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[SOLVED] Solution for LED strip fade in/fade out

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1-3-2-4

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I was looking around and I was thinking about doing this.. I have a LED light strip behind my TV anyways From what I hear using a trimmer pot and a capacitor wont work?

I was looking for something to be like 30 secs fade in and 30 sec to fade out..

Right now I'm running the LED strip at 12V at 1A I guess it has maybe 60 LED's that go around the 40" tv.
 

Re: LED fade in/fade out

The best approach for dimming LEDs is to use pulse-width modulation (PWM). PWM supplies full voltage/current to the device, but does so in short bursts. By making these pulses fast enough, they are invisible to the human eye (much like a movie on filmstrip flashes fast enough that you don't see the stripe between the frames... ~30 fps, or 30 Hz).

For a purely analog circuit, use a 555 timer. Use the PWM output signal to drive the gate of an N-channel MOSFET, which is used as a low-side switch on your LED lights. Search this forum for "LED dimmer PWM" and you'll find lots of threads on the related topics. I'd start with this one: https://www.edaboard.com/threads/233880/
 

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Re: LED fade in/fade out

Man I was hoping it was going to be something a little more simple then that.. I do have a 555 here but I can't see why the other way wont work.
 

Re: LED fade in/fade out

1-3-2-4 said:
I was looking around and I was thinking about doing this.. I have a LED light strip behind my TV anyways From what I hear using a trimmer pot and a capacitor wont work?

I was looking for something to be like 30 secs fade in and 30 sec to fade out..

Right now I'm running the LED strip at 12V at 1A I guess it has maybe 60 LED's that go around the 40" tv.
Click to expand...

When you want 30s fade in and fade out?
Allways repeated or after power TV on and off?

How turn leds now? Same time with TV?
How look 12V power adapter?
 

Re: LED fade in/fade out

js said:
When you want 30s fade in and fade out?
Allways repeated or after power TV on and off?

How turn leds now? Same time with TV?
How look 12V power adapter?
Click to expand...

You mean why do I want it 30s?

Right now the LED's are on a switch that I turn on and off.. However fading in and out will give my eyes better time to adjust.
 


Re: LED fade in/fade out

js said:
maybe diode - R -C filter + FET do the job!
similar like:
https://www.electro-tech-online.com...cuit-car-interior-lighting-off-slow-delay.gif
see bellow picture!

When you power ON RC is charged and FET is opened slowly ..... and if you powerd off ... C is disharged slowly!
You must calculate right values of RC and FET selection....
Click to expand...


Hmm I think I have all of that stuff here but I don't think I have a large enough cap.. I tried a 3300uF and it still fades pretty quickly.
 

Re: LED fade in/fade out

1-3-2-4 said:
Man I was hoping it was going to be something a little more simple then that.. I do have a 555 here but I can't see why the other way wont work.
Click to expand...

Simple may work, but a little extra hardware could make the circuit much more configurable. Using the 555 PWM controller, and another 555 as a ramp-generator should do the trick, all in hardware... you could always burn a microcontroller to do it, too :wink:.
 


Re: LED fade in/fade out

Consider that LED output is roughly proportional to
current.

If you use a single supply op amp as feedback from
a current sense resistor (LED cathode to Gnd) in a
noninverting configuration, op amp output driving
(say) a 2N2222 BJT base, collector to +V, emitter
to LED anode, then you will have a voltage controlled
current.

You can drive the noninverting input of the op amp
with a RC network and realize a pretty long time
constant. 1Mohm, 33uF would be a 30sec tau. SPDT
switch (on=VCC, off=0) to drive that network.
 

Re: LED fade in/fade out

I want to say I counted the LED's the other day and I have 154 of them so I don't know how that plays on the current issue.
 

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