I've never worked on anything like this, but here are a few thoughts off the top of my head. Do the LED's have to blink in unison, turn on in sequence, or anything fancy like that? I.e., what are the exact specs.? If not, you could just plug in a two watt series resistor and diode into each one every so far apart, in parallel (very small circuit board encapsulated in epoxy comes to mind), and run it off of either 120 or 240 VAC. If you used LED's with the resistor and diode built in (I think someone makes that, but a bit more spendy), all you'd need is some sort of plastic LED connector you can crimp onto the cord that the LED's neatly fit into (not unlike christmas tree lights), and that works reliably (I'd hate to have to climb that tree to fix a bulb). Obviously, you'd want some sort of fuse and/or power crowbar setup where it plugged in at for safety. To light up sections of LED's, like one section of a 7 segment LED display, you could have a PIC at each segment, that turned on the HV power to that segment via a zero crossing triac (or pre-rectify, and use a HV Mosfet), and have an X-cap or VB409 there to power the PIC. You'd need something like an X-10 setup or RF reciever on each segment to communicate with each PIC. Obviously you'd need a "master" PIC to control the others, via X-10 or RF transmitter, that would also communicate with a PC or something. I know, running high voltage to each led is a bit more "dangerous", but low voltage ain't gonna go far unless your using really big wires between each LED (more cost). Even high voltages drop a bit at those distances. I make a power supply that sends out 1.5~1.7vac down a four foot 16 gauge cord to a resistive load (at upwards of 16 amps), and the voltage drops to less than half near the load. Obviously an LED won't drop the voltage that much, but by the time it gets to the last one (I'm assuming several in parallel), it may not be very bright. At 100 LED's per 10,000 feet (1 LED per 100ft/25~30m), you'd need at least 2 amps of low voltage DC to power it (including line losses, add another amp or two per 100ft), or more likely, you'd need a lot more sections. At any rate, unless you have "a lot" of small sections, or your probably going to have the LED's up front running a lot brighter than the ones on the end of the line, with a low voltage DC supply. Again, these are thoughts just off the top of my head, no flamage please..... Bob -----Original Message----- From: Dave King To: PICLIST@MITVMA.MIT.EDU Date: Thursday, December 27, 2001 4:19 PM Subject: Re: [EE]: big led display (kind of) >This isn't quite the same problem but the title still fits. I'm working on >a real big LED >display that's on the order of 2 miles long. Think of it as the worlds >longest Christmas >tree light string. When my mouth opened it yap and said "oh yah I can do >that" my >brain wasn't paying too much attention. Now I need to find a way to power >this "thing" >so it works without making the smoke come out of something. Right now I'm >thinking >along the lines of using a Pic controlled switching power supply to >generate pwm and >slowly ramping things up. I'm sure I need to have several feed points but >I'd like to be >sure. > >Anyway I was wondering if anyone has run across any good information on >working with >something this sized. I've got a few ideas on it but I'd like to be a bit >more sure before I >start. > >Cheers > >Dave > > >The only thing that helps me maintain my slender grip on reality is the >friendship I share >with my collection of singing potatoes -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics