause. It is not an OSI-approved open-source license and is not GPL-compatible; commercial use is prohibited.

Credits

FreeTRX stands on the shoulders of OpenGD77. Huge thanks to the original authors: conceived by Kai Ludwig (DG4KLU), development led by Roger Clark (VK3KYY), assisted by Daniel Caujolle-Bert (F1RMB), Alex (DL4LEX) and Colin (G4EML). Without their years of work on the free firmware this fork wouldn't exist — 73 & many thanks!