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Fading LED

Hi there,

I'm trying to figure out if I can design a circut that would cause a LED to fade in and out. I'm pretty sure that LED's are only on or off, but my computer has a LED that "breathes" while it's sleeping.

Can someone please tell me if this is possible?

Thanks,

m7n

Reply to
m7n
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Sure. If you vary the current through a LED its brightness will vary.

Now you need to find a circuit to vary the current. ;)

If you want it to be logically controlled I guess you could do it with a cheap DAC followed by a buffer ... You'll need a resistor in series with your diode to limit the current.

Stephen

Reply to
Stephen Boulet

Couldn't it also be done by varying the switch on/off time (frequency) to fool the eye into seeing fade in/out?

If you switch a LED on and off rapidly, with more on than off, wouldn't the eye see it as lit solid? Start reversing the on/off to more off and it would "appear" to dim...

???

Just an idea...

Jack

Reply to
Rather Play Pinball

Thanks for all the info... I appreciate it.

Reply to
Michael Davie

Thank you for that link... looks like I have a lot of fun ahead of me.

m
Reply to
Michael Davie

Heres one:

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Adam

Reply to
Adam Aglionby

Yes, this is called PWM - "pulse-width modulation."

Yes it is possible. LED's are not just on-off devices. They are kinda like a lightbulb. If your flashlight batteries wear out, the light gets dim - same with a LED. If you use less power, the LED will be less bright.

In the case of your PC, there is a little circuit in there to vary the power to the LED, making it appear to "breathe."

May I recommend you start your journey here:

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-M

Reply to
Mark Jones

PWM is often used for LED brightness control. It's quite easy to implement with most MCUs.

Leon

Reply to
Leon Heller

I read in sci.electronics.design that m7n wrote (in ) about 'Fading LED', on Mon, 20 Dec

2004:

Yes. You must use current-drive. Start with 12 V and 1.2 kohms in series with your red, green or yellow diode. Now turn the 12 V down slowly. For blue or white, you may need to start with 15 V.

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Reply to
John Woodgate

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