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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

THE DRIVER BOARD

The driver board uses eight bits of digital data to control eight 25-W 120-VAC lamps. Each bit controls a MOC3031 zero-crossing optical isolator, which in turn controls the gate input of a 2N6344 TRIAC wired in series with a lamp. The zero-crossing feature was used to help minimize the inrush current when a lamp is switched on. Figure 5 shows the schematic of the driver board.

An LED wired in series with each digital input allows a visual indication of the state of each lamp. Note that the lamps are controlled statically and are not multiplexed. So, if all 64 lamps are turned on, the panel uses a total of 1600 W! This is why a GFI receptacle is used on each panel, which requires over 13 A of current when all the lamps are on. Also, note that even though the TRIAC shuts off when the AC line voltage crosses zero (twice each cycle), it turns right back on if its associated digital input is high. Thus, a 64-bit pattern loaded into the panel will maintain the lamp pattern indefinitely.

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