Two blinking LEDs

This is a classic project. The IC (Integrated Circuit) NE555 is around and popular for many decades. Its main application is to form oscillator circuits. This project is about creating an oscillator with two LEDs connected to its output. The two LED blink alternatively in constant period.


The project is an introduction to oscillator circuits and to ICs.

  • You see how breadboards, resistors, capacitors, ICs and LEDs look like.
  • You understand how breadboard works.
  • You understand the difference between schematic and real circuit.
  • You understand what an oscillator does.
  • You can note that the function of an oscillator based on the charging-discharging cycle of a capacitor.

The Schematic

This is the circuit in action.


On breadboard


You can see a way to set up the circuit on the breadboard. Remember, there are many correct ways to transfer a circuit on the breadboard.


  • The resistors which are in series with the LEDs has nothing to do with the charging/discharging the capacitor. So, it has nothing to do with the blinking frequency. Its role is to reduce the IC’s output current to avoid any damages to ICs or the LEDs.
  • You can change the frequency of the blinking by using different capacitor or different resistors which are evolved in capacitor’s charging/discharging. For example use a capacitor with more capacitance and you will get a slower blinking.