Portable Bluetooth-enabled scrolling LED matrix display- Part 1

LED matrix displays are great fun. They are visually charming, and readable from a far viewing distance with a much wider angle of view as compared to many other types of electronics displays. They can display all kinds of information, including text, graphics, and animation. This project is about making a portable Bluetooth-controlled 8×64 monochromatic LED matrix (total 512 LEDs) for displaying scrolling text message. I made this display to use at home parties or other occasions for displaying greeting messages. The text data to be displayed can be sent from a smartphone using the Bluetooth connection. The display is Arduino-controlled and uses the HC-06 Slave Bluetooth transceiver module for receiving data from the smartphone. I am also using the Bluetooth SPP Pro (freely downloadable) App (developed by Jerry.Li) on my HTC One Android smartphone for sending text message to the matrix display. The complete project has got a nice enclosure made by myself using furring strip boards bought from the Home Depot. We looked at a similar project earlier made by Jollyfactory, who used bi-color LED matrices, which required two MAX7219 devices per 8×8 matrix.

Hardware design

This project uses eight pieces of 60.5mm x 60.5mm (2.4″ x 2.4″) monochromatic 8×8 LED matrix modules with A-type polarity, which means the rows are common-anodes and the columns are common-cathodes. The total size of the display area thus becomes about 2.4″ x 19″ (60.5mm x 483mm). Making one big piece of PCB of that size usually costs more than making small and cascadable modules. So I designed 8×8 LED matrix modules and daisy-chained eight of them to make the 8 rows x 64 columns matrix required for this project. Each module consists of an 8×8 monochromatic LED dot matrix display with onboard MAX7219 driver chip. I have named this module Easy Matrix. It consists of a 5-pin angled male header (J1) on the right side and a 5-pin angled female header (J2) on the left side of the board. Both the headers are precisely aligned along horizontal so that the male header of one module gets easily plugged onto the female header of second module, and so on. Two 1×8 straight female headers are used as sockets to hold the LED matrix module. One of the header socket is marked with a “circle with 1” to indicate where the pin number 1 of the LED matrix display should be inserted. Four 3.5 mm mounting holes are also available at four corners of the PCB. The MAX7219 data and control signals are fed from the J1 header of the first module (the right-most module) in the chain. The complete schematic and board files can be downloaded from a link provided at the end of this section. Here are some pictures of an Easy Matrix module below.

For more detail: Portable Bluetooth-enabled scrolling LED matrix display- Part 1