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Wagge 2nd January 2012 12:12 PM

Troubleshooting a music powered LED light box.
Hi, I recently build a LED light box with inspiration from motadacruz over at instructables (Music LED Light Box). But I of course had to take it one step further, so I built a plexibox three times the size with 54 led in three different colors, made split audio cable so the sound could pass through and still make the leds flash. I also integrated a three-way-crossover to be able to make the red color flash to higher frequencies, the green to midrange and the blue to the bass. Or at least that was my original thought, I sketched up a circuit layout

and built it. The only problem know is that the crossover doesn't seem to be working as planned because I realized I had calculated the crossover with the wrong impedance over the LEDs (used 4 Ohm for all color circuit for some reason -.-). I corrected my error and are know pretty sure the impedance should be 35, 33.5 and 33.5 Ohm for the red, green and blue circuit. I now can redesign the crossover and hopefully get it to work, but the problem is I'm not certain that it will work and I don't want to spend money for no use. So now to the big question, have I jumped to the right conclusion when I said that the crossover is the problem or doesn't the idea work at all the way I planned?

I also got one other problem. After forwarding the audio trough the box (via the split) I only get mono sound, I guess that got someting to do with my soldering but I have to check with you guys if you got any other idea? The split is a female to female to LED-circuit and is not shown in the circuit layout above.

dangus 4th January 2012 02:26 AM

There's a certain amount of stuff at Instructibles that isn't well-designed, and that would be one of them. Notice the critical comments.

Sound to light things are tricky because music has a huge dynamic range, while LEDs go from off to on with a small change in voltage. You're better off using a bar-graph LED driver chip, since some of them have logarithmic steps. Some devices use a compressor or AGC circuit. A simpler and more elegant option might be to borrow the "beat LED" circuit from a DJ mixer.

Search diyaudio for "color organ" and you should find something.

Wagge 5th January 2012 11:56 PM

the new theory
Thanks for the great reply dangus. I think I found what I was looking for over at ( the only problem is that I need to hook up some more leds per chanel. I'm no expert on electrical cicuits put even I realise that I need to make some changes to this part of the circuit.
Also if I just start adding leds in serie I will soon run out of voltage and if I start adding parallell circuits the collector current will keep rising until the transistor says stop (200 mA) or the powersuply run out of juice. I'm thinking that if remove the resistor and connect 4 blue leds on serie I will get a voltagedrop of 12-13.4V over the leds (3-3.4V per led) and every led need 20 mA so the collector current will rise 20 mA for every parallell led-cicuit I add until the power source runs out of juice. Wich should be, according to my doubtfull calculation, at 1A/3=0.333...A (since the power source provides 1A of max current divided at 3 chanels). This I don't want to happen since the maximum collector current the transistor can take is 200 mA. So theoretically I should be able to add 10 parallell led-circuits with 4 blue leds in serie. That will never be the case since I won't be needing more then 20 leds of each color, so 5 parallell led-circuits it is. I can do exactly the same for the green leds since they got the same voltage drop per led. But for the red leds I need to connect 6 leds in serie since the voltage drop per led is only 2-2.1V, and hence to get roughly the same amount of red leds I just need 3 parallell circuits. Did anyone follow? If you did, did I get anything right at all? Will this work?

I get all my info about the leds from the datasheet provided by the retailer on ebay (eBay - New & used electronics, cars, apparel, collectibles, sporting goods & more at low prices).

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