# Monostable 555 Multivibrator Working Principle and Circuit diagram with Animation

Monostable 555 timer multivibrator circuit (one shot monostable multivibrator) is a retriggerable mono shot pulse generator. The name ‘Mono stable’ indicates that it has only one stable state. The unstable state is called ‘Quasi stable state’. The duration of stable state or the pulse width is determined by the charging time constant of the RC network. We can transfer the multivibrator from stable state to quasi stable state by using  push button trigger switch. The animated (simulated) working of the mono stable 555 multivibrator is shown in this article. You can use our monostable 555 timer calculator tool to find the duration of pulse(width) easily.

## Components required

• IC 555
• Resistors (1MΩ, 100Ω)
• Capacitors (1µF, 0.001µF)
• LED Push button switch

## Working of monostable multivibrator

• Output of monostable 555 multivibrator remains in its stable state until it gets a trigger.
• Primarily the transistor and capacitor are shorted to ground, this state is considered as the stable state of monostable 555 multivibrator.
• As we know, when the voltage at the second pin of 555 IC goes below 1/3 Vcc, the output becomes high. This high state is known as ‘Quasi stable state’. (Refer Astable multivibrator using NE 555)
• The trigger causes the transition from stable state to quasi stable state.
• So when we press the button (Trigger), the voltage at 2nd pin become less than 1/3 Vcc (disconnected from Vcc) and hence the output becomes high.
• Then the discharge transistor is cut off and capacitor starts charging towards Vcc (Refer the internal circuit below). Charging of capacitor is through the resistor R1 with a time constant R1C1.
• As the capacitor voltage increases and finally exceeds 2/3 Vcc, it will reset the internal control flip flop, there by turning off the 555 timer IC (more than 2/3 voltage at the threshold pin (6th pin) causes IC to reset).
• Thus the output goes back to its stable state from Quasi stable state.

## Design equation for monostable multivibrator

ON time, T=1.1 R1 C1

## 18 thoughts on “Monostable 555 Multivibrator Working Principle and Circuit diagram with Animation”

1. Rishiraj says:

I need to run one DC motor of 12V for 5mins in an hour.
What can i do to run that ?

• Jaseem vp says:

Hi Rishiraj,
For your application we have 2 options, either classic approach with linear ICs such as 555 timer or with Microcontrollers. I suggest you to work with Microcontroller.
Please take a look at our PIC Microcontroller series and design your own circuits according to your requirements.

Your requirement also possible via Astable Multivibrator with ON time=5min and OFF time =1Hr.
The circuit diagram is given in the following link Astable Multivibrator using NE 555 also our 555 Timer Astable calculator may be help full to you for designing. Remember this is a kind of classic approach. It is better to utilize microcontrollers for this applications.

2. SRI LAKSHMI says:

HI SIR…. UR BLOG IS VERY USEFUL FOR ME…. I M 2ND YEAR ECE STUDENT FROM CHENNAI…. U HAVE PRESENTED THE CONCEPTS IN VERY EASY & UNDERSTANDABLE WAY… THANK U SOOOOOOO MUCH SIR…… 🙂

• lutfi says:

hi can you sen 555 pulse one

3. Suresh Dhamsania says:

Very goooood

4. Suresh Dhamsania says:

Stable state at pin 3 is zero. triggering as per this circuit voltage AT pin 2 goes to vcc not below 1/3 vcc please clarify

• Suresh Dhamsania says:

Push switch is to be NC push

5. Plainaldinho says:

its a very good literature

6. Suresh Dhamsania says:

Trigger switch is to be NC push or alternatively you can also connect NO push switch as vcc to register to pin 2 and pin 2 to NO push switch and to ground

7. naman verma says:

i need ic 555 timer as bistable multivibrator
working principle, circuit diagram etc…

8. endowedbaron says:

I love your works. it helps me so much. good work sir. thanks so much.. but sir, how can I connect ir receiver to my locally made audio amplifier, so that I can on/off it with TV remote

9. Rajan naman says:

The way of explaining is thourly good.

10. Aldrin says:

Hi sir, i was studying your circuit. I thnk the connection on our pin 2 trigger is wrong. the push button shuold be connected to the ground from pin 2

• Ray Beebe says:

Pin 2 is active low so it should be grounded for reliable triggering. Generaly it is not a good idea to leave any IC pin floating.

11. himil kashyap says:

Im trying to make a remote control car. I have a robo but its not remote control. Please tell what should i learn first for making simple remote control car circuit. I dont know much as i m a begginer. Please advise me. I will be very much thankfull.

12. Ray Beebe says:

The 555 timer is not retriggerable. Retriggerable implies when a trigger event ( button press ) is received before the end of the timming cycle the cycle begins again. So if you press the button and start a 30 second timing cycle and then press the button again 20 seconds into the cycle ( retrigger ) the total cycle would be 50 seconds.

13. Amol kadam says:

if trigger plus is continuously ON state and applied to pin2
what happen that condition .