Servo - March 2013

Building a Large Scr lling Display — Part 2: Adding a Second Panel

● by Pete Smith

Buoyed up by my success in getting one panel to work, I decided to add a second panel to increase the impact of the display and to make it a little easier to read.

FIGURE 1. Wiring for two panels.

in the middle of Figure 1 (ignore the other wiring for now), and making a small change to the code so that the microcontroller recognizes the second panel.

You simply change the command “#define DISPLAYS_ ACROSS 1” to “#define DISPLAYS_ACROSS 2.” Load the code onto the Freetronics Eleven as before; now the display will run across both panels, but at a reduced brightness.

To restore the panels to full brightness, you need to add a 5V power source directly to them. I bought a small 5V 3A power supply on eBay for about $10 (Figure 2), then connected a power cord to it and output wires that feed both panels (refer again to Figure 1).

CAUTION: Line voltages are dangerous and can injure or kill.

FIGURE 2. 5V power supply.

If you are not experienced with how to safely connect and shield line voltages, then get a laptop or wall wart type power supply. Mine will be inside a protective box in the final display so that the high voltages will not be accessible.

The display, however, currently still needs the computer to be connected to power the microcontroller. To be able to run the display without the computer, you need to be able to replace the 5V provided by the USB cable.