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.
This LED flasher circuit, which is suitable for beginners in electronics, uses only two transistors to flash a tri-color LED between two different colors: red and green.
Click the above link to see the circuit diagram.