Radio Interface for DV-DONGLE operation
October 17th, 2009

I wanted to extend the operation range around my DV-DONGLE using PC by connecting it to ( analogue- ) two way radio. Basicly for this only two additional audio connections are required. One is between PC soundcard output and radios external microphone input and the other one from speaker output to soundcard input. In addition also criteria must be found for controlling the PTT functions in both directions. Switching ON the radio transmitter simply can be done by using an audio vox ( vox = voice operated switch ). Compared to this, the DV-DONGLE is running under operation software DV-TOOL, where PTT control is a little bit more complicated. Normally this is done by positioning the cursor overhead the corresponding control field on screen and pushing the left mouse button, but alternatively it also is possible, to use the space buttom of PC keyboard instead. This feature only will be activated after starting the program and using the standard PTT control methode at least one time. This extended feature allows solutions for PTT control by e.g. external ( foot- ) switches or like in our case, via signals coming from external radios. For remote PTT control the function of an external keyboard must be simulated with sending same key code character sequences as being generated when pushing the space buttom of internal PC keyboard. This must be a MAKE code when pushing the keyboard buttom and a BREAK code when releasing it. Both can be generated by using an external microcontroller circuit like e.g. shown in schematics Fig.1. Control program must be stored within flash memory of processor. For sure, because software is quite simple, also smaller microcontrollers could be used here, but i did it with ready available ATMEGA8.

 
Fig.1

Key code data will be send to PC by using an PS/2 interface with 6pin Mini-DIN plug, but it could happen, newer PC's no longer are equipped with suitable type of connector. In this case the connection must be made by using a PS/2-USB adaptor ( Fig. 2 ). Adaptors like this are available on market at very low prices. Supply voltage for powering the processor is available  via PS/2 connection. PTT control is via switch "S1" ( Port PC0, Pin 23 ). A LED connected to port PB1 ( Pin15 ) will be "ON" as long as "S1" is closed.. Schematics also is showing the connections needed for possible "In Circuit Programming".


Fig.2  PS/2 to USB adaptor
( made for connecting external mouse and keyboard in parallel )

Two independent audio voxes and a microcontroller circuit similar to the one desribed above have been used for constructing a complete bidirectional radio interface adapter ( Fig.3 ) . One vox is for controlling transmitter of two way radio. Depending on it's type, this can be done by using a combined MIC+PTT signal or by separate PTT control.  In addition audio from speaker output of radio must be used for controlling PTT function of DV-TOOL. For this a second identical vox circuit is used. It's switching output is going to control input "PC0" ( Pin 23 )  of ATMEGA8. Compared to circuit shown in Fig.1, it has been simplified a little bit ( no ICP ). 5V supply voltage for entire adapter unit can be via PS/2 or USB and so no separate power source is needed. Most of adapter circuit is self declaring according to Fig.3. Those two audio transformers shown could insure galvanic isolation between soundcard in/out of PC and attached adapter, but can be omitted in most cases.


Fig.3  ( click for full size view )

HINT:  Some two way radios also are providing a COS ( carrier operated squelch ) output signal. Often it directly can be used for controlling input "PC0" ( Pin 23 ) of ATMEGA8. In this cases the second vox circuit is not required any more, but depending on available signal logic, maybe some sort of small interfacing is necessary instead ( PTT control of DV-TOOL is by switching input "PC0" to ground ). 

Programm for ATMEGA8 is written in BASCOM-AVR and can be downloaded here. Included HEX-File directly can be used for programming the ATMEGA8 ( Don't forget also setting the fuse for external crystal use ). People wanting to modify the source code with making their own compilation after this, also will need bibliotheque file: "at_emulator.lbx".  It's available ( not for free ) from MCS Electronics or see more detailed:
http://www.mcselec.com/index.php?page=shop.product_details&flypage=shop.flypage&product_id=35&category_id=6&option=com_phpshop&Itemid=1
On request also small quantities of already programmed processors and crystals could be made available from author.

 


This project only was possible by help of Michael, DG3SBD, Ivo, DL9MB/ OE6RIG and article: "Zusatztastatur für den PC mit programmierbaren Tasten" written by Dr.-Ing Klaus Sander in FUNKAMATEUR, February 2008, page 163-165. Circuit of audio vox has been created and published by DF3OJ.

Assistance for bringing this text into better English would be appreciated very much!