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.
You may also love to read this article: Blinking LED Circuit using LDR
Circuit Diagram
Connecting an External Transistor for Higher Loads
Video Clip:
PCB Design
Dom says
Like the unusual circuit! So many references to “simple LC flasher circuit” on internet, but nothing found. Where to find a tiny circuit to flash LED string?
Swagatam says
Please provide the specifications of the LED string? I will try to suggest a suitable circuit.
Dom says
Specifications are difficult to find. The strips are mostly available in 12V, 300 LEDs, available batteries are 5V, time on is 300ms, frequency is ~2HZ. So the circuit has to boost the voltage. The operation period will be <2 minutes usually. I have some BTA16 800B if they can be used.
Swagatam says
A DC load cannot be used with a triac, it will get latched. You can probably try the second circuit from the above article. You can replace the 2N2222 with a bigger transistor such as TIP142 and connect your LEDs across the load points.
Kerry Anort says
I need your assistance or advice on which transistor circuit diagram I can use to suit my needs. I need a circuit diagram which takes action e.g blinking the LED when base voltage is supplied and blink LED when base voltage is removed.it can have either 1 or 2 output terminals for signal.
Swagatam says
That looks a bit difficult. Blinking an LED with a base voltage applied is possible, but blinking it with base voltage removed looks difficult…can’t figure it out right now.
Kerry Anort says
Thanks for responding! Who do you think can help with such idea?
Swagatam says
I don’t seem to have anybody in my contact who would do this for you…. maybe some knowledgeable person visiting this page is able to throw some light on this.
Vin Ferrante says
I found a circuit driving 10 LED with 4.5V battery using a Henry HR706 but can not find any info on the HR706. Is it just NPN transistor or more ?
The circuit uses the HR706 to drive the LEDs to flash every second or so.
The circuit has a 10 ohm resistor from the Base to Gnd, E (?) to LED and C (?) direct to +4.5V. Other side of LED is tied to 4.5V.
Swagatam says
There’s indeed no online information about HR706, so it is difficult to tell whether it is a transistor or IC.
Muje says
I like the part where you included the diode
FC says
thank you!
Pratik Mukherjee says
Can this circuit be modified to run on a 1.5V or 3V coin cell battery? If no, why, and if yes, how?
Swagatam says
Unfortunately, the above circuit cannot run on voltages below 9 V. The transistor requires at least around 9V to conduct using the indicated configuration
Gleiner says
Thank you Swagatam for your post. It is as cheap as recommended for my applications. I’m looking for a circuit that lights up a 10watts (or more) led lamp as the night comes in and turn off as the night comes out. It’s easy to find out this kind of circuit but the ones that uses relays to turn on and off the loading but what I need is a circuit that operates in fading mode, increasing charge in ascending way to lights up in the evening and decreasing charge like the morning comes to produce effects like a gradually lightening and dimmering the lamp.
Could you suggest me something to help, please?
Thanks a lot.
Gleiner.
Swagatam says
Thank you Gleiner, you can try the following concept for implementing the specified slow fade action of the lamp in response to dawn and dusk.
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
Swagatam says
No, this circuit will not work with 3 v supply, it will need a minimum of 9 V too operate correctly.
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.
Robert says
I need a circuit for a 5v led flasher using power from a USB cable.
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
Swagatam says
Connect the positive voltage from the relay source with the collector of the transistor, or the anode of the LED
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?
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
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 ?
Swagatam says
for MOSFeT gate resistance may not be required, so you can safely replace the 1K with a short link.
Aju says
Dear Sir,
How to obtain a positive output in higher load connection? (in the collector Point of 2n 2222)
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
Swagatam says
sorry changing duty cycle may not be possible in this design
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.
Swagatam says
Thank you jonathan, you can modify the design in the following manner
For a joule thief circuit you a refer to the following post:
https://www.homemade-circuits.com/1-watt-led-driver-using-joule-thief/
Jonathan says
Thanks so much, very new to electronics and programming, this will help alot, what is minimum voltage it will work with.
Swagatam says
You are welcome, the minimum operating voltage is 9 V.
Aju says
Ok sir
Thanks for the information. 👍🏼
N Syed says
Hello Swagatam, Awesome circuit repo here.
Two things: —
1) I need an exact circuit as Jonathan but with the opposite effect. I need the flashing LED when there is “no contact” in water i.e ‘no signal’ from water. Meaning, when the water-tank is empty I need the alarm [buzzer and LED both to blink] on, but when there is water in the tank the circuit should not make any noise!. Being a newbie myself in the field I can’t seem to make any head or tail to reverse the signal effect in this circuit. May be I can use the ‘not used’ base pin of T1 for the purpose? I thought if there is any signal/pulse to T1-base then the LED would be off totally, but it doesn’t, why not? How can I do this?
2) If I need to get a buzzer to go ‘beep’, ‘beep’, ‘beep’ … continuously and parallel/alternative to LED until there is a signal on the T1-base, I presume the buzzer can go parallel to the LED in circuit?
Can you please point me to a direction to solve? I’d really appreciate any help.
Swagatam says
Thank you N Syed,
You can probably try the following design:
for better response please connect another 1K resistor between the base and emitter of T2.
Yes you are right, you can connect a piezo buzzer in parallel with the LED for getting the required beep beep sound.
Kayode says
It doesn’t work. How will current go from collector to emitter without the base current?
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.
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!
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
SOUVIK DEY says
The circuit only when I touched the base of bc547 transistor. Otherwise it is not working. Why?
Swagatam says
May be the transistor is not good, or there may be a connection fault… please recheck everything carefully.
ian says
yeah i had same issue. i had a high load led so after fiddling with capacitors and resistors – had to use 500Ω and 1KΩ resistor and changed caps from 100 – 470uƒ to get working.
Jack021 says
How to connect only 2n2222 directly without LED diode and resistor R2. 2n2222 case is TO-92 or TO-18?
Swagatam says
You can try replacing the LED with a direct link!
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?
Swagatam says
Yes that’s correct, the package doesn’t make any difference!
Jack021 says
Thanks Sir.
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
Swagatam says
Aakash,
I have updated the required diagram in the above post, you can check it out!
aakash karekar says
Sir,
How can i adjust its blinking time?(.(like “ON” for 1sec and “OFF” for 1 sec.)
Thank you
Swagatam says
By using different values for R1, or C1. But it may not be too accurate
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..
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..
David Anderson says
Awesome u’ve made my day
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.
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/
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
Swagatam says
that’s exactly why I never rely or use simulator softwares, they are no match for an human brain.
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…)
Swagatam 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.
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!
Swagatam 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.
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..
Swagatam 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.
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
Swagatam says
Paul,
it may be possible, but you will have to add an additional BJT buffer stage for powering the lamps.
Sean Selley-West says
Hi, how could I make this circuit flash twice every second like a police or ambulance vehicle?
naveen bankapalli says
how to test transistor emitter Base collector
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.
Swagatam says
Hi Mohan, you can refer to the following circuit and do it accordingly for getting the required results:
https://www.homemade-circuits.com/2011/12/how-to-make-efficient-led-emergency.html
Harsha Vardhan Reddy A says
Nice bro I am satisfied with this ckt. Can you please help me to blink some more faster
Swagatam says
thanks bro, just decrease the value of C1 to make it blink faster
Siddarth Naik says
Hi Swagatam, were you able to write the comprehensive article explaining how this works?
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.
Mukesh says
Please reply soon thnkx:-)
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..
Swagatam says
Mukesh you cannot use the above circuit, instead you can try any of the following designs:
https://www.homemade-circuits.com/2012/01/how-to-make-any-light-strobe-light.html
ibrahim shafeeg says
Hi, can you please tell me how the transistor is activated without the base connected?
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
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
Swagatam says
It will need to be tweaked and verified practically for those results….there are no formulas for it.
Roquiya says
Can you tell me in technical prospectivem, why cant we use this circuit??
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.
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
Swagatam says
the above circuit won't be appropriate, search for:
transistor astable multivibrator circuit …..or 555 astable multivibrator circuit
Roquiya says
HI
will this circuit work for 16v?
Swagatam says
yes…
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
Swagatam says
sorry, presently I do not have this circuit.
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?
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.
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.
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?
Alessandro Riva says
What are the formulas to calculate the timing of the flash?
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)))
Swagatam says
you can try this one:
https://www.homemade-circuits.com/2011/12/make-yourself-simple-led-flasher-at.html
Swagatam says
congrats!
Emmanuel says
Can any TV remote control the circuit
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