Does anybody have any good leads on really cheap LEDs?? I want to build this 7 x 80 led moving text sign, but don't want to go broke buying the 560 leds. Are modules cheaper? Are they available in 4" height? -----Original Message----- From: Bill Kichman To: pic microcontroller discussion list Date: Thursday, August 05, 1999 9:51 PM Subject: Re: Re: LED Moving Message Display >Yes, I do building power distribution systems in my day job. We never allow >separate, isolated grounding to exist due to these problems. Wned a process >vendor requests an "isolated" ground rod, he gets a ground rod outside the >building, and a copper #4/0 stranded conductor extended to the main building >ground (loop, counterpoise, building steel, pipe, etc.). In the case you >describe, there was easily chance for a serious ground potential and ground >currents. The solution would've been to ground the coax shield at the >building entrance. >For what it's worth... > >Bill Kichman, P.E. >Cornwall, PA USA >-----Original Message----- >From: Tim >To: PICLIST@MITVMA.MIT.EDU >Date: Wednesday, August 04, 1999 8:02 AM >Subject: Re: LED Moving Message Display > > >>Using common grounds (-ve wire) from to supplies is a common method in >micro >>based alarm systems and rearly causes problems. I have however beenadvised >>by a client that in a CCTV system, 2 cameras in separate buildings cabled >>back to 1 monitor with coax had a problem caused by the building earth >>stakes being at different potentials causing the camera to blow up. >> >>Never encounted the problem myself though. >> >>Tim Norton >>----- Original Message ----- >>From: Jonathon Doran >>To: >>Sent: Monday, August 02, 1999 8:28 AM >>Subject: Re: LED Moving Message Display >> >> >>> > Thanks, that's a start, but not quite what I had in mind...looking for >a >>PIC >>> > or similar microcontroller-driven set of multiplexed LEDs to allow >>roughly a >>> > 7 x 80 pixel field to be controlled. Perhaps use a Hitachi LCD display >>and >>> > a few buttons for operator interface. Any other suggestions will be >>greatly >>> > appreciated. >>> >>> How big do you want it? The HCMS 2975 has a 7*80 field :-) I asked >about >>> this earlier on the list, with no response so far. >>> >>> But seriously, you might want to build your display the way they did. A >>> 320 bit shift register, with some latches. Serially clock your data into >>> the shift register, then latch the display. Shifting 5*7=35 bits and >then >>> latching will cause the display to scroll. >>> >>> The problem I'm running into with my displays (and I believe all my >>problems >>> are now related) is that current surges from the LEDs are causing my PIC >>to >>> brown out. HP recommends splitting the supplies, but when you >have >>> pins like: >>> Vled >>> Vlogic >>> GND >>> >>> on the smaller displays, I have no idea how to wire them up without >>causing >>> ground loops. Surely HP wasn't asking me to connect the grounds of two >>> different supplies together. Perhaps they were... >>> >>> Returning to our original subject, consider using separate supplies. >>> >>> Jon Doran >> >