Introduction: Blinking Leds

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:

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.

Step 4: Step 4

Picture of Step 4

Now it’s time to make the P2 connector. You can see that the P2 connector have 3 pins, they are, left channel, right channel and ground. So you have to decide to get the left or right channel and connect with the left pin from the Tip31. Remember that if you connect the P2 using the left channel, if only the right is enabled on the computer, this circuit won’t work. Usually the ground pin is the bigger one, and the other are small and similar. You have to connect the ground from P2 connector to the right pin of the Tip31 (right pin from Tip31 is ground)

Step 5: Step 5

Picture of Step 5
On the other pin from the switcher, you must connect to the ground from Tip31. If the switcher if closing circuit with the Tip31, the leds will only blink if there is any signal coming from the P2 connector, and if it’s in the other direction, the leds will be always ON.

Now it’s time to put everything together in the box, as you can see in this picture, it’s not very organized, but after closing the box, it’ll look much better.

Job's Done! =)

And for more of my DIY projects, please visit my website:
Pasteler0's Tech Stuff


Jakester98 (author)2015-01-07

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!

kiyu60 (author)2012-10-26

can anyone help me make a diagram of this with 63 red LEDs

vishal17 (author)2011-04-18

hi everyone
which transistor can i use other than tip 31?
please answer me fast :)

djbogdy43 (author)vishal172012-05-27

BD135,BD137 and BD139! :D

audio_mod (author)djbogdy432012-06-10

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_mod (author)2012-04-30

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. :)

sin3kveer (author)2012-04-05

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....

whayle (author)2011-10-12

Hey guys if you want free LEDs go here and sign up free:
All you have to do is sign up, earn points by playing games and doing offers, and get your free rewards. It is actually super easy. You also get $2.50 just for signing up. You can also get free transistors and circuit boards.

Epimetheus (author)2010-03-02

 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..

absalam (author)Epimetheus2011-08-25

Try changing the TIP31...i blew mine once and had the similar problem as yours.

TheMrWolf1994 (author)2011-07-19

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

deko69 (author)2009-08-18

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 (author)deko692011-07-03

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 (author)deko692011-04-29

man i have done that before ..... just like you show here , it is working ok ... ;)

pyro-jim (author)deko692009-11-06

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.

Arbitror (author)pyro-jim2010-02-26


Inverters change direct current to alternating current, which is what cold cathode lights need.

SmAsH! (author)Arbitror2010-04-03

They also step it up to something like 500v low A, i did the cc mod at home and it works fine...

yahya2coool (author)2010-03-27

 if tip 31 is not available then which other transistors can b used? plz help 

aroman3 (author)yahya2coool2011-04-29

i am using bd239c i think it is even better :DD

DRodriguez (author)yahya2coool2010-05-03

Here's a great deal on them: 10 for like $3.50 ea.

SmAsH! (author)yahya2coool2010-04-03

Almost any npn transistor will work.

aroman3 (author)2011-04-29
Look my video i have made manyy circuits /w leds and cold cathodes ask me everything in the comments on my channel

chandeepa (author)2011-01-06

cooooool case mod bro.....

Bisjon (author)2010-10-26

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 (author)Bisjon2010-11-26

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

ST4N13Y (author)2010-06-07

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 (author)ST4N13Y2010-08-12

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

funnyman953 (author)2010-07-11

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

sharkawien (author)2009-03-13

where is the P2 connected??

deko69 (author)sharkawien2009-08-18

to music output from your computer,ipod etc

bmxlive (author)deko692010-06-15

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

kishansukumar (author)2008-07-16

wud a tip32 work insted of a tip31? does it make a diffrence?

Algag (author)kishansukumar2010-05-22

 tip32 is pnp not npn

daystoolate (author)2008-10-06

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?

Algag (author)aussiecowslip2010-05-22

 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

pyro-jim (author)daystoolate2009-11-06

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

bmxlive (author)daystoolate2009-08-04

Hi, wich transistor would i use if i want the circuit with 12Volts LEDs

xmastex (author)daystoolate2008-12-21

hey man, is the RED wire the positive and the BLACK the negative one?

daystoolate (author)xmastex2008-12-21


g0tmk (author)2010-04-07

Hi, I have a bit of a problem with mine.  I set mine up as kind of a pass-through, you plug a jack into the box and the box into speakers.  When I plug speakers into it though, it stops strobing.  How do I manage to get enough power through the transistor to strobe while it is still hooked to speakers?   I am using a 2n7000.  Thanks!

Algag (author)g0tmk2010-05-22

 this is an addition to my comment carful though cause it would need a power souce too

Algag (author)g0tmk2010-05-22

 you could probably just add an amplifier circuit (two bucks)

hape0 (author)2010-04-24

if i want to plug it into the electric power of a house, what i have to change??

DRodriguez (author)hape02010-05-03

You would need to use a 'wall wart' rated for twelve volts, cut off the plug on the end, find the polarity with your multimeter, and connect it that way.

anura92 (author)2010-04-07

Hey... i tried it and it only works when i set the volume knob of my speaker(altec lansing headphone jack) to the highest.... the led i am using was salvaged from a pc fan...
So do i have to change the transistor or change my led to the right voltage ones? Psl help me :( 

yahya2coool (author)2010-03-28

 can i use d313 other than tip 31

laptaper (author)2010-03-10

help me please.. cant get my light to flash.. im using tip31c.. please help me with this..

Soksume (author)2009-10-02

hmm I've hooked this system up once before with a couple ultra bright blue LEDs in some clear globe speakers it was sweet but i was wondering if it would work with a cathode in place of the leds?

Arbitror (author)Soksume2010-02-26

You can, just make sure it is getting the right amount of AC voltage.

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