ATtiny85 Scrolling LED Matrix
David Johnson-Davies’ ATtiny85 scrolling text display uses four 8x8 matrices.
The ATtiny85, while limited compared to more modern and/or physically larger chips, can be incredibly useful for its diminutive size – and its mere eight pins for IO, reset, and power. In David Johnson-Davies’ latest Technoblogy project, he’s taken full advantage of this little powerhouse, using it to scroll text across four 8x8 LED matrices.
The system is designed to fit on a full-sized breadboard for simplicity, stacking the four displays side by side. An ATtiny85 controls each display via I2C, leaving three IO pins free. Two of these pins are used to interface with a keyboard (using the PS/2 protocol), allowing users to set up the scrolling message. The third is connected to a potentiometer that controls the scrolling speed.
The build was inspired by a friend of Johnson-Davies' son who enjoys model trains, and is meant to simulate the type of scrolling screen that is often seen on real trains and platforms. Messages are stored in EEPROM, so if you feel like leaving the same text on display between power-up cycles you can at least temporarily forgo the keyboard.
The device runs on a switched battery box with two 1.5V AA batteries, making it portable from model station to model station. As usual, this Johnson-Davies project looks like a fun electronics experiment, and something that could be very entertaining for young (or old) model railroad fans alike!