Astable Multivibrator

Introduction: Astable Multivibrator

The Astable Multivibrator is a really important circuit in electronics. This circuit deploys a signal back and forth between transistors. This circuit can be used for example in emergency lights. The circuitry presented in this instructable shows the symmetric characteristics of this circuit. 

You will need two 10KΩ, two 1KΩ resistors, two LEDs, two 47µF, two 2N2222 transistors, 9V battery, breadboard and jumper wire. 

Step 1: Connecting Power

Configure your breadboard to have the power from battery.  Connect positive with positive lines and if you want you can connect a LED and resistor to the main input just to make sure there is power as seen in the photo.

Step 2: Connecting Transistors

Connect the transistors as seen in the image. Please connect them vertically, remember horizontal lines are connected. 

Step 3: Connecting Transistor

Connect bottom N type end of the transistor to negative as shown in the photo.

Step 4: Connect Resistors

Connect resistors to the other N type end and to positive, also connect resistor to P type to positive. 

Step 5:

Put everything together. 

The video of the circuit  working :)

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1 Person Made This Project!


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7 years ago on Introduction

Not sure if the author still active, but i am trying to learn about electronics as a hobby.

I have looked this concept and it is confusing me. I get the fact that while one bjt is off the other is on, and the charging/discharging cap will then "flip" the states of each bjt respectively.

However in two examples (this one and they use 2 of the same bjt's.

I am trying to understand how it is possible for two transistors of the same type to be in different states when power is supplied?


Reply 4 years ago

sorry bro i am very late you know that no two transistor is same (even if they are of same type)because of its parameters can be slightly different because of this difference the conducting of a transistor changes.......

so we assume t1 is first ON then t2 will be ON............... :-)


Reply 5 years ago

the general way it works is this: transistor one (Q1) is turned on by capacitor one(c1), allowing a current to flow through Q1 and charge c2. As this happens, c1 eventually runs out of charge. This means that c1 outputs no current while c2 outputs current. This means that c2 now powers q2 opening it to charge c1 whilst discharging c2.

Sorry the answer is a bit late but even of it isn't relevant to you it may help someone else with the same question.