At 04:26 AM 10/6/2009, Michael Rigby-Jones wrote: >I have to ensure full isolation between all the channels, I must not add >any significant load to the RS232 line and I must stick as closely as >possible to the standard RS232 logic level thresholds > >My first though is to power an RS232 line driver (MAX232 etc.) from an >isolated dc-dc converter and then isolate the TTL logic from the micro >using opto-couplers. I have been doing something similar for several years now to receive DMX lighting data. In my case, I use a tricky little homebrew DC-DC converter to generate 5V @ 50 mA which is then used to run the receiver chip and an opto. I can share the DC-DC converter with you but would ask that you don't release it into the wild, at least until I finally get around to submitting it to one of the design mags. I had actually planned to do that several years ago but just never got around to it. Best estimate is that the total parts cost of the converter is about US $0.25 in hundreds, not including magnetics. That's after building several hundred of them. Converter runs from 6-30 Vdc and is probably about 60% efficient. I've used it with a variety of transformers, even gone so far as to use it with a common-mode choke that I purchased surplus (several thousand pieces). The only component that runs warm is the resistor in the snubber network. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist