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My first project——LED strip flash to music
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Amyni02



Joined: Oct 10, 2016
Posts: 1
Location: London

PostPosted: Tue Oct 11, 2016 1:26 am    Post subject: My first project——LED strip flash to music
Subject description: My LEDs don't blink at full brightness only ~60-70% of what the LEDs light up hooked to 12v directly
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This is my first electronics project, I'm really new at this and struggling to understand everything, just learned so solder a few days ago.. Smile

I'm using this circuit as my starting point
Posted Image, might have been reduced in size. Click Image to view fullscreen.
I'm using a 12V power supply, and a 12V LED strip. Instead of TIP31 I have TIP35 (guys at my local electronics shop said that in my case they don't really make a difference..)

I hooked up the schematic but I had problems with audio output splitting, not enough was passed to the TIP35, so I added an amp circuit with LM386 something like this
Posted Image, might have been reduced in size. Click Image to view fullscreen.
Having read that powering the LM386 with 12V results in heat and stuff, I wanted to be safe(er) and I'm passing 5V to it with a TO220 regulator that drops 12v to 5v. I'm not using the Gain pins, because I noticed that it doesn't influence brightness, only the "sensitivity", and the LEDs would flash to the smallest sounds (which is not what I want). So I'm passing ~70% volume and amplifying that, so my LEDs react to more lower sounds.

The problem I am facing is that the LEDs do not blink at full brightness. That was the problem I had without having the amp in, I though that might help but it doesn't. The LEDs I believe never reach ~60-70% of brightness compared to just passing 12v and having them on. I thought it might have to do with the length of the strip (5 meters), I cut it down to just a 9 LED length strip - same result with low brightness.

I've stumbled across this pdf that shows different pins for input/ground/output. I've hooked up in this order: input/output/ground while this pdf ground/input/output. Could that have anything to do with it?..

I'm sorry for the newb questions - I am one..

Edit: Here is how I've connected everything (sorry if it's messy..)

Oops I messed up the colors of the output to the LEDs, they should be switched (blue-red, red-blue)
Posted Image, might have been reduced in size. Click Image to view fullscreen.
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bubzy



Joined: Oct 27, 2010
Posts: 594
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PostPosted: Tue Oct 11, 2016 8:15 am    Post subject: Reply with quote  Mark this post and the followings unread

you could use an lm3915 circuit instead, this way you could also get a VU style out of those LED's

maybe im not quite understanding but why is there no resistor in this circuit?
i think from previous experience, running led's in series isn't a wonderful idea for the brightness.

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PHOBoS



Joined: Jan 14, 2010
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PostPosted: Tue Oct 11, 2016 9:05 am    Post subject: Reply with quote  Mark this post and the followings unread

bubzy wrote:
maybe im not quite understanding but why is there no resistor in this circuit?
i think from previous experience, running led's in series isn't a wonderful idea for the brightness.

If I understand correct it is a LED strip and those already have current limiting resistors. Running LEDs in series is actually pretty useful
if you have a bunch. It keeps the current down instead of wasting it in heat by using a lot of resistors. Of course the voltage has to be high
enough.

As for the circuit itself, simply using a transistor will not work very well. They are great for switching LEDs (FETs are even more useful here)
or providing current, but audio signals usually are rather dynamic and you might only get full brightness on some short peaks. If you really want to
have music controlled LEDs you first have to convert the audio to a suitable signal. You can take a look at this thread where I posted some info.

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