Introduction: Know Your IC: 555 Timers

Picture of Know Your IC: 555 Timers

Hello and welcome to a new instructables series called "Know Your Integrated Circuit"

Know Your IC seeks to demystify common Integrated Circuits and allows people to understand them to a point where they can use them in their own projects.

The first circuit in this series is the widely used 555 timer.

If you have suggestions for future chips we should cover, please shoot me an email!

I decided to make the layout pictures easier to read, i know it was confusing some people. I hope this helps!

Step 1: History of the Chip

Picture of History of the Chip

The 555 timer was created by Hans Camenzind (b. 1934) in 1970 while he was working for Signetics. The design process took about a year. Designing the chip was all done by hand, using rubylith which made the process take much longer than by today's standards.

The 555 timer replaced 23 transistors, 15 resistors and 2 diodes and allowed manufacturers to use this problem solving method much easier.

Today with billions of the chips in exsistence, it is one of the most widely used chips. Most people who do electronics hear of the 555 timer first. It is the gateway drug to the world of integrated circuits.


Step 2: Function of the Chip

Picture of Function of the Chip
The 555 integrated circuit is commonly called the "555 timer" but that is only one of it's uses. The chip can be used both as a timer and as an oscillator.

Well i'm glad you asked. An Oscillator is something that produces and constant electrical wave, like a sine or square wave. The timer will pulse at a specific interval depending on the components attached.

The 555 chip has 3 main modes:
  • Monostable Mode for "One Shot" pulse generation:
  • Astable Mode for putting out a continuous stream of pulses. (aka timer):
  • Bistable mode for acting like a Schmitt trigger.

The Pin out of the 555 timer is as follows:
Pin 1: Ground
Pin 2: Triggering the timer, connecting this to ground starts the chip up.
Pin 3: Output, stays at whatever Vcc is
Pin 4: Forces pin 3 to low if grounded
Pin 5: Used to adjust trigger threshold.
Pin 6: Threshold that ends timer when 2/3 of Vcc is reached.
Pin 7: Discharge, connects to ground when output is low
Pin 8: Power, denoted in most contexts as Vcc

Images above are borrowed from:

Step 3: Project: 555 Timer Light Blinker

Picture of Project: 555 Timer Light Blinker

For our project i will be building a simple LED flasher.

For this project you will need the following:
1 555 chip (Radio shack sells them, or get them for 25 cents each online)
1 100K Ohm Resistor
1 12k Ohm Resistor
1 220 Ohm Resistor
1 4.7 uF  Capacitor
1 9v Battery Snap
1 9v Battery

Then to lay it out you will want:
1 Breadboard
some solid core wire for hook ups.

Step 4: Project: Layout and Schematic

Picture of Project: Layout and Schematic

We will go over the layout by pin number, Just do the following the the circuit should work, if it doesn't take a look at my breadboarded version

Pin 1: Ground
Pin 2: goes to pin 6
Pin 3: hooks up to the 220 ohm resistor, then to the led and then the ground of the led goes to ground.
Pin 4: Unused
Pin 5: Unused
Pin 6: Has the 100k Ohm resistor between it and pin 7 and the 4.7 uf capicitor from it to ground (Make sure you get the polarity right!).
Pin 7: Has the 100k Ohm resistor between it and pin 6 and a 12k resistor that goes to power
Pin 8: Power

Once that is put together, test it out. The LED should blink on and off slightly quick. again if something doesn't seem right check the pictures and if your IC gets hot remove power immediately or you'll fry your chip.

Step 5: Project: Analyising the Circuit

Picture of Project: Analyising the Circuit

If you understand what the pinouts of the 555 timer chip mean, you can see what is happening with this circuit. This project is a simple implementation of this chip.

The capacitor controls the blink speed so you could change that out to make it blink slower or faster. Higher capacitance  = lower speed.

Step 6: Final Thoughts

Picture of Final Thoughts

I hope you enjoyed this first edition of know your IC. If you have suggestions for this series or would like to do you own "Know Your IC" installment, Please contact me!


pooter1433 made it! (author)2017-06-10

Great info and clear instructions thanks!

RaviJ1 made it! (author)2017-02-12

simle project

tim789jesus (author)2016-01-24

thanks, it worked!

BrendanTheSequeira (author)2014-10-27

I would like to make it alternate the spinning direction of a motor. How to i do this and how do i modify the time before it changes direction?

Like in his schematic, design a simple RC circuit with a time constant of your choice.

oolostoo (author)2015-12-12

I would be cool if you would go into more detail about the IC. Or like a section the gives Examples of its use or real world applications. One thing i did enjoy is its simplicity. I was actually looking for a timer circuit because im building a circuit that have parts that have to be run at different time intervals. I was thinking of using D flip flops but then i would need to get my hands on a clock and i would need more resistors. This will fit perfectly. Thanks!

SINGARAJV (author)2015-09-09


leesmith404 (author)2015-03-30

DITTO the requests for 741 ic. Do you have instructables for 555, 385, 741 with Arduino?

vijaym.vijay.56 (author)2014-08-08

555 is alalog or digital ic?


vijaym.vijay.56 (author)2014-08-08

555 is alalog or digital ic?

vijaym.vijay.56 (author)2014-08-08

555 is alalog or digital ic?

vijaym.vijay.56 (author)2014-08-08

555 timer is a analoge or digital ic?

how to determine the analog or digital ic in electronic ics?

akhandelwal2 (author)2014-01-12

Hello everyone

I want to make a circuit using astable mode of 555 ic in which

1. I need to generate Biphasic or Bipolar pulses at particular Frequency like 500hz

2. I want to control current between 10uA to 100uA

currently 555 ic in astable mode giving mopolar pulses (0 to +5 v ) but i want to generate +5 to -5v

Kindly guide me about this

waldosan (author)2013-06-28

just as an addition here for trouble shooting, if you've had you're ic for a while there might be stray charges in it; you'll know this is happening if it is mono stable so the led with blink once and then stay off. what you want to do to fix this is just connect pin 4 to vcc 9v, this will pull the reset up and away from ground.

Ghild.Zero (author)2013-03-19

Hi , I want to build mobile phone jammer use ic555 , will you help me please ? thx

knexpert1700 (author)2012-10-06

Thanks! Right now I'm trying to put a potentiometer on it so it will blink faster and blink slower. :)

MatthewEnderle (author)2010-10-28

Here is a better schematic

trurl23 (author)MatthewEnderle2012-07-08

This schematics seems to be slightly wrong. Pin 6 (THRES) should IMHO connect directly to the capacitor (not via the 100k ohm resistor which should be placed only between pin 6 and 7).
There is a nice schematics on page 10 in the data sheet from TI which can be obtained here:

jbaker22 (author)2011-11-19

Can you show us about ne556n in another tutorial? It is like 555, but it is a dual timer.

Amar143institute (author)2011-10-29

cool i like it..........

nodoubtman (author)2011-09-05

Thanks a lot! :) i have got a blue light flashing after 6 hours rushing and working :`)

Have a great day! :)

viper518 (author)2011-08-07

Keep them coming. I love it!

makincoolstuff (author)2011-07-26

howed you get the animations on?

spikedeath69 (author)2011-02-01

At radio shack there were two kinds of 555 timers and im not sure which to get also is the resistance of the resistor 1/4 watt or what? please reply thank you.

what are the volts on this capacitor?

Resistors are measured in Ohms of resistance. Watts measure power, which will vary based on your circuit.

Similarly, Capacitors aren't really measured in volts, if that's what you're asking. Capacitors are measured in Farads. One would apply a current of some voltage to a capacitor to charge it, and expect it to produce a current as it discharges. Both are exponential functions of time, if you were wondering.

The author said that you'll need a 220 Ohm resistor, and a 100 Ohm resistor.
As far as capacitors, you'll want a 4.7 uF (that's micro Farads the 'u' should be a 'mue' character from Greek.).

It sounds like you sort of figured circuit analysis is just a matter of adding up a few numbers (once in a while it is), but usually its a bit more complicated than that.

I suggest reading about basic circuits. if you're still in school, take a physics class in electricity and magnetism. You'll be glad you did. You should be able to find some good tutorials floating around otherwise.

cbates3 (author)SpudGunTechie2011-07-21

Resistors are indeed measured in Ohms, but they are also measured in Watts to indicate how much power they can dissipate before they stop working. 1/4 watt resistors are one of the cheapest and most common, so I would suppose they would be sufficient.

Similarly, capacitors also have a voltage rating on them to indicate what the maximum voltage that the capacitor could hold a charge for. There are millions of different voltage values on capacitors, each made for a specific use. It is a good Idea to double the maximum voltage that you will be using in the circuit to get the proper voltage rating on your capacitors.

SpudGunTechie (author)cbates32011-07-22

That's actually really good to know, thanks!

Snappy83 (author)2011-06-09

Thanks for the tutorial man! much appreciated! allways wondered what they ment by mono and astable. cheers!

junits15 (author)2011-05-25

every time i tried to use a 555 to make a monostable multivibrator....i burned it out, went through 3 of them then gave up and made it with transistors.

circuit555 (author)2011-05-18

in this diagram how would you wire 2 or more independent seperate flashing lights

noobduino (author)2011-03-22

will this work for the 555 timer

115494 (author)2011-03-16

Hey I was wondering if you could show me how to make a monostable mode without the lights. Thanks.

Jeffery Mouse (author)2011-02-28

I like this series! This is a great help to a novice like me!

shubhneesh (author)2011-02-13

bravo... i like it very much.

protostack (author)2011-01-13

Great 555 astable calculator over here

ziga321 (author)2010-12-26

have been searching for LED blinking all day and this is the first one that actually DOES work. Thanks-a-lot!

Waren-Neutron (author)2010-11-19

that's i know

lordxenosi (author)2010-11-03

I would love to see more of these 'Know Your IC' instructables. I have little experience with common ICs and I found this simple tutorial to be educational and enjoyable.

frikkie (author)2010-10-22

I personally love the 555 chip there so many circuits one can build with it.
I build my first light effect with the same circuit as the author used.

YOGESH YADAV (author)2010-10-19

what are the adjustable timer circuit of 555.....???

vince29 (author)2010-10-11

i agree with xtank5, SW,and rabbitkillrun. there are a few incionsistancies between the text and the photos. When I first put it together the LED stayed on w/o blinking. In trying to correct this I m nable to get the LED lit again.
This could be the start of a very interesting development but answers should be forthcoming.

waldosan (author)2010-10-07

i really like this series, it's opening my mind up to different ways you can use electronics.

Abume4life (author)2010-09-29

please i need a step-by-step guide on lm741 on bread board

suckafish (author)Abume4life2010-10-07

use google.....

Abume4life (author)2010-09-29

i have lm741 cant arrange the other component cause i dont have the circuit diagram

xtank5 (author)2010-09-12

I can't get it to work. All of my connections are good, they are just as you describe, but my LED just stays on. I've tried using larger caps to slow it down in case it was blinking faster than I could see, but even with 100uf it just stays on steady. Are you sure your plans work? Help would be nice.

frenzy (author)xtank52010-09-13


I updated the layout picture so it's easier to read, and i tested it out and it works. Post some good pictures of your layout and i can try to help you!

arhodes18 (author)2010-09-09

I like this i'ble, but i wish there was just a little more explanation as to what the pins do. and yes i agree that the next should be LM386

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