I made this project for Valentine's day.. Ana also made me a Valentine's "card".. It's a Attiny26L, a 3V cell (CR2032) and a 5x7 LED matrix display. Since the supply voltage is low, and the circuit was to be the smallest possible the MCU ports are connected directly to the LED matrix i.e. no resistor. It is clear from the video that the more LEDs are on, the lower the intensity. I thought about correcting it with PWM (time on depending on the number of LEDs on) but for simplicity I left it like this.
A better alternative would be to use the display as a 7x5 and characters 5x5, some people have dificulty reading running messages if only one character appears at a time (as in the video).
Developed in C and assembler using linux avr-gcc tools and the Atmel USB-ISP.