astable multivibrator mode of 555 timer ic

IC555 operating modes

IC555 has three different operating modes. These operating modes actually correspond to three different multivibrator configurations. 

     1.  Astable mode – it is also known as self triggering or free running mode. It has no stable state. It has two quasi stable states that automatically changes from one to another. It changes from high to low state and low to high state without any trigger input after pre determine time. This mode is used to generate square wave oscillations, clock pulse, PWM wave etc.

     2.   Monostable mode – it is also known as single shot mode. It has one stable state and one quasi stable state. It jumps into quasi stable state from stable state when trigger input is applied and comes back to stable state after pre determine time automatically. It is used in generating pulses, time delay etc.

      3.   Bistable mode – it is also known as flip-flop mode. It has both stable states. Two different trigger inputs are applied to change the state from high to low and low to high. It is used in automatic switching applications, to generate pulse of variable time etc.

frfrequncy modulation can be done using astable multivibrator mode of 555 timer 

8^th and 1^st pin of the 555 are used for giving power, Vcc and GND respectively. 4^th pin is the Reset pin which is a active low input, since it is tied to Vcc. When the output is high, capacitor C1 charges to Vcc through R1 and D. When the output is low, capacitor discharges through resistor R2 and 7^thof the IC. This charging and discharging time periods determines the time period of output. Message signal is fed to 5^th (Control Voltage) pin of the IC through a coupling capacitor and the output can be taken from the 3^ed pin of the IC.