30th January 2016 Cat: Circuit Diagram with No Comments »
The post discusses a cool chasing LED light circuit that features a timed delay fading slow transition effect across the whole illuminated sequencing LEDs. The idea was requested by Mr. Tamam

 The Request

Dear Swagatam, I want to design a circuit consisting equal no. of Red, Green, Blue, Yellow, Violet, Orange and White LEDs. I want to have these LEDs in a continuous and smooth transition effect like

At first, Red branch of LEDs lit for a preset time then slowly fade out and then Green branch of LEDs fade in and fade out then next branch fade in and so on…..

I would like to have control on transition time delay, light timing, fade in or out timing if possible. And I don’t want to use any Programmable IC for this. So please please let me know if it possible without any programmable IC. It is okay even if I need several ICs to accomplish the job. You just show me the way !!

Thank you very much once again for your valuable time and for a quick reply! I am looking forward to you response!!


The Design

The proposed chasing, fading LEd light circuit may be understood with the help of the above schematic and the following description:

The upper circuit is a standard LED chaser design comprising of a decade counter IC 4017 and a clock oscillator using IC 555 astable configuration.

This IC 4017 generates a sequencing high logic (equal to supply voltage)  across its entire output pins in response to the clocks at its pin14 from the IC 555.

If we connect LED directly across the 4017 outputs and ground, the LEDs would illuminate in a dot mode fashion from the first pinout upto the last in a sequencing pattern resembling a chasing effect.

This effect is pretty ordinary and we all probably have come across and built such light chasers circuits quite often.

However as per the request the effect needs to be enhanced by adding a slow transition over the LED illumination as it sequences across the entire channel. This fading transition on the sequencing LEds is expected to generate an interesting group LED chasing effect instead of an illuminated dot like appearance.

The above intriguing show could be easily implemented by connecting the LEDs to an intermediate BJT delay generator circuit.

This BJT circuit becomes responsible of generating the intended transition delay over the LED illumination and can be witnessed in the lower design.

This stage needs to be repeated across all the selected outputs of the 4017 outputs for achieving the desired chasing, fading slow transition over the LEDs.

As requested the rate of the above fading slow transition could be controlled by adjusting the given pot.

The circuit is basically a simple delay timer which sustains the illumination on the sequencing LEDs for a few moments depending upon the set value of the pot. The stored charge on the capacitor produces this timed delay effect on the LEDs which could be predetermined as per ones own choice.

The speed of the sequencing could be also altered by tweaking the 555 IC 100k pot as per individual choice which this could in turn interfere with the delay transition effect and thus is a matter of some trial and error until the most attractive set up is determined.

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