The PCBs for the updated version of mobile interface are in the mail and I expect to build and test them next week. Additionally to a small hardware fix to the previously tested revision, the shipment contains the boards for a brand new design featuring a smaller USB hub chip and measuring only 23x40mm in size. Why bother shaving millimeters off an already tiny board you ask? Because of this:
This is a small extruded aluminum enclosure that is widely and inexpensively available everywhere online and 23x40mm happen to be its internal dimensions. All it needs is few connector holes drilled in the end covers to give Digirig mobile a proper home. I’ll publish ordering links for the enclosure after the fit is confirmed. Did you know that it also comes in red?
Somewhat optimistically, I went ahead and panelized the new PCB design. If the new prototype tests well then it can immediately go into production. Penalization is the standard method of grouping multiple boards for automated manufacturing.
The prototype of the shack version of the interface featuring isolation of the radio still awaits the arrival of opto-couplers. They are used for serial RTS and DTR lines which some of the digital mode applications utilize for PTT/CW control. Meanwhile I tested the isolated audio and non-isolated serial interface of the partially completed prototype and they work without any issues. As far as I can tell, there was no noticeable difference in results from the mobile version, but further testing is needed.
Speaking of isolation: I had this idea that instead of isolating each of the interface functions on the side of radio (opto-couplers for PTT/CW and CAT, audio transformers for audio etc.), we can just isolate the interface on the computer (USB) side instead. This way no matter how many and what functional elements the interface features, they all will be galvanically isolated preventing any ground loops between the radio and computer.
In my research of USB isolator ICs I came across this little creation which not only isolates the data lines, but also provides isolated power to the other end eliminating the need for separate power source. Apologies for Comic Sans font in the graphics; it is shamelessly borrowed from the webs.
I’ll work on incorporating the same approach into the shack version of the interface, but this off-the-shelve board can also be used for isolating mobile version of the interface when necessary. Also, I’ll need to see if power isolator introduces any noise. If it does, then we might need separate power line from radio side which many of the rigs offer anyway.
That’s all for now, stay tuned for the next update and please signup for the updates if you would like a unit or few from the upcoming early access production batch.