3 LED Chaser circuit using transistor without IC

Let’s make a 3 LED chaser circuit using transistor. Since my daughter has tried making the LED chaser using ICs (CD4017 and NE555), it has worked well. But recently, she has been learning how to use transistors.

 

So she had a question: Can we use transistors instead of ICs? The answer is yes. Also, the LEDs can still flash in a chasing manner, like when using the IC.
We hope you guys will enjoy the transistor circuit as much as we do.

 

Circuit Experimentation

We will start by looking at the circuit shown in the picture below. This circuit is similar to a 3-LED flasher using a 3-transistor astable multivibrator. However, we changed the position of the LEDs, with different results.

My daughter tried to assemble them on the breadboard.

Note: If you want an easier-to-see component layout on the breadboard, Let me know, and we will draw it for you.

Then, we adjust VR1 and observe the changes in LED1, LED2, and LED3.

When VR1 is fully rotated counterclockwise, all three LEDs will turn off. Because the resistance value is too high. But when rotating VR1 clockwise slowly, all three LEDs will start to turn on and off alternately. Until we see all three LEDs turn dimly because flashing is too fast for our eyes to see.

 

Understanding LED Chaser Circuit Using Transistor

Creating a circuit is not difficult. But understanding how it works is challenging for my daughter. But let’s try to learn them together.

Generally, we know that all three LEDs are controlled by transistors that turn off or on with the charge and discharge of each capacitor.

Conclusion

We can see that they always behave in this order. If the transistor stops working, the LED in that set will light up. Each duration is controlled by the value of each capacitor. For example, if we want to have LED1 stay on longer, then increase C3, C1 for LED2, and C2 for LED3, respectively.

From the result of experimentation with this circuit. We know that we can use a voltage supply ranging from 5V to 15V.
For capacitors in this circuit, we have tested from 10uF to 100uF; the higher the capacitance, the longer the LED will stay on.
If we want to add more LEDs, we will need to increase the number of transistor sets accordingly.

If compared to the IC circuit, this circuit doesn’t work as well. Sometimes the blinking is inconsistent. Anyhow, it is still good for learning about transistor circuits. Do not forget that all-powerful ICs consist of many transistor circuits that work perfectly together. Learning transistor circuits first is a good foundation for electronic work.