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Trying to improve an LED strip circuit thats activated by music

post #1 of 8
Thread Starter 
Hoping for some help from electronics pros around here. I basically found the following circuit that uses a transistor connected to the LEDs and a headphone jack to switch the circuit on and off with music output:



I am also using the LED strips described in this thread http://www.overclock.net/t/1246458/easy-cheap-led-case-lighting, which I believe have resistors in series for LEDs so I am ignoring the 200ohm resistor in the circuit.

So apart from the LEDs I finished hooking up the circuit as is, and It looks pretty great so far, but theres a few things I would like to improve. I am pretty good with a soldering iron but my knowledge of creating and improving circuits is 0 tongue.gif

- Right now even at max volume the strip doesn't get to its brightest state (comparing next to an always ON strip). I believe adding a capacitor somewhere on the headphone input would help with this ?

- I am currently using multiple LED strips in parrallel (each goes out to a different location in my case, and am not sure if this is safe or correct). I simply connect the + wire from each strip together and those go to the + end of the 4 pin molex (single 12v rail), and the ground from all the strips meets and is connected as shown in the circuit to the center pin of the transistor. Is this safe and will it be ok for prolonged operation of the 40-50 LEDs in this circuit?
Edited by zerocraft - 12/11/12 at 7:53am
post #2 of 8
I'd consider replacing the 20K ohm resistor with a potentiometer with a wider range. This will allow you to dial in the "sensitivity" to sound input. That, and make sure the output you are picking audio off of is turned to maximum volume.

You can use as many strips of LEDs as you like, up to the rated current capacity of the transistor. You may also want to mount that transistor to a heatsink to help keep it cool. It'll be working hard to switch the lights on and off.

The 220 Ohm resistor is to current limit your LEDs. If you are connecting multiple strips in parallel, make each parallel set have it's own resistor. Also, I'd consider splitting up your parallel strips into several sets, each with it's own transistor. With a potentiometer, you can adjust each circuit to begin lighting at a different level, kind of giving a VU meter effect.

Everything is perfectly safe as long as you don't feed any of the components more voltage or current then they're rated for. LEDs have a minimum voltage to turn on. They have a maximum voltage at which they quickly lose lifespan. Keeping them undervolted slightly will make them run happily for practically forever. Transistors will fry if you try to hook up too much stuff (draw too much current through them). Check the specifications sheet for your transistor (just Google the part number) and make sure you keep it under the limit.
post #3 of 8
Thread Starter 
Quote:
Originally Posted by TLHarrell View Post

I'd consider replacing the 20K ohm resistor with a potentiometer with a wider range. This will allow you to dial in the "sensitivity" to sound input. That, and make sure the output you are picking audio off of is turned to maximum volume.
You can use as many strips of LEDs as you like, up to the rated current capacity of the transistor. You may also want to mount that transistor to a heatsink to help keep it cool. It'll be working hard to switch the lights on and off.
The 220 Ohm resistor is to current limit your LEDs. If you are connecting multiple strips in parallel, make each parallel set have it's own resistor. Also, I'd consider splitting up your parallel strips into several sets, each with it's own transistor. With a potentiometer, you can adjust each circuit to begin lighting at a different level, kind of giving a VU meter effect.
Everything is perfectly safe as long as you don't feed any of the components more voltage or current then they're rated for. LEDs have a minimum voltage to turn on. They have a maximum voltage at which they quickly lose lifespan. Keeping them undervolted slightly will make them run happily for practically forever. Transistors will fry if you try to hook up too much stuff (draw too much current through them). Check the specifications sheet for your transistor (just Google the part number) and make sure you keep it under the limit.

Thanks for the detailed reply. I do have the volume maxed out in windows for the sound card output (it splits from there to the LED strips and my headphone amp where I lower the volume to my needs). Even maxed out and WITHOUT the 20k ohm resistor in place, I dont see the LEDs maxing out in brightness, so not sure if lower resistances will help? The TIP31 came with a heatsink built in as pictured and I did feel it multiple times and it was cold to the touch even after 20-30 minutes of playing, so I don't think heat is an immediate concern. Initially I kind of just want to make do with a single transistor and see if that holds up, it only cost 1 dollar so replacing it wont be a pain tongue.gif

I am only using the strips in parallel to avoid too much wiring (case is getting messy with cables arleady), would doing it in series reduce the current load? The transistor is rated for 3A(http://www.radioshack.com/product/index.jsp?productId=2062610), ill try and figure out what the LEDs are going to pull. Just need to pick up my old physics books and re-learn this stuff haha.
Edited by zerocraft - 12/11/12 at 4:00pm
post #4 of 8
I would recommend checking the peak voltage on the audio. You are probably losing current needed to operate the transistor by splitting the signal.

Here's the part datasheet if you want to drown yourself in fiddly details. http://html.alldatasheet.com/html-pdf/20165/POINN/TIP31/124/1/TIP31.html
post #5 of 8
I may be wrong but: Whenever I have put the LEDs in parallel I experienced dimming. Just my two cents. tongue.gif
post #6 of 8
Here's a quick little question... did you also hook up the diode (identified as a 1N914)? Since an audio signal is a waveform, the input into your circuit can fluctuate between + and -. The diode inverts the - part of the waveform. Instead of this ^v^v^v^v^v^v you get this ^^^^^^^^. If you're not using the diode, half the waveform is pulling negative and canceling out your switching through the transistor.

Also, for anybody following along, here's a great site for calculating resistors for LEDs... http://ledcalc.com/#calc

And I've never had dimming of LEDs when hooking them up either in series or in parallel. In fact, here's a series/parallel setup I did for a blue panel light with NO resistors... works perfect. The LEDs illuminate perfectly evenly, none dim. And that's all hand soldered...

post #7 of 8
Thread Starter 
Quote:
Originally Posted by TLHarrell View Post

Here's a quick little question... did you also hook up the diode (identified as a 1N914)? Since an audio signal is a waveform, the input into your circuit can fluctuate between + and -. The diode inverts the - part of the waveform. Instead of this ^v^v^v^v^v^v you get this ^^^^^^^^. If you're not using the diode, half the waveform is pulling negative and canceling out your switching through the transistor.
Also, for anybody following along, here's a great site for calculating resistors for LEDs... http://ledcalc.com/#calc
And I've never had dimming of LEDs when hooking them up either in series or in parallel. In fact, here's a series/parallel setup I did for a blue panel light with NO resistors... works perfect. The LEDs illuminate perfectly evenly, none dim. And that's all hand soldered...


Ok Ill check out the diode this week, will also pick up a DMM so I can check whats happening with the voltages. It's definitely not due to using parallel because like I said if I remove the transistor from the equation they are fully bright. Its just that when they are music activated they never get as bright. 1 thing a friend suggested was that I try and invert the circuit so that the music signal dimms the LED instead of lighting them. Do you have any idea how I could go about setting that up?
Edited by zerocraft - 12/19/12 at 2:42pm
post #8 of 8
Theoretically, flipping the diode around should have that effect. Worth a try. Otherwise you'll probably be getting into a chip with some X/OR logic to it.

As far as a multimeter goes, I would recommend an analog meter if you can find one/afford one. If not, no big deal. Just that when you're dealing with voltages that vary rapidly, circuits that are intermittent., or that pulse only very slightly, a digital LCD meter won't show the tiny fluctuations. Their refresh rate for the display is usually 1/4 second. If you get a tiny blip with one, it won't register. With an analog needle, you'll at least see the needle quiver. My dad was pretty thoughtful when he purchased an analog meter for me as a Christmas present when I was a teen. I still use it.
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