We were recently asked if we could help with the setup of a local AllStar Link radio repeater for our area.

AllStar Link is a radio repeater system which uses Voice over Internet Protocol to allow distant radio hams/amateurs to communicate via a local access repeater. More details about AllStar Link can be found at https://www.allstarlink.org.

The AllStar Link software runs on a Raspberry Pi or other compatible hardware and uses a modified CM108 USB sound card as an interface to the radio.

A Tait TM8110 PMR Radio was purchased for the repeater from a local ham radio rally.

Radio
Radio

The Tait TM8110 radios have a 6-pin RJ45 connector on the front panel for the microphone and an auxiliary connector on the rear panel using a 15-pin D-Sub connector.

Programming Cable

There are commercial programming cables available for the Tait radios but the only models we could find were in America and had expensive shipping charges.

The radio uses a UART connection at 3.3V for programming and we initially tried to connect the radio to the computer using our USB MultiComms interface via the front RJ45 connector.

Prototype testing
Prototype testing

We were unable to get any response from the radio and after further investigation, we found that the Tait radios use an inverted UART signal.

After adding a logic inverter via a breadboard, we were able to communicate with the radio and the programming software.

Making a USB Programming Adapter

Once we knew that we could program the radio, Andrew designed a very compact USB to Serial interface with logic inverters and ordered the PCBs. After a couple of weeks, the new boards arrived, and the components were soldered to the board.

The interface uses an FTDI FT230X chip and a pair of SN74LVC1G04DBVR inverter chips to invert the output to the 3.3V logic the radio requires.

PCB
Finished PCB

Bill of Materials

Name / Part No Value / Description Quantity RefDes
CAP_0603 47pF 6 C1, C2, C3, C4, C5, C6
TX Red LED 1 D1
RX Red LED 1 D2
48037-0001 Molex USB Connector 1 J1
MI0805K601R-10 FERRITE BEAD 600 OHM 0805 1LN 1 L1
RES_0603 27R 4 R1, R2, R5, R6
SN74LVC1G04DBVR Texas Instruments Inverter 2 U1, U3
FT230X FTDI USB Full Speed to Basic UART IC 1 U2
Radio
Schematic

The PCB and schematic can be downloaded in Diptrace format from github.com/briandorey/USB-Programming-Cable-for-Tait-TM8110-PMR-Radios

The pinout for the RJ45 connector is:

Pin Signal name Description Signal Type
1 PRG_RX_AUD Receive audio output Analog
2 +13V8 Power supply output. Switched off when radio body is switched off. Power
3 PRG_TXD Asynchronous serial port - Transmit data. 3.3V CMOS
4 PRG_PTT PTT input from microphone. Also carries hookswitch signal. Digital
5 PRG_MIC_AUD Fist microphone audio input. Analog
6 AGND Analog ground Ground
7 PRG_RXD Asynchronous serial port - Receive data. 3.3V CMOS
8 PRG_ON_OFF Hardware power on/software-power off input. Active low. Digital

Links

USB Sound Card: www.amazon.co.uk/gp/product/B099DZYV5Z/

USB Sound Card Modifications: allstarsetup.com/how-to-modify-a-cm108-for-allstar/

Tait TM8100 Series Programming Software: www.radiotronics.co.uk/tait-tm8100-series-programming-software

Hamvoip software: hamvoip.org