How to Sync an LED Pixel Strip with MIDI Song Files

Instructions & Code/Sketches

About this Project     Supplies & Tools Needed     Soldering & Assembly    

Programming Microcontroller     Using MIDI Software     Main Page     Contact

 

About this Project

The best way to understand what this does is to watch some videos. Here are some with classical music:

Colors correspond to notes as follows:
C: red
C#/Db: red-orange
D orange
D#/Eb: yellow
E: yellow-green
F: green
F#/Gb: teal green
G: aqua blue
G#/Ab: blue/purple
A: purple-magenta
A#/Bb: magenta-red
B: magenta-red with more red

Colors can vary with different LED's and cameras, possibly monitors, and the colors can be adjusted in the code or changed completely to your own preferences.

This project can be used with other types of music, if the songs are available in MIDI form. A search engine can often find numerous MIDI files from a variety of genres. The LED response is automated and based off the notes of the music. You do not need to program every light turn-on and it's timing because that is handled in the code.

In its current form, there is no separate display for percussion. However, there are 2 forms of percussion sketches elsewhere on this web site. Those can be adapted to run another display or dedicated LED's on the same display, with some code editing. Future versions of the code will likely include something different for percussion, when I have some more time.

The software used in this tutorial does not work with MP3's. To use this project with MP3's requires MP3-to-MIDI conversion and software that can simultaneously play an MP3, read a MIDI file, and send USB MIDI. This is unexplored and untested at this time.

If there's enough interest, I might sell kits or finished products in the future. At the moment, this is just a how-to page for motivated DIY people.

This tutorial uses an APA102 LED strip, however the code can be adapted to use other types of LED pixels, also known as addressable LED's. It's important to use a libary that uses DMA (Direct Memory Access). See this for more details. This sketch has example code of how to use Neopixels (WS2811/WS2812/WS2812B) on a Teensy with a DMA-based library. The APA102 LED's are easier to film without aliasing and transfer data faster. Neopixels are less expensive.

 

Supplies & Tools Needed

Here's a list of supplies and tools needed. Most of these can be purchased from hobbyist web sites like Sparkfun and Adafruit.

Supplies

  • Teensy 3.2   (Teensy LC will work with some future code releases, or if you don't need very much buffering to compensate for audio latency.)
  • Teensy Prop Shield LC (Regular version also works but costs more)
  • APA102 LED strip with at least 88 LED's and maximum of 128 LED's. The photos and code in this tutorial use 101 LED's, but the settings in the code allow the use of other numbers of LED's.
  • Hookup Wire
  • 5-Volt Power Supplies: 1 or 2. The amount of current needed depends on how many LED's you plan to light up at the same time. Each LED can usually draw up to 0.06 Amps on white at full brightness. If you plan to use this hardware setup for other purposes, then you might want enough current to light up all LED's at full white. However, for the purposes of this project, a small 5-Volt 2-Amp output power supply may be sufficient for some songs. This tutorial uses 2 of these. 1 larger power supply could be more convenient.
  • Barrel Connectors for Power Supplies
  • Micro USB Cable. Longer is more convenient. For 10' and 15' cables, I have found good deals on Bestlink Netware.
  • 2 Fuse holders and 2 Fuses. Optional but strongly recommended for permanent installations or unattended operation. As a general rule, they should be fast-acting and rated for no more than 50% of what the connected power supply can deliver. A better answer is to look at the time curves in the fuse datasheet. Use at least 2 fuses per power supply if you want to be able to use the maximum current that it can deliver. This tutorial does not show fuses, but I've never left mine turned on while unattended.
  • Diffusion material and mounting material. This can be made from strips of translucent acrylic and a strip of plywood or aluminum channel. Another option is using channel designed for LED strips. Hobbyist web sites usually don't carry LED channel, but distributors like 1000 Bulbs carry some options. Amazon and eBay have some good deals that can be found by searching "led channel diffuser" on their web sites. Make sure it's wide enough for the LED strip that you're using.
  • Glue. I used Loctite GO2 Gel. If you use silicone, make sure it's a neutral cure and not acidic (vinegar smell) if you plan on having the glue contact any bare wires or leads. Otherwise it can only touch the insulation.
  • Screws and spacers or standoffs.
  • Rubbing alcohol and paper towels for preparing surface to stick LED strip.
  • Screw or hook for hanging on wall. If you're unable to find or use a stud inside the wall, it's a good idea to use a drywall anchor.

Tools

  • Soldering Iron and Solder, wet sponge, holder for solder iron, maybe tip cleaner and brass wool/brush to extend life of tip. If you're new to soldering and don't own any tools, it might be easier to start off with a kit: https://www.sparkfun.com/products/14681
  • Wire Strippers
  • Wire Cutters
  • Drill and drill bits for pilot holes
  • Possibly Electrical Tape
  • Possibly an Exacto knife or another brand equivalent.
  • Possibly a table saw to cut strips of diffusion or mounting material.
  • Laptop running Windows, Mac OS, or Linux. This helps to eliminate ground loops (humming noise) in the audio that might occur with using a desktop computer. If you only have a desktop or wish to use one, there is another way to eliminate hum. While it's not safe to ground lift the power supply in a desktop, there are USB ground lifts sold on the Internet that can help with ground loop issues.
  • Speaker System or Headphones
 

Soldering & Assembly

This is potentially one of the easiest projects on this web site because it doesn't require building a custom circuit on a prototyping board. The details of your build can, however, affect the complexity. Photos are below. There is no particular order in which to do anything, besides the obvious. I've included some important notes with some of the photos. On each photo you can click to enlarge and see more details.

My build uses scraps of translucent acrylic. Since it may be difficult to order translucent acrylic in small quantities, I recommend using a channel and diffuser meant for LED strips. Amazon and eBay have some really good deals:
https://www.ebay.com/sch/i.html?_from=R40&_nkw=led+channel+diffuser&_sacat=0
https://www.amazon.com/s/ref=nb_sb_noss_2?url=search-alias%3Daps&field-keywords=led+channel+diffuser
Milky diffusers might blend the colors better than frosted diffusers at short distances. Verify that the channel can accept the width of the LED strip that you're using.

It's important to have enough distance to the diffuser to properly mix all 3 component colors (red, green, blue) but not so much distance that each LED blends into the nearby LED's. I found 3/8" to be a good distance between the diffuser and the mounting surface of the LED's, but the best distance may vary with different diffuser materials and thicknesses. I used dabs of Loctite GO2 gel glue to hold the acrylic to the plywood. The 2 acrylic pieces are bonded together with Acrifix 117. The thin solvent version of Weld-On seems to be a more common acrylic adhesive but also contains methylene chloride which generates more toxic fumes.


In this photo, the LED strip is attached to a smooth laminate layer on the top of the plywood. I wiped the laminate surface with rubbing alcohol and let it dry first. Regular plywood does not bond well to structural tapes and requires painting, sealing, or even smearing some wood glue into it. For a rough surface, it's a good idea to lay down some foam tape first. Test compatibility of bonding 2 tapes together. Sometimes it works, and sometimes it doesn't.


Bottom end of LED strip. On this Sparkfun APA102 LED strip that I ordered, the wire colors are

  1. red: VCC (+5 Volts of power supply that connects to lower barrel connector)
  2. blue: clock
  3. green: data
  4. yellow: ground (negative of same power supply)

Colors may vary with different products, but any APA102 strip will have these 4 connections. Other types of LED pixels and addressable LED's can be used. However, it's important to use a DMA-based library. See this page for more details. This sketch has example code of how to use Neopixels (WS2811/WS2812/WS2812B) with DMA on a Teensy.


In the middle of the strip, I cut the Vcc copper trace with an Exacto knife because I used 2 power supplies. Connecting both the positives and negatives of 2 power supplies is a bad idea because small differences in voltage may cause overheating. In this project, the grounds (negatives) of both power supplies and USB power are connected together, but none of the power sources share any of the +5V (Vcc, positive) wires. If you use a single power supply, it is not necessary to cut this notch but might be a good idea if you're running fuses to the top and bottom of the LED strip, depending on the resistances of the copper traces and the fuses.


With the hookup wire I used, the wire colors are

  • yellow: VCC (+5 Volts of power supply that connects to upper barrel connector)
  • black: ground (negative of same power supply)

To solder wires to LED strips, the soldering iron will have to be turned up hotter than you normally do for circuit boards. With lead-free solder, 800 °F is a good temperature (750 °F for leaded) and don't spend too much time to avoid overheating the LED chips and IC chip inside, but there is some cooling across the copper traces and wire so it's not like you're directly touching a part with the iron. For an iron that does not have a temperature setting, a 25W iron is probably fine for leaded solder and 40W for lead-free. The shape of the tip makes a difference (sharper thinner points deliver less heat, blunter tips deliver more heat) as well as the airflow of a fan. A 60W iron can be cooled with a fan, and a 25W iron can get hotter by letting it sit for awhile between solders. Using a fan to suck away the fumes usually won't cool the iron as much as blowing air onto the iron. Avoid using solders with antimony or silver because they are more difficult to work with and have higher melting temperatures.

It helps to hold the wire down with a weight or an alligator clip. Even better: cross-locking tweezers. The stripped end should be touching the copper pad. Apply a little solder to the iron tip first to help transfer the heat, then touch the bare wire and copper pad, then feed more solder (experiment with the speed of feeding the solder). As soon as it sticks to the copper pad, pull away the solder, then pull away the iron afterwards.


The left side in the photo is the bottom, the right side is the top.

  • You can barely see the black hookup wire here. It connects the ground of the lower power supply barrel (left barrel in the photos above) to the yellow wire that curves off the black connector on the left side of the photos above.
  • The yellow hookup wire of the lower barrel (+5 Volts) connects to the red wire that curves off the black connector. This powers the bottom half of the LED strip. It does not connect to the yellow wire on the Teensy even though at first glance it kind of looks that way. If you zoom in, you'll see that it's a darker yellow and goes to the side of the Teensy. The photo below shows this better.
  • The upper barrel (right barrel in photos above) connects to the long yellow and black wires which power the top of the LED strip.
  • The Teensy has no +5V connection wire (see photo below). This is because it's powered by the USB cable. You don't want excess current flowing between your computer and one of the power supplies because this could overheat your computer, the power supply, or the USB cable. That's why there's nothing connected where it says "5" on the prop shield.
  • The grounds of all 3 power supplies (2 wall warts + USB/computer) are connected through the black plastic connector and a copper trace in the LED strip. None of the positive wires are connected together.


Teensy 3.2 plugged into Teensy Prop Shield LC. The code in it's current form runs on Teensy 3.2 only. Future releases may work with Teensy LC. The female headers need to be soldered onto the prop shield, and male headers may need to be soldered onto the Teensy. Only clock, data, and ground connect to the prop shield. Do not connect +5V (red wire of LED's, yellow hookup wire) to the prop shield because it is powered by the USB connection. Otherwise overheating or damage may occur due to small differences in voltage and very little resistance.

If you've never used Teensy before, here's a guide that can help:
https://learn.sparkfun.com/tutorials/getting-started-with-the-teensy


For each power supply, it's a good idea to connect a 1000uF capacitor in parallel. Be sure that the negative sign on the cap is connected to the negative of the power supply, also know as DC ground or signal common. This is not the same as earth ground, although a desktop computer will connect both grounds together. To figure out which wire is which, you can look at a diagram on the power supplies or test with a voltmeter. Usually the barrel is negative and the tip is positive. Then you can use an ohmmeter to see which wire connects to barrel and which connects to tip.


Upper capacitor is connected in parallel with upper barrel connector. The slot for hanging is on the right side of the photo (top of the piece of wood). To hang on the wall, I used a long screw with a wide head. For studs, drill a pilot hole first. For drywall or plaster, an anchor is highly recommended.

Cords can be hidden inside a wall using an electrician's snake, also known as fish tape, available at a hardware store. The thin ones that are 1/4" wide are easier to use than the thick ones that are 1/8" wide. After the snake is pushed through both holes that you've drilled, you can tape cords to the end (stagger the plugs to keep it low profile) and pull through the wall.

 

Programming Microcontroller (Using Teensyduino)

The software for the Teensy can be downloaded from here, and there are instructions for Windows, Mac OS, and Linux. It modifies the Arduino software to also work with Teensy devices, so whatever computer you are using, you'll need to install a compatible version of Arduino software first.

Here are the sketches to load onto the Teensy:

They have the same general code, but one has settings for piano, the other has settings for organ. To use a sketch: download, unzip, then run Teensyduino and open the file with the same name as the folder. Click on the a_global tab to edit settings. Time delay must approximately match buffering time of MIDI software and can include additional milliseconds to account for distance from speakers. There are many other settings in this a_global tab. The fade up and fade off features use bit-shifting (powers of 2). "mS" means milliseconds.

Compile with MIDI selected. This is necessary for software to recognize the Teensy as a MIDI device. See screenshot below:

In it's current form, this sketch works best with Teensy 3.2, although it may run on Teensy LC if you don't need much buffering time or number of notes buffered. It's not the most efficient use of RAM, so I'm rewriting the code. A future release of this will likely work fine on Teensy LC, and I'm eliminating the bitshifting and replacing with division for ease of use and more customization.

A future release that includes a dedicated display/response for percussion and has different displays or responses to each instrument type would likely require using the Teensy 3.2 and not work with Teensy LC.

 

Using MIDI Software (LMMS)

The LED setup should work with any software that can send USB MIDI and play sound at the same time. This includes free software as well as commercial software like Ableton. For this tutorial, we're using LMMS. It's formerly known as Linux MultiMedia Studio and despite the name, it is available for Windows and Mac's, not just Linux. It's also free and open source.

You'll want to install LMMS on a laptop to avoid potentially having a ground loop which creates annoying hum in the speakers. If you must use a desktop, there are some USB ground-lifting devices sold on the Internet that can help with that issue. Ground-lifting the power supply (3-prong to 2-prong adapter) is unsafe and not recommended.

To get started with LMMS, you'll need to adjust the settings. Top Menu: Edit > Settings, then you'll see a pop-up window that contains 5 icons on the left side of the new window. Changes to settings take effect only after restarting LMMS.

The buffer size has to be large enough to have good sound quality. If you're not connecting a musical keyboard to your computer, then there's no concern about latency. The Teensy can compensate for the latency by adjusting the number in the sketch to match the latency shown in the settings window. If the speakers are far away you can also add 0.89 milliseconds per foot of distance (2.9 milliseconds per meter).

Click on the folder icon, and at the bottom of this menu you can select a soundfont. This will need to be downloaded from another source because this is not included with LMMS. I used the FluidSynth sound font, also available for free. I used the command line apt-get method of installing in Linux Mint, then located the .SF2 file within the install and used that file with LMMS. The filename is called "FluidR3_GM.sf2". At this time I can't find a reliable and reputable source for downloading this directly, and I don't see the license file. This might be the same file:
https://github.com/urish/cinto/blob/master/media/FluidR3%20GM.sf2

Here's a direct download from a newer version of FluidSynth:
https://github.com/FluidSynth/fluidsynth/blob/master/sf2/VintageDreamsWaves-v2.sf2
This file works but is lacking a piano sound and other acoustic sounds. However, it does have quite a few synth sounds

Here's another soundfont that someone posted for the purpose of direct downloading:
https://timtechsoftware.com/general-midi-soundfont-download/
I haven't tested this and do not know much about that web site.

What's the best soundfont? There are plenty of opinions on the MuseScore forum as well as links to other soundfonts:
https://musescore.org/en/node/103046
https://musescore.org/en/node/33656
https://musescore.com/groups/young-composers-group/discuss/166635

After you've installed a soundfont, click on the speaker icon. You'll have to select an audio interface. I've used ALSA and SDL in Linux. You'll have to experiment and see what works well on your computer. You might have to click on the keyboard icon and experiment with the MIDI settings to send USB MIDI.

You'll want to close LMMS and re-open each time to test settings.

To play a song, you'll need to import a MIDI file using the menu option Project > Import... and then select the MIDI file that you have downloaded from somewhere or created yourself. The instrument can be selected by clicking on the "SF2 Player" button to the left of the volume knob for the track.

A new window will pop up. Click on the wrench icon to the right of where it says "Patch" and whatever instrument is currently selected.

To send USB MIDI to the Teensy, you'll have to click on the gear symbol next to each track and select MIDI > Output and then select the Teensy which should show up. If it does not show up, then you may have forgotten to compile as a MIDI device when loading the code.

After this, you can click the Play button (triangle). If sound and lights work, then it's all ready to enjoy and play more music. Otherwise experiment with settings and restart LMMS to try again.

LMMS may have occasional bugs that have to be worked around by trying things. Sometimes when I load a MIDI file it says the soundfont failed. When this happens I have to re-select the soundfont file by clicking on "Sf2 Player" for each track and re-selecting the SF2 file and instrument in the pop-up window. If the Teensy is disconnected and then re-connected later via USB cable, you may have to re-select the MIDI output for each track.

 

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