View Full Version : DIY Blinking LED's

12-09-2008, 11:01 AM
This tutorial is the work of Daniel Andrade and copied here with his permsission. For more great projects visit http://www.danielandrade.net

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!

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


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:

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:

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.

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)


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 is done!!


I’ve recorded one video with my first test doing this blinking leds, you can find here (http://www.ovelha.org/pasteler0/files/led-blinking.mpg).
Obs: In this video, I made just with one led to see if it would really work.

You can download the video of the final job HERE (http://ovelha.org/pasteler0/files/blinking-leds-final.avi).


I dont know if I was clear enought in this HowTo, I will re-check this sometime.
If you liked this, have any correction or advice, please leave a comment!
And would be great too if you could suport me by clicking on the ads on the site.
Thanks for reading!

This tutorial is the work of Daniel Andrade and copied here with his permsission. For more great projects visit http://www.danielandrade.net

12-09-2008, 12:28 PM
thats neat, I may just have to make one :up:

12-17-2008, 05:11 PM
MUST MAKE one!!!!!!!

12-19-2008, 01:08 AM
Nice Circuit!

One small thing you could do would be replace the TIP31 with an opto-relay that way if something went wrong your sound card would be protected. With this one if the TIP31 shorts you may damage your sound card.

Other variations could include a low pass filter on the Audio line, this way the LEDs only light when the bass hits. Make two for a variable light show!!

This circuit could be the basis for several very cool light effects, Very cool!!
Thanks for sharing it!!!

12-20-2008, 11:47 PM
I made this, works great. I changed the circuit slightly (no switch, different transistor, battery not PSU). And I also didn't put it it into a fancy little box.

I might re do this later but using super bright blue LED's with a molex plug to get power and a microphone instead of 3.5mm jack. And use a fancy little box :D

01-22-2009, 08:52 AM
Sound activated LEDs! Excellent! +Rep
Looks alot better than the sound activated CCFLs.
I imagine you could experiment with different color LEDs,
For a cool effect, that would match your theme.

08-30-2009, 09:32 PM
Built this circuit recently (pics after I get unlazy with camera) and it works well, I suggest replacing the tip31 with a tip41, can handle more power and seems to gate better.

08-31-2009, 03:31 PM
And that is how you do that.

09-01-2009, 09:55 PM
video is no longer up :down:

09-02-2009, 01:35 AM
the link to download it still works even if the youtube one has been pulled.

02-13-2011, 07:02 PM
Were must I put P2 plug .. When i put it where i must put speakers it doesnt work .. if i put it in where i put headphones it doesnt work .. of I put it in headphones hole on speakers it works, but there is no sound