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555 timer IC

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A circuit using a 555 timer. The timer is the black rectangle.

The NE555 is a common IC (or integrated circuit) introduced in 1972 and invented by Hans Camenzind. It is popular among hobbyists and can be found in many electronics stores that sell components.

The basic 555 timer got its name from the three internally connected 5kΩ resistors used to generate voltages. The 555 timer is able to produce stable square waves that are often needed to control electronic circuits. You can set the frequency or number of pulses per second by using different voltages. It can also produce different types of waves that alternate or flip-flop. A very common use is in timers to control when something turns on or off.

NE555 Circuit Schematic
NE555 Pin Layout