Author Topic: Isolating a colour changing LED  (Read 1244 times)

GermanCdn

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Isolating a colour changing LED
« on: January 19, 2012, 08:16:11 AM »
In the vein of fashion over function, I've come across a little problem, wondering if anyone here can help out.

I've used multicolour LEDS in a couple of builds, only because they look cool, especially in trems with the LED flashing in conjunction with the speed.

Problem is, everytime the diode changes colour, there is an audible rising squeal until the LED reaches the next stable colour (a little problem in modulation pedals, a big problem in distortion pedals).

Anyway of isolating the LED so that it doesn't squeal?

Thanks,

Curtis
The only known cure in the world for GAS is death.  That's my story, and I'm sticking to it.

Scruffie

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Re: Isolating a colour changing LED
« Reply #1 on: January 19, 2012, 08:35:05 AM »
I remember Dr.Scientist had an issue with this where he had to recall some pedals, apparently it can vary with brand (i.e. he didn't experience it with some so didn't notice the issue crop up when he bought a new lot of LEDs) so you might try different types.

Otherwise I can only think of using shielded wire and maybe adding seperate power filtering for the LED, it's the oscillator in the LED bleeding in to the circuit I guess.
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stecykmi

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Re: Isolating a colour changing LED
« Reply #2 on: January 22, 2012, 10:18:53 AM »
there may not be a good, easy way to stop the noise and that particular brand of LED may have to be removed.

you can try capacitor decoupling the LED more, maybe even a choke inductor if you happen to have some. use some big electros, probably like 100uF, you'll want to filter off as much switching from the power supply as possible.

interestingly, power switching of this type represents sort of the "worst case" for power supplies because of the step function switching, meaning power consumption starts at high, jumps to zero (during the color switching cycle), then back up to high again. This is hard to filter out because it has very high harmonics.

whatever you do, i highly recommend refraining from daisy chaining the power supply because all that switching junk is propagating all the way down the line.

madbean

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Re: Isolating a colour changing LED
« Reply #3 on: January 22, 2012, 10:30:59 AM »
Maybe use a BJT with slow turn on to supply the LED and then use a cap to set the time? I'm kinda making this up.
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GermanCdn

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Re: Isolating a colour changing LED
« Reply #4 on: January 23, 2012, 02:03:22 AM »
Thanks to all for the input, I think the consensus is to go with the five cent solution and change the LED.

Thanks again,

Curtis
The only known cure in the world for GAS is death.  That's my story, and I'm sticking to it.

nzCdog

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Re: Isolating a colour changing LED
« Reply #5 on: January 27, 2012, 01:17:44 PM »
you can try capacitor decoupling the LED

+1
I put a colour changing LED in my poindexter (an ultra high gain circuit).  Used a 220uF cap in parallel soldered directly to the diode... and no noise at all.  I can't say for sure which brand the LED was however, as I pulled it from one of my kids broken toys ;D