LED Blinking

LED Blinking

This beginner project presents LED blinking circuit in which blinking of two LEDs through combination of couple of transistors and capacitors take place. The basic principle behind these blinking LEDs is the charging/discharging of capacitor that enables and disable the flow of current that ultimately let the LEDs blink.

Very easy to build:

This is one of the very easiest LED blinking circuit to built and get it working. It can be made on veroboard, breadboard or you can design its PCB. It requires only a few minutes to get it done and see your circuit working!!! It costs only a few bucks here are the couple of components you are required to make this project.

1 × Breadboard

2 × 470 ohm resistors

2 × 47k ohm resistors

2 × 22uF capacitor

2 × BC548 NPN transistor

1 × 5mm Yellow LED

1 × 5mm Green LED

1 × 9V battery

1 × 9V battery connector

Few Jumper wires

Let’s make

Now we are couple of minutes away from your very own LED blinking circuit project. If you are available with all these required components than let’s start. Here down below you can see the LED blinking circuit diagram that is built using Proteus.

Start by upper first branch that starts with 470 ohm resistor in series with Green LED that is further in series with a 22uF capacitor and this ends up to the base of NPN BC548 BJT and a bypass 47k ohm resistor touches its base with power source. Now you are completed with half of your circuit as you can see below:

Keep in mind LED’s polarity it must be in forward bias or its cathode should be connected to the capacitor’s leg for its proper functioning. Similarly you can now build the other second branch. When you are completed with the second branch here it goes like

Now you have two independent branches that are to be connected carefully for its proper outcome. Look at the circuit diagram carefully and connect both of the NPN BJT BC548 to the ground and the collectors of both NPN BJT BC548 must be connected to opposite LEDs cathode terminals.

Now as soon as you plug the battery it must have started blinking. Here you go LED blinking circuit is ready.For other more interesting projects keep visiting


In case you have built the complete circuit but its not blinking. You have to analyze the circuit carefully.

Check if the LEDs are fine or replace both with new ones.

Check if the polarity of LED is same as shown in diagram.

Check if the circuit has been properly wired or try rewiring the circuit again.

Check if the BJT NPN BC548 are fine or replace both with new ones.

Check if the capacitors are ok or try replacing with new 22uF electrolytic capacitors.

Check if the battery terminal are properly connected and the polarity is not wrong.

Understanding the circuit

It’s a simple LED blinking circuit in which charging and discharging of a capacitor plays a very important role to blink LEDs. Now as you can see there are two branches in this circuit which are exactly the same but both are dependent on each other. The charging of capacitor in one branch allows discharging of the capacitor in other branch this enables one LED to stay ON in one cycle (charging/discharging). If you observe carefully while the circuit is power up both of the LEDs lighten up because both capacitors get charge instantly.

Blink rate

In our LED blinking circuit its blinking rate can be increased or decreased by changing capacitor or by pass resistors value or both. One way can be if we place one variable resistor in series with these two by pass resistors, varying the resistor will change the blink rate of these two LEDs.