Online Resources for 555 Timer IC

The 555 timer IC was first introduced by the Signetics Corp. in 1971. It has been more 35 years and this IC is still very popular among hobbyists and is used in numerous projects. With just a few external resistors and capacitors, it can be used to build many circuits and you don't even need to understand the function of each pin in detail. It has 8-pins and it is frequently used in astable mode to generate a continuous series of pulses, and in monostable mode too when one shot or pulse of desired time period is required.

The internal block diagram of a 555 Timer IC is shown below.

Source: http://www.ibiblio.org/kuphaldt/electricCircuits/Exper/45005.png

Online Resources:

• 555 Theory: The story began around 1971, when Signetics Corporation first introduced the SE555-NE555, "The IC Time Machine". By that time, it was the first and only integrated circuit with timer functions for commercial use. the original design has change many times since it's birth,...

• The IC Time Machine: The 555 timer IC was first introduced around 1971 by the Signetics Corporation as the SE555/NE555 and was called "The IC Time Machine" and was also the very first and only commercial timer IC available.

• 555 and 556 Timer Circuits: The 8-pin 555 timer must be one of the most useful ICs ever made and it is used in many projects. With just a few external components it can be used to build many circuits, not all of them involve timing! 
• The web's favorite 555 timer resource (Google Top)