It is possibly the smallest 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 I have explained 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 by 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.
At that time, I was unaware that this was occurring as a result of the transistor's negative resistance characteristics.
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
Calculating the LED Flashing Frequency
You can use the following formula for approximately calculating the LED ON/OFF blinking rate
Frequency (f) ≈ 1 / (2.1 * R * C)
Where:
- R is the resistance in ohms
- C is the capacitance in farads
This formula gives us a rough idea of what the flashing frequency might be. But the actual frequency can be affected by a hand full of different factors, for example like the specific components you are using in the circuit, the voltage of the power supply and also the temperature.
To adjust the flashing rate:
- Increase the resistance (R): If we make the resistance higher, it will take longer for the capacitor to charge up which means the flashing rate will be slowed down.
- Decrease the capacitance (C): On the opposite side, if we lower the capacitance vaalue, the capacitor will charge up faster causing the flashing rate to speed up.
Connecting an External Transistor for Higher Loads
Video Clip:
PCB Design
Hi. Why doesn’t that work so well with a small blue led?
Hi, it should work well with all types of LEDs regardless of color or any other specifications, as long as the voltage input is between 9V and 12V DC. Try adjusting the resistor value for optimal illumination.
Thanks. Blue led works fine with a 1K resistor.
Ok, sounds great, thanks for the feedback…
Dear Swagatam, i have 2 diff. questions.1. For flasher with single transistor, as per the diagram, Not sure what is the issue, only when i touch the emitter or collector , ( Some earth effect), the flasher is working. Not sure why. I verbatim did as per your diagram. can you help.
2. A FEW Weeks back i sought your advice for spike arrestor / suppressor circuit, and With GDT / MOV, You were very helpful. I have a doubt, that the client site, is basically an explosive environment kind of, since any unsafe act will lead to probable safety issue. Is the GDT usage, is common for all environments or it should not be used in an exploisve or fire hazard environment. I ask this query since, i saw some videos on nice working of GDT, but it conducts in the hydrogen gas environment within the tube with pop up sound. Is it a safety issue for a fire / explosive hazard environment pl.
Thank you KRAB Babu, for posting you questions.
The above flasher circuit is tested by me and I did not encounter any such issues. The flasher that I build started working immediately upon switching ON.
Make sure the transistor you are using is a good quality one and not a duplicate one, also make sure the power supply is a 12V DC.
Let me know how it goes.
As for the GDT issue, yes it can be hazardous to use GDTs in explosive environments because GDTs are not intrinsically safe.
In explosive environments, make sure to use only those devices that are certified as intrinsically safe.
Dear Swagatam, thank you very much for your rpely. i dont know if i used poor quality as i buy that from market. I WILL Try that again, as you said.
Thanks for your inputs on GDT Also. your support is excellent and prompt.
You are most welcome Dear KRAB Babu, all the best to you.
Let me know if you have any further questions.
May I ask you question, but a bit diff.. Along with the flasher circuit with one transistor, I plan to drive using a Toggle switch for alerting an Operator . In addition, upon this flashing signal, the OPERATOR has to push down a push button switch ( Latching – to Normally closed position ). But, upon changing the push button switch to NC condition, the flashing must stop. I am setting up the circuit, that current flows to low resistance path and it will work.
The latching and unlatching of the relay should be through a single push button, right?
The application looks possible to me.
thanks for the reply swagatam. THE LATCHING and unlatching of the relay is one part. But, some flashing action, i want to happen , that needs to be stopped by a push button that is part of latching circuit. i also shared some pictures to you by mail. could you please advice me.
Thank you KRAB Babu, I think it is possible to design a circuit diagram as per your requirement. Once the relay is latched and then unlatched the flashing LED would stop simultaneously.
In which email ID did you send the pics, I checked my two email IDs but could not find your email.
Thank you for your reply. i sent the pictures in this mail id sorry though for confusion from me. since, i did not have any other mail id . no-reply@homemade-circuits.com
Sorry, that’s not the correct email ID.
You can find the email IDs on this page:
https://www.homemade-circuits.com/contact/
Also, for a given transistor you might find it helpful to “play around” with the power supply voltage.
Hi Swagatam.
Thanks for your enthusiasm and willingness to answer questions.
Do you think it would be possible to put a capacitor between T1 and the LED to make that fade in and out?
I’ve developed spinal cancer and getting back into electronics as I’ve lost mobility.
Hi Dave,
I think a capacitor put in parallel to the LED will be enough to produce a certain of fading effect.
I am sorry about your illness, I wish you a speedy recovery.
I dont think the circuit works looking at the diagram for how can the current flow from positive to ground in that npn transistor?
Well this may have been a typo error, the collector and emitter should be interchanged.
The diagram is actually correct. The configuration indeed appears to be wrong, but it actually works, and it works only when connected in the way it is shown. It works by using the transistor’s negative resistance characteristics.
hi i was wondering if there was a way to make a 5v “flasher” i am building a simulator with a real dash out of a truck and want the original turn signals to work on the dash i have replaced the 12v lights with 5v leds and want them to flash when i use the turn signal switch and hazards button any help is appreciated
You truck flasher will have a relay….so the 5V LED can be wired parallel to the relay coil or the contacts with a series resistor, for getting a synchronized flashing action.
but the factory flasher and relay are 12v im using a generic joystick controller to power the turn signal switch and thats 5v i was looking for something to use in line the original circuit to replace the factory flasher and relay
Would the circuits from this article work for you? You can use 5V for these circuits with slight modifications:
https://www.homemade-circuits.com/3-pin-solid-state-car-turn-indicator-flasher-circuit-transistorized/
The post indicates the BC547 which is an NPN yet the schematic indicates the Emitter connected the + potential down stream of a current limiting R with a voltage dropper from the collector to the LED. Is this correct? I was under the impression the junction of the transistor would not allow current to pass reverse such as indicated here. Just curious as I never tried working with negative resistance as in stated in the text above, for that matter I never heard of negative resistance until here as far as I can remember. Just wanting to know if this a was an oops in the drawing or the way it actually works. I suppose I could just build it as is since I have all the parts on hand. I have a perfect use for this circuit in a project I’m working on now, if works that’s great, other wise it’s a flashing LED when they arrive in the mail in a week or so.
Yes, the circuit really works, as you can see it in the video.
It is actually a special type of configuration in which the BJT works using its negative resistance theory to conduct in reverse.
You can try it, it will surely work.
Well I can say that it did work for a while. It appears the bread board I’m using is wore out. Darn it. I was attempting to adjust the flash rate and had the capacitance up to 1000uf to get the flash rate slowed down to a more suitable timing, was pretty happy with it but would like to have had it a bit slower for my purpose. I like the bright on and the short duration but would like to have the duration on a bit longer. I guess I will try a different board to see if I can get it flashing again and then experiment with the On duration and pulse rate. But the idea is the simplicity and very low component count, kind of defeating the purpose going beyond what it is. I guess the ever popular 555 is my alternative now so it’s good to know what I have learned here today.
Thanks for the feedback!! You can also try varying the R1 resistor to adjust the flash rate
I came across this by accident as well, it does work and I have been wondering
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?
Please provide the specifications of the LED string? I will try to suggest a suitable circuit.
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.
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.
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.
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.
Thanks for responding! Who do you think can help with such idea?
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.
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.
There’s indeed no online information about HR706, so it is difficult to tell whether it is a transistor or IC.
I like the part where you included the diode
thank you!
Can this circuit be modified to run on a 1.5V or 3V coin cell battery? If no, why, and if yes, how?
Unfortunately, the above circuit cannot run on voltages below 9 V. The transistor requires at least around 9V to conduct using the indicated configuration
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.
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.
If I want to run this Strobe effect on 3V ? is the same circuit or I have to change specification of Resistance capacitor
No, this circuit will not work with 3 v supply, it will need a minimum of 9 V too operate correctly.
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.
I need a circuit for a 5v led flasher using power from a USB cable.
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
Connect the positive voltage from the relay source with the collector of the transistor, or the anode of the LED
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?
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
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 ?
for MOSFeT gate resistance may not be required, so you can safely replace the 1K with a short link.
Dear Sir,
How to obtain a positive output in higher load connection? (in the collector Point of 2n 2222)
You can connect a TIP147 to the collector of 2N2222
sorry changing duty cycle may not be possible in this design
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.
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/
Thanks so much, very new to electronics and programming, this will help alot, what is minimum voltage it will work with.
You are welcome, the minimum operating voltage is 9 V.
Ok sir
Thanks for the information. ????????
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.
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.
It doesn’t work. How will current go from collector to emitter without the base current?
Is there a circuit simulator that I can use to reproduce the same results? I’ve used many and none of them work.
Hi! Great tiny circuit! Will it work with 24V DC supply? If not, what changes have to be made? Thanks a lot!
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
The circuit only when I touched the base of bc547 transistor. Otherwise it is not working. Why?
May be the transistor is not good, or there may be a connection fault… please recheck everything carefully.
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.
How to connect only 2n2222 directly without LED diode and resistor R2. 2n2222 case is TO-92 or TO-18?
You can try replacing the LED with a direct link!
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?
Yes that’s correct, the package doesn’t make any difference!
Thanks Sir.
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
Aakash,
I have updated the required diagram in the above post, you can check it out!
Sir,
How can i adjust its blinking time?(.(like “ON” for 1sec and “OFF” for 1 sec.)
Thank you
By using different values for R1, or C1. But it may not be too accurate
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..
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
Thanks a lot sir..
Awesome u’ve made my day
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.
If it is a 12C DC then You can probably try this circuit
https://www.homemade-circuits.com/how-to-make-single-transistor-led/
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
that’s exactly why I never rely or use simulator softwares, they are no match for an human brain.
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…)
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.
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!
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.
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..
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.
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
Paul,
it may be possible, but you will have to add an additional BJT buffer stage for powering the lamps.
Hi, how could I make this circuit flash twice every second like a police or ambulance vehicle?
how to test transistor emitter Base collector
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.
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
Nice bro I am satisfied with this ckt. Can you please help me to blink some more faster
thanks bro, just decrease the value of C1 to make it blink faster
Hi Swagatam, were you able to write the comprehensive article explaining how this works?
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.
Please reply soon thnkx:-)
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..
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
Hi, can you please tell me how the transistor is activated without the base connected?
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
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
It will need to be tweaked and verified practically for those results….there are no formulas for it.
Can you tell me in technical prospectivem, why cant we use this circuit??
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.
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
the above circuit won't be appropriate, search for:
transistor astable multivibrator circuit …..or 555 astable multivibrator circuit
HI
will this circuit work for 16v?
yes…
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
sorry, presently I do not have this circuit.
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?
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.
a flashing LEd could have an automatic flash rate changer built-in, so it could go on changing the flash rate by itself.
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?
What are the formulas to calculate the timing of the flash?
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)))
you can try this one:
https://www.homemade-circuits.com/2011/12/make-yourself-simple-led-flasher-at.html
congrats!
Can any TV remote control the circuit
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