>Date: Tue, 13 May 1997 17:12:11 -0700 >From: "Jann P. Kaminski" >Subject: LED Signboard >I am interested in making custom signboards out of LED modules (5x7) >using PIC uC's. Signboards are those scrolling displays or marquees seen >wherever advertisers want their message observed. Is there a schematic / >program for this project? Useful features would be expandable character >table, string length, panning, scrolling, .... Any information would be >helpful. >J Kaminski In a nutshell, you need more horsepower than you might think for projects like this. These displays are typically scanned, and that imposes a lot of overhead on your CPU to keep the display refreshed properly. If you don't go fast enough, you get flickering. It's important to note that the flicker can be acceptable if you're looking straight at it, but can be very annoying if your eyes are moving around (as in our industry, where we make these kinds of signs for use in casinos). As the sign increases in size, you need to make some hard decisions regarding the kinds of information you want to present. If you're only interested in character data, then you can store font images and assemble a display screen with fairly small amounts of storage. If you plan to display graphics, you'll need more space. If you want animations, plan on *lots* of space, since you won't have time to do any clever mathematical transformations in real time. You'll need to just store every frame of the animation, then play them back sequentially. Most manufacturers use high-current drivers like the Allegro parts, which combine a shift register and output drivers. You need to work out a column and row scanning system that will refresh your display, and then send the appropriate clock, enable, data and strobe signals to the driver chips. It's not a trivial amount of work. We have several people devoted full-time to display development. After you've got all that stuff working right, then you can start worrying about the higher-level issues of scrolling, flashing, blinking and the types of information you'll present. Note that you may have to modify your display refresh algorithm depending on the kind of motion or effects you're trying to achieve. They aren't cheap to build, either. LED modules go for $5-6 each in small-ish quantities, and you can easily put several hundred dollars into the display modules alone. Good luck with your project. Mark G. Forbes, R & D Engineer | Acres Gaming, Inc. (541) 766-2515 KC7LZD | 815 NW 9th Street (541) 753-7524 fax forbesm@peak.org | Corvallis, OR 97330 http://www.peak.org/~forbesm mforbes@hq.acresgaming.com "There has been an alarming increase in the number of things I know nothing about." ---Anomalous