This is probably the most compact led matrix display ever, you need the ATtiny2313 and 8×8 Led matrix and off course two AA batteries for power. The micro controller is on the back of the display, soldered directly to the pins, since the voltage of two AA cells is around 3V you don’t need the current limiting resistors either. Just remember to use the low voltage type of micro controller like the ATTINY2313V-10PU the ATTINY2313-20PU won’t work, and in case of powering from 5V put some 100Ohm resistors in series with the leds.
This project can be easily adapted to other controller or display, but the ATtiny2313 and the LEDMS88R’s pin configuration fit together perfectly, no need for wire bridges to match the right pins.
With the 64 pixels you can’t display complex messages but there is enough resolution to achieve some eye catching animations, and the battery will last for two weeks. The size can be further reduced if you use small, coin shaped lithium cells instead of the bulky AA batteries.
Compact 64 pixel display: [link]