Sound Reactive LEDs





Introduction: 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

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

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

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

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

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

Step 9: Using Opamps

Step 10: Final Circuit

Step 11: Final Circuit

Step 12: Soldered Circuit

Step 13: 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!!



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150 Discussions

I've built this circuit according to the diagram and changed R4 to give a lower base brightness because when the lights flash, it isn't much brighter. I noticed there is a capacitor in the circuit you built. Where does that fit in to the diagram and what is the capacitance?


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.

what kind of diode is used

i don't understand where are the ground wires going

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

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.

1 reply

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.

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.

1 reply

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.

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.

1 reply

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

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 )


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.

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?

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 :(

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!


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


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.