Flashing LED circuit using transistors on Breadboard – Basic Electronics Projects


Hi, welcome to Elonics. In this video I’ll show you how to build a simple flashing LED circuit using transistors and and a few other electronics components and later you’ll see using a different valued capacitor changes the flashing rate So let’s get started The components you need to build this circuit are a PNP transistor we are using BC557 here, an NPN transistor for which we are using BC547 here an led, a capacitor of capacitance 2.2 microfarad 22ohm resistor, 1kohm resistor. 1megaohm resistor A few b readboard connectors and 3 to 6v of power supply If you are new to breadboard, note that the holes along the lines shown in the image are interconnected Place both the pnp and npn transistors on the Breadboard this is the PNP transistor BC557 and this is the NPN transistor BC547 such that their flat surfaces are facing towards you so from the right the pins will be emitter base collector and it’s the same for the PNP transistor emitter base and collector place 1kohm resistor on the breadboard with one of its terminals connected to the base of the NPN transistor and the other terminal connected to the collector of the PNP transistor Place the capacitor such that it’s negative terminal is connected to the colector of the NPN transistor and the positive terminal is connected to the base of the PNP transistor Now connect the emitter of the PNP transistor to the positive rail Here we are using the last row as the positive rail and the above row as the ground Now connect a 1mega ohm resistor between the base of the PNP transistor and the ground Now connect a 22 ohm resistor between the collector of the NPN transistor and the positive rail Place LED on the breadboard, such that it’s negative terminal which is towards the flat surface is connected to ground and the positive terminal is connected to the emitter of the NPN transistor Now, finally to the final step We have to connect the positive terminal of the power supply to the positive rail and the negative terminal of the power supply to the negative rail or ground So here is how the LED flashes with different capacitors used: This is with 2.2 microfarad capacitor this is with 5.6 microfarad capacitor this is with 10 microfarad capacitor and, this is with 22 microfarad capacitor so if we keep increasing value of the capacitance, then, the time gap between the LED flashes increases Thanks for watching do subscribe to this channel and checkout my other videos if you have any queries feel free to ask them in the comments section below

62 thoughts on “Flashing LED circuit using transistors on Breadboard – Basic Electronics Projects

  1. So there is a project I want to do just for fun, I have a 9V battery and 50 white leds. I want to place them in parallel with maybe 5 LED's in each row, however, how do I find out what resistor do I need for each line of Led's? also, would I need to add other components such as a capacitor or stuff like that?

  2. For PCB version of this project, view this video: https://www.youtube.com/watch?v=D3Kp9CFTnoQ

  3. Do you think this could replace bimetallic relays used for car indicators (flash). Please suggest a workable circuit and the capacitor to be used. I am talking about two flash lights with 21 ohm resistance and one small 5 ohm indicator light on the car's rear view mirror.

  4. simple question… i find all my stuff needed to make that electronic board at the sameplace…
    can i use other type of transistors npn pnp, i found some packages at radioshack ( can't found bc547 and bc557)
    heres the numbers i've found… came in packages of 15, 5 of each)
    pnp : 2N2907, 2N3906 and 2N4403.
    npn : 2N2222, 2N4401 and 2N3904.

  5. I followed this and it worked, but after a few seconds it stopped blinking. What could be the cause? i tried changing capasitors and resistor, but now the LED is just on and doesn't blink.

  6. The LED is glowing constantly instead of blinking, what might be the problem.
    I'm using 10kohms instead of 1kohm, the input voltage is less than Capacitor reading…

  7. Thanks brother. I was looking for this project to make flashing LED for my cycle. Works like a charm!
    I have used 10ohms resistor instead of 22ohm with 9v battery.
    You have an awesome channel for beginners!

  8. i have 5 leds in parallel circuit can i use instead of one led or which resistor to be use. and can i use this circuit on 12v battery. thanks

  9. hey bud can u build me a circuit dig for
    head light, tail light, break light and blinkers and can be used alternatively only with one switch can we program any ic or programmable chip for this pirppse can u explain or help. if only possible thanks.

  10. My first project and it worked BIG thank you! By changing capacitor value it gave me an idea as to build my own security alarm in my garage. With a larger capacitor it gives me enough time to open my garage door and switch off my alarm that have build earlier. I will subscribe!

  11. Here is why this works:
    Step 1. The battery charges up the capacitor.
    Step 2. When Capacitor is full, the PNP-Transistor BC557 is activated.
    Step 3. PNP-Transistor BC557 activates NPN-Transistor BC547.
    Step 4. Activation of NPN-Transistor BC547 discharges the capacitor current through the LED, which activates LED (on)
    Step 5. The capacitor is discharged, LED is deactivated(off).

    Step 1(again). the battery charges up the capacitor again, and so on….

  12. gracias por ese proyecto me sirvio para las luces de mi avion rc de 3 mtrs de enbergadura……FELICITACIONES….

  13. Here is why this works(revised):
    Step 1. The battery charges up the capacitor.
    Step 2. When Capacitor is full, the PNP-Transistor BC557 is activated.
    Step 3. PNP-Transistor BC557 activates NPN-Transistor BC547.
    Step 4. Activation of NPN-Transistor BC547 allows current from capacitor and battery to flow through the LED, which activates LED (on)
    Step 5. The capacitor is discharged, which deactivates PNP-Transistor BC557, which in-turn deactivates NPN-Transistor BC547.
    Step 6. Current flow from the battery to the LED is cut-off. LED is deactivated(off).

    Step 1(again). the battery charges up the capacitor again, and so on….

  14. Can you please send me the circuit diagram for this? I will use a 5v buzzer and a 5V diode bulb instead of the small diode in the video.

  15. Can i get detail explanation that how does it works…from where current pass through and how makes it to blink led ….. what's the concept behind that….plz someone help!?

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