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Creating a fading Effect!

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Terminator

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Hi there

I'm new to this forum and am in need of some help. I really would like to know how to make LEDs fade on and off instead of instantly coming on and off. Here is a video of what I mean below. If any of you are familiar with Star Trek, I'm talking about the gradual activation of the deflector. For those of you who are not familiar with the "deflector", the effect I seek can be seen at 00:31 of the 02:18 video. Notice how the light gradually gets brighter as it activates. Can anyone tell me how to achieve this effect?

https://youtube.com/watch?v=G_-SSu4CTXY

Any help will be greatly appreciated!
 
A resistor can slowly charge a capacitor. An emitter-follower transistor is fed the rising voltage which applies a rising current to an LED.
But I think you don't know what I am talking about.
 
To boldly go . . .

Hi Audioguru,

audioguru said:
But I think you don't know what I am talking about.

You're probably right but maybe he can find someone like
Krumlink to build it for him.

on1aag.
 

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Last edited:
At fist I also thought of using an opamp as an integrator. Then changed it to a simple RC with an emitter-follower.
 
Hi Audioguru,

audioguru said:
At fist I also thought of using an opamp as an integrator. Then changed it to a simple RC with an emitter-follower.

Does this mean that I have to start all over again ? :D

on1aag.
 
on1aag said:
Hi Audioguru,

Does this mean that I have to start all over again ? :D
Your circuit has a very nice linear ramp. But it uses a lot of parts.
Just a resistor charging a capacitor and then an emitter-follower transistor sensing the capacitor's charging voltage can slowly fade-in an LED. A diode can discharge the capacitor when the power is turned off because he didn't say he wants the LED to slowly fade down.
 
I think you could get the effect using a 555 timer like here:



Or there is another circuit that slowly fades up and down here:

https://www.redcircuits.com/Page51.htm

If you need more control over exactly how and when it fades then a small microcontroller using pwm, time delays etc. may be required.
 
The RED Circuits circuit uses an opamp as an integrator so it slowly brightens and fades the LED.
 
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