• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Get free circuit help 24/7

  • 1000+ Circuits
  • Privacy Policy
  • About Us
  • Contact
  • Disclaimer
  • Videos – Circuit Test Results
You are here: Home / Sensors and Detectors / Single Transistor LED Flasher Circuit

Single Transistor LED Flasher Circuit

Last Updated on December 20, 2019 by Swagatam 82 Comments

It is possibly the smallest 12 V LED flasher to date, which is able to flash an LED ON/OFF infinitely using a single transistor, a resistor, and a capacitor.

Can you imagine making a great looking LED flasher or blinker with just a single transistor and a couple of other passive parts? That's exactly what we learn in this post! This is perhaps the world's simplest and the tiniest LED flasher you can get!

How it Works

I came across this phenomena some eight years ago (2006), accidentally, while trying to make a smallest possible motorcycle side indicator flasher, and was surprised the phenomenon.

However, then I realized that the phenomenon was already discovered by Mr. Dick Cappels while investigating the negative resistance theory in BJTs by the Japanese researcher Mr. Reona Esaki (Aka Leo). Reona Esaki's thesis work in the relevant field and on tunnel diodes ultimately won him the Nobel Prize in 1972.

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

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

The flashing rate could be varied either by changing the value of R1 or C1 or both together. But the supply voltage not be less than 9V otherwise the circuit might fail to work correctly.

Circuit Diagram

LED flasher circuit using single transistor

Connecting an External Transistor for Higher Loads

Video Clip:

PCB Design

single transistor flasher PCB design



Previous: Automatic Voltage Stabilizer Circuit for TV sets and Refrigerator
Next: How to Calculate Transformerless Power Supplies

About Swagatam

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials.
If you have any circuit related query, you may interact through comments, I'll be most happy to help!

You'll also like:

  • 1.  How to Measure Gain (β) of a BJT
  • 2.  Aquarium Fish Feeder Timer Controller Circuit
  • 3.  Single IC Piezo Driver Circuit – LED Warning Indicator
  • 4.  How Flex Resistors Work and how to Interface it with Arduino for Practical Implementation
  • 5.  220V Mains Operated LED Flasher Circuit
  • 6.  3 Automatic Fish Aquarium Light Optimizer Circuits

Please Subscribe (Only if you are Genuinely Interested in our Newsletters)


 

Reader Interactions

Comments

    Your Comments are too Valuable! But please see that they are related to the above article, and are not off-topic! Cancel reply

    Your email address will not be published. Required fields are marked *

  1. Search Related Posts for Commenting

  2. Prashant says

    If I want to run this Strobe effect on 3V ? is the same circuit or I have to change specification of Resistance capacitor

    Reply
    • Swagatam says

      No, this circuit will not work with 3 v supply, it will need a minimum of 9 V too operate correctly.

      Reply
  3. Steve says

    Just to point out to people, that if you can’t get the transistor mentioned, the more common 2N3904 (included in a lot of starter kits) will do just fine.

    Reply
  4. Robert says

    I need a circuit for a 5v led flasher using power from a USB cable.

    Reply
  5. Ramachandran N says

    Dear, I am looking for a simple time delay circuit using this flasher for a 12 volt relay operation, the LED should glow stable once the relay is on. Thank you

    Reply
    • Swagatam says

      Connect the positive voltage from the relay source with the collector of the transistor, or the anode of the LED

      Reply
  6. Aju says

    Dear Sir, i done it using bc 548 and working fine. Let mw know how to connect a high watt led eg. (3wattx3 series) to flash in this way or to use a 12volt relay instead of the led?

    Reply
    • Swagatam says

      Dear Aju, please see the second diagram, you can the replace the LOAD with your LED, make sure to add appropriate limiting resistors with the LEDs, and also replace the 2N2222 with TIP122

      Reply
      • Aju says

        Dear Sir,
        I had used a mosfet 80to3gp and put high load. Its working fine. I have Doubt that whay resistance should i use in across gate ?

        Reply
        • Swagatam says

          for MOSFeT gate resistance may not be required, so you can safely replace the 1K with a short link.

          Reply
          • Aju says

            Dear Sir,
            How to obtain a positive output in higher load connection? (in the collector Point of 2n 2222)

            Reply
            • Swagatam says

              You can connect a TIP147 to the collector of 2N2222

    • Kevin says

      is there a way to increase the time the led is lit and thus reduce its non lit time? cheers

      Reply
      • Swagatam says

        sorry changing duty cycle may not be possible in this design

        Reply
  7. Jonathan says

    Good day Swagatam,
    Awsome circuit, I’m trying to make a flashing led circuit like this but need it to activate on contact with water, do I simplify add a transistor to circuit so base closes on contact, if so where in circuit and how to incorporate a joule thief into circuit. If you have such schematic it would be much appreciated.

    Reply
    • Swagatam says

      Thank you jonathan, you can modify the design in the following manner

      water activated LED flasher circuit

      For a joule thief circuit you a refer to the following post:
      https://www.homemade-circuits.com/1-watt-led-driver-using-joule-thief/

      Reply
      • Jonathan says

        Thanks so much, very new to electronics and programming, this will help alot, what is minimum voltage it will work with.

        Reply
        • Swagatam says

          You are welcome, the minimum operating voltage is 9 V.

          Reply
      • Aju says

        Ok sir
        Thanks for the information. 👍🏼

        Reply
  8. Kayode says

    It doesn’t work. How will current go from collector to emitter without the base current?

    Reply
  9. Jack says

    Is there a circuit simulator that I can use to reproduce the same results? I’ve used many and none of them work.

    Reply
  10. Rodrigo Bordin says

    Hi! Great tiny circuit! Will it work with 24V DC supply? If not, what changes have to be made? Thanks a lot!

    Reply
    • Swagatam says

      Hi, Thanks, I am not sure whether it will work with 24V or not, but you can give it a try. The only change the circuit might need for this is the resistor, which could be increased to some higher value such as 4k7

      Reply
  11. SOUVIK DEY says

    The circuit only when I touched the base of bc547 transistor. Otherwise it is not working. Why?

    Reply
    • Swagatam says

      May be the transistor is not good, or there may be a connection fault… please recheck everything carefully.

      Reply
  12. Jack021 says

    How to connect only 2n2222 directly without LED diode and resistor R2. 2n2222 case is TO-92 or TO-18?

    Reply
    • Swagatam says

      You can try replacing the LED with a direct link!

      Reply
      • Jack021 says

        Did you mean this change? https://drive.google.com/open?id=1hWoMbVoXlW7XV_cBq9DYQzzY7w3ybYl8 You did not tell me 2n2222 case is TO-92 or TO-18?

        Reply
        • Swagatam says

          Yes that’s correct, the package doesn’t make any difference!

          Reply
          • Jack021 says

            Thanks Sir.

            Reply
  13. Aakash Karekar says

    Hi sir,

    1)In above circuit,can the blinker time be adjusted.(like “ON” for 1sec and “OFF” for 1 sec.).
    And instead of led,how can i connect transistor which can act as a switch.(the transistor switch will be “ON” for 1sec and “OFF” for 1sec.)

    2)The circuit diagram is shown in the link below
    https://drive.google.com/file/d/10bVfTV6iDspl3Ma76lMcr33gFKMPpgy8/view?usp=sharing

    how to adjust the blinker time ((like “ON” for 1sec and “OFF” for 1 sec.).
    And instead of led,how can i connect transistor which can act as a switch.(the transistor switch will be “ON” for 1sec and “OFF” for 1sec.)

    Thank you

    Reply
    • Swagatam says

      Aakash,

      I have updated the required diagram in the above post, you can check it out!

      Reply
      • aakash karekar says

        Sir,
        How can i adjust its blinking time?(.(like “ON” for 1sec and “OFF” for 1 sec.)

        Thank you

        Reply
        • Swagatam says

          By using different values for R1, or C1. But it may not be too accurate

          Reply
          • aakash karekar says

            Sir can you please tell me the value of r1 and c1 for “OFF” 1sec and “ON” for 500Msec or 1sec.

            Thank you sir for your kind reply and patience..

            Reply
            • Swagatam says

              Hi Akash, I don’t have the formula for calculating the values, the best way to find is by some trial and error. Try 470uF for C1 and see if that produces 1 second ON/OFF

      • Aakash karekar says

        Thanks a lot sir..

        Reply
      • David Anderson says

        Awesome u’ve made my day

        Reply
  14. sven says

    I have a switch with implemented LED which is extra connected to minus. Is it somhow possible to get the LED flashing while switched on? I had to connect this circuit somehow after the LED on the negative pol.

    Reply
    • Swagatam says

      If it is a 12C DC then You can probably try this circuit

      https://www.homemade-circuits.com/how-to-make-single-transistor-led/

      Reply
  15. Justin says

    Ha! If I did not see the video i would not have believed it.
    Does not work in simulator.
    http://www.falstad.com/circuit/circuitjs.html?cct=$+1+0.000005+12.050203812241895+53+5+50R+656+160+656+80+0+0+40+12+0+0+0.5g+656+464+656+528+0r+656+160+656+256+0+2700r+656+464+576+464+0+100162+576+352+576+464+1+2.1024259+1+0+0+0.01t+384+336+576+336+1+1+0.00012985325697745242+-0.30249585765328524+500w+576+320+576+272+0w+576+272+656+256+0209+656+256+656+464+0+0.00033299999999999996+0.8571050617707789+1o+4+64+0+4099+0.625+0.00009765625+0+2+4+3

    Reply
    • Swag says

      that’s exactly why I never rely or use simulator softwares, they are no match for an human brain.

      Reply
      • Johnny A says

        Considering simulators like LTspice can easily simulate op-amp and power supply circuits, it should easily be able to simulate your circuit, but try as I might, I too cannot get it to simulate.

        BC547 A, B or C ?
        LED: which one did you end up using (what breakdown voltage, forward current, partnumber…)

        Reply
        • Swag says

          When only BC547 is written it means any BC547 can be used since the supply voltage is only 12V, in the video you can see that the LED is a 5mm 20mA type.

          A simulator may have difficulty in simulating because the circuit works with unconventional principles.

          Reply
  16. Theuns says

    Hi Swagatam,

    I have seen it’s possible to make this LED stop blinking by disconnecting the capacitor. Is it possible to disconnect / reconnect the capacitor by means of an additional transistor on the cap side of the circuit? I would like the LED to be on then when the second transistor gets signal the cap is connected and flashing starts. I’ve achieved this with relays but as I will have many of these in my circuit the cost of relays isn’t a good choice.
    Thanks for an excellent website!

    Reply
    • Swag says

      Thank you Theuns, yes that may be possible, but instead of modifying the C1 section, I would recommended you to configure the ground supply line of the above circuit with an NPN such that when the NPN is triggered the circuit gets activated. For this you may connect the collector of the NPN with the ground line of the circuit,and the emitter with the supply negative.

      Reply
  17. Paul says

    Thank you for your response sir.. How can i accomplished that? Can you please show me a circuit diagram with BJT circuit that i can follow sir..
    Thanks again sir..

    Reply
    • Swag says

      Paul, I’ll explain you verbally:

      In the above circuit, remove the LED and join R2 directly with collector of T1, but make R2 = 1K

      now take a TIP127 BJT, connect its base directly with the above junction of R2 and T1 collector, join its emitter with the +12V line…and connect the collector with the bulb…bulb other end will go to the ground line…I hope you understood.

      Reply
  18. Paul says

    Sir Swagatam,

    Can I use this circuit as replacement for my turn signal flasher on my motorcycle? or is there another circuit you can refer to me..
    As a 12v signal flasher for 12v led light.

    Thank you very much..
    Paul

    Reply
    • Swag says

      Paul,

      it may be possible, but you will have to add an additional BJT buffer stage for powering the lamps.

      Reply
  19. Sean Selley-West says

    Hi, how could I make this circuit flash twice every second like a police or ambulance vehicle?

    Reply
  20. naveen bankapalli says

    how to test transistor emitter Base collector

    Reply
  21. Mohan kumar says

    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.

    Reply
    • Swagatam says

      Hi Mohan, you can refer to the following circuit and do it accordingly for getting the required results:

      https://homemade-circuits.com/2011/12/how-to-make-efficient-led-emergency.html

      Reply
  22. Harsha Vardhan Reddy A says

    Nice bro I am satisfied with this ckt. Can you please help me to blink some more faster

    Reply
    • Swagatam says

      thanks bro, just decrease the value of C1 to make it blink faster

      Reply
  23. Siddarth Naik says

    Hi Swagatam, were you able to write the comprehensive article explaining how this works?

    Reply
    • Swagatam says

      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.

      Reply
  24. Mukesh says

    Please reply soon thnkx:-)

    Reply
  25. Mukesh says

    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..

    Reply
    • Swagatam says

      Mukesh you cannot use the above circuit, instead you can try any of the following designs:

      https://homemade-circuits.com/2012/01/how-to-make-any-light-strobe-light.html

      Reply
  26. ibrahim shafeeg says

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

    Reply
    • Swagatam says

      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

      Reply
  27. Roquiya says

    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

    Reply
    • Swagatam says

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

      Reply
  28. Roquiya says

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

    Reply
    • Swagatam says

      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.

      Reply
  29. Roquiya says

    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

    Reply
    • Swagatam says

      the above circuit won't be appropriate, search for:

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

      Reply
  30. Roquiya says

    HI
    will this circuit work for 16v?

    Reply
    • Swagatam says

      yes…

      Reply
  31. Madhu Babu says

    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

    Reply
    • Swagatam says

      sorry, presently I do not have this circuit.

      Reply
  32. pat tee says

    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?

    Reply
    • Swagatam says

      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.

      Reply
    • Swagatam says

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

      Reply
  33. pat tee says

    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…www.youtube.com/watch?v=Rj5tqhGypAE&feature=player_embedded. I found 3mm flashing LEDs …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?

    Reply
  34. Alessandro Riva says

    What are the formulas to calculate the timing of the flash?

    Reply
    • Swagatam says

      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)))

      Reply
  35. Swagatam says

    you can try this one:

    https://homemade-circuits.com/2011/12/make-yourself-simple-led-flasher-at.html

    Reply
  36. Swagatam says

    congrats!

    Reply
  37. Ryan Hebron says

    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

    Reply


  38. COMMENT BOX IS MOVED AT THE TOP


Primary Sidebar

Electronic Projects Categories

  • 3-Phase Power (15)
  • 324 IC Circuits (19)
  • 4017 IC Circuits (51)
  • 4060 IC Circuits (25)
  • 555 IC Circuits (92)
  • 741 IC Circuits (18)
  • Amplifiers (49)
  • Arduino Engineering Projects (82)
  • Audio Projects (83)
  • Battery Chargers (75)
  • Car and Motorcycle (87)
  • Datasheets (44)
  • Decorative Lighting (Diwali, Christmas) (31)
  • DIY LED Projects (81)
  • Electronic Components (96)
  • Electronic Devices and Circuit Theory (34)
  • Electronics Tutorial (99)
  • Fish Aquarium (5)
  • Free Energy (34)
  • Games (2)
  • GSM Projects (9)
  • Health Related (17)
  • Heater Controllers (23)
  • Home Electrical Circuits (98)
  • Incubator Related (6)
  • Industrial Electronics (25)
  • Infrared (IR) (39)
  • Inverter Circuits (94)
  • Laser Projects (10)
  • LM317/LM338 (21)
  • LM3915 IC (24)
  • Meters and Testers (52)
  • Mini Projects (152)
  • Motor Controller (64)
  • MPPT (7)
  • Oscillator Circuits (12)
  • PIR (Passive Infrared) (8)
  • Power Electronics (32)
  • Power Supply Circuits (64)
  • Radio Circuits (9)
  • Remote Control (46)
  • Security and Alarm (55)
  • Sensors and Detectors (115)
  • SG3525 IC (4)
  • Simple Circuits (72)
  • SMPS (30)
  • Solar Controllers (60)
  • Timer and Delay Relay (51)
  • TL494 IC (5)
  • Transformerless Power Supply (8)
  • Transmitter Circuits (36)
  • Ultrasonic Projects (12)
  • Water Level Controller (45)

Follow Homemade Circuits

Facebook
Twitter
YouTube
Instagram
My Facebook-Page
Quora

Feeds

Post RSS
Comment RSS

Circuit Calculators

  • AWG to Millimeter Converter
  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Small Signal Transistor(BJT) and Diode Quick Datasheet
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator

© 2021 · Swagatam Innovations

We use cookies to ensure that we give you the best experience on our website. If you continue to use this site we will assume that you are happy with it.Ok