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The 555 is an Integrated Circuit (chip) implementing a variety of Timer and Multivibrator applications. The IC was designed and invented by Hans R. Camenzind . It was designed in 1970 and introduced in 1971 by Signetics (later acquired by Philips ). The original name was the SE555/'''NE555''' and was called "The IC Time Machine". It is still in wide use, thanks to its ease of use, low price and good stability. Even today, Samsung in Korea manufactures over 1 Billion units per year ( 2003 ). The 555 timer is one of the most popular and versatile integrated circuits ever produced. It includes 23 Transistor s, 2 Diode s and 16 Resistor s on a silicon chip installed in an 8-pin mini dual-in-line package ( DIP ). The 556 is a 14-pin DIP that combines two 555s on a single chip. The 558 is a 16-pin DIP that combines four, slightly modified, 555s on a single chip (DIS & THR are connected internally, TR is falling edge sensitive instead of level sensitive). Also available are ultra-low power versions of the 555 such as the 7555. The 7555 requires slightly different wiring using fewer external components and less power. The 555 has three operating modes:
USAGE The connection of the pins is as follows: Using simply a Capacitor and a Resistor , the timing interval, i.e. the time during which the output stays low, can be adjusted to the need of the specific application. An example configuration is shown below: Example 555 schematic The interval time ''t'' is given by : which is the time it takes to charge C to 63% of the applied voltage (exact figure: ''(1-1/e)V''). See RC Circuit for an explanation of this effect. SPECIFICATIONS These specifications apply to the NE555. Other 555 timers can have better specifications depending on the grade (military, medical, etc). DERIVATIVES Many pin-compatible variants, including CMOS versions, have been built by various companies. The 555 is also known under the following type numbers: EXTERNAL LINKS
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