555 timer

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, delay, pulse generation, and oscillator applications. Derivatives provide two (556) or four (558) timing circuits in one package. It was commercialized in 1972 by Signetics. Numerous companies have made the original bipolar timers and similar low-power CMOS timers too. In 2017, it was said over a billion 555 timers are produced annually by some estimates, and "probably the most popular integrated circuit ever made."

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