Rotating Beacon LED Simulator Circuit

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


Rotating Beacon LED Simulator Circuit

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.

GIF image for Rotating Beacon LED

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Dr Ankit said…
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 said…
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
Abu-Hafss said…
Dear Swagatam

Please inform the function of R1, C3, R15 and 1000µF.
Swagatam said…
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

abhijit kundu said…
Sir I am interested in circuit design. I want to know more from you .
Dr Ankit said…
Can an LDR be added in this circuit so that the flasher functions automatically after dark.
Kindly advise
Swagatam said…
you can add the last circuit from the following link and use it to keep the above circuit switched OFF during daytime
ubaid said…
Hello sir,
Please sir can you modify this
Circuit to controll Ac 220volt bulb
Swagatam said…
Ubaid, it can become much complicated due to the inclusion of a PWM stage and a MOCxx opto coupler stage...
ubaid said…
Thanks you sir for answer.
Nelio Abreu said…
Hi Swagatam,
What is the value of R1 in the circuit?
Best Regards,
Swagatam said…
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.
Nelio Abreu said…
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.
Nelio Abreu said…
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.

Swagatam said…
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.
Swagatam said…
the 1000uF could be experimented for smoothing the fading effect, although it's not so crucial....
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
Swagatam said…
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
Vaisakhan said…
Can I connect a 6no 4pin RGB LEDs in place of 1Watt led. What modification to do for that?
Swag said…
please first build and confirm with a 1 watt LED then we will proceed with RGB

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