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AN ELECTRONIC LITESHOW DISPLAY

Part 1ýThe Electronics Behind the Lights
by James Antonakos

Start ý The Big Picture ý Inside a Panel ý The Driver Board ý The 64-Bit Shift Register Board ý Interfacing with the PC ý A Little Math ý The Real Thing ý Sources and PDF

A LITTLE MATH

Because the overall operation of the LiteShow display requires numerous updates to the panel patterns, it is reasonable to ask some questions. For example, what is the data rate on the cable? How long does it take to update the display? And, is the PC fast enough to animate the display?

With 384 lamps to control, a 384-bit stream of data must be fed to the display to update all six panels. Even if 500 ns are allowed for each bit time (plenty of time to allow for the slow rise and fall times of the 1488 and 1489), that gives 192 ýs for a single update of the entire display. Animating the display by outputting at least 10 new patterns each second is easily accomplished because the total time is less than 2 ms. Actually, the time between bits is even longer (several microseconds) in order to keep the data rate low enough to prevent distortion of the signal on the cable. However, even at 500 ns per bit, a slow 40-MHz PC running Windows is able to control the display with no problems (over 7600 PC clock cycles per bit time, which implies several thousand instructions per bit time).

Plans for four additional panels increase the number of data bits required for an update to 640. There is still plenty of time available for the software in this scenario. In fact, several students are already working on a BASIC Stamp project that will replace the PC and drive the LiteShow display directly.

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