Cobra 19 DX IV Upgrade

Upgrade of Cobra CB for use in New Zealand and to interface with a car stereo.

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On a trip to the USA I purchased a Cobra 19 DX IV CB transceiver for use in my 4WD. I chose it as it was available near my hotel, the schematics and PLL data were online and it looked hackable. New Zealand use 26MHz for CB but 27MHz is now legal too so I wanted to make it dual band. As I am developing a stereo system at work I wanted to also be able to interface it to that too for better audio, music break in and remote operation.

The PLL is a TB31202 with a serial interface so I used an Arduino Nano module to watch the PLL data and work out how the native processor was communicating with the PLL. After that I intercepted the PLL data to determine what native processor was doing and rewrite the data I wanted to the PLL. From this I was able to remap the USA channels to the New Zealand channels and that my project was viable.

I then planed my objectives:

  • Allow selection of any US or NZ channel from the existing CB front panel.
  • Add a scan function.
  • Add remote control via the accessory port on the stereo system head unit.

For dual band operation I simply swap bands at wrap around between channels 1 an 40. So for example if you are on NZ channel 40 and you use the channel knob to go up you will be on US channel 1. Stepping down from channel 1 will also swap the band and take you to channel 40. To provide feedback about which band you are on I replaced the yellow backlight with a RGB LED. Green indicates NZ channel when receiving with the squelch closed, blue indicates the same for US channels. Other colours are used when the squelch is open and when transmitting.

For scanning I redirected the CH9/19 button as a scan start stop.

For remote control I based it on the CAT interface used on my Yaesu FT-857. I added audio to that connector to make for a tidier cabling solution. I started using the Yaesu CAT protocol but didn't find it very flexible so switched to the protocol used on the head unit and created a new message type specifically for the task at hand.

The project is almost complete with the remaining work being head unit features.

  • Completed and installed

    David Annett12/22/2015 at 11:07 0 comments

    The code is finished to a feature complete state so I have installed the whole system in my Suzuki Jimny.

    The Cobra CB is installed where the ash tray was and looks really tidy tucked away down low. You can be listening to music on one of the other sources and when the squelch is opened by a signal the head unit will make the CB the active source switching over to it and showing the channel, frequency and RSSI. When the squelch closes it returns to the original music source. If the source was Bluetooth or USB playback it will be paused and will resume where it left off.

    Testing so far is positive with it all working as I hope at the start of the project.

  • About the software

    David Annett11/23/2015 at 07:44 0 comments

    Now I have someone following the project I guess I should give some more detail.

    For this project I have created 4 programs:

    • A C program for the AVR on the Nano board in the Cobra CB.
    • A C program for the stereo system head unit.
    • A C++ QT program that simulates a transceiver.
    • A C++ QT program that controls a transceiver.

    The program for the head unit is a modified version of the original software so is copyright of my employer. Therefore I can not make the source available for it. I may be able to make a binary available.

    The rest of the software is my own work so I can make the source available under some open source licence.

    The AVR code started life as an Arduino project but I find the IDE painful and the sharing of code between project is not ideal. I moved the project to a more conventional AVR/GCC/Eclipse project but it is still using some of the Arduino libraries.

    Because I based the CB interface on the Yaesu FT857 CAT interface I was able to use an USB to mini-DIN 8 cable designed for that radio for testing with a PC. The QT PC programs allowed me to get the bugs out of the protocol and also gives me simple remote control for the CB from a PC should I want.

    All of the software is functional complete and reasonably bug free except the head unit code which has the main features working but still needs refining and debugging.

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David Annett wrote 09/05/2017 at 06:55 point

Hi Chris, not sure why I didn't see you comment at the time you posted it.  Just saw it today.

Putting the files and instructions up takes a bit of effort so I wasn't going to bother unless someone specifically wanted then.  I don't think many people bother with hacking CB sets these days so was not sure if anyone would want to replicate my efforts.

  Are you sure? yes | no

chris.fry wrote 01/14/2017 at 21:03 point

I am new to this site, so maybe I am missing something. Where are the files and instructions?

  Are you sure? yes | no

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