Designing an even cheaper isolated digital interface for amateur radios

A few months ago, the ACMA made changes to the amateur LCD that allowed foundation class licensees to operate digital modes.

Excited to get into this in the new year, I begun looking into digital interfaces for the radios I already have. There’s many different ways this can be done, from as simple as not using a cable and relying on microphones and speakers, creating a straight through cable from the PC mic input to the radio speaker output and visa versa, to expensive isolated interface boards custom made in the USA.

I wanted an isolated board, because I have enough trouble with interference and noise in my apartment already, so the first two were out (although I did make a straight through cable for my Baofeng UV-5R for SSTV on 2m/70cm).

So I turned to the expensive isolated interfaces.

There’s plenty to choose from l, with different feature levels and prices! From the $230USD RigBlaster, the $200AUD SignalLink USB, and even the cheapest of the bunch, the Easy-Digi coming in at $30-50AUD shipped with slow shipping…

Naturally being a cheap ass I wasn’t overly satisfied with these options..

Luckily though, the Easy-Digi, saved the day! It’s such a simple design, with a published schematic, that it’s not too hard to roll your own with a few changes!

I jumped into EasyEDA and learnt how to do a basic schematic, then designed the interface circuit for audio using two 600:600ohm isolation transformers, and a PTT circuit using a DB9 rs232 connector because it’s easy, although I plan to replace that with a USB-C connector and a ch340 rs232 IC in a later revision!

I used components that I either already have laying around, or can get easily from JayCar for the most part.

The connectors and transformers I ordered from China at about $4-5 for 10pcs each.

With the layout done, I generated a PCB, and moved components around into a rough layout I was happy with, and hit the autoroute button :^)

I forgot to label the PC side connectors for the first revision, but I imagine there will be plenty of other changes I make anyway.

I uploaded the gerbers to JLCPCB to produce a test run of the PCB, which I should have within 2 weeks with the cheap shipping :^)

So if everything goes according to plan, I cluding parts and PCB manufacturing for 10 boards, I’ll have spend about $30-35 total, and I should be able to sell some of the boards to friends for $5-10 each offsetting my costs even more !

4 thoughts on “Designing an even cheaper isolated digital interface for amateur radios”

  1. Hi lewis:
    I was just reviewing an email you sent to us to [email protected] regarding an interface cable for a Dell library, just had to look at your blog. I am also an amateur radio operator call is KE8A. Kathy and I are owners of Midwest Technical. We will take care you if you order from us we are experts in all aspect of data storage and we operate one of the most technically orientated tape drive repair facility in the USA Technical Geeks who have made a living doing what we enjoy for over 30 years.
    Cheers

    Regards,
    Dan

    1. Thank you Dan!

      Looking forward to your reply so I can get my library working :))

      VK2FAJC here!
      (I’m jealous of your short callsign, mine doesn’t even work with ax.25 😭 )

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