Thursday, December 8, 2011

How to Make a Single Transistor LED Flasher at Home

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 tue, however the following diagram will simply prove that it's really possible to create a legal LED blinker 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

57 comments:

  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

    ReplyDelete
  2. Hi Sunjay, I've already given you the entire diagram in Bright Hub, you can check it out there.
    Regards.

    ReplyDelete
  3. 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

    ReplyDelete
  4. 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.

    ReplyDelete
  5. 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

    ReplyDelete
  6. 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.

    ReplyDelete
  7. 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.

    ReplyDelete
  8. 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.

    ReplyDelete
  9. 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.

    ReplyDelete
  10. Hi Sunjay,
    Yes, that makes the procedure much simpler, put the pair of F terminals at the point where the water enters the UHT.

    Regards.

    ReplyDelete
  11. Sunjay, The relay diode is wrongly shown in the diagram, invert it in your circuit.

    ReplyDelete
  12. 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

    ReplyDelete
  13. Hi Sunjay,
    If you want a circuit only for controlling the motor pump, then you may refer the following diagram.
    http://homemadecircuitsandschematics.blogspot.com/2011/12/how-to-make-simple-water-level.html

    If you have any further doubts, feel free to comment.
    Regards.

    ReplyDelete
  14. 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 . .??

    ReplyDelete
  15. admin i m new to the electronics.....
    pls tell me...
    negative terminal battery ka kaha lagega??
    diagram me to + terminal hi show kara hai na
    pls tell me.......

    ReplyDelete
  16. 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

    ReplyDelete
    Replies
    1. the arrow head of the transistor symbol is the emitter.

      Delete
  17. 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?

    ReplyDelete
    Replies
    1. Not sure what's wrong, my circuit worked superbly with the shown components and supply.

      Delete
    2. is there a kind of LED that I should use, sir?

      Delete
    3. i used all the components shown and it didn't work the first time. it works now because i changed out the transistor until the led started blinking

      Delete
  18. 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 :)

    ReplyDelete
    Replies
    1. any type led would work....I had used a 5mm green led, and 12V supply.

      different capacitor values will produce different flash rates.

      Delete
  19. Hi swagatam,

    Can we use 3 to 9v supply for this circuit ?

    Regards,

    Bibin Emdond

    ReplyDelete
    Replies
    1. Hi Bibin,

      A 9V supply might just work, but not 3V.

      Regards.

      Delete
  20. Hi Swagatam
    I tried the above circuit ,but it didn't worked
    I used 4k resistor in place of R1

    ReplyDelete
    Replies
    1. Hi Sirj,

      this circuit is so simple, it should start working immediately... assemble everything exactly as given in the diagram, it will work.

      Delete
  21. 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

    ReplyDelete
    Replies
    1. Hi, yes it's dependent on the values of R1/C1, but only to an extent beyond which it just stops functioning.

      Delete
    2. 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.

      Delete
  22. dear sir pls give two led alternate flasher with adjustable flash rate circuit

    ReplyDelete
    Replies
    1. you can try this one:

      http://homemadecircuitsandschematics.blogspot.in/2011/12/make-yourself-simple-led-flasher-at.html

      Delete
  23. What are the formulas to calculate the timing of the flash?

    ReplyDelete
    Replies
    1. t = -log((V-Vc)/V)R*C

      To calculate Vc at a specific time, the formula can be modified to:

      Vc = V-(V*exp(-t/(R*C)))

      Delete
  24. 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?

    ReplyDelete
  25. 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?

    ReplyDelete
    Replies
    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.

      Delete
    2. a flashing LEd could have an automatic flash rate changer built-in, so it could go on changing the flash rate by itself.

      Delete
  26. hi my name is madhu i want electronic variable wattage choke circuit diagram for flurocent tube. pls send to the mail below
    email: madhubabu.sv@gmail.com

    ReplyDelete
    Replies
    1. sorry, presently I do not have this circuit.

      Delete
  27. HI
    will this circuit work for 16v?

    ReplyDelete
  28. 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

    ReplyDelete
    Replies
    1. the above circuit won't be appropriate, search for:

      transistor astable multivibrator circuit .....or 555 astable multivibrator circuit

      Delete
  29. Can you tell me in technical prospectivem, why cant we use this circuit??

    ReplyDelete
    Replies
    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.

      Delete
  30. 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

    ReplyDelete
    Replies
    1. It will need to be tweaked and verified practically for those results....there are no formulas for it.

      Delete
  31. Hi, can you please tell me how the transistor is activated without the base connected?

    ReplyDelete
    Replies
    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

      Delete

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Readers are advised to proceed with the construction of the presented circuits only after understanding the concepts from the core. Not adhering to this can lead to failures and frustrations.