Oscillators and Basic Feedback Circuits

Key Insight

Electricity drives motion, as seen in devices like clocks, fans, and compact disc players. A simple and elegant demonstration involves electric buzzers and bells, which utilize self-interrupting relay circuits. When a switch is closed, an electromagnet pulls down a flexible contact, completing a circuit. However, this action simultaneously breaks the circuit, causing the electromagnet to lose magnetism, and the contact flips back up, re-completing the circuit. This continuous, alternating opening and closing of the circuit creates sound, producing a 'rasping sound' for a buzzer or ringing a bell if a hammer and gong are attached.

An alternative implementation of this continuous oscillation uses an inverter. Although an inverter's output is typically the opposite of its input, wiring its output to its input, along with a relay, causes continuous alternation between states 0 and 1 due to the relay's inherent time delay. This self-running circuit, termed an oscillator, fundamentally differs from previous circuits that required human intervention. Oscillators are crucial for automation and ensuring synchronicity within computers, providing a foundational 'clock' mechanism.

An oscillator's output consistently alternates between 0 and 1, representable on a time-based graph where the horizontal axis signifies time and the vertical axis denotes the 0 or 1 state. A full cycle is defined as the interval where the output changes and returns to its starting state. The time for one cycle is the period; for instance, a period of 0.05 second results in a frequency of 1 / 0.05, or 20 cycles per second. This measure, 'cycles per second,' is now universally known as Hertz (Hz), named after Heinrich Rudolph Hertz, who was the first to transmit and receive radio waves.