led sign

Posted on Feb 5, 2014

This sign I designed uses no microprocessor. It has an eprom and multiple counters. As in most electric signs, the LEDs are matrixed, and strobed very quickly to make it possible for all 70 LEDs to appear lit. This sign is strobed horizontally, unlike most large signs which are strobed vertically. I did it this way because electrically it was simp

led sign
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ler. The eprom has 8 outputs, of which I used 7 of them to drive the 7 horizontal rows. The eprom outputs are not strong, so they are buffered. The 10 vertical columns are activated in sequence, giving a 1/10 duty cycle. I used the 8th output of the eprom to drive the reset for all the counters, so the circuit loops when empty memory is reached, allowing for short or long messages. With a 27C512 eprom(64k bytes), messages and animations can be almost a minute long! Filling 65536 bytes of memory is easy, but "quality time" takes some programming. I wrote a little message compiler program that produces binary files compatible with an eprom programmer. The first program I wrote(the latest version is cgrom7. exe) allows you to write a message or import a text file. It uses a font map(cgrom. dat) that I created. The letters look like standard 5x7 dot matrix letters. Not quite two letters fit side by side on the display, because I allowed a one-pixel wide column between each letter. The effect is quite pleasing, because the message moves horizontally one pixel at a time(In truth, each frame is displayed several times before it moves). The second program I wrote(romart03. exe) is a paint and animation program. You "light up" pixels on a large screen and have a 7x10 window that you can move around, and write frames to a binary file as you choose. The program does a couple of other things that allow you to chain files together, etc....

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