The 555 is an integrated circuit first introduced by Signetics, but now produced by many semiconductor manufacturers. The usual package is an 8-pin DIL. Internally the 555 is DC coupled. It can be used for monostable and astable oscillators. The internal construction of the 555 is as follows:

555 internal circuit

The 555 IC may be used to form an astable oscillator:

555 astable circuit

The 555 IC may also be used as a monostable:

555 monostable

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