A simple doorbell with two tones with the famous 555 timer.
It's an interesting circuit to learn the basics of the 555 and to learn how to solder and fabricate DIY a Through-Hole printed circuit board.
Also it's useful to learn the basics of EDA free-software KiCad.
This design was created to the MakersUPV Workshop: Taller fabricación casera de circuitos impresos (in Spanish)