555 Timer
1) 555 is a precision timer that can operate as either a single shot timer
(monostable mode) or an oscillator (astable mode).
2) 555 is "programed" by wiring it with resistors and capacitors.
These create RC circuits that control the timing.
3) Easy to use, cheap and has many applications such as led/light flashers,
tone generators, on shot timer circuits, etc
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