Picture of Blinking leds
Listening to music on my pc (proudly using WINAMP), I was wondering how would be to have some leds blinking with the sound that came out from the P2 connector, so I decided to make a simple circuit to do that. It worked pretty fine, so I decided to write a HowTo telling step-by-step how to do it. Hope you enjoy it!

If you want to see more of my DIY projects, please, visit my website:
Daniel Spillere Andrade Website

Material and Equipment:

1. 4 LEDs (any collor)
2. P2 plug
3. 2 position switch
4. TIP31 component
5. Box to put all the stuff (if you want)
6. Soldering iron and accessories
7. Cable

Video of the final project:

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Step 1: Step 1

Picture of Step 1
This project will work this way, you connect 4 leds in the +12V from your computer, they are soldered to a 2 position switch that will connect to a component called TIP31, this component gets the intensity transmitted by the P2 connector, and with that, makes the leds blink with the music.

You can follow this scheme:

Step 2: Step 2

Picture of step 2
For this project, I decided to install everything inside a small black box I had here, so I made 6 holes on it. Four in the top for leds and one in each side for the switcher and cables. You can follow by the pictures:

Step 3: Step 3

Picture of step 3
With the box ready, its time to connect everything. I started with the leds, soldering one small cable connecting each one, so would be easier to arrange them inside the box after.

After connecting all leds, you must connect the cable coming from the leds to the center pin of the switcher. One side of the switcher goes to the middle pin of the Tip31 component, and the other one goes to ground cable.
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Jakester982 months ago
Would I be able to hook up a parallel circuit of 50 LEDs to this? Still 12 volts. If not, what part should I use instead? Thanks!
kiyu602 years ago
can anyone help me make a diagram of this with 63 red LEDs
vishal173 years ago
hi everyone
which transistor can i use other than tip 31?
please answer me fast :)
BD135,BD137 and BD139! :D
Thanks, i found one of those and the output on the emitter is 5v as opposed to 100v (?) according to the data sheet. Not sure what that means but there is logic there. I'll try, thanks :)

Also in another place i saw about putting a diode on the live input of the audio input. Apparently it will protect positive voltages beign fed back into a soundcard. Any ideas on that one? Which diode?

Thakns, hehe.
audio_mod2 years ago
Sorry, can't help anyone below; i am a noob.

I made this and it works - so thanks for an entertaining weekend, but today i am noticing feedback through the speakers when the led are at their max. Any ideas? A bad ground somewhere?
I am using a headphone splitter and i am powering 12 leds from a 12v supply. I put the extra led's in parallel; i figured the power pack was fine, didn't think about the tip31. Am going to blow myself up or worse my speakers? Thanks if ya can help. Alternatively what would i need to put in the circuit to prevent feedback up the P2 connector. :)
sin3kveer2 years ago
Hello, I want add 11 White leds in circuit for blink.... tell which transistor i have to use. i am 32 DC power suppy. please answer fast....
whayle3 years ago
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Epimetheus5 years ago
 Hey guys having a little bit of trouble here. I had this wired up temporarily last week and it worked great! I went to solder it all together today with more LEDs and it didn't work. It would switch on but when I flipped it to the other side nothing happened. I checked the wiring about four times and found nothing wrong, but I went to measure the P2 connection and it wasn't putting out any voltage. Yes it was plugged in, the volume was up, the multimeter was functioning properly and set to DC -- minimal to no voltage on the wires, sound on/off doesn't affect voltage. So I go to cut up another 3.5mm cable, same thing. But when I put the bare wires on the jack of headphones, the sound kicks in? This is not making any sense to me! I'm so lost on this one guys..
Try changing the TIP31...i blew mine once and had the similar problem as yours.
Can I wire together both wires from right and left speaker in one wire to the transistor? Will it be then stronger current through the tip31 and later through the LED's, cause i need a liitle bit stronger current cause my LED's are not blinkinkg so bright..thanx in advice
deko695 years ago
Hi! I did this mod and it's great. but I want to improve it a little more. I would like to hook up a cold cathode instead of these four leds for more light but the cathode isn't responding to music(won't light up). the cathode requires 12V and the input is 12V (same as leds) but I'm afraid that the current which is flowing trough tip31 isn't enough to light up the cathode Am I right? or what am I doing worong? Is there a way to add other component to make it work? I connected it to the circuit before inverter. should it be after inverter? but I'm afraitd if it won't damage the cathode when I do it that way. please take a look at the picture. any help appreciated
Rhamkota deko693 years ago
Most likely the cold cathode can't respond fast enough to the current change, it most likely requires a quarter of a second to warm up, same with with the inverter
aroman3 deko693 years ago
man i have done that before ..... just like you show here , it is working ok ... ;)
pyro-jim deko695 years ago
what is the inverter for? If the cathode take 12v and you are using 12v then why do you need an inverter? Do you mean that the inverter allows the cathode to use 12v? Otherwise I doubt it should be there.

Inverters change direct current to alternating current, which is what cold cathode lights need.
SmAsH! Arbitror5 years ago
They also step it up to something like 500v low A, i did the cc mod at home and it works fine...
yahya2coool5 years ago
 if tip 31 is not available then which other transistors can b used? plz help 
i am using bd239c i think it is even better :DD
Here's a great deal on them: 10 for like $3.50 ea.
Almost any npn transistor will work.
aroman33 years ago
Look my video i have made manyy circuits /w leds and cold cathodes ask me everything in the comments on my channel
chandeepa4 years ago
cooooool case mod bro.....
Bisjon4 years ago
Hi, I was just wondering what "P2" is. I cut the wire from my ipod headphones, but I'm guessing that isn't it because it doesn't work.
zack247 Bisjon4 years ago
P2 is a power connector, the plug from your ipods headphones inputs the music into the leds.

look for it (it doesn't have to say "P2" on it. any regular power connector will work) coming out of your power supply
ST4N13Y4 years ago
could i use TIP33 ???? ....and....what i need to change in this scheme if i want to ude 9volt battery ??? thank you very much
Algag ST4N13Y4 years ago
add a resistor to the leds or take off an led because they are wired as suck there is a 3v drop (they are 3v each) across each LED so four is the max it could hold BUT if you used 1.5v leds and a 9v battery you could put on 6 leds in that pattern
funnyman9534 years ago
instead of a 3.5 mm jack can i put a mini micrphone instead cause i will connect it to my power supply's molex connector and will i need a resister if i do use my power supply's molex connector
sharkawien6 years ago
where is the P2 connected??
to music output from your computer,ipod etc
bmxlive deko694 years ago
i set to max the master volumen & wave level on audio pc control then i plug my p2 to my computer output but the signal in too weak to turn on the led, i plug an earphone and it was working... So i was wondering if the signal of the pc isn´t strong enough to make my circuit works... please help me
wud a tip32 work insted of a tip31? does it make a diffrence?
 tip32 is pnp not npn
daystoolate6 years ago
this wiring diagram sucks. The way you have it drawn makes no sense as there are 4 negative leads coming off of the 12v supply. Your switch will not work in this diagram because either way that you flip it, there will be a ground connection. If you flip the switch toward the transistor, you may be able to get this thing to work. But you have a ground connection on BOTH SIDES of this switch. Unless your goal her is to turn off the P2 input and leave the LEDS on solid, then the bottom ground on this switch is not needed. Here is a wiring diagram that is more accurate than this one.
what does the X mean?
 its unused in the diagram from he instructables maker(i like that one better) he makes it so you can leave the leds on solid or make them blink
I admit it isn't done very well but what you are saying is wrong. The SPDT switch allows the LED's to either flash to music or be on solid. The bottom ground connection is needed so that when in the permanently on mode the circuit is completed
Hi, wich transistor would i use if i want the circuit with 12Volts LEDs
hey man, is the RED wire the positive and the BLACK the negative one?
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