IC 555 timer
The 555 timer IC is an integrated circuit (chip) used in a variety of
timer, pulse generation, and oscillator applications. The 555 can be used to provide time delays,
as an oscillator, and as a flip-flop element.
The IC 555 has three operating modes:
- 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 bounce-free latched switches.
- Monostable mode - in this mode, the 555 functions as a "one-shot" pulse generator. Applications include timers,
missing pulse detection, bouncefree switches, touch switches, frequency divider,
capacitance measurement, pulse-width modulation (PWM) and so on.
- Astable (free-running) mode - the 555 can operate as an electronic oscillator. Uses include LED and lamp flashers,
pulse generation, logic clocks, tone generation, security alarms, pulse position modulation and so on.
The 555 can be used as a simple ADC, converting an analog value to a pulse length (e.g., selecting a thermistor as
timing resistor allows the use of the 555 in a temperature sensor and the period of the output pulse is determined by the temperature).
The use of a microprocessor-based circuit can then convert the pulse period to temperature, linearize
it and even provide calibration means.