Dublin Institute of Technology has a history and detailed explanation of the 555 pinout. ElectronicsTutorials has an excellent 555 oscillator tutorial that describes the ways a timer oscillator can be configured. Beavis Audio Research also has some very simple schematics that illustrate these configurations, and Williamson Labs has a cute animation.
| [thumb | 300px](/File:555-556_pinout.png “wikilink”) |
555 pinout
1 GND
2 TRIG
3 OUT
4 RESET
5 CTRL
6 THR
7 DIS
8 V+/Vcc
556 pinout
14 Vcc
13 DIS
12 THR
11 CTRL
10 RESET
9 OUTPUT
8 TRIG
7 GND
555 → 556 Correspondence
1 => 7
2 => 8
3 => 9
4 => 10
5 => 11
6 => 12
7 => 13
8 => 14
In astable mode, the 555 timer can be used as a simple pulse generator; this pulse generator can be modulated via the control pin, e.g. to construct an audio-modulated driver for a Plasma Speaker. It may also be used to construct a simple overload protection circuit.