555

Few chips are as widely taught as the 555 timer, an 8-pin IC that produces timed pulses or a continuous square wave depending on how it is wired. Circuits here show its three modes: astable, where two resistors and a capacitor set the frequency and duty cycle of a flashing LED or buzzer; monostable, where a trigger gives one pulse of fixed length; and bistable, where it acts as a set/reset latch. For example, "555 timer - Astable Mode" blinks an LED at a rate set by its timing resistors and capacitor.