When you want to make a video wall such as those found on the sides of buses and bus stops in New York, you need a panel with a matrix of LEDs. These are very handy for displaying short video clips or animation. Adafruit has quite a few of them in different matrix sizes such as 8×8, 8×32, 16×24, 32×32 and 64×32. The last one is available in pitches of 3, 4, 5 and 6 mm.
LEDs on the panel are placed close together in a 3 mm pitch, so that you can appreciate it from up close. With the matrix being made of bright RGB LEDs, you have a 160-degree wide-angle view and the panel looks great both in either ambient light and indoors. You can use panels with a larger pitch if you want it to be read from still farther.
In the matrix on the panel there are 2048 gleaming RGB LEDs arranged in a grid of 64×32 in front. The backside of the panel sports a pair of IDC connectors – one of them is for input and the other for output. You can drive the display with a 1:16 scan ratio when the two connectors are chained together. For this, you need 12 numbers of 16-bit latches.
Along with each panel, Adafruit provides an IDC cable, a plug-in power cable, four mounting screws and mini-magnets (for mounting quickly on a magnetic base). You will have to buy the regulated 5V power supply unit separately. The panel consumes about 4A. The panels need 13 digital pins of which 6 bits are required for data and 7 bits for control. That makes the panels perfect for being driven with the tiny, inexpensive, credit card sized SBC, the Raspberry Pi or RBPi.
You cannot drive these displays by FPGAs or any other processors using high speed, as there is no PWM control built into the panel. Instead, you need to refresh the display manually by redrawing the screen repeatedly. For example, for displaying a 4096 color image (12-bits), you will require about 3200 bytes of RAM for buffering and the process will take up about 40% of CPU time. Adafruit provides support with complete wiring diagrams and library code for drawing pixels, circles, rectangles, lines and text.
An RBPi cannot directly drive the RGB LED display matrix directly. The GPIO pins on the RBPi cannot provide the necessary drive. Moreover, signals from the RBPi will have to be level shifted as the panel works off 5V, as compared to the 3.3V for the RBPi. Adafruit has a drive board – the RGB Matrix Hat. This sits on the RBPi and makes it easy for the RBPi to control the RGB matrix for creating a colorful scrolling display.
It is very simple to link up the RGB Matrix HAT with the panel on one side and the RBPi on the other. Plug in the HAT on to the RBPi, plug in the IDC cable and turn on the respective power supplies. Now, run the Python code from Adafruit. The 5V, 4A wall adapter plugs into the HAT, which protects against under, over and negative voltages to the display.
