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 !