Parts, tools and supplies for the electronics experimenter.
A metronome is a device used by musicians to help them keep a steady beat. This classic beginner circuit is often called an electronic metronome because it produces a steady stream of clicks.
This type of circuit is called a relaxation oscillator. When the circuit is first activated the capacitor begins to charge. When the charge on the capacitor reaches the threshold required to activate the PN2222A transistor, current begins to flow through the two-transistor portion of the circuit, discharging the capacitor. The charge on the capacitor quickly drops below the threshold required to keep the PN2222A activated. With the transistor circuit now off, the capacitor begins to charge again and the process repeats. The transistor circuit also acts as a small amplifier, driving enough power to the speaker to produce an audible clicking sound.
The rate of the oscillator is controlled by the potentiometer. Rotate the potentiometer clockwise to increase the rate, and counter-clockwise to decrease the rate. You can also experiment with different values for the resistor, potentiometer and capacitor.
(All parts for the project are available in our store.)