A LED flasher circuit is a great starting project for beginners in electronics. This simple build flashes two LEDs alternately using just two NPN transistors and a few passive components. It’s suitable for a wide range of voltages, from 5V to 12V, and can be built on a breadboard for easy testing.
If you’re looking at building a 9V LED flasher circuit, then this circuit is right for you. The 5 volt to 12 volt LED flasher circuit diagram is included which also works at 9V. This project is both educational and practical.
Table of Contents
- How the LED Flasher Circuit Works
- LED Flasher Circuit Diagram
- Adjusting the Circuit for Different Voltages
- Tips for LED Flasher Circuit
- Did You Know About LED Flasher Circuit?
- Two Transistor Astable Multivibrator Circuit Technical Explanation
- Frequently Asked Questions About LED Flasher Circuit
- Conclusion
How the LED Flasher Circuit Works
This two transistor LED flasher circuit operates as a basic astable multivibrator. It alternates power between two LEDs, making them blink on and off continuously.
Here’s a breakdown of how it works:
- Two NPN transistors switch on and off in turn.
- The base of each transistor is connected to the other’s collector through a capacitor.
- When one transistor turns on, the other is forced off, causing the LEDs to flash alternately.
The flashing rate depends on the values of the resistors and capacitors. You can tweak these to change the blink speed.
For the technical explanation of this circuit, see the Two Transistor Astable Multivibrator Circuit Technical Explanation video further down this page.
LED Flasher Circuit Diagram
Below is the LED flasher circuit diagram for this project:
Component List
Although the KSP2222 transistor is shown in the circuit diagram above, different NPN transistors can be used in its place. When substituting a different transistor, be sure to check the datasheet for the device to check its pin numbering or pinout.
| Component | Value / Type |
|---|---|
| Q1, Q2 | NPN transistors (e.g., BC547, 2N2222, PN2222, KSP2222A) |
| R1, R4 | 470Ω or 680Ω (change R1 and R4 to 1kΩ for 10V to 12V operation) |
| R2, R3 | 10kΩ to 22kΩ |
| C1, C2 | 47µF to 100µF electrolytic capacitors |
| D1, D2 | 5mm or 3mm LEDs |
| Power | 5V to 12V DC supply (e.g., 9V battery) |
This is a simple LED flasher circuit you can easily build as a LED breadboard circuit before soldering it to a PCB.
Adjusting the Circuit for Different Voltages
This alternating LED flasher works across a voltage range of 5V to 12V. When powering with more than 10V:
- Change R1 and R4 to 1kΩ to limit current through the LEDs and avoid damage.
- Use transistors rated for the voltage you’re using (e.g., KSP2222A, PN2222 for 12V).
This makes the design flexible enough for hobbyist applications like indicators, decorations, or educational demos.
Tips for LED Flasher Circuit
- Use a breadboard first to test the layout. This helps avoid soldering errors.
- If the LEDs don’t flash, check your capacitor polarity and transistor orientation.
- For a brighter flash, consider using high-brightness LEDs. Be sure to adjust the current-limiting resistors to match your supply voltage and the LED specifications.
- To slow down the flashing rate, increase the capacitance of C1 and C2 (e.g., use 100µF, 220µF).
Did You Know About LED Flasher Circuit?
- The astable multivibrator design used in this circuit dates back to early transistor-based computers and timers.
- This design is also used in LED blinker circuits for automotive and toy applications.
- The circuit is symmetrical—so you can flip it horizontally, and it will still work the same.
Two Transistor Astable Multivibrator Circuit Technical Explanation
The following video explains the technical details of how this type of circuit works. This circuit is an ‘astable multivibrator’ circuit.
Frequently Asked Questions About LED Flasher Circuit
What is a LED flasher circuit used for?
LED flasher circuits are used to create blinking lights for indicators, toys, decorations, or as an educational tool to learn about transistor switching and timing circuits.
Can I power this circuit with a 9V battery?
Yes, a 9V LED flasher circuit works perfectly. Just make sure your LEDs have appropriate current-limiting resistors (typically 470Ω to 1kΩ depending on LED specs).
How do I change the blink rate?
Increase the capacitance of C1 and C2 or increase the values of R3 and R4 to slow the blink rate. Decrease them to speed it up.
Can I use other transistor types?
Yes. Any general-purpose small NPN transistor like 2N2222, PN2222, or BC547 will work. Just make sure the pinout matches the layout in your build.
Is this circuit the same as a LED blinker circuit?
Yes, LED flasher circuit and LED blinker circuit are commonly used interchangeably. Both refer to circuits that blink LEDs on and off using timing components.
Conclusion
This LED flasher circuit is an excellent project for beginners to understand how basic electronic components work together to create a timing sequence. With only two transistors and some passive components, you can create a reliable LED blinker circuit that runs from 5V to 12V. Try building it on a breadboard and experiment with different values to see how the flashing behavior changes.
For more fun and educational circuit ideas, be sure to explore our Circuits & Projects section.