An op-amp is used as an oscillator in this LED flasher circuit. This is another circuit that can easily be built on an electronic breadboard by beginners in electronics. Click the above link for the circuit diagram.
This circuit uses a 555 timer IC and produces a fixed frequency audible tone that is played through a loudspeaker. No amplifier is necessary as the 555 puts out a signal of high enough amplitude. The circuit is easy to build for beginners in electronics and can be built on an electronic breadboard. Click the above link to find the circuit diagram.
This two transistor metronome circuit can easily be built on an electronic breadboard. The circuit is easy enough for beginners in electronics consisting of only six components, a loudspeaker and a nine volt battery or 9V power supply.
Find the circuit diagram for the metronome at the above link.