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USB powered LEDs that react to music - HELP ?

 
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SammYSkywalker
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Joined: 18 Jul 2011
Posts: 1
Location: New Zealand

PostPosted: Mon Jul 18, 2011 2:10 pm    Post subject: USB powered LEDs that react to music - HELP ? Reply with quote

Okay. So, I want to build something along the lines of this... http://www.instructables.com/id/Music-LED-Light-Box/
In that Instructable, the 6 LEDs are wired in series. I want to be able to wire them in parallel and replace the 12V DC adapter with a USB connector so that the box may be powered via my laptop's USB port. This way I won't need another cable going off to a power point in the wall and things will be nice and tidy around my laptop.

Now, I know that the USB 2.0 ports (which is what my laptop has) are 5V @ 500mA.

The specifications for the LEDs I have are:

Emitted Colour : OCEAN BLUE
Size (mm) : 5mm T1 3/4
Lens Colour : Water Clear
Peak Wave Length (nm) : 465 ~ 470
Forward Voltage (V) : 3.2 ~ 3.8
Reverse Current (uA) : <=30
Luminous Intensity Typ Iv (mcd) : Average in 6000
Life Rating : 100,000 Hours
Viewing Angle : 10
Absolute Maximum Ratings (Ta=25C)
Max Power Dissipation : 80mw
Max Continuous Forward Current : 30mA
Max Peak Forward Current : 75mA
Reverse Voltage : 5~6V
Lead Soldering Temperature : 240C (<5Sec)
Operating Temperature Range : -25C ~ +85C
Preservative Temperature Range : -30C ~ +100C

So that's pretty much 6000MCD 3.8V LEDs @ 30mA, correct? And this guy here: http://www.youtube.com/watch?v=svWz3xQkkx4&feature=related has his version of the LED music light box USB powered. Would I be correct in saying that this USB powered version still needs the 3.5mm connection to the audio output, just as the 12V DC powered version does?

Seeing as my LEDs are 3.8V, I will need a resistor that will drop the 5V power supply down to 3.8V, correct? If this is correct, this resistor calculator http://led.linear1.org/1led.wiz?VS=5;VF=3.8;ID=30 tells me I need a 47 ohm resistor.

This calculator http://led.linear1.org/led.wiz when I put in my values 5V source voltage, 3.8V diode forward voltage, 30mA forward current and 6 LEDs in my parallel circuit, comes up with this:
+----|>|---/\/\/----+ R = 47 ohms
+----|>|---/\/\/----+ R = 47 ohms
+----|>|---/\/\/----+ R = 47 ohms
+----|>|---/\/\/----+ R = 47 ohms
+----|>|---/\/\/----+ R = 47 ohms
+----|>|---/\/\/----+ R = 47 ohms

So, in other words, I chuck the 12V DC adapter out and hook it up to a USB connector instead, stick a 47 ohm resistor in before each LED, then hook up the 6 LEDs in parallel and it goes. If any of what I said was correct, it should work, right ?

If anybody has any suggestions, comments or improvements, advice, please feel free to share! Smile
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joewatts
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Joined: 24 Jan 2012
Posts: 1

PostPosted: Tue Jan 24, 2012 9:58 am    Post subject: Reply with quote

Quote:
So that's pretty much 6000MCD 3.8V LEDs @ 30mA, correct? And this guy here: http://www.youtube.com/watch?v=svWz3xQkkx4&feature=related has his version of the LED music light box USB powered. Would I be correct in saying that this USB powered version still needs the 3.5mm connection to the audio output, just as the 12V DC powered version does?


You need a controller chip that is programmed to change the music to the beat. You can buy smallish controllers on ebay where you might be able to take the circuit board out. Ether way you will need an audio input ether a line in or a small microphone.


Quote:
Seeing as my LEDs are 3.8V, I will need a resistor that will drop the 5V power supply down to 3.8V, correct? If this is correct, this resistor calculator http://led.linear1.org/1led.wiz?VS=5;VF=3.8;ID=30 tells me I need a 47 ohm resistor.


Yes you need to drop the voltage or you will damage the LED's
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