The post explains a simple LED flashing beacon circuit which exactly simulates a rotating police beacon light by generating alternating pulses of suddenly rising and fading illumination effect on the connected LED. The idea was requested by Mr. Ankit Agarwal
Technical Specifications
Can you advice on how to make the following circuit A single flashing LED circuit, in which the LED flash simulates that of beacon ie when the LED flashes, first it glows slowly, then to full intensity, and then fades.
This gives the effect of a rotating beacon OR just like the lights on an aircraft tail.The circuit is intended to be used in the car (as a flashing rear light) so the circuit may function on 12v and the LED may be bright enough to be visualized clearly so it may be 1 watt smd led.
Kindly advise
Thanks
The Design
The proposed idea of a single LED rotating beacon lamp simulator can be implemented using the above shown circuit.
Here the IC 4017 and the IC 555 together are configured to generate a sequential chasing high logic across the 10 pinouts of the IC 4017.
The IC 555 is wired as a standard astable which feeds the clock or the flashing signal at pin14 f the IC 4017.
The IC 4017 responds to these clocks and generates a shifting high logic across its 10 outputs from pin#3 to pin#11.
These pinouts are integrated via individual diodes, and the common terminal can be seen connected with the base of a TIP122 transistor.
This transistor includes a 1 watt LED across its base emitter points which enables it form an emitter follower configuration with the LED.
This means that the LED will be supplied with a voltage level that may almost equal to the base voltage of the TIP122, and if this varies, the LED supply can be expected to vary accordingly.
The resistors connected across all the shown outputs of the IC 4017 is selected with an incrementing order or in way such that it forms an incrementing potential divider with reference to the preset resistance which may be seen across the base and ground of the TIP122.
Therefore as the 4017 IC generates the shifting or chasing high sequence across its pinouts, the resistors with reference with the preset resistance value generates a correspondingly increasing or decreasing potential difference at the base of the TIP122 transistor.
This effect in turn allows a varying potential difference to develop across the LED, which responds to this and produces the required sudden rise and decay effect and viec versa on the LED simulating a rotating beacon light.
The speed at which this happens can be set or adjusted with the help of R2.
The light intensity on the LED can be adjusted by suitably setting up the preset at the base of the TIP122 transistor.
The values of the resistor across the pinouts of the IC 4017 may be selected and swapped as per the user preference for generating different random flashing effect with due experimentation.
A rough simulation effect of the above explained rotating beacon simulator circuit using LED may be witnessed as given below.
An easier and cheaper alternative for a revolving LED beacon light can be seen below, although the effect may not be as impressive as the above design.
Please note that you may have to play with the 10K, 1K and the capacitor values to get the most desirable revolving lamp effect from the above circuit.
Simple Emergency Flasher
The next emergency lamp flasher can be used for distress calling, during a car accident or car breakdown:
Jerry says
Thank you for the website! Very educational for a novice like me. I’m looking for a circuit that will “fade” up a single LED and then “flash” at the end of the sequence. Imagine a laser cannon building up power then firing. I believe this circuit will accomplish this with the exception of only wanting the sequence to run one cycle until it is manually reset (a button is pushed). Is there a better alternative circuit.
Swagatam says
Thank you, and glad you liked the website. Do you mean, the LED must first illuminate brightly, then fade, then flash, then manually reset for a new cycle?
Jerry says
Just the opposite. Start off dark then gradually brighten with a flash once it reached the brightest illumination.
Swagatam says
I have designed it, you can see it in the following diagram:
Jerry says
Thank you! I’ve compared this with the original design and now have a better understanding.
Swagatam says
Thanks! Glad to help!
Richard says
First of all, thank you for putting this out here and helping fellow enthusiasts. I was wondering if there is a video of the actual circuit running? Before buying the parts and building it, I’d like to make sure the effect is what I am looking for. Thank you.
Swagatam says
There’s no video at this moment, however The circuit should work perfectly according to my understanding.
Sison says
Appreciate if you could update the circuit achording to comments.Hence we can assemble without hazzle.Expecting the updation soon.
Swagatam says
I have updated the drawing at the bottom of the post!
Pradeep says
Sir,
Thanks for your prompt and swift reply. My requirement was bit different, ie, two numbers of LED lamps of 10 Watts each working in a flip flop manner. kindly suggest the modification to be carried in your given circuit.
Thanks
Swagatam says
Pradeep, you can try the following concept:
https://www.homemade-circuits.com/led-obstruction-light-circuit/
Eliminate the entire LDR stage along with D1/D2.
And replace R9/R10 with 10uF capacitors for getting a slow fade effect
Pradeep KT says
Sir,
Can I have a modified version of above rotating beacon circuit with two numbers of 10 watts or less LED lamps with adjustable/selectable On/Off (ie 20 or 30 flashes etc) period?
Swagatam says
Hi Pradeep, you can use two TIP142 in parallel and put two 10 watt LEDs at their emitter terminals for getting the effect. For speed adjustments you can tweak the R2 pot.
juan says
que valores son las resistencias 5 17
Swagatam says
You can use 1K for R5—R14
Vaisakhan says
Can I connect a 6no 4pin RGB LEDs in place of 1Watt led. What modification to do for that?
Swagatam says
please first build and confirm with a 1 watt LED then we will proceed with RGB
Swagatam says
Cuyler, sometimes this happens, if you refresh the page and try then mostly it will start loading normally again, anyway I am glad you found the solution
cuyler wilkinson says
Swagatam, this post section was not loading and I posted my question in the simple wind generator post.Now I think I have my answer after reading Nelio's comments! Thanks for your time
Nelio Abreu says
Hi,
In the original circuit you miss a 1000uF capacitor, but present in the simulation! Is it needed? Since I'll be using 2 standard LED's, can I replace TIP122 by another ref., smaller, that can withstand both LED's?
Best Regards.
Nélio.
Swagatam says
the 1000uF could be experimented for smoothing the fading effect, although it's not so crucial….
Nelio Abreu says
Hi,
Thanks for your replay. I remember this circuit. Replacing R5-R14 with trimmers what would be the maximum value? 10K? Considering TIP122, I can connect 2 LEDs in series, right?
Best Regards.
NA
Swagatam says
Hi, yes the preset can be 10K, it's basically for setting up the base voltage for the TIP122 such that it varies from the minimum LED fwd drop value to the max LED fwd drop value….for two LEDs this could be from minimum 5V to a maximum 7V
the above range should be uniformly distributed across the 10 outputs of the 4017.
Nelio Abreu says
Hi Swagatam,
What is the value of R1 in the circuit?
Best Regards,
Nélio.
Swagatam says
Hi Nelio, R1 is not required, you can do without it, I lifted the drawing from one of my other application designs, and forgot to remove it for this design.
ubaid says
Thanks you sir for answer.
ubaid says
Hello sir,
Please sir can you modify this
Circuit to controll Ac 220volt bulb
Swagatam says
Ubaid, it can become much complicated due to the inclusion of a PWM stage and a MOCxx opto coupler stage…
abhijit kundu says
Sir I am interested in circuit design. I want to know more from you .
Abu-Hafss says
Dear Swagatam
Please inform the function of R1, C3, R15 and 1000µF.
Swagatam says
Dear Abu-Hafss,
the 1000uF is not required, I forgot to remove it in the simulation.
C3 is for resetting the IC 4017 on power switch ON, but here this may not be required so it may be removed…R15 is for enabling the C3 resetting action, therefore it can also be removed and pin15 can be directly connected to ground
Dr Ankit says
Dear Sir, many thanks for promptly building the schematic.
If the desired effect is 1 cycle of flash then a pause for 10-15 sec or more, then again a cycle of flash and so on, what probable alteration shall be done in the component values
Swagatam says
Dear Ankit, for that you may do the following steps:
remove the diode and resistor from pin11, and make it blank
next, connect pin13 to ground through a 2.2M resistor
Now connect pin11 with pin13 via a 470uF capacitor, (+) to pin11, (-) to pin13
Dr Ankit says
Can an LDR be added in this circuit so that the flasher functions automatically after dark.
Kindly advise
Swagatam says
you can add the last circuit from the following link and use it to keep the above circuit switched OFF during daytime
https://www.homemade-circuits.com/2012/01/how-to-make-light-activated-day-night.html