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". The 555
gets its name from the three 5-kOhm resistors used in typical early
implementations. It is still in wide use, thanks to its ease of use, low
price and good stability. As of 2003[update], 1 billion units are
manufactured every year.
The 555 timer is one of the most popular and versatile integrated circuits
ever produced. Depending on the manufacturer, it includes over 20
transistors, 2 diodes and 15 resistors on a silicon chip installed in an
8-pin mini dual-in-line package (DIP-8).
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 and
TLC555. The 7555 requires slightly different wiring using fewer external
components and less power.
The 555 has three operating modes:
- Monostable mode: in this mode, the 555 functions as a "one-shot".
Applications include timers, missing pulse detection, bouncefree switches,
touch switches, Frequency Divider,Capacitance Measurement, Pulse Width
Modulation (PWM) etc.
- Astable - Free Running mode: the 555 can operate as an oscillator. Uses
include LED and lamp flashers, pulse generation, logic clocks, tone
generation, security alarms, pulse position modulation, etc.
- Bistable mode or Schmitt trigger: the 555 can
operate as a flip-flop, if the DIS pin is not connected and no capacitor is
used. Uses include bouncefree latched switches, etc.
Alarm Using NE 555
Rangkaian dasar dari rangkaian alarm ini adalah kombinasi
dari rangkaian astable multivibrator menggunakan IC NE555, yaitu terdiri
dari dua buah IC NE555 dengan rangkaian seperti pada
Gambar 1. Rangkaian IC pertama adalah membangkitkan frekuensi rendah,
sedangkan yang IC kedua, frekuensinya bergantung dari tegangan keluaran
rangkaian IC pertama.
Gambar 1. Rangkaian Alarm Menggunakan IC NE555.