Understanding IC 555. Design note 3

We all used IC 555 in many applications. Why it is called as 555 Timer? There are three 5K resistors inside the IC that makes it as versatile IC for Timer applications. IC555 was introduced in 1971by the Signetics corporation as SE555 / NE555 and was called as IC555“IC Time Machine”. Later its CMOS version IC 7555 and Dual Timer IC 556 were introduced.
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Design Your Circuit. Part XI- Schmitt Trigger in Action

Design of the popular Timer IC 555 is so interesting and this tiny chip can be exploited in various ways to make different types of circuits. It can be a Monostable, Astable, Bistable, Toggle, Schmitt trigger etc. The Schmitt trigger action is achieved by exploiting the activities of its two internal comparators. Let us make an Automatic Porch light using the Schmitt trigger property of IC 555. It is an ideal circuit to light the premises of home even if the inmates are not there.

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