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.).

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,

– Rui and Sara

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