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Basic Electronics » Speakers with LEDs that light with the music

November 14, 2011
by Azh321
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Hi all, I am a programmer and still very new to electronics, so I am attempting a project that doesnt involve an MCU at all, just some basic electronics. I have disassembled a few pairs of computer speakers, which I want to run together, powered from a wall socket preferably, but I want to wire a bunch of LEDs with the speakers and have them light up with the music.

A friend of mine did this, based on this: http://www.instructables.com/id/Music-LED-Light-Box/step6/Building-the-circuit/ but it has a few problems. The lights are very dim and it only works when he turns the music up extremely loud. So how could I do this, hopefully with the supplies from my 3 nerdkits + the extra LEDs I bought? The project I listed is calling for a TIP31c resistor which I do not have.

Any help? I wanna jam to my music with lights! Thanks

November 14, 2011
by Azh321
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Typo, TIP31C transistor, not resistor.

November 14, 2011
by mongo
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I did a similar thing back in high school. Color organs were very popular in the 1970's and there were good ones as well as bad. The better ones were wired to the sound system so the room noise would not have an effect on the results.

What I did was took a traffic barricade yellow light. (You know, those yellow lights you find at construction sites). I removed most of the guts and installed a 12v transformer and ran the light from it, through an SCR. Between the gate and cathode of the SCR, I put a small audio transformer and a small electrolytic capacitor (to de-couple the circuit) and connected the audio transformer to my sound system, again capacitive coupling so it wouldn't throw off the speaker impedance too much. The AC signal of sound would turn on the SCR at the positive swing of the signal and off on the negative swing. The louder the signal, the brighter the light would blink.

It was only a single channel but the effect was really cool. By adding an L-pad (basically a speaker volume control) to the circuit, I could adjust the sensitivity and even at low volumes it worked nicely.

November 14, 2011
by mongo
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BY the way, TIP31C can be swapped for just about any other NPN power transistor. It is a 50 HFE transistor so just about anything with a higher number should work for your circuit. Try the 2N5194, which has a higher voltage and similar HFE (25 to 100, typically around 100) or you can go with the 2N3055. Though it's the larger TO-3 case, it has similar ratings. (but a lot higher current capacity - 15 Amps) It has HFE around 10 to 75, typically around 60.

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