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!
Contents
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
Have Questions? Please Comment below to Solve your Queries! Comments must be Related to the above Topic!!
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… Read more »
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
is there a way to increase the time the led is lit and thus reduce its non lit time? cheers
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… Read more »
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.