Picture of Sound Reactive LEDs
Lets first see what the final effect is going to be like!!

We will work our way through to the circuit needed.
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Step 1: What you will need

In my setup I used two 5m LED strips from Amazon. Each of these strips requires a 2A supply and because I had ordered separately I got two 2A supplies. However you can just use a single 4A supply to power your circuit and your strips. Since I have the circuit with two supplies I will list components according to that.

1> 2 x 5m Led Strips  amazon
2> 2 x 2A DC adapters amazon
3> LM324N Quad opamp available at Radioshack
4> 2 x TIP29C transistors
5> 2 x SPDT slide switch
6> 2 x 100K Ohm resistors, 2 x 5.1k Ohm, 4 X 100 Ohm
7> Wires, Soldering equipment, Solderable PC Breadboard like this 
8> 2 x DC Power jack
9> Aux cable(to be stripped at one end)

Step 2: How others have done it before

Picture of How others have done it before
Many websites have information about doing it directly with transistors. TIP 29 or 31 can be used. We will discuss circuits, their shortcomings and solutions so a little bit of electronics knowledge is recommended

Audio cable coming out of the PC has three wires in it: Ground, Left and Right. The best way of getting audio signal is to take an aux cable and strip its wires.

If you see bare threads, they are ground and the two insulated ones are left and right

Step 3: How others have done it before

Picture of How others have done it before
Connect Ground to the emitter of the transistor and Left or right to the base, connect one end of LED to external power source and the other to the collector of the Transistor
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Great circuit. One question, I'm not very good with analog circuit design. I wasn't too smooth the output for an Arduino to read and control a servo operated puppet mouth. Can you suggest a capacitor/capacitor-resister combination? My experimenting has only yielded a soft constant pulsing.
*I want to smooth. Phone keyboard plus morning equals fails.
MarcosC21 month ago

How does the audio input works? On the AUX cord you gonna have three wires, L+, R+, and ground. So how to wire that in the circuit?

andymic2 months ago

Nice setup! Just a question not directly related to this project, how would I need to modify the circuit for the LEDs to switch between on/off without fading? In other words they remain on when there's sound and off when silent (or close to silent, I'm hoping there can be some kind of threshold implemented). Cheers!

soulengineer2 months ago

Does the above circuit work for any less input ? ie lower then 2amps/12volts ? also is the led responsive to any smart phone or mp3 player regardless of the intensity of the output given via aux, if not.. can you please help me out with a method in which the output of the music signal can be maximized more? ?

saurabh.harsh (author)  soulengineer2 months ago
The circuit should work for lesser current ratings as well, but 12V is required for the opamp chip to be powered and also the LED strips are usually rated 2A/12V. If you have anything like 1.5A-2A it should still work fine. Regarding the source audio I have tested it with a laptop and an iPhone, it should also behave similarly with any Mp3 players because all 3.5mm outputs produce similar signals. As you will notice though, the intensity of the lights depends on the volume of the source. This is true for any device that you use and I could not think of an easy way to overcome this (Look into spectrum analyzer if you are interested in doing that).
tamlani2 months ago

need help..!!! NEWBIE

well every thing is clear in schematic except for few...

where am i going too wire LED +ve and -ne? & where am i going too wire Adapter +ve and -ne?

there are 5 grounds in schematic as shown in circuit image if anyone can label them as which will be use for led or adapter, it will be really helpful.


Power Supply's V+ is connected to LM324's V+ pin and also directly on the LED Strip's V+.

Led Strip's GND is connected above R4. Use 100ohm as R4.

All other GND is connected to Power Supply's GND.

Thank you so much =D...!!

saurabh.harsh (author)  tamlani2 months ago
All grounds are connected together to the ground of the power supply (or what some also call -ve). This is usually called common ground in DC circuits. The +ve side of the DC adapter is connected to what is marked as 12V on the diagram. The LED +ve and -ve are marked on the diagram. I hope that helps.

Thank you so much =D...!!

TeXNoiZed3 months ago

A question my friend, what about if we decide to use a RGB strip? How do we wire then that up so we still get both of the functions working :)

I did the same circuit but bought a strip of rgb leds and accomplished music flashing and the remote for the rgb still functions. Here are the leds I bought

Here is the picture of my schematics uses 3 transistors let me know what you think btw I didn't add any switches just goes to music. And I'm not a master of electricity either so please tell me if I messed up
silasgreave4 months ago

what are those two diodes attached to the circuit. you didn't mentioned in the requirement list. please tell me

vickyv24 months ago

hey bro... thanx for this... it works perfect... :)

can you plzzz help me in one thing??

I want to give input as "Electrect mic"

I've tried amplifying that mic ... but I failed

i've used bc547 trans and rest circuit ...

so can u plz help me as fast as possible bro...

thank you ...

I have created a PCB that can be printed in a really small PCB. If you don't understand the schematic in the post above you can see the connections in my PCB.

(Havent tested the PCB yet since I just ordered them, although I am sure they work since I have used the exact same in a prototyping board and it works 100%)

Here is a picture of the PCB in EAGLE:

Here are the PCB files and schematic:

Any questions, ask me! :)

Have fun :D
saurabh.harsh (author)  Orestis Mokas1 year ago
This looks awesome! How much are you getting it made for? I would want to make a nicer looking circuit which I can enclose in a small box or something to make the wiring part look much better.
Thank you :)

You can order these PCBs from They create PCBs in a really nice purple colour. Check them out!

With my design you can buy 3 PCBs (I think that is the minimum) for 16.00$

Hope it works 100% though, I will receive them in 3-4 weeks since I live in Greece and shipping from USA takes about 15 working days. It might take 5 weeks :(

Hey, can you validate if the PCB design works 100% the way it should?

Yes of course it does!

adi-sreyaj4 months ago

Bro can u provide a good circuit diagram for this as I'm not able to get an idea from the above circuit........anybody pls

aka619ASH8 months ago

Saurabh, hie!

I need some help with your circuit, I was trying to build it but I don't want to use the sliding switch, also I am a beginner in ECE. So can I get simplified version of the circuit. Also for Diodes I am using IN4004, is that fine. I build it but the leds are at constant glow. It will be great if you can post a simple version of your circuit. Also I do not understand the TIP 29 connections for Base, Collector and Emmiter.

bikec11 months ago

nice tutorial,it is working with transistor TIP 31. The circuit is 100% right,

Thank you

tamlani1 year ago

heyy nice tutorial but i am new to ths all n few request...can you please explain step 6 the solution given and image is not clear to me moreover step 10 and 11 final circuit is also not clear...a simple diagram with images would be appreciated if u cn do it...waiting for your response...and yes thngs i have are 5m led strip, 1 x TIP31, 1 x 12v adapter.. plz help me out

saurabh.harsh (author)  tamlani12 months ago

I am going to try making it with only the tip31, will let you know if I have success.

Another easy way to do this is this design:

Just replace the 4 LED lights with a 5m LED strip (cheap on Amazon). And if you want to use this design for bigger stereos (I did) or car amps then replace with a TIP3055 Transistor (3 pin w/ lower specs and looks like the TIP31). Wire it the same way. I have 5 strips in my room off a home theater and it works amazing and plays well with the visitors :) I can post pics if anyone wants to see and feel free to ask questions.

plz do it as i am facing difficulty...i am using tip31c transistor and 5m blue led strip.

I built on of these using a TIP2955. My lights seem to dim to music and stay on during silence, is this because of the type of transistor used, or is this the way it is supposed to work? I want the LEDs to be off during silence and flash on when there is sound, what am I doing wrong?

You may have the polarity of the input to the transistor wrong. Otherwise you just probably have the wrong transistor. You might be able to use the transistor if you check each pins function and then adjust the wiring??

phunguy1231 year ago

not too experienced in electronics but ive looked at the datasheets for the tip31, and its nearly identical to the 29, could that be used instead?

saurabh.harsh (author)  phunguy1231 year ago

If the datasheet says they both have the same current gain it shouldn't be a problem.

Here is my setup ! :)

I used 10metres led and a 12V 5A supply :)

(Sorry for low sound, it was recorded 3:00 AM)

saurabh.harsh (author)  Orestis Mokas1 year ago
awesome! I am so happy to see my ideas travel across the atlantic !!
Actually I will improve the PCB I showed you last time in another comment of mine. I am thinking of adding frequency filtering like this schematic here

I would like to ask you some questions though because in this schematic some weird resistor values are used instead of 100k and I am not updating my PCB until we solve these so we can make something really nice.

Currently I am loading the same track in 2 decks in my DJ Console, I play both tracks the exact same time, but I have connected the PCB in the headset output and I turn headset ON in the 2nd deck. On the 2nd deck (that the PCB is connected) I cut LOW and MID frequencies. Although in my speakers only the 1st deck is playing to be able to hear all frequencies.

Thanks for your help again ! :)
saurabh.harsh (author)  Orestis Mokas1 year ago
I took a look at the circuit diagram, its not too complicated but if all you want to do is split frequency and get intensities across different freq ranges, you could use a spectrum analyzer IC. We should tratehr take it on pm from here.
I'd really like to be included in that conversation. I've been building bluetooth speakers with an led array that uses both left and right channels and displays the channels in separate colors. I've having some issues with it, and I have no idea where to turn for help. Here is one of the ones I built.
How could I do this with a 24v led strip?
You can power the LM324 with another power source (lets say 5V) and the led strip from 24V. The only thing that must be connected to the circuit is the ground wire of the 24Volt (Pins 10 + 11). Since that goes to the transistor and the transistor just connects the GND with the LED strip GND.

Sorry for my english !
Thank you!
You're welcome :)

Forgot to tell you that I don't know much about op amps and I don't know if the current schematic works with 5V power source for the LM324.
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