555 Timer Oscillator/Led Flasher


It’s a 555 IC based LED flasher that is very useful for beginners. It demonstrates basic operation of 555 timer IC as Astable Multivibrator.



An oscillator is an important and essential part of many of the electronic circuits. It function in electronic circuit is as our heart function in our body. It pumps electronic parts pulses and makes them functional. So many electronic parts work on time basis. These perform different piece of work at different time such as timers shift registers and sequential logic ICs like CD4017. These all give different response or result on coming next pulse from oscillator. In other words oscillator instructs these ICs to perform their next function or operation. Counters increment on pulses and give different result on each pulse, shift registers shift internally loaded data on each pulse etc. So an oscillator or timer has very important role in our electronic circuits.
In above circuit diagram 555 IC with some additional parts work as an oscillator. It is also called an astable multivibrator. It outputs on/off(1 or 0 logic) on it’s pin 3. To describe it’s functionality first we see it’s internal diagram

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Internal circuit of 555 IC consists of 2 comparators, 3 resistors of same value, one transistor for discharging of capacitor C connected outside, 2 transistors for output stage and 1 flip flop. network of three resistors form a voltage divider and using this scheme 1/3 of the supply voltage are feed to 2nd op-amp at non-inverted (+ve) input for comparison reference voltage.