Ham Radio Bridge Interface

While working from home and being kind of bored, I’ve been thinking about trying to build an interface board for my ham radio to be able to take the audio signals (mono microphone / mono audio out) to / from the radio and also expose a USB to serial com port that has an RTS or CTS signal that I could use with combination of WSJT-X, or the Soundmodem TNC to trigger the PTT (push to talk) pin. The radio in question is Yaesu FT-3dr that has a TRRS (tip ring ring sleeve) audio interface. The pins are Speaker, Mic, PTT and ground. I’d rather not have to use VOX (voice control) and would instead prefer that I use the RTS or CTS from a serial port to trigger this PTT pin. I believe it essentially grounds the PTT portion to enable push to talk.

In my searching for something that might be suitable I came across https://www.silabs.com/products/development-tools/interface/cp2615ek-2-evaluation-kit

Would this chip work as a) USB audio interface for the computer that I could connect mono speaker and mic and eventually wire an RTS pin to ground the PTT connection on the 4 connection audio cable?

Is there a better chip that would do what I’m looking to do? I realize I could order a Mobilinkd 3 TNC and also get Bluetooth. I also realize that this could be biting off way more than I can chew, but I’m not leaving the house much these days so I figured, why not play around with it?


You didn’t say what software you plan to use. Going to write your own? Or where the USB goes.
It looks like the chip will sample the audio and give you a data stream. The sw will need to chew on that and likely turn it into one of the standard data formats.

I made a small pcb with a CM119 codec that works with Allstar VOIP. There are drivers for the chip in Linux and it just plugs into a pi and works. You need to investigate WSJT and/or drivers for the CP2615.

Barry w0iy

I was hoping it would show up just as a standard usb audio device on Windows with input / output. Is that not the case?


This made me believe that it would show up as a serial port and an audio interface. Wsjt-x should be able to use RTS on the serial port and audio to / from the device as long as it is wired correctly to the right pins on the connector. I would think.

I believe you are on the right track. My concern is that while this chip has lots of nice features, I suggest using a device that has known good drivers. That is always the challenge with Win. CM108/109/110 family of codecs are in many of the headsets and audio fobs. I use CM119B. US distributor is Symmetry.

Thanks, that does look like a great chip. What I don’t have any ideas of how to do though is combing a serial device and an audio device on a singular USB jack. Do you have any recommendations? Would I need to use an onboard USB hub along with an FTDI chip or something like that? I’m not entirely even sure how to google this. I’m mostly a software engineer. Thank you!

You really only need PTT and maybe a Carrier Detect discrete signal each direction, unless I misunderstand. Look at the CM119 (or any of that family) as there are GPIO pins on the device you can use for PTT output or COS input. They are pulled up inputs (External signal goes open/gnd) an open collector outputs (the GPIO can provide a Gnd signal).

Does that help? I can send you a schematic of what I made.

Oh, I was trying to be lazy as the WSJT-X has support already for a RTS or CTS signal on a Serial Port. I would have to have a virtual device driver or something like that to enable the PTT from within WSJT-X, no? I suppose Hamlib has support for GPIO on Raspberry PI. I could use something like that and then I wouldn’t even really need to do anything other than a physical adapter to connect the right pins together.

In the interest of learning though, I’d love to take a look at your schematic.

Ah, I forgot about the serial from WSJT. A couple of thoughts:

  1. Since you are a sw guy, get the source to WSJT and modify the output to drive the discrete in the CM119. I believe it is open source.
  2. Have sw intercept or somehow look for the CTS/RTS and have that drive the CM119.
  3. Use a 2nd USB, which would require a USB hub. Not expensive but not elegant.