This“IC Time Machine“ was the very first and only commercial timer IC available. It provided circuit designers with a relatively cheap, stable, and user-friendly integrated circuit for both monostable and astable applications.It works as square-wave form generator with duty cycle varying from 50% to 100%, Oscillator can also provide time delay in circuits. The 555 timer got its name from the three 5k ohm resistor connected in a voltage-divider pattern.
555 Timer Schematic:
The 555 timer comes as 8 pin DIP (Dual In-line Package) device. There is also a 556 dual version of 555 timer which consists of two complete 555 timers in 14 DIP and a 558 quadruple timer which is consisting of four 555 timer in one IC and is available as a 16 pin DIP in the market.
The 555 timer has two basic operational modes
Monostable (one shoot)
In the one-shot mode, the 555 acts like a monostablemultivibrator. A monostable is said to have a single stable state–that is the off state. Whenever it is triggered by an input pulse, the monostable switches to its temporary state. It remains in that state for a period of time determined by an RC network. It then returns to its stable state.An astablemultivibrator is simply and oscillator. The astablemultivibrator generates a continuous stream of rectangular off-on pulses that switch between two voltage levels. The frequency of the pulses and their duty cycle are dependent upon the RC network values.
- NE555 Bipolar Timer
- 9V Voltage Battery
- 1uF Electrolytic Capacitor
- Two 1K Resistors
- One 470k Resistor
This circuit uses the 555 timer in an Astable operating mode which generates a continuous output via Pin 3 in the form of a square wave. This turns the LED (D1) on and off. The speed at which the LED (D1) is turned on and off is set by the values of R1 and R2. The time of turning on & off for the LED can be set through the electrolytic capacitor as follows
t = R X C
There are thousands of different ways that the 555 can be used in electronic circuits. In almost every case, the basic circuit is either a one-shot or an astable, for example One-shot pulse generator in Monostable mode as an Oscillator in Astable Mode or in Bistable mode to produce a flip/flop type action.The application usually requires a specific pulse time duration, operation frequency, and duty-cycle. You can use the 555 chips for basic timing functions, such as turning a light on for a certain length of time, or you can use it to create a warning light that flashes on and off. You can use it to produce musical notes of a particular frequency, or you can use it to control positioning of a servo device.