NE555 - Single Timer

The NE555 is a stable controller capable to produce accurate timing pulses. With a monostable operation, the time delay is controlled by one external resistor and one capacitor (read more about Capacitors). With an astable operation, the duty cycle and frequency are controlled by two external resistors and one capacitor.

LM555/NE555/SA555 Internal Block Diagram

In the monostable operation, the timer generates a pulse whenever the trigger voltage drops down below Vcc/3. In the astable operation, the threshold terminal and the trigger terminal are connected so that a self-trigger is formed, operating as a multi vibrator.

Read and download the datasheet.

NE555 from Farnell