PWM (pulse-width modulation)
Pulse-Width Modulation — controlling power by rapidly switching a signal on and off, where the fraction of "on" time (duty cycle) sets the effective level. A simple digital output can thereby emulate an analog level. Drives fans, LED dimmers, motors, and servos.
Mechanic: a fixed frequency but varying pulse width — 25% duty = a quarter power, 75% = three quarters. Since the switching is much faster than the load can react, the motor/LED "sees" only the average. Win: efficient (the transistor is either fully on or off → low heat loss, unlike an analog voltage divider), easy to generate digitally. Use case: CPU/case fans (4-pin PWM control), LED brightness, motor speed (ESC), servo position. Trade-off: the wrong frequency can give audible whine or flicker. Fundamental in embedded control and power electronics. A classic first-project building block with Arduino/Raspberry Pi.