Here is an interesting hobby circuit of a “crank” door bell! The circuit is built around a timer 555 and a musical piezo-buzzer. The circuit works off 9 volt battery supply. One 9volt PP3/6F22 compact ...

If you try to press switch S2 a second time when the first ding dong sound is still being produed, it has no effect whatever and the two ding-dong bell sounds will be invariably produced. I love all ...