Flashing LED Using an Astable 555

This project will use the 555 timer IC to flash an LED with the eventual aim of using the timer to provide a regular timing pulse.


Use the 555 timer to flash an LED with a period of 1 second.


The timer being used is a standard NE555N timer. This is a cheap general purpose timer circuit and has been around for many years. In fact I remember using them when I first became interested in electronics at school.

The circuit for setting this chip up in astable mode is as follows:

So along with the chip itself we will need 3 resistors, 2 capacitors and an LED. Thye values of R1, R2 and C1 determine the frequency of the pulses according to the following equation:

A frequency of 1 Hz was chosen to make the pulses clearly visible to the observer. A little reordering of the equation and a sift through some standard components gave the following values for these components:

Component Value
R1 1 KOhm
R2 2 KOhms (two 1 KOhm resistors in series)
C1 470 micro Farad

Putting it all together

Gathering all of the components together along with some breadboard gave a LED flashing at approximately 1 Hz. I say approximately as I’ll need to feed that output through a logic analyser / oscilloscope to verify the exact frequency.

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Sunday, February 20th, 2011 at 6:08 pm • ElectronicsRSS 2.0 feed Both comments and pings are currently closed.

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