Josh, If you can use 422/485 differential I/O, you could look at the max1480 / 90 stuff. What you would get is the isolation, speed, use of a simple single dc supply and it would be fairly small -- 4 28 pin DIP packages and 1 8 pin DIP. But these things are about $10 a piece in qty. I have used a couple hundred of these in DMX equipment over the past 4 years without a single failure. Bill -----Original Message----- From: pic microcontroller discussion list [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Josh Koffman Sent: Friday, February 13, 2004 9:49 AM To: PICLIST@MITVMA.MIT.EDU Subject: [EE:] Isolated Splitter Hi All. I'm building a little signal splitter/repeater/isolator for a 250KBps signal (no, not DMX sadly, I'd feel more comfortable with that). For the original, I won't have any isolation between the input and output. My idea is to have one receiver chip feeding all four inputs of a quad buffer/driver chip, and each output then feeds its own transmitter chip. Question is, can I tie all four inputs together like that? I don't think there's a problem. Second, would a 74lsXX (don't know the number, I'm not near a catalog at the moment) handle the 250Kbps stream ok? For the slightly more advanced version, I want to have isolation between the input and each output to avoid ground loops in larger systems. My thought is to add an optoisolator to each output of the buffer chip in the above circuit. First off, would a garden variety 4N25 (from memory, might be a wrong part number) or similar work at those speeds? Second, to truly avoid loops, each transmitter chip would have to be on its own power supply to avoid connecting the grounds of all the chips together, correct? Is there a semi-easy way to do this? At the moment the only thing I can think of are independant 120V-5V switching power supplies for each chip, or some sort of DC-DC convertor for each chip. This will get expensive and large very quickly. Is there any other way? Thanks, Josh -- A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools. -Douglas Adams -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.