Not mission critical, more embarrassing when the calls start coming in and I get asked why my circuit didn't detect this ;) I just want something that will trigger if there is a power loss remotely. Obviously it should work, but if it doesn't sometimes, no big deal. Guess I should explain more - the remote site that I want to detect power loss is a outdoor radio aerial installation. It has a (heated, and with a fan and thermostat to maintain constant internal temperature and no condensation) electrical cabinet nearby which contains all the electronics and the wire terminates here. I want something that I can plug into the mains supply and a twisted pair that'll do something if there's a power fail. Right now, I'm liking the sound of the opto-isolator, 20mA constant current source or the wallwart. The equipment would go into an ingress-sealed box inside the cabinet, so I don't think the fact its outdoors is a significant issue. Could I do this: Remote site: 5V wallwart -> 20mA CCS (any recommendations? I was looking at the LM3950 CCS 'White LED Driver', but it requires a resistor to set the Iout, and its only available in SOT23, would prefer DIP for this) | Twisted Pair with ground and LM3590 output from the remote site | Central Site: The twisted pair terminates at an optoisolator (HCPL-2731) which is then connected to a PIC. How does that sound? On 24/10/2007, alan smith wrote: > > Guess need to ask > > 1. is this a mission critical type sensing? > 2. how reliable do you want it to be > > > Ben Wheare wrote: > That was one of my thoughts, but won't the voltage drop over such a long > cable make such a solution impracticable? > > On 24/10/2007, Harold Hallikainen wrote: > > > > How about a "wall wart" transformer powered by the AC you are watching. > > The DC output drives one pair of the cable directly. At the far end, a > > resistor and LED indicates power is present. An LED based opto coupler > > could be substituted for the LED to drive a PIC. > > > > Harold > > > > -- > > FCC Rules Updated Daily at http://www.hallikainen.com - Advertising > > opportunities available! > > -- > > http://www.piclist.com PIC/SX FAQ & list archive > > View/change your membership options at > > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- > 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 > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist