I usually see lights in Nairobi scrolling text from right to left. It is an interesting thing to see, and if done right is usually beautiful. I wanted to make one, and so this is how I went about it.
To light and LED one needs 5V supplied to cathode and GND supplied to anode. This means if we have 2 leds, both receiving 5V and only one receiving GND, only one LED will light. The same occurs when both receive GND and only one receives 5V. This is the basic building block of an LED matrix.
So how does one keep this so. Well, one option is using a microcontroller. The microcontroller's pins can be set to output a HIGH (5V) or a LOW(GND/0V). So having a microcontroller will help us out in choosing which LED to use.
The following is the schematic I then came up with:
To have the scrolling effect, I then wrote code that turns on and off LEDs at a particular pattern. Making this faster will result in less flickering of light. I used an atmega 8 for this and added the respective current limiting resistors. The circuit and code for this can be found here:githublink.
Here is the image of the final fabricated circuit:
You can find the video of the working circuit here. The text being shown is "HAPPY EASTER" in case it is the video is not clear enough.