This is pretty old circuit but I found it interesting to describe here.
24×24 LED display is formed by using 9 8×8 Dot LED matrix displays, that are connected to AT90S2313 MCU. MCU scans an indicator lines in series. Special PC program is written which allows drawing images on screen and transfer them via COM port to device. You can send images in series what gives an animation effect.
Circuit is was built using obsolete AT90S2313 MCU which can be replaced by Attiny2313 MCU with minor modifications of firmware.
To make program work you event don’t need to connect device to computer COM port. You can store images in other master MCU EEPROM memory Each received byte from UART is immediately sent to 8 LEDs, second byte to next 8 LEDs and so on. Bytes has to be sent one by one without delay. USART is working at 115200 baud, 8bits, no parity.
Demo movie (137kB);
Originals source svv.on.ufanet.ru