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Single Transistor LED Flasher Circuit

Can you imagine of making a formidable little LED flasher or blinker using just a single transistor and a couple of other passive parts.

That looks too good to be true, however the following diagram will simply prove that it’s really possible to create a legal LED flasher circuit using just one general purpose transistor as the main component.

I came across this phenomena some eight years ago, accidentally, while trying to make a smallest possible motorcycle side indicator flasher, and was really amazed.
However, then I did have not any idea that it was happening due to the negative resistance characteristics of the transistor.

 The circuit actually exploits the negative resistance factor in transistors to produce the blinking effect.

 I’ll be soon writing a comprehensive article on this and we’ll see there how the concept can be modified in many different ways.

Parts List for the proposed single transistor LED flasher circuit

R1 = 2K7,
R2 = 100 Ohms,
T1 = BC 547,
C1 = 100 uF to 470 uF
LED = Any Type, any color

LED flasher circuit using single transistor

68 comments on Single Transistor LED Flasher Circuit

  1. I actually wanted a circuit of water flow controller which will be fitted in the overhead tank only. When the level of water in this overhead tank goes below a certain level, the pump is switched on and it starts pumping water from the underground tank; when the overhead tank is full, it is switched off; plus motor protection in case there is no water in the underground tank. my email id is sanjay8040@gmail.com
    thanks

  2. As i understand, the circuit in Bright Hub is of a level indicator and motor protector , to be installed in the overhead tank; the water level controller is to be installed in the underground tank. Now I want a controller cum motor protector which can be installed in the overhead tank itself. Our underground tank is very big so it may not be practical to put the controller there. Thanks

  3. Hi Sunjay,
    You can install the entire circuit in your overhead tank, only the points at "F" needs to be positioned in such a way that it comes in contact with the water that's entering the motor.
    Thus, as long as water supply is present to the motor, it remains switched ON and the moment water supply stops, the motor also stops.

    Regards.

  4. I shud use the last circuit meant for the overhead tank, with IC 4049. When water level reaches point A, the motor will stop; and when water level goes below point E, motor will start. My doubt was that at point E, there are only 2 points from the IC. Will this work to start the motor? I hope my understanding is correct. Thanks a lot for your guidance. Regards

  5. Hi Sunjay,

    The ground point shown at the bottom, inside the tank is the common point for all the sensing terminals, it must be immersed in the water at the bottom of the tank permanently.
    Here the motor does not have any connections with the sensors in the upper tank.
    The motor will switch ON and OFF depending upon the water supply present to it, as long as there's water entering it, it remains switched ON, as soon as water supply ends, the motor stops, this is the only way through which we can protect the motor.
    In simple words as long as water is present across point F, the motors is switched ON and vice versa.
    So you can position this point anyway you want, whether in the upper tank or in the underground tank, it will depend on you how you want to switch the motor.
    Regards.

  6. hi swagatam..thanks for your quick reply. Since our underground tank is very big, the OHT will start overflowing with the system in question. I am looking for a system similar to the one for the UGT. Actually it will be reverse of the UGT system. At C, the motor starts and at A, the motor stops. And if u can provide F type protection, all the more better. I hope i am able to make myself clear. Best regards.

  7. OK, it means you require motor control from both the tanks, it can be done simply by introducing the point F near the brim of the OHT.
    May be today or by tomorrow I'll be posting a new article on this subject, I'll post the diagram there and inform you. You can check it once it gets published.
    Regards.

  8. Just a minor clarification. I want to put the controller only in the OHT; nothing to do with the UGT. Point F will be put at the entry point of water in OHT.

  9. hi swagatam..ref ur msg of 14th..i was waiting for the circuit diagram of the water level 'CONTROLLER' for the overhead tank. The circuit given by you for tha OHT in Bright Hub, as i understand, is that of a level indicator. Thanks n regards

  10. Hello Swagatam . . i want to ask u that i am making a joystick car project and i want 4 l.e.d blinking on and off . . at the corners of my car . . so can i use this circuit . .??

  11. Mr.Swagatam, the emitter of T1 in the circuit diagram is connected to R1 or to positive side of the LED? Just a clarification. Thanks

  12. Sir, I have followed the circuit above and I have the right components needed but the LED is not flashing. It just lights up. What must gone wrong?

  13. Mr. Swagatam, i have question from the above circuit. By how much voltage of LED should be use? another question is, is the supply voltage (12v) should be exact or can we increase or decrease it?

    and lastly, what is the difference of using 100uF capacitor in using 470uF? what should be the voltage of the capacitor?

    thanks for answering 🙂

  14. Hi, i was wondering if you could change the blinking time playing with the RC values. It works with the simple RC constant or is it more complex to calculate this time?

    Thanks in advance

    1. You need to add an ic which is 555 to this circuit. You can get its datasheet and some good circuits if you search on google. Using this circuit as controlling timing is just wastage of time.

  15. I am trying to imitate cloud to cloud lightning using the smallest possible circuit. I found this project that uses only the flashing LEDs and a battery…http://www.youtube.com/watch?v=Rj5tqhGypAE&feature=player_embedded. I found 3mm flashing LEDs …http://lighthouseleds.com/led-component-lighting/animated-leds-flashing-blinking/3mm-led-flashing-round-top.html
    Can I power 2-3 of these (amber and/or white) using one CR2032 battery? Can I get them to flash at different rates? …I think that may drain the battery too quickly since there are no resisitors used, is that correct?

  16. I am trying to imitate cloud to cloud lightning using the smallest possible circuit. I found this project that uses only the flashing LEDs and a battery (Candle Flicker Hair Bow). I found 3mm flashing LEDs (3-3.4V, 20mA, 1 Hz flash frequency)
    Can I power 2-3 of these (amber and/or white) using one CR2032 battery? Can I get them to flash at different rates? …I think that may drain the battery too quickly since there are no resisitors used, is that correct?

    1. you can include a 22 ohm resistor in series with the LEd in order to make the battery drain slower.
      alternatively you can employ a joule thief circuit for making the batt last for ages.

  17. I want to design a LED Flasher Cirrcuit with Input : 9V-16V, On time : 0.5s +/- 10%, Period : 1s +/- 10%, Reverse polarity protection : required can you help me with the above circuit? Will it work for this conditions?
    need your response
    thank you

    1. the above circuit is not configured in a conventional manner so could have limitations in terms of interval setting accuracy…you can try it out, though.

  18. Hi,

    thanks for your prompt response.
    Could you Just modify the circuit for this specifications LED Flasher Circuit with Input : 9V-16V, On time : 0.5s +/- 10%, Period : 1s +/- 10%, Reverse polarity protection required, by using any other stage of RC or any other way. Using astable multivibrators is cost effective for my project, need a simple circuit. Hope for your response.

    Thanks in advance

    1. In the circuit, the capacitor is charged by R1 until the voltage becomes large enough to get the emitter-base junction to avalanche which lights up the LED and also discharges the capacitor to trigger a fresh cycle….it basically takes place due to the negative resistance characteristic of the BJT

  19. Hey buddy,i have installed 12v3led strip in my bike and i need them to blink.i knw i can use this circuit but what all i need to alter?to adjust speed and to power led 12v..

    1. Hi Siddarth, sorry no I could not complete it due to lack of time and other more complex assignments…you can Google "Esaki single transistor flasher circuit" to learn more about it.

  20. Hi Mr swagatam,
    Can you guide me to make an automatic switching for my led emergency light using Transistors? I have connected 50 no's of led and planned for 6V/4.5 Ah battery.pl explain with circuit diagram.

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