Posts Tagged ‘NE555’

Flashing LED Using an Astable 555

Sunday, February 20th, 2011

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.