We now use the Zum MMDVM v1.0 as a spare.
The Zum MMDVM board for the Arduino Due served GB7EB well for several years, it was replaced in 2020 by an STM32 which itself will be replaced by a Motorola DR3000 DMR Repeater. Two versions are avaliable, with or without a TJC screen. The UVIYN Hotspot is a MMDVM Openwrt Hotspot with a mmdvmhost-, iotboard (l107) and rechargeable batterie (s). TETRA has been in use in the Public Safety market in Europe.
This radio takes pride in its new feature, which comes in the form of its Bluetooth connectivity. Another fantastic choice of any potential DMR radio users is the BridgeCom Systems AnyTone AT-D878UV with Bluetooth and GPS. BridgeCom Systems AnyTone AT-D878UV Radio. Because Allstar is running in the background you can also connect to other Allstar or Echolink connections (via SDS**) Please beware the repeater cannot connect to DMR. You can use other Phoenix talk groups if you wish, they are user activated via SDS codes**. The MMDVM firmware supports the following digital modes: D-Star The repeater default talk group is (DMR) TG844 which links GB7TX, GB7EB and GB7YL. This does seem possibly at odds with the GPL licence, but is likely to do with digital codec patents. MMDVM is an open source software project licensed under GPL v2, but with a note to say that it is intended for amateur and educational use only, with commercial use strictly forbidden.
Link to BlueTooth LE and Serial Interface board setup instructions.
Link to How to Update FIRMWARE on Either SIMPLEX or DUPLEX boards. Link to SETUP instructions for DUPLEX board.
Now, TETRA supports both full duplex calling and simplex repeating as. Closest thing similar is the full duplex calling feature Simoco offers on their Xd line which essentially uses both slots for a full duplex phone call. The hardware is physically capable of doing it (maybe not a MMDVM board) but no one has really written firmware for it.