IC 555 Timer
IC-555 Timer is a versatile Monolithic timing circuit that can produce accurate and highly stable time delays or oscillations. It can be used as an Astable and Monostable multivibrators. It is available as an 8- pin mini DIP-package.
IC Timer 555 as a Monostable Multivibrator
Monostable Multivibrator has only one stable state. We can change the stable state by applying a trigger pulse. The capacitor charges through R. The larger the time constant RC, the longer it takes the capacitor voltage to reach 1/3 VCC. The time constant controls the pulse width. After the time period given by R and C elements the circuit goes back to its stable state. Even the trigger pulse is removed in between still the circuit will not comeback to its stable state until its time period is reached.
Practical circuit of Monostable Multivibrator
As shown in the figure circuit contains 555 IC power supply is connected to the vcc and reset of the 555IC. When ever we don't use reset pin at that time we will connect it to the vcc power supply because in IC 555 reset is active low signal whioch is connected to the pre set of the flipflop. so if you dont usse then connect it to the vcc which is positive power supply.
For monostable we need to apply the trigger signal to the trigger pin of the 555 IC. So to give the trigger continuously we will connect it to the pulsating voltage source. Please make sure that value of the trigger signal must be below the (1/3)*vcc value. Whenever trigger signal goes below this level we will get the output.
Output pulse width is depend on the value of the resistance and capacitor . As per theory of the IC 555 T out = 1.1*Ra*C.
Here we have already set the value of resistance and capacitor. You can change this value as per requirement of the output signal.To show the output signal we have used oscilloscope which is connected across the load resistance.
As shown in the figure whenever input trigger signal which is in blue colour goes negative below the value of the (1/3)*Vcc, we can get the output signal for Tout duration. Here output signal is in pink colour.
Application of Monostable multivibrator using IC 555
monostable means when we applied trigger signal then we can get output signal. So it can be used in alarm system it can be used to turn on the light for certain duration, it can be used in research lab to generate short signal pulse .
If you want to do this practical on multisim on your own then you can download it from here.
To download multisim file from here please click here.