Can you imagine of making a formidable little LED flasher or blinker using just a single transistor and a couple of other passive parts.
How it Works
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
Circuit Schematic
Video Clip:
PCB Design
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
Swag says
that’s exactly why I never rely or use simulator softwares, they are no match for an human brain.
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!
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.
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..
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.
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
Swag says
Paul,
it may be possible, but you will have to add an additional BJT buffer stage for powering the lamps.
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://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://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…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?
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)))
Anonymous says
dear sir pls give two led alternate flasher with adjustable flash rate circuit
Swagatam says
you can try this one:
https://homemade-circuits.com/2011/12/make-yourself-simple-led-flasher-at.html
Diego Corona says
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
Swagatam says
Hi, yes it's dependent on the values of R1/C1, but only to an extent beyond which it just stops functioning.
Anonymous says
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.
siraj shaikh says
Hi Swagatam
I tried the above circuit ,but it didn't worked
I used 4k resistor in place of R1
Swagatam says
Hi Sirj,
this circuit is so simple, it should start working immediately… assemble everything exactly as given in the diagram, it will work.
Bibin Edmond says
Hi swagatam,
Can we use 3 to 9v supply for this circuit ?
Regards,
Bibin Emdond
Swagatam says
Hi Bibin,
A 9V supply might just work, but not 3V.
Regards.
Anonymous says
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 🙂
Swagatam says
any type led would work….I had used a 5mm green led, and 12V supply.
different capacitor values will produce different flash rates.
Sean Selley-West says
Hi, how could I make this circuit flash twice every second like a police or ambulance vehicle?
Anonymous says
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?
Swagatam says
Not sure what's wrong, my circuit worked superbly with the shown components and supply.
Anonymous says
is there a kind of LED that I should use, sir?
Swagatam says
any 5mm led will work her…
Anonymous says
thanks 🙂
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
Swagatam says
congrats!
Anonymous says
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
Swagatam says
the arrow head of the transistor symbol is the emitter.
ELECTRO ASTRO TECH says
At the ground point…??
Swagatam says
Yes that's correct!
ELECTRO ASTRO TECH says
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…….
Swagatam says
At the junction of R2 and C1
Anonymous says
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 . .??
Sunjay says
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