Electronics Radio and RF

USB Programming Cable for Tait TM8110 PMR Radios

Making a USB Programming Cable for Tait TM8000 series PMR Radios to use as Ham Radio repeaters

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 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 a 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

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6 comments

avatar
Robin
31 October 2022 at 11:34 am
Is there any chance to use PL2303 or CH340 for this schematic?
avatar
Brian
31 October 2022 at 12:55 pm
Either of these chips should work for the UART communications
avatar
Petir
02 November 2022 at 11:58 pm
Would you please to tell me the pin of TX and RX in J3?
avatar
Brian
03 November 2022 at 9:19 am
Hello Petir

The pins are:

1 - TX
2 - RX
3 - GND
avatar
Petir
16 November 2022 at 12:05 am
I'm sorry that I am mistakenly mention in my question before.

What I mean is the position of TX, RX and Ground in RJ45 pin of Tait mic's pinout

Thank you
avatar
Brian
16 November 2022 at 10:37 am
Hello Petir

The microphone connector pinout is listed above

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