Introduction: Blinking LEDs to Music

Picture of Blinking LEDs to Music
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.

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

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.

Step 3: Hooking Up the Audio Input

Picture of Hooking Up the Audio Input

Take the audio cable, strip the ends, and determine which wire is right and which is left. Red is usually right and white is usually left.
Another way to determine the sides is to take a multimeter and do a connectivity test with each wire and part of the jack
The tip of the jack is right.
The middle of the jack is left.
And the bottom of the jack is ground.
Decide which set of LEDs will be right and which will be left.
Then connect the corresponding wires to the left pin of the TIP 31s

Step 4: Final Assembly

Picture of Final Assembly

Connect the positive part of the battery clip to one side of a switch and the positive ends of the LEDs to the other.
Then mount it all in a case (i used an old jewelry case).
I used a hot gluegun to secure everything, and some electrical tape to protect against any shorting.

Step 5: Testing and Modifying

Picture of Testing and Modifying

Plug the jack into an audio source and turn it up until you see the lights. Some players will not be powerful enough to drive the lights. I suggest any song with a distinctive beat. (I used Crazy Train)
If you want to listen to the music as well you need to get a splitter.
Now its your turn. This is just one of many ways to wire up this circuit. Good luck and be creative.
Thanks to the following for some of the original ideas:
This is my first instructable and i would appreciate any feedback.

Step 6: Updates

Picture of Updates

Here are some additions/modifications that people have been suggesting and asking for.
1. The first addition is adding an output jack wired in parallel to the audio input wire. Unfortunately the case I used was a little too small for this.
2. Different configurations of LEDs. Many people commented on using different numbers/colors of LED. The main thing to be careful of is VOLTAGE that you draw. (Series vs parallel). The next step I am going to try is maybe using a RGB LED.
3. Transistors. I am not an expert at transistors. Use a NPN that is rated for the appropriate voltage.
4. Mounting the LEDs in interesting cases. I am going to try mounting them in a pair of portable speakers.
Thanks for the comments and good luck!


AdarshG8 made it! (author)2016-08-14

Hey guys.. Ive done this project long back. But i wana do it with ac mains
. i have a wire of leds in series. 93 bulbs in series.. And i used a bridge rectifier to change ac to dc.. But the circuit is dangerous since it is mains voltage.. But to power up that wire it has to be plugged into the wall socket.. It is a wire and has a plug..i got it to work on ac mains but the audio pin gives a really bad shock..but the leds work like a party house.. I can upload a video on youtube .. I wana make a trippy led music room.. Can anyone be generous enough to send me a circuit of how to get it to work on mains with safety.. May be an isolation transformer...just remember.. I have 93 bulbs in series.. Peak voltage on ac = 220*1.4 = 308.. And 3v is the drop per bulb so it gives exactly 93 bulbs. thats why the bulbs light up without a problem.. I tried using an opto-isolator or foto-transistor as most would know it.. It gives me a very lousy output... And its not really in sync with the beats.. Im attaching the circuit which is dangerous as it is.. But since i do not know beyond that it would be great help from you guys..once you just upload a circuit il decode it.. Just need the kickstart on how to make it work..the circuit i sent converts ac to dc and uses the above concept with an npn transistor.. Its dangerous because the audio pin is connected to the mains circuit.. So plzzz help me isolate it and get it to work... The audio signal does not trigger the IR led mechanism in the foto transistor i have.. Even if u sujjest me an option plz remember that my 93 leds are in series so make sure of the voltage i need.. If u can sujjest an alternative to simply isolate the audio circuit it would be best help !!

TheReplay (author)2015-12-08

Can anyone tell me what does this symbol mean?

ReefS (author)TheReplay2015-12-09

I think he just used the wrong symbol for a switch.

NipunS1 (author)2015-09-09

I need to build this without audio jack input.. With a positive and negativ iput. +,-

Aaronniehaus (author)NipunS12015-10-05

I think you can get adapters from headphone jack to +,- leads. If not, the internal layout of an aux cord can be found online, there should be a lot of diagrams.

Dashing Rainbow Dash (author)2015-06-10

I want to do this to my headphones, except using a 3.7v li-ion. Would that work?

SirajH (author)2015-05-12

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

Annanasi (author)SirajH2015-06-03

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

Therelslmsheedy (author)2015-06-01

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

vladereign.hyuuga (author)2015-04-01

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

I use 12 V power source.

Here is the video

ausieking (author)2014-03-10

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 (author)ausieking2015-01-17

It woudn't work unless you use smaller sized leds

daz.williams.1840 (author)2014-12-29

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


jomarieandi4ever (author)2014-07-26

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. .


Ploopy (author)2014-03-11


wouterdoornbos (author)2013-09-13

What is the output voltage of the transistor?
Can i use a 12 volt led strip instead or is the voltage too low?

junits15 (author)wouterdoornbos2013-12-14

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

mariaa ahmed (author)2013-09-05

i want complete list of components with specification please it would be very useful for me..thanks..

mariaa ahmed (author)2013-09-05

very useful...:)
i want complete list of components i can purchase them..please help me...:)

mra02135 (author)2013-06-12

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

ThaXified (author)2013-06-08

Video of my Working Prototypes! i maked 4 DIFFERENT WAYS!

SabrinaReedz (author)2013-05-07

could you post the full part number of the transistor please?

jjmaia (author)2013-02-21

Hope you can help me.
I have done everythimng as you said and it wont work.
This is the result:

solid nrg (author)2012-10-17

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?

kewiss (author)2012-09-11

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

bunso (author)2012-05-10

can it use any players? like chine mp4 or mp3?

ARJOON (author)2012-04-19

can i add a pot at the gate of each transistor to adjust sensitivity?

ARJOON (author)2012-04-19

better use LED strips and a 12V power supply

alastairflindall (author)2012-04-11

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?

sin3kveer (author)2012-04-05

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

pete54321 (author)2012-03-01

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 :)

megadethfan3000 (author)2011-02-26

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...

Anoopsingh50 (author)2011-08-15

Hey i made this just like the guide said but my LEDs are flashing but they are very dim.

Please help, thanks.

samalert (author)Anoopsingh502012-01-08

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

cowarrior (author)samalert2012-01-25

i think its because of the low voltage battery/power supply/adapter/transformer...

Scratch17 (author)2011-09-27

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?

bobdan (author)Scratch172011-12-06

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.

drobbins2 (author)2011-08-31

Would be neat to use this with a mic and Musical Equipment

FatRider (author)2010-09-10

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 ^^

Sandisk1duo (author)FatRider2010-10-28

what color leds are you using?

how many of them are you using?

FatRider (author)Sandisk1duo2011-02-22

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 ^^

Sandisk1duo (author)FatRider2011-02-22

You will have to wire them like this:

(+) (-)
<--(led)--(led)--(330 ohm)-->
<--(led)--(led)--(330 ohm)-->

nodoubtman (author)Sandisk1duo2011-08-30

assuming the power of the led is how many Volt?

Thank you!
Have a great day!

nodoubtman (author)Sandisk1duo2011-08-29

Can you put leds in parralel??

thank you!
Have a great day! :)

FatRider (author)Sandisk1duo2011-02-23

Thaks, I'll do that :)

DaHandy (author)Sandisk1duo2010-12-10

I have 2 blue leds (so they need about 4V each) and a 12V voltage. Can I use the TIP31C transistors with them? Can I make the same connections as in the tutorial but with different resistors?

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