The 555 is a basic but very useful timer IC (integrated circuit).

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.

We have two types of 555 chips in the lab. The NE555P and the low-power TLC555.

NE555P from Texas Instruments

TLC555IP from Texas Instruments

  • Very Low Power Consumption
  • Sink Current 100 mA
  • Source Current 10 mA
  • Voltage 3V to 15V
  • Same Pinout as the NE555
  • Download Datasheet

A simple circuit that blinks an LED once per second:

NE556N from STMicroElectronics

General Purpose Dual Bipolar Timer DIP14