Understanding ground isolation #ubitx #filters #teensy


Rob French (KC4UPR)
 

Hey there,

I'm looking to try making a DSP audio filter, for both transmit (e.g. compression) and receive (narrow, wide, notch filters) using a Teensy 3.2 and Teensy Audio Board.  My plan for the receive audio is to put it inline in my uBITX v5 between the audio preamp and the volume control (i.e. before the volume control), and use a pair of 1:1 isolation transformers on the input/output to connect it to the preamp (input) and volume pot (output) respectively.

I would like to run the Teensy as both a standalone DSP filter in the uBITX, but also as the interface to the computer (i.e. as a combined USB audio/serial device).

My plan is to power the Teensy off the 5V from the Raduino, and also connect it to the Raduino via serial (D0/D1 pins on the Raduino) so that (a) I can pass thru CAT commands from the computer to the Raduino via the Teensy when applicable, and (b) control filter parameters from the Raduino when operating standalone.

My question is, what exactly needs to be isolated?  I understand I need ground isolation between the Teensy audio I/O and the uBITX audio I/O, so I plan on 3 isolation transformers.  But how does this really isolate the ground?  If I'm running the Teensy off the Raduino 5V, there's a ground connection there presumably, and from what I can tell, all of the grounds on the Teensy Audio Adaptor are unified (except for the VGND for the headphones, which I'm not using).  So I feel like all of the grounds are connected, and I'm not really sure what the isolation transformers are buying me.

Do I need to use a separate regulator for the Teensy? (Although that would still have a ground connection to the uBITX ground, so...)

I freely admit I don't know a lot here.

Regards,
-Rob

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