I bought a cheap christmas tie, but I thought that it was a shame that it only played the same medley of traditional North American christmas songs. So when it ran out of batteries, I did a a quick design to replace it with a ATTiny85 and a CR2032, using the same LED and speaker.
The simplest way of designing this was to have a pushbutton (open by default) that pulls down the !RES pin of the ATTiny, effectively restarting it. Upon boot, it will read its ADC1 pin, which is floating, to get a random number. This will be used to seed the minimalistic pseudo-random number generator, which will be used to select a song. After the song is played using the PWM hardware (square waves) on the speaker, the ATTiny will enter a sleep state where almost all internal functions are shut down.
I built this using an ATTiny85, a battery (CR2032), a pushbutton for reset, a
small speaker, a LED and a resistor for the LED. A simple sketch of the wiring
from the ATTiny view is available in src/main.c.
I have been using sonic-visualiser to figure out notes, and mscore to note down the sheet music.