Homemade USB Digimodes Interface

I am a big fan of Digimodes as you maybe know already!
Therefore, I am always in the search of the “perfect” Digi Interface which also has to allow me to control the radio via Ham Radio Deluxe, one of the best of it’s kind…
I already have a RiGExpert Standard interface but this is assigned to a Kenwood TS2000 radio at YO3KSR, our club station and this made a big “gap” in my shack.
My “ideal” interface has to be wired to a PC only with one cable.
I want to have a “hardline” PTT and a Carrier Detect (for Echolink use) and a CAT port.
Of course, a sounboard because want to be able to use the interface with some digital voice software which requires two sound boards (one in the laptop).
I made a lot of interfaces in the past; most of them was “the simple” type; only providing isolation between PC and transceiver with two little transformers and a optocoupler for PTT but these ones required a external USB2COM adapter and a lot of wires…
So, my “dream” was still in the “cloud”.

A few days ago, while I was inspecting the junk box, I found a lot of unused “components”…
A USB sound card from Behringer (UC202), some USB2COM adapters and a very little USB hub…
Hmmm… I wonder if I can use those to homebrew a nice versatile Digimodes interface!
I often see fellow hams that build things from scrap! I admire them because this need a lot of time and commitement! I have the last "thing" but I don't have the time so, I think I do not "cheat" by using demo boards or some finished "scrap" in my junk box.


Here is the plan (click to see the "big pictures"):

I choose a USB 2.0 HUB with four outputs as a simple math will show that we need 3 of them in our setup and we can use one for further "developments".
A short trip to a local DIY store provided all the necessary components; the case, the board and some LED’s because I didn’t have the green ones!



I agree with “one picture made a thousand words”, therefore I let you see what is the result.
So, I made a "motherboard" where I put the USB plug, the LED's, and the I/O volume potentiometers. There is some pads left for external DC input regulation with a 7805 circuit (not populated yet) and for isolation transformers (in the eventuality of 50 Hz hum).
I also provided some common ground because I choose not to use isolation. Hmmm, the "isolation" story seems to be a humbug of sime sort because, from what I seen in the market, the CAT port is not isolated so, despite the isolation of the audio and PTT, the PC IS connected to the transceiver! So, why try to complicate my life?
In the upper

The audio USB board UCA-202 from Behringer:
This board has a Stereo Line input and a Stereo Line Output. There is also a "monitor" headphones output, but this is not used. Maybe I will put a little speaker inside the box but is not yet necessary!
The USB2COM adapters:

The USB2COM adapters was tested before te see how they works!

If you can see them here it's a proof that they passed the test, HI!
Like I said, I used one for CAT control. This one was left "in one piece" to provide some mechanical fixing. The one for PTT and CD (Carrier Detect - Open Squelch) was removed from the DB9 connector. This was necessary because all the signals (including Audio I/O) will be sent to the transceiver via one cable).
The PTT was set on COM's RTS and the CD on the COM'S CD (to be clear, HI). Here I use two K817 optocouplers. The PTT port can whitstand about 50 mA at 70V.

The LEDs

I like to have some visual information about the working state of the interface, so I desoldered the original LED from every board and reroute them on the front panel.

From left to right:

-Blue: Power on USB HUB;

-Green: Power on CAT COM1;

-Green: Audio Board recognised by the OS;

-Red: PTT on COM2

-Yellow: CD on COM2.

-Blue: not connected.

The "look":



After closing the case, the HM Interface looked fantastic, especially in the dim light!
On the rear panel, I provided 3 RCA for Audio I/O and for PTT/ They are not wired yet.

Further development may include a second USB audio board for digital voice...

OK, it is not perfect, but the tests showed that this "box" performs well... I have only one complain: the Input level is often too small for the sound board. Despite this, the excellent S/N ratio of the Behringer board made me think twice before adding a small input preamplifier!
The two potentiometers are unused...
The cost is much under a commercial interface... Much!

And, for the final, what will be a CAT-Digimodes interface without a Tom-CAT?

73 de YO3HJV

LATER EDIT:

I added a small preamplifier (around 6 db) on the audio input of the interface. The signal goes into one of the two potentiometers (reserved on the motherboard) to fine tune the input volume. A small Switch on the front panel allow me to bypass the preamplifier because the signal from ICOM IC7000 is loud enough to drive irectly the soundboard.
I also put a 4 GB flash memory for various purposes (the HRD Logbook, audio recording of my QSO's and a small collection of digimodes software-around 300 Mb).