Astable 555 Timer Multivibrator

Astable Multi-vibrator using 555 Timer


>> Pin 4 and Pin 8 are short circuited ; Because Pin 4 is Active low pin and if it is leaved free and it will reset the flip flop , so to avoid such condition the pin 4 is connected to a ‘high’ state

>> Pin 2 and 6 are short circuited; By doing this we tied together upper comparator and lower comparator pins (upper comparator Non inverting and lower comparator Inverting.

>>  The Resistor RA is connected Between Pin 4 and Pin 7.

>> The Resistor RB is connected Between Pin 6 and Pin 7.

>> The power supply is connected between Pin 1 and Pin 8 ( 9V ) , Positive terminal is connected to pin 8 and negative terminal is connected to pin 1.

>> The output is generated at pin 3 , a LED is connected between Pin 3 and Pin 8 , aternatively can be connected between Pin 3 and Pin 1.

>> The frequency LED blinking is given by the formula .

555 timer ic physical structure

555 timer led glow

555 Timer LED

9v battery to operate on 555 timer

555 timer on pcb

Dc Battery Printed Circuit Board

capacitor 555timer

three 5k resistor in 555 timer

Capacitor Resistor

Internal structure of 555 Timer.

SR Flip Flop

In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information. A flip-flop is a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Flip-flops and latches are a fundamental building block of digital electronics systems used in computers, communications, and many other types of systems.

555 timer ic has sr flipflop

The design of such a flip flop includes two inputs, called the SET [S] and RESET [R]. There are also two outputs, Q and Q’. The diagram and truth table is shown below.

S=1, R=0—Q=1, Q’=0

This state is also called the SET state.

S=0, R=1—Q=0, Q’=1

This state is known as the RESET state.

S=0, R=0—Q & Q’ = Remember

If both the values of S and R are switched to 0, then the circuit remembers the value of S and R in their previous state.

S=1, R=1—Q=0, Q’=0 [Invalid]

This is an invalid state because the values of both Q and Q’ are 0. They are supposed to be compliments of each other. Normally, this state must be avoided.



In electronics, a comparator is a device that compares two voltages or currents and outputs a digital signal indicating which is larger. It has two analog input terminals V_+\,and V_-\,and one binary digital output V_o\,. The output is ideally


 NOT Gate (inverter)

The output of NOT gate is the complement of the input.

555 timer ic  b tech projects

Detail Explanation of Astable Multi-vibrator 555 Timer Circuit .

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