Icom CI-V USB/TTL Rig Cable Design Using the FTDI Chipset

July 25th, 2011 § 38 comments

I spent some time this weekend with the fine folks over at NYC Resistor hacking on some ham radio related stuff. We took a crack at a USB CI-V interface for an Icom radio. Googling around, we found lots of level converters for RS-232 serial ports, but very little with USB in mind. In addition, most of the circuit designs for homebrew cable assemblies were quite complicated, and generally speaking, published in about 1992.

It turns out that the Icom CI-V interface is TTL-based, with the TX/RX cables bridged together, with a ground reference on the sleeve of the 3.5mm connector. Given the popularity of Arduino and similar chipsets that require a TTL serial interface to program and operate, we figured we could do better with a prefabricated USB-TTL cable like the TTL-232R-5V from FTDI. It turns out the resulting build is stupid-easy.

Here’s a diagram of the resulting assembly, for those who are searching for how to do this:

We turned out to require a stereo Ring-Tip-Sleeve connector rather than a mono two-conductor one, despite much documentation claiming the contrary. Your mileage may vary.

If necessary, one could also use the RTS/CTS contact-closure as a push-to-talk switch setup, which most of the popular ham radio software packages support. The total cost of this assembly is roughly $20, which is how much the cable costs. To cut costs even further (down to about $5), you could hack this together using the bare FT232RQ chip which you can get from Mouser for $4.95 as of this writing. In any case, this is a pretty massive improvement over the $60 that Icom likes to charge for the equivalent.

The drivers are available for all major platforms and are bundled in the Linux kernel already so the additional software needs are minimal for this over a ‘traditional’ RS-232 cable. We tested this on Mac, Linux, and Windows with perfect results.

§ 38 Responses to Icom CI-V USB/TTL Rig Cable Design Using the FTDI Chipset"

  • Windsor says:

    This was really helpful. I have an ftdi break-out board, and wanted to know if the CI-V interface on my 706mkiig is TTL. This will save me the trouble of putting the ‘scope on my rig to find out. Thanks!

  • [...] described by Guy Dickinson the RX and TX pins of the converter are soldered together. The only additional wire needed is [...]

  • Ron Harding says:


    i design/build c# based remote control applications since 2006 on the job(smart terminal emulator applications) I do so today as well and i offer my services to create customized applications on a project basis. although many will end up using this interface in the VCP(virtual com port mode), I suggest that much can be gained by using the FTDI D2XX driver library instead.

    i am working on my first CI-V c# application at this time on my IC7000 rig and be porting the control app to a samsung galaxy tablet where i will provide gesture based control for use in my 2009 Xterra. i learned how to port the gear pdf programmers reference guide efficiently into reliable GUI controls. CI-V protocol is pretty straightforward.

    I have been working with the FTDI chipsets for about the past decade. c# .net wrapper libraries have recently been made available to the public, so no worrying about so much datamarshaling/pinvoke of the D2XX ‘unmanaged’ code into c#.


    Ron Harding
    Grand Blanc, Michigan

    i recently moved for new job to Michigan, I was in WA state but moved for the job.

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    Chipset gdickinson.co.uk” was in fact a very nice posting, .
    Keep composing and I will continue to keep reading! Thanks a lot -Estella

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  • You really make it seem really easy along with your presentation but I in finding this matter to be really one thing that I believe I would by no means understand. It sort of feels too complicated and very extensive for me. I’m having a look forward for your subsequent post, I will try to get the hold of it!

  • best of luck! give it a try.

  • Xenofon Labiris says:

    Hello, I owned the following USB to TTL converter


    Can I use it to make your simple CI-V interface for ICOM IC-820H radio?
    It has the PL-2303HX chip installed.

    BTW, for now I am using a serial CI-V home made interface with MAX-232 chip with success. IC-820H hex code 42

    Thank you in advance


  • Guy Dickinson says:

    Xenofon: I don’t see why not, at least from a hardware perspective. You may need different drivers, though.

  • Xenofon Labiris says:

    OK, I’ll try to use the three TTL pins Ground,RX,TX after installing the appropriate drivers from here…


    Maybe have’em already in my PC as I also use 2 USB to serial cables (COM3,COM4)

    I don’t need any extra components, so I’ll let you now asap..

    Thank you,

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  • James French says:

    Thanks for your previous work on this. This page was the first one I visited after
    googling for ‘ci-v ftdi’. looking to interface with my Icom IC-820h like a previous

    I was wondering about the level voltages since I am still learning about the differ-
    ences. Never had to worry about this with ‘normal’ db-9 and -25 ports.

    Thanks again for the posting.

    James W8ISS
    Lincoln Park, MI

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  • Ben says:

    Just to double triple check, your using 5v on the FTDI right? I have one from adafruit or sparkfun (i forget) and it can be used for 5v or 3.3v and just want to make sure I get that right before I plug it into my very new and very expensive HF radio! :)

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