Picture of Blinking LEDs to Music
schematic 1.JPG
This is a fairly simple project for anyone with some electronic skills.
Plug this circuit into an audio source and the LEDs will blink to the rhythm of the music. All it is really is using the voltage from the audio input to activate a transistor and turn on the LEDs.
This is circuit is very customizable. The setup of the lights is really up to you. The main thing to consider when choosing layout for the LEDs is your audio source and the power supply you will be using.
For this particular one I choose to make it run off a 9v battery and use an IPod for input.

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Step 1: What You Need

Picture of What You Need
Depending on the configuration of you setup you may need to modify the number of parts below.
Superbright LEDs, the number and color is up to you (I used 4 blue ones).
2 x TIP 31 NPN Transistor, the heart of the project.
Audio cord (a headphone cord will do or just an 1/8 inch jack)
case (I used a spare thick cardboard box)
9v battery clip (or the power supply you are using)

Soldering iron
Wire cutters/Strippers

Step 2: Hooking up the LEDs and Transitors

Picture of Hooking up the LEDs and Transitors
schematic 1.JPG
1.Solder 2 of the LEDs together in series. Connect the anode (long pin) of the first LED to the cathode (Flat side/short pin) of the second LED.
***NOTE you can add more LEDs in series or a resistor depending on the voltage of the power supply.
2. Now connect the Cathode of the first LED to the middle pin of the TIP 31 (the collector).
3. Repeat steps 1-2 again (for the second part of the stereo input)
4. The Anodes of the last LEDs go to positive voltage.
5. The right pins of the TIP 31s (emitter) go to ground.
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I want to do this to my headphones, except using a 3.7v li-ion. Would that work?

SirajH1 month ago

please someone help me to build this without audio in , instead can use a microphone.

Annanasi SirajH1 month ago

You can try it like this picture shows, if the microphone generates enough voltage to trigger the transistor (0.7Volts) it will work.

What does splitter mean? How do I make this and hear sounds from a speaker??

I made it, I use 2 channels, four LEDs each Channels.

I use 12 V power source.

Here is the video

ausieking1 year ago

could i power this using usb i know a usb gives off 5 volts but if i just use two LED,s would it work

KifahM ausieking5 months ago

It woudn't work unless you use smaller sized leds

would this work using a left and right rca feed as the inputs? want to make it but with a few more leds so i can decorate my sub box in my car


SIR, i have a problem on what type of audio cord am i going to used .. . i have a headset cord but i don't know how to connect it into the ground and into the emitter of the transistor coz i find it hard determinig which one is the groud and which one is from the right of from the left. . what am i going to do sir?

do i have to buy an audio cord?? if so, then please tell me what is the cord needed for this. .


Ploopy1 year ago


What is the output voltage of the transistor?
Can i use a 12 volt led strip instead or is the voltage too low?
I don't understand what you mean by output voltage of the transistor. You would be better off with a power transistor like a 2n3055 for that as the LED strip will draw a lot of current and might overheat the small transistor
i want complete list of components with specification please it would be very useful for me..thanks..
very useful...:)
i want complete list of components i can purchase them..please help me...:)
mra021352 years ago
hi everyone,

is it possible to make a simple passive rc filter for either of the led branches? it would be nice to throw a couple capacitors in there and get different frequencies to affect each side, but I am not sure where to begin with figuring out capacitor values and if anything else needs to be taken into consideration. thanks
ThaXified2 years ago
Video of my Working Prototypes! i maked 4 DIFFERENT WAYS!
could you post the full part number of the transistor please?
jjmaia2 years ago
Hope you can help me.
I have done everythimng as you said and it wont work.
This is the result:
solid nrg2 years ago
how would you get sound if your audio cord is going to your ipod and to the led blinking box were would the sound come when the audio cord is in the ipod it thinks that is connected to a audio device or somthing no sound thogh dont you need a Y cable audio splitter for it?
kewiss2 years ago
ok so let's clear something up first... I'm a complete noob, i've never done any electrical circuits or anything...all i know about electricity is from my highschool basic physics course. PERIOD!

BUT.... i'm pretty positive i can do this... WHY?... coz i love my car

so, here's the deal: i want to apply this same idea to my car stereo but instead of:
1- leds - led strips (12V)
2- 9V battery - car battery (12V)

Will these transistors work? will the whole idea work?

when i tried to connect them directly to the speakers, no light at all but i didnt try at high volume (pure imagination: based on the voltage drop i notice at high volume, aka all car lights slightly blink to the beat at high volume, i think it might light up just a bit) will this system work even at relatively low volume? (about 70% of the volume)

and should i connect it to the amplifier or speakers? or doesn't matter?

thanks in advance
bunso3 years ago
can it use any players? like chine mp4 or mp3?
ARJOON3 years ago
can i add a pot at the gate of each transistor to adjust sensitivity?
ARJOON3 years ago
better use LED strips and a 12V power supply
Hey, I want to buy what you've made, I'm awful at making these things, no patience and I'm afraid that it wouldn't pass the PAT test at my university, and it needs to be finished for 3 weeks time. Is there any chance you know where I can get this or in fact buy yours?
sin3kveer3 years ago
My plan
11 LED
32V DC power supply
so need of registor..
I had placed LEDs on a plastic stripe accurately.
Did i use Transistor. TIP31 for this circuit
pete543213 years ago
Hey guys. Great tutorial. I just bought a 5 meter strip off eBay with 300 LEDs in it. Would it be possible to hook that many up to this? If so what sort of stuff would I need? I plan to plug it into my receivers audio output, which is already hooked up with circuit breakers and resistors so I don't think that they'll be nessesseary.
Any help is appreciated!
Thanks everyone :)
I need to know, would such a circuit be functional (See picture below) Considering this is supposed to be 6 LEDs for left and 6 LEDs for right, would it actually work?

Thanks in advance for any helpful advice :)
hey what is that object which is joined with tip31 transistor?
the 9volt battery?
you must have used resistors for this experiment. The diagram above is not an ideal one..but it was a good try..
It does, tried it, works great...
Hey i made this just like the guide said but my LEDs are flashing but they are very dim.

Please help, thanks.
my leds are also flashing so dim its jst ridiculous to see those of mine also my left and right set of leds blink the same is there a way i did wrong
i think its because of the low voltage battery/power supply/adapter/transformer...
Scratch173 years ago
Is there a way to alter this circuit to force a current through the LEDs to keep them at a dim light level, then they grow brighter as sound is introduced, instead of going from off to bright?
One way to do it is put a bypass resistor across the collector and emitter. I ran a circuit simulation with a 2N2222A npn, two diodes in parallel(unlike his in series), and the two resistors. The R(emitter) was around 80 ohms and R(collector to ground) was about 500 ohms. It allows normal current flow while there is a signal on the base, and cuts the current way down when there would be no sound. There are better ways of doing but it would take redesigning.
drobbins23 years ago
Would be neat to use this with a mic and Musical Equipment
FatRider4 years ago
Hi. Love your post and I want to do a similar thing.

Exept I don't have a 9V power supply but 12V.
What type of resistor or something like that i need to use?

Sorry my english and I'm new with this ^^
what color leds are you using?

how many of them are you using?
Probably 4 blue LED's, like yours, I'm hoping to install that on my computer using the 12v power supply.

Thank you in advance ^^
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