I was thinking of a 12VDC wall wart...that way it takes care of any drop, and then put a resistor and LED... so what if you drop a few volts across it? He answered the question..one off design, semi-reliable, and not mission critical. LED off....you got trouble! Dr Skip wrote: WOW, you guys are really into feature creep!! More like a feature race! ;-) KISS! Use a plain ol' CV wall wart and a series resistor to the twisted pair, LED on the other side, and if you want comm (remember, no comm other than a binary on/off constant needed so far), use a FET or transistor to short across the pair and do it at 1 or 2 Hz and you'll have no sync/sample issues reading it, minimal bandwidth, and still be able to send voltage and temperature once a minute or more! No timing or freq. issues on reading it either. You could even use just a pic on the sending end, gather the parameters you need, and use morse code so it's person readable without add'l hw on the other side... -Skip Richard Prosser wrote: > Sorry - forgot about feature-creep :-). > > Running RS485 mght then be an option (3 wires) - or a couple of old > modems on the twisted pair. > > RP > > > > On 25/10/2007, Jinx wrote: >>> 5V Wallwart -> 470ohm resistor -> cable -> opto -> PIC. >>> >>> I don't see what the constant current source is going to give you >>> with an ~constant cable resistance of up to a couple hundred >>> ohms >> Possibly/probably, OTOH if you wanted to get fancy and measure >> some remote parameters ..... >> >> Value-added service ? >> -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist