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Author Topic: USB powered LEDs that react to music - HELP ?  (Read 1410 times)

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Offline SammYSkywalkerTopic starter

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USB powered LEDs that react to music - HELP ?
« on: July 18, 2011, 01:49:30 PM »
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:
LED music Box
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, please feel free to share. :)

Offline Soeren

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Re: USB powered LEDs that react to music - HELP ?
« Reply #1 on: July 23, 2011, 12:47:31 PM »
Hi,

Please enlighten us about the robotics implication of this.


Okay. So, I want to build something along the lines of this... http://www.instructables.com/id/Music-LED-Light-Box/

Ahh, you wanna make a sound card eliminator   ;)

That "circuit" sure takes the price for stupidity  :o


A hint to keep you a little safer in this world... Never take electronics advice from a guy who states "Since I have no experience in electronics whatsoever, this was [...]"


If anybody has any suggestions, comments or improvements, please feel free to share. :)

It's hard not to improve that "circuit". For starters, at least add a base resistor of 3.3kOhm.

An amplified input would remove the need for going full blast and even the simplest form of AGC would lessen the influence of a varying sound level.
But then you'd need a real circuit and you didn't mention if you are up for that.

As a side note... How are you gonna hear the music when it's plugged in?  My PC mutes the other sound outputs and I'd somehow think all PC's did that (you usually wear headphones to not bother your surroundings).
Regards,
Sren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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