i have a set of baofeng radios i am interfacing with echolink. i have isolation transformers on both audio channels and serial activation of the ptt on the radio but i want to be able detect when the squelch is open and send a serial signal back to the computer. i'm trying to design a circuit to activate a relay off the audio out of the radio. it works if i don't have the isolation transformer connected but when i connect the transformer it stops working. any help would be appreciated.

 

Schematic?

 

Have you considered using an opto-coupler to provide the isolation for that signal?

Tutorial just in case:
http://www.electronics-tutorials.ws/blog/optocoupler.html

 

here is a sketch i threw together, sorry for the poor quality. i did some more experimenting today. if i remove the 100 ohm resistor it will work but it also activates when signal is coming from the computer back to the radio. the relay i am using draws about 100 mA. i'm going to get another relay today that only draws 10 and see how that works.

 

is there an led that lights up when recieving a carrier? if so, just detect light from that.