This Auto-Rotating Scrolling LED Matrix Display Is Controlled by an ATtiny85

The ATtiny85 is one of the smallest and least powerful microcontrollers in the AVR lineup, but it is still useful and has become a favorite of makers building simple projects. ATtiny85 chips are very cheap (especially when purchased in bulk), but still have an 8-bit processor that can run at clock speeds from 1MHz to 20MHz, 8KB of program memory, 512 bytes of RAM, 512 bytes of EEPROM memory, and up to six I/O pins (including the reset pin). That is enough for basic projects, but TUENHIDIY has really pushed it to the limits with this auto-rotating scrolling LED matrix display.

This project is built around a Digispark development board, which contains an ATtiny85 microcontroller along with a USB chip and a voltage regulator. The Digispark doesn’t, however, have any additional processing power or RAM over a bare ATtiny85, which is why this project is so impressive. Not only does the humble ATtiny85 need to detect the orientation off the display, it also needs to control the entire 13x15 LED matrix. That is a total of 195 LEDs, which is quite a lot when you remember that the ATtiny85 only has a maximum of six I/O pins to work with.

TUENHIDIY achieved this wizardry by using both I2C and SPI for communication. The MPU-6050 accelerometer and gyroscope module sends data to the ATtiny85 via I2C. The ATtiny85 uses that information to determine which direction is up, so the text can be flipped when necessary. It then outputs to the hand-built LED matrix through SPI, using two TPIC6B595 shift registers, two 74HC595 shift registers, and a series of A1013 transistors. The shift registers essentially expand the number of pins that the ATtiny85 has to work with, which is the only way it is able to control all 28 of the LED matrix rows and columns. Power comes from the USB port built-into the Digispark board through the voltage regulator. Short alphanumeric messages can be stored in memory or can be sent via USB serial if the Digispark is connected to computer. We love projects like this, because they do a great job of demonstrating how much you can accomplish with basic hardware.