Know Your IC: 555 Timers





Introduction: 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

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

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

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

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

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

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!

2 People Made This Project!


  • Epilog Challenge 9

    Epilog Challenge 9
  • Paper Contest 2018

    Paper Contest 2018
  • Pocket-Sized Contest

    Pocket-Sized Contest

We have a be nice policy.
Please be positive and constructive.




The plugblock appears correct but the schematic shows the 12K resistor in the wrong place. It should connect between 8 and 7. The 100K resistor connects between 7 and 6.

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.

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!

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