Arduino Powered Musical Christmas Lights




After exploring the Instructables website I found a few projects that peaked my interest and those lead me to thinking, I could make some musical Christmas lights. Most of what I spent my time on came from Amanda Ghassaei's Instructable on Frequency Detection. I owe a lot to her work! The rest is simple use of relays.

I also want to preface this Instructable with the fact that I did not make this one to look pretty behind the scenes and some of the pictures will not match my instructions because after doing the project myself there are a few things that I would do differently, which I include in the Instructable. Also, I am by no means a professional! This is a recent hobby and I am sure that many improvements could be made, so feel free to make improvements but please leave comments so that people can use them in the future as well.

Items you will need:
Mp3 player (any will work)
Stereo with audio in (or transmitter if you already have the know how to broadcast like the cool houses)
3.5 mm audio cable (from old head phones or wherever)
3.5 mm audio splitter (one lead to the Arduino the other to the stereo)
Arduino Uno
2.1mm power plug (for the Arduino)
Extension Cord (that you can cut up and use)
2 10k resistors (brown, black, orange)
1 10 µf capacitor (polarized)
5 150 ohm resistors (brown, green, brown)
1 pack of jumpers and headers  (
5 Solid State Relays  (digikey part number 425-2395-5-ND)
Protoboard (preferably one with the copper rings)
Solder-less board (optional but encouraged)
5 electrical Sockets from local hardware store
Electrical boxes for the sockets
4 Zip ties and a drill

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Step 1: Setup Audio Input

The first thing that you will want to do is setup the audio input and test it to make sure that you are reading frequencies. To do this you will want to set it up the components like in the schematic shown on this page. I recommend doing it on a breadboard first so you can test it before soldering and committing to the setup.
Attached to this step is a compressed file with an Arduino Sketch you can load directly to your Arduino. Once you load the program and start playing a song you can look at the frequencies using Arduino's serial monitor or make a txt file using the program I built, which is also in the file.
Once you are sure that the configuration is working for you, solder a pair of the jumpers from the jumper kit to the bottom of a protoboard to plug into your Arduino and solder your other components together on the top with the resistors soldered to the jumpers.

Your Arduino will power itself through the USB cable, but if you are like me you don't want your computer attached to this all of the time. So this is where your power connector comes into play. The Arduino uses a center positive configuration and can use 7-12 volts ideally (see for details). Find what wire goes to the center and hook that to the positive of your power source and the outside sleeve to the GND or negative. You can use a 9V battery or any other power supply that meets the Arduino's requirements. I personally tried a 9V battery and changed to one of the 12V leads from the PC power supply that I use to power my car stereo deck converted to home stereo that I use with this project. Just a warning, if your battery voltage drops below about 7V the 5V output drops to about 2.49 and your display stops working. I had this happen once, right after making a few changes to my setup, and it took a few minutes to figure out for sure that the battery was too low and causing the problem.

Step 2: Test the Digital Outputs

Now you will want to speed up your program. To do this comment out the lines:

Serial.println(" hz");

Once you have commented out these lines and uploaded it into the Arduino you can test your output one of two different ways. You can either skip this step and just hook up your relays and test with the relays, or you can use LEDs. I personally tested it with LEDs first because they have the same power requirements, depending on your LED, as the solid state relay. 

To test with LEDs just use a jumper to bring the ground from the Arduino to the ground rail on the breadboard. Plug each LED's cathode into the ground rail and then use the 150 ohm resistors to connect pins 8-12 to the anodes of the LEDs. Enjoy the light show!

Step 3: Wiring the Outlets

After testing to make sure this all works you will want to assemble the outlets and test the relays themselves.  I apologize for not having more pictures but I made the lights and then decided to do the Instructable and I don't want to take it apart just for pictures. So please make sure that you read all the way through first, then do. 

The first thing that you will want to do is connect your electrical boxes that you got for outlets. To do this you will be making two pairs of holes, one set towards the top of the outlets and the other towards the bottom, about halfway from back to front. These wholes will be for the zip ties to go through. Start by grabbing a box, I recommend a bigger one first, and drill the first pair of holes about an inch apart and then drill the second set about the same. You will have to do this again in the other boxes to link them together so I recommend using a marker, or something you can see on the boxes, to mark through the holes you just made and onto another box. This is why I recommend starting with a larger box. Once you have drilled the holes, lace the zip ties through and tighten them to link the boxes. If you like you can use other creative methods. 

After you have the boxes together then start wiring. Here is where you will want your extension cord. I used a stiffer wire, generally used in walls, and it was much more difficult to work with and made soldering problematic. Inside your cord there should be three wires black, white, and green.The black is the "neutral" wire, white the "hot" wire, and the green is the true ground wire which is connected to that bottom third prong. Connect the neutral wire (black) and the ground directly to your outlet. if you don't know how to do this ask someone at the hardware store or a friend who knows more, otherwise just don't do this project because this is high voltage and can hurt you or others. Since the neutral and ground are directly connected you can link all the plugs together with the neutral and the ground. It is the hot wire that we will be using with the relays. DO NOT string the hot wire (white) together between outlets or your lights will always stay on. Use the hot wire from the cord, left over from connecting the outlets neutral and ground together, to make a separate lead for each outlet which will connect to the relays.

Now the relays. On each relay there is 4 pins two marked "~", one "+" and one "-". Place each relay on the protoboard with 3 rows between them so that they won't touch each other when soldered together. Solder all of the "-" together with a wire, or jumper, for easy connection to the Arduino's GND on the digital side. Now solder each of the 150 ohm resistors to their respective relays. Use a row of 5 jumpers to easily and cleanly connect the jumper wires to the Arduino, then connect the other end of the jumper wires to the resistors that you just soldered to the relays "+" terminals.

Now solder all of the inside "~" terminals together and solder the hot wire from your extension cord to the row as well. Now Solder the individual wires from your outlets that you connected earlier to their respective relays outside "~" terminals.

Once you have soldered all of these together make sure that your outlets are covered and plug in a string of lights to each outlet set and test your configuration just like in step 2.

Step 4: Enjoy!

Now that you have everything hooked up and ready to go, feel free to tinker with the code but make sure to put comments on the page if you find anything better so that others can enjoy the improvements as well.

I will try and do my best to answer any questions and others feel free to answer questions if you know the answer. 

Youtube video:

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40 Discussions


2 years ago

there are three wires in the audio cable ground,right,left which one do i use for reading hz on the arduino

1 reply

Reply 1 year ago

I apologise for the delayed response. You would use either the left or right. The ground goes to the ground on the Arduino and your chosen channel goes to the analog readout of the Arduino.


Reply 1 year ago

That question is fairly broad so I hope this reply helps. I wanted to be able to use this with any audio so I found another instructable that broke out frequency, credit given above. That instructable is where I got the voltage splitter and all necessary parts for the audio input. It's not the most accurate for timing but is the best I could come up with for a live display.


Reply 3 years ago

It worked, the wiring took a while. I made an out of focus video, but, it's still fun.


3 years ago

Nice project, made it, but I can't figure out how to put the pictures. Just curious if anybody had the problem of the lights not lining up with the music sometimes?


3 years ago

Thanks for sharing! I'm going to try this out with my mega and an 8 relay module that I have. I'm thinking that I'll wire a 1/4" audio input to the protoboard rather than cutting up a cable. Would I just drop that in front of the capacitor?

2 replies

Reply 3 years ago

I did it with a mega. The big change from the uno code is the pin numbers for the port manipulation. Once I figured that out it was all smooth sailing.


Reply 3 years ago

I got the port mapping worked out with some work, the Arduino documentation for the port mapping is not correct for the mega 2560, but I found which has correct mapping and it looks like I'll have to use some of the high pins to find 8 contiguous pins in the same port. Should be smooth sailing the rest of the way.


3 years ago

Is it possible to read from A0 and A1 simultaneously using the method in your code? I'm just not that familiar with the method you're using. Basically I'd like to set this up with stereo audio.... left audio (a0) controls 'left lights' and right audio(a1) controls 'right lights' Thanks! If I cannot use your method, is using analogRead() going to give me too much lag on the outputs? I'm already using solid state relays.


3 replies

Reply 3 years ago

Thanks for the reply, I was afraid I wouldn't be able to use Adch to read both simultaneously but that's alright. I currently have an Uno (16MHz clock) but if analogRead() is noticeably laggy with the light outputs, my housemate has offered up his RaspberryPi (900MHz clock) to try. I think the analogRead() command is only ~10 or 15 executions so with a 16MHz clock it should take 625ns-940ns (or 11ns-17ns with a RaspberryPi). If I use the command twice it should only add ~2ms per loop max with an Uno. If I can notice that.... I'll be surprised :) I'll post code and results when I have a finished product in a couple of weeks here :)


Reply 3 years ago

Just found this helpful tidbit on the arduino website "It takes about 100 microseconds (0.0001 s) to read an analog input" so using it twice I add about .0002s of delay. Seems like that shouldn't make a difference. Will update.


3 years ago

Can anyone tell me a better place to get the relay because I don't want to spend $2000+ for 500 of them when I only need 7 at most any ideas are greatly appreciated.

Also is the lights to be powered by the ardunio if so how? I have my roof covered in incandescent lights but the front in LED there is absolutely no way a 9 volt or even 12 volt could power that so am I misunderstanding something if so can someone enlighten me. Again any information is greatly appreciated.

2 replies

Reply 3 years ago


I am sorry that I haven't replied to this comment before. I am not online very often due to work. DavidR231 basically summed it up. To further clarify, the relay should have four prongs. Two are for the AC current and need to be rated for 120 volts and enough amps to support your lights. The other two are for your 5 volts DC that are coming off of the Arduino. The AC prongs basically go in the middle of one of the AC lines going to the outlet for the Christmas lights. One of the DC prongs will go to the ground on the Arduino and the other will go to pin 8, 9, 10, 11 or 12. There is one relay per pin and each pin is for a different zone.

I hope this helps. I am probably too late for your light competition.


Reply 3 years ago has the relays at a reasonable price and you can order in small quantities. I ordered 10 to take advantage of the price breaks, but you could probably only get one if you wanted to.

The lights are powered from a wall outlet. The Arduino just switches the relays which determine which of the project's outlets has power at a given time. The author uses a cut-up extension cord to wire the outlets, I am using regular 12/2 electrical wire.

If you are at all unsure about wiring outlets, you should definitely look for some help.


3 years ago

I have this mounted in my garage and ready to go. I am feeding it with the output of a radio that I leave on, but everything is controlled by a timer. In the evening the timer kicks on, the radio powers up, the arduino boots, and power is sent out to the lights.

I have tinkered with the code a bit, and I do have one channel that seems to get stuck. I'm not sure if a specific relay is getting sticky, or I have altered the code in a way that leaves on relay on for an extended of time. Since I'm only running lights off of three of the four channels, I just plugged the stuck lights onto the unused channel and I still have a show where all lights flash.

One channel runs two Christmas trees created by covering inverted tomato cages with garland and lights.

Thanks for a great project.

2 replies

Reply 3 years ago

Thanks for the complement. I went through and did this just for fun as I was getting into electronics as a hobby and just thought I would share what I had since so many other Instructables helped me to build this setup.


Reply 3 years ago

Thanks for the complement. I went through and did this just for fun as I was getting into electronics as a hobby and just thought I would share what I had since so many other Instructables helped me to build this setup.