Astable Multivibrator Using 555 Timer. The 555 timer ic affords exact time delay from ms to hours. The designing and working of astable multivibrator using a 555 timer ic is done by using ransistors and operational amplifiers.
The 4th pin is reset pin which is active low and is connected to vcc to avoid accidental resets. The modulating signal is applied at the pin 5 of the first ic 555 that is operating in astable mode. In order to achieve pulse position modulation two 555 timer ic s are used in which one operates in astable mode and the other in monostable mode.
Above figure shows the circuit diagram of a 555 timer wired in astable mode.
The output of this ic 555 is a pulse width modulated wave. When initially power is turned on trigger pin voltage is below vcc 3 that makes the lower comparator output high and sets the flip flop and output of the 555 chip is high. The output of this ic 555 is a pulse width modulated wave. In order to achieve pulse position modulation two 555 timer ic s are used in which one operates in astable mode and the other in monostable mode.
