555 Timer

The 555 timer is an integrated circuit used in a wide variety of timer, delay, pulse generation and oscillator applications, and one of the most popular timing chips because of its flexibility and low price. Derivatives provide two timing circuits in one package, the 556, or four, the 558. It was designed in 1971 by Hans Camenzind under contract to Signetics, which had hired him in 1968 to develop a phase locked loop circuit; he proposed a universal circuit built on the oscillator he had designed for it, and the first prototypes were completed in October 1971 as the NE555V in a plastic package and the SE555T in a metal can. The design was first marketed in 1972 by Signetics and used bipolar junction transistors, and twelve companies manufactured it that year. Later low power CMOS versions followed, and by 2017 more than a billion were said to be produced annually.