Introduction: Sound Reactive LEDs

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.

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

Step 4: Problems With This Circuit

Picture of Problems With This Circuit

Because currents allowed are really small even with the gain in the transistor it allows only about 40mAs of current to flow at max sound intensity

Voltage of the signal varies from +/-0.8 at max intensity and because of internal voltage drop the transistor gate doesn’t even open till 75% intensity from PC

Even using darlington pairs doesn’t help because of the internal drop.  We also want better control for current for running an LED strip instead of a single LED

Step 5: Problems With This Circuit

Picture of Problems With This Circuit

The transistor allows current to pass through only half the time, The other half of the signal when there is negative voltage coming from the audio is simply neglected so the maximum brightness you get from the LED is only 50%, because the signal is so low you cannot use a diode full wave rectification circuit since the diodes have forward drop of about 0.7V

Step 6: Problems With This Circuit

Picture of Problems With This Circuit

SOLUTION: Connect the audio in the exactly opposite way(ground – base, L/R - emitter) to another transistor and connect the collectors of the transistors together (shown here in figure: colored arrows indicated path of current)

Step 7:

This is where this circuit can get you. (Sorry for the bad taste of music, thats the first thing that came to my mind that day)

Okay so now this circuit can pull 40mA(max) through the LEDs connected in series but the LED strip we have need 2A(max) current for full intensity. There's no other way left to us than to use Opamps. All we are going to do is jack up our signal 20 times( in voltage) and run that through a transistor to control the current.

Step 8: Using Opamps

Picture of Using Opamps

Step 9: Using Opamps

Picture of Using Opamps

Step 10: Final Circuit

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Step 11: Final Circuit

Picture of Final Circuit

Step 12: Soldered Circuit

Picture of Soldered Circuit

Step 13: Setting Up the Lights on the Wall

Picture of Setting Up the Lights on the Wall

I used insulation tape to create the surface to paste LED strips on, if you are trying to be low on cost use your creativity!

Step 14: Final Effect

Questions and suggestions are welcome!!


manojkumar999 (author)2017-10-12

okay my led strip has 4 ends.. how to connect them

I have not worked with RGB strips for this instructable but I my guess would be that each of those is a 12V line for R,G and B and one more for ground. If you connect all three to the same signal you should get a white(ish) light, overkill of an RGB strip for this project though.

manojkumar999 (author)2017-10-12

what kind of diode is used

manojkumar999 (author)2017-10-12

i don't understand where are the ground wires going

manojkumar999 (author)2017-10-12

i want to make one of those, but my led strip is RGB and has 4 wire endings.

tnbhatia (author)2017-04-02

So I had a question, I got one of the sound sensing microphones from Keyes and well one of my questions was I'm trying to make a sound activated led strip but every time the sound sensor senses sound, the led starts blinking and I just wanted to know if there was any way I could get it to fade instead of blinking. This is for an architectural project and I really want to figure this one out.

My code goes like

if (sensorvalue >= threshold) {

digitalWrite(3, HIGH);


else {

digitalWrite(3, LOW);


Its set to only be on when threshold is met and off when threshold is not met. but what I want it to do is fade and get brighter when sound is on and fade out slowly once the sound goes off instead of just switching off.

Please help, it ll be much appreciated.

saurabh.harsh (author)tnbhatia2017-04-02

I believe you are doing this by programming a microprocessor, and by looking at the code I guess it is an arduino. I remember you can do PWM on an arduino to get a fade effect so you could always do that. I think it will be all based on code. Another purely analog way of getting a fade effect is to put a capacitor in parallel between your pin and led strip.It gets charged when your pin goes high and once it goes low will let the light fade slowly as it gets discharged. You may have to play with capacitors of different capacity.

ozyhasari made it! (author)2017-02-27

I Made It,

first thing first i want to thank to the author of this creative idea (saurabh.harsh)

so i made it with first order passive LPF right before amp.

i use 100ohm and 3x47uF capacitor in series which means the frequency cutoff is around 100Hz.

here's the schematic

but in the schematic i use 2nd order passive LPF but untested. i believe it also work as well.

PallabD (author)2016-10-03

Need help,I haven' t use any resistors in my circuit, I used TIP31c & 5cm led cuted from a smd3528 strip red, as I thought that the led have resistors in them, supplu volt is 12v dc from ac to dc adaptor @1amp or from my psu in my pc.I have a few questions1. When I connect the circuit on psu nothing works more over my pc is conducting current.? Q2. What is the quantity of leds can I use as 5cm has 3 led and 1 resistor it drawing somewhere 0.24 watt and 0.02Amp (0.08*3) = 0.24/12v =0.02Amp.and the TIP31c can handel 3Amp ?Q3. Without using any resistor will I fry my audio device ( pc,Mobile)?.Q4. Can I connect additional 100ohm resistro per 1m strip and one 47k ohm resistor to the right prong of tip31c and another 4.7k Resistor at the left prong of the tip31c will it secure the curcuit? Sorry for such a long post plz reply I need help.

saurabh.harsh (author)PallabD2016-10-25

So you are trying to power your lights using the current from your audio device ? That's never going to happen and is probably going to fry your audio output circuit. I think you should consult some of the other instructables which are based on the TIP31C, the circuit is pretty straightforward for that.

PallabD (author)2016-10-24

As a rooke in electronics I want to try yous schamatics but your circuit is a bit confusing asin the parts list tere is no diode an in diagram there is no switch.

saurabh.harsh (author)PallabD2016-10-25

The figure in step 10 shows how to connect the ends of your strip to the circuit, and what switch are you looking for ?

PallabD (author)2016-09-27

I have made with TIP31c , and cut the led strip (1 pice with 1R ,3led) , and connceted with12v dc , my question is how many led can I connect (wants to connect 1M strip )

Makersteve (author)2016-08-19

Awesome! Very nice explanation! I'm definitifly going to build this. (Already prototyped it - works flawlessly) Since the Lm 324N is a quad op amp, i'm going to make it stereo with a single powerful led each (red & green) and im going to use it with my homemade boombox (instructable coming soon!), wich also features built in VU-meters.

matej1408 (author)2015-09-15

when i hooked it up it didnt work and my op-amp was relly hot, it i probably burnednow. Can someone tell me what is the problem?

ljenkins11 (author)2015-07-25

Tested my circuit on stripboard, and it doesn't seem to be working right at all unfortunately. There seems to be a fault that the circuit always thinks there is an audio signal- as my LEDs are lit even when the aux cord is not plugged in or the wires to the IC are even disconnected. This worked on breadboard though so I think I'll have to retry it for the third time :(

ljenkins11 (author)2015-07-22

Little bit late to the party, but I've built my own inside a small project box. Still yet to test it, but at least it looks nice!

damjan.mihelic.94 (author)2015-07-03

Which diode did you use? 1N4007? or?

yourdaddy766 (author)2015-06-21

Low pass filter added pre-amp causes leds to respond only to bass notes.

yourdaddy766 (author)2015-06-18

I've built this and it is working very well. Thank you for this instructable! I do have one question.
How would I tune the setup to respond to lower frequency? In other words , more bass vs mids. I am using it for a friend subwoofer setup in her car.

Errrmmm... you will need a little more knowledge of electronics and signals to get to that. The basic block would be a spectrum analyzer chip, (google and find the one suitable for your needs). This chip will split the signal and give you decibel levels on different frequency ranges. And then you appropriately scale up the output using this circuit to get desired results. You may want to make this on a breadboard and test before you actually build it.

Ok, I will look into that.Thanks. Were you thinking of something like the lm3915 or its sisters 3914 and 3916?
At first I assumed I could adjust frequency sensitivity by changing the values of r1 and r2 in your circuit . If i did change r1 and r2 I think it would just alter the gain vs frequency response. If I do find an easy way to adjust the frequency response I can let you know if you would like. What are your thoughts on using a high/low pass filter vs a spectrum analizer IC? Do you know of a simple high/low pass filter circuit? I'll ask google but I thought I would get your take on it as well. Thanks again btw :)

I don't think you will be able to adjust freq. sensitivity by choosing r1, r2. Since there are no capacitors in the circuit this circuit can't do any of that stuff. Making a high pass/low pass filter is a good practice but it may make your board look messy and it may be prone to mistakes. If there are spectrum analyzer ICs already available I would suggest to not reinvent the wheel. Let me know which way you take and what are the results.

So far Ive tried the a low pass filter. This added only 2 components to the circuit. It seems to work fairly well so far. The filter is added pre-amp and consists of a cap and a pot. I'll post a drawing. As the resistance is increased the frequencies allowed through the filter become lower. I'm still looking for a spectrum analizer to try next.

Mad scientist - ieks (author)2015-04-19


im working on the same thing only i want that i can still use al the colors of my rgb led strip. So i can ir remote the color and it will jump with it on the music. Until know not mutch succes. Im just useing transistor's, driver and adapter, and a +12V 3A remote then (adapter the same specs) the strip is 4m long, and 4 wire's (afcorse) and if i possibly can then i want to have a switch between so i can turn it off - flashing on sound - normal on

I hope to hear from you!

PeopleDontLikeMe (author)2014-12-05

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

savdd (author)PeopleDontLikeMe2015-04-14

Hi. I'm also trying to do what you did and I was wondering how you would know which is the positive and negative of each RGB light in the controller. Thanks!

savdd (author)savdd2015-04-14

Also can you send a pic of your final circuit? Thanks.

Orestis Mokas (author)2013-11-01

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

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 :(

tlau3 (author)Orestis Mokas2014-11-17

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

Orestis Mokas (author)tlau32014-11-18

Yes of course it does!

tlau3 (author)Orestis Mokas2015-03-31


Snowsongwolf (author)2015-02-19

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.

MarcosC2 (author)2015-02-08

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?

andymic (author)2015-01-23

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!

soulengineer (author)2015-01-17

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? ?

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).

tamlani (author)2015-01-06

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.

Orestis Mokas (author)tamlani2015-01-06

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.

tamlani (author)Orestis Mokas2015-01-07

Thank you so much =D...!!

saurabh.harsh (author)tamlani2015-01-06

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.

tamlani (author)saurabh.harsh2015-01-07

Thank you so much =D...!!

TeXNoiZed (author)2014-12-18

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 :)

silasgreave (author)2014-11-22

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

vickyv2 (author)2014-11-18

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 ...

adi-sreyaj (author)2014-11-02

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

aka619ASH (author)2014-06-30

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.

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