While searching for a "decent" USB-RS232 converter, I turned up the following two fascinating creations which have status LEDs for all the signal lines:
This concept really appeals to me from a debugging/verification point of view (although I do NOT get what the GND signal LED is expected to do... stay on all the time?). My only problem is that the blue one is $25 and the black one is $35 (despite the fact that they both appear to be identical - they're probably based on the same reference design). In my opinion, that is way too much for a device I can essentially go and grab the barebones version of off eBay for less than $3 shipped. Thus, my question is, how do these LEDs work, and would it be possible to mod the same kind of functionality into a cheaper converter (perhaps one of the FTDI breakout PCBs on eBay)?
I'd like to make the point that while I am likely to wind up with a small collection of USB converters as time goes by, this is something I see I'm only likely to need one of any time soon, so I don't mind having to put a bit of effort into building it, although I don't (yet) have the tools to work with SMT componentry; I also have no need for the end result to be compact/self-contained - [premade] PCB-based solutions are fine.