Introducing 555 Timer IC – Tutorial

In this blog post, we will introduce the 555 Timer Integrated Circuit (IC). You’ll explore what it is, the three different modes and its pinout.

555 Timer (EN555)

The 555 timer is an integrated circuit, it is extremely versatile and can be used to build lots of different circuits.

The EN555 is usually used to generate continuous series of pulses. These series of pulses allow you to continuously blink an LED, for example.


The 555 timer can operate in three different modes:

  • Monostable mode: usually used to create time delays
  • Astable mode: outputs an oscillating pulse signal
  • Bistable mode: the 555 timer changes its output depending on the state of two inputs

In this post, you’ll see an example in astable mode.


If you search on Google 555 timer datasheet, one of the first results should be a PDF datasheet.

This is a document with a lot of information, but what you really need to pay attention right now is to the pinout. Here’s the EN555 pinout:

EN555 pinout

This IC has 8 pins:

  1. Ground
  2. Trigger
  3. Output
  4. Reset
  5. Control Voltage
  6. Threshold
  7. Discharge
  8. VCC

In a circuit diagram, usually the 555 timer is drawn as follows:

EN555 represented in a schematic diagram


Pin 3 is the output. This pin generates an oscillation. The voltage is high, then low, then high, then low again and so on (this is called astable mode).

Voltage output versus time in astable mode

Astable mode

To make the 555 timer work in astable mode, you should wire your circuit like this:

EN555 circuit diagram – astable mode

The frequency of the oscillation can be adjusted by changing the values of the resistors R1 and R2 and the capacitance of the capacitor C.

The frequency can be calculated using the following expression:

With the output voltage that comes from pin 3, you can control anything you want (like an LED, speaker, motor, etc.).

Flashing an LED with the 555 Timer

In this section, you will flash an LED using the 555 timer in astable mode. So, we just need to add an LED to the output of the previous circuit.

Required components

These are the components you’ll need:

You can use the preceding links or go directly to to find all the parts for your projects at the best price!

Circuit diagram

This is the circuit diagram:

Wiring the circuit

You can either follow the previous schematic or follow the breadboard wiring diagram below. Finally, power up your circuit by connecting the battery to your breadboard:

In the end, you should see your LED blinking like this:

Note: replace your 1uF electrolytic capacitor with another capacitor that has a lower capacitance and see the LED flashing at a different rate. With lower capacitance values, the flash rate increases.

Wrapping up

I hope you’ve learn something new today and you’ve found this explanation useful.

If you’d like to know more about electronics basics or if you’d like to start into the world of electronics make sure you check out our Electronics for Beginners eBook.

Thanks for reading!

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22 thoughts on “Introducing 555 Timer IC – Tutorial”

  1. You may find it hard to believe but when I studied engineering at university in the early 1970’s, the 555 was already around for a few years. So this chip is almost 50 years old! Other components that also come to mind is the 741 and 105/155 opamps, 2N2222, BC107, BC109 transistors, 1N4001 diodes, and CMOS chips such as the CD4000 series.

  2. Ah, the 555! It’s been around a long time…since the early 70’s as I recall. I’ve used them in many different applications. A fun little chip!

  3. Great choice for a tutorial.

    I first used 555 ICs in a circuit forty years ago. It’s a great IC for experimenting. If you look around online, you can get them for a dime each if you buy 50. They aren’t indestructible, but they will tolerate a lot of electrical mistreatment. Their power supply can be a 5 volt digital circuit or a car battery.

    The only time I ever had an unexpected outcome was in a room where it was cold in the morning and it warmed up later in the day. I couldn’t get an NP0 capacitor, so its frequency changed over the morning just enough to throw it off and I had to adjust the resistance to get it back to working. Then the next morning I had to adjust it the other direction to get it started.

    I hope lots of people try them out.

  4. Not a bad beginners tutorial, but this chip goes Way Way Way beyond this and warrants a whole lot more to be called sufficient. This is all data that is easily obtained in almost every data sheet from vendors.

  5. If I sent a block diagram of a simple device would you be able to provide a solution to the request. I find it difficult to believe that their a lot of unsuccessful commercially sold wireless links (Not line of sight) that keep failing at only 200 meters

  6. Thank you for this neat little tutorial. I actually ordered a bunch of them not long ago out of curiosity.
    I couldn’t help but grin, when I saw your notification saying you offer a tutorial about this little fella.

  7. Did you know that the 555 got its name from the three internal 5K voltage divider resistors? Today there are low power alternatives to the old 555. Some of these are surface mount but that’s no problem for hobbyists. I just use the Schmartboard EZ series to let me hand solder SMT components for my own breakout board.

  8. Great refreshment tutorial!
    NE555 was stable IC and remembered early days used to develop Switching applications such Security Alarm systems and used as clock ICs. Interested to know How Mr. Rui may integrate this tiny IC to modern day Arduino and ESP series micro controller applications in near future tutorials.

  9. A useful addition to this would be how to use it as a monostable – in particular, how to lengthen a pulse. For example, a brief pulse on an I/O pin to turn on a LED for say 1/2 second. (To avoid using delay() or more complex timer based software)
    Like many of your commenters, I was using these over 40 years ago.

  10. I used to have a book on all kinds of circuits for this little gem, I think it was titled ‘the 555 cookbook”…lot of cool memories, back in the “simpler” days.


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