A crystal radio is a simple radio receiver that was popular in the early 20th century. It requires no external power source and is able to pick up radio signals using only the energy present in the radio waves themselves.
The basic components of a crystal radio include a tuned circuit made up of a coil of wire and a capacitor, a diode (typically a germanium diode), and a set of headphones. The coil and capacitor are used to tune the circuit to a particular frequency, while the diode acts as a detector, allowing the radio waves to be converted into an audio signal that can be heard through the headphones.
