If I power the TX module with 12V and send data to it from a PIC at 5V, do I need to worry about isolation from the PIC data/USART pin? The walkthrough seems to sugest that it’s fine, and the datasheet doesn’t seem to say otherwise. I just wanted to check before plugging it in a possibly burning out a PIC. 
So, nobody has tried this? Odd.
ttabbal:
So, nobody has tried this? Odd.
I haven’t found a need to run the transmitter at 12v as I’m getting reliable results of just under 100 feet in open space running at 5v. Perhaps if the path wasn’t as clear or if the distances were greater, I’d try the higher voltage. My educated guess is that the 5v keying line is isolated from the 12v line. Otherwise, you’d toast your PIC. You can always add a small resistor from the PIC to the keying line and a 5.6v zener across the keying line to protect the PIC in case of a failure in the transmitter.