Thanks Larry, haven't been able to get at your site yet, but I began to think the same way. After reading the posts on LED traffic signals and remembering how many vehicles use LED's as the third stop light, that may indeed be the way to go. It would sure keep the drive power down to more reasonable levels. Need to work out the logic yet as I am very inexperienced on the software side. Thanks also to the rest of the replys out there. This project may take me a while to implement. "Larry G. Nelson Sr." To: PICLIST@MITVMA.MIT.EDU Subject: Re: High Current Serial Sent by: pic Display Driver microcontrolle r discussion list 11/15/99 04:19 PM Please respond to pic microcontrolle r discussion list Super bright LEDs may do what you want. I have a sign being used for race tracks that is used day and night and is very visible. Take a look at my web site to see what it looks like. I have 2 incandescent lamps on the top that I blink to gain attention. 4 LEDs in series for each segment in the 7 segment displays. At 01:43 PM 11/15/99 GMT, you wrote: >I was thinking about using 12V 4 or 7 watt bulbs but, you're right that >adds up to a lot of power in a hurry. If 40% were on using 7 watt bulbs >that would be 1176 watts using a 5 x 7 matrix! Think I better scale this >down and do some experimentation to see what bulb size I really need. I >want the display easily readable from a distance of 50 - 75 feet at night >(I think the night part will help a bunch). Thanks for giving me a start >on this, will probably be back with more questions since I'm fairly new to >the software end of PICs. > > > > > Donald L > Burdette To: PICLIST@MITVMA.MIT.EDU > NO.COM> Subject: Re: High Current Serial > Sent by: pic Display Driver > microcontrolle > r discussion > list > A.MIT.EDU> > > > 11/13/99 11:43 > PM > Please respond > to pic > microcontrolle > r discussion > list > > > > > > >You haven't mentioned what bulbs you intend to use, but I'm guessing you >want 1/4 or 1/2 watt bulbs. At 12 Volts, that's about 20 or 40 mA per >bulb. I'm also guessing you'll use a standard 5x7 matrix per character. >At 12 characters, that's 420 bulbs. If worst case is 40% of bulbs on >(I'm guessing here!), that's 42 or 84 watts, and 3.5 or 7.0 amps. > >While these numbers are not unreasonable, they are not trivial to work >with. > >Multiplexing sounds great. Since you'll have a 7x60 matrix, you'd have >60+7 drive pins to work with rather than 420. However, I don't know that >a 1/60 duty cycle is reasonable for incandescent lamps. I think you'd >want about 12*(60^0.5) = 93 volts drive (somebody correct me here if i'm >wrong). Of course, at that voltage your average current would be less >than 1/2 or 1 amp. > >If I were doing this, I think I'd go for 1/4 W bulbs, grouped into 4 >groups of 3 characters. That would give me a 28 x 15 matrix, and 1/15 >duty cycle, requiring about 46.5 volt drive (round to 48?). I'd use >74HC595 shift registers, 4 for rows and 2 for columns. I'd make the rows >the low side, with a 1K resistor driving the base of a ZTX453 transistor. > Columns would be the high side, with ZTX553's, 1K resistor to a ZTX453 >being driven by the '595 (see the current thread on high side drivers). >These parts are all available from Digi-Key. Suitable substitutes could >be found easily. > > My code would look kind of like this: > > Shift out 4 bytes to row drivers (each row is a full byte to make >software easier) > Shift a 1 into first column driver > Strobe the '595 output latch pins to update the output data > Wait for 7 mS > > Shift out next 4 bytes for row drivers > Shift the 1 to the next column driver > Latch the outputs > Wait 7 mS > > ... > >This would give about 9.5 Hz refresh rate, which Wagner says is adequate. > You could trim the 7 mS down if you see flicker. > >Let us know what you end up with! > > >Don > > Larry G. Nelson Sr. mailto:L.Nelson@ieee.org http://www.ultranet.com/~nr