How to Build a Synth With Handmade Wooden Keys (and Cardboard!)

If you're looking for a project that will put your DIY skills to the ultimate test, look no further! This synth has a little bit of everything: woodworking, 3D modeling, electronics, programming... you name it. The keys are handmade out of Oak and Walnut, and the body is a combination of Fiberglass-reinforced cardboard and steam-bent Walnut.

The idea for this project had been floating in my head for a while, but building a full keyboard at home seemed daunting. Recently though, I began teaching piano lessons, which I thought was the perfect excuse to dive in and learn how keyboards actually work. For the sake of novelty, I also decided to use cardboard as the main building material. It definitely added some challenges, but it also gives the final synth a charming, homemade look that I love.

If you'd like to try this project out yourself, you'll find all the materials, tools, and templates I used in the next step. And if you're not quite that adventurous, stick around and take a look at the pretty pictures scattered throughout this Instructable! Many of these were taken by my amazing dad - you can look at more of his photography here.

Well without further ado, let's get started : )

Here’s everything you’ll need for this project, broken down by category:

Exterior:

1. Walnut Plank
2. Cardboard
3. FiberGlass Cloth
4. Two-part epoxy
5. Spray Paint

Keys:

1. Oak Board
2. Washers, 4mm ID 8mm OD 0.5mm Thick
3. Springs (This is an assorted kit, I like the .4 * 5 * 15mm size the best)
4. 1/8 inch Metal dowel
5. Metal Channel
6. Scrap Wood and metal

Electronics:

1. A Raspberry Pi 5.0
2. Micro SD Card
3. A touch-screen display for the Raspberry Pi
4. Heat Sinks
5. Teensy 4.1 Microcontroller
6. 1/4" Female Audio Jack
7. RaspiAudio Sound Card
8. Male-to-female USB-C cable
9. Rubber Dome Switches
10. Carbon Contacts
11. 40-Pin ZIF Connector
12. Wires (I like these that have Dupont connectors but you can get nomal wires too)
13. Solder

Tools:

1. Scissors
2. Tape
3. Router
4. Jigsaw/Bandsaw/CNC Machine/Cutting tool of choice
5. Electric Sander
6. Sandpaper
7. Soldering Iron

Files:

Gerber File for PCB Manufacture

To start this project off, we need a template to go off of. I used a combination of Google SketchUp and TinkerCAD to draft up a model, and I used Pepakura Designer to turn the model into a printable template. You can find the 3D model in the files step.

As far as the design goes, I tried to keep things simple and organic. One of my gripes with modern synthesizers is they often feel lacking in human touch. Unlike pianos or guitars, which are assembled by hand, synthesizers are usually made of plastic and mass-produced.

I tried to remedy this in the design by using steam-bent walnut for the outer edge of the synthesizer, giving it a more crafted, organic look. I took some inspiration from old-school record players and cut some ovals into the side of the walnut to serve as speaker holes, giving it a minimalistic, retro aesthetic. (Important to note here - the finished piece does not have internal speakers! It was a nice thought but I didn’t have the time to implement it). Once I had the template made, it was a matter of printing it out, cutting it, and taping it together.

Once we have the template printed out, we can use a pencil or pen to trace the edge piece onto the walnut (In the picture above you can see me foolishly using a sharpie, which I realized bleeds into the walnut and won't give you a precise line.)

I used a jigsaw to cut a rough outline of the piece, finishing it off with an electric sander to cut the remainder.

For the speaker holes, I used a drill to make a small hole in the wood, and then a handheld rotary tool with a sanding attachment to finish the job.

One last thing we need to do here: because walnut is a notoriously difficult type of wood to bend, it's important to cut kerfs into it to make it more pliable. Although there are some lines marked on the template, these are just suggestions; the quantity, spacing, and depth of the kerfs depend on the wood you are using and the taper of your bit. However, here are some pointers to keep in mind:

1. Use a tapered router bit instead of a typical router bit; this will allow the wood to bend perfectly in on itself (in theory)
2. Since we are bending the wood at a 90-degree angle, take the taper angle of your bit and divide it into 90 - this is the ideal number of kerfs you'll need to cut.
3. If you don't know the taper angle of your bit, you can use this online calculator to figure out your taper angle.
4. Space out the cuts as evenly as possible; depending on the tools you have at your disposal, you may need to construct a jig that lets you do this, as you can see in one of the pictures above.
5. Use scrap pieces of walnut to test out kerf depth and see what works for you; I left only about a millimeter of wood at the bottom of each kerf, but you'll need to experiment to find what depth gives you the best bend.

Now that we have our walnut in shipshape and Bristol-fashion, it's time to make the mold that we'll be using to bend the wood into a 90-degree angle. I traced the bottom panel onto a piece of scrap wood and cut it out, leaving a negative mold for us to use. I then cut around this piece, making an edge small enough that a clamp could fit comfortably around it.

And so begins the most challenging part of the project.

Walnut is an especially difficult type of wood to bend, as the grain is denser than other woods - this makes it hard for steam or water to absorb evenly into the wood. The fibers in the walnut grain are also shorter than in other woods, making the piece more susceptible to cracking or springback. It took a lot of trial and error on scrap pieces of wood before finally finding a method that worked.

I opted to use boiling water to bend the wood, and found it much faster and gave me better results than using a steambox. I used an electric tea kettle to boil the water, as it works quickly and I could be sure it was at the right temperature.

The kerfs that we cut into the wood earlier help make the wood more pliable, but here are a couple of tips I learned along the way:

1. Make sure the water you are using is boiling; Lignin, the natural glue that holds wood fibers together, begins to soften around 180°F, but ideally, the water should be at 212°F to ensure the wood is properly heated.
2. If you have the means to (which I did not), adding a metal backing strap on the tension side of the bend can prevent the wood from cracking.
3. Soaking the wood in a mixture of water and fabric softener will make it more flexible.

For more tips, I found this jocular fellow on YouTube demonstrating how to Kerf-bend wood.

Phew! Now that the steam-bending is out of the way, we can focus on something a little easier: crafting the top and bottom panels that make up the rest of the exterior. Using the template we cut out earlier, we'll transfer the pattern onto the cardboard. I used a Tri-Fold cardboard piece I found at Michaels. For the fold lines, I simply used a razor to score them onto the cardboard. Fold the model together accordingly, then use hot glue to glue everything together.

After working with fiberglass, I've gotta say, it's a magical material. You start off with an unassuming piece of fabric, and slowly, layer by layer, watch it transform into a sleek plastic. Fiberglass was commonly used in the '50s for automobile bodies, so it's often associated with a retro-futuristic aesthetic - a perfect choice for our synth. Fun fact I learned while researching this article: the process for making fiberglass was patented in 1938, and the word "Fiberglass" itself reached peak usage in the English language in 1977.

There are two main types of resin you can choose from: Polyester resin or Epoxy resin. I chose to use Epoxy, as it is stronger and less prone to warping. The fiberglass itself also comes in a few weaves, but for this project I went with a Plain Weave Fiberglass cloth. If you'd like to learn more about the different types of fiberglass, here's a website that breaks down the different types of fiberglass reinforcement.

Once you have your cloth, cut out a piece big enough to cover the panel, making sure to leave plenty of excess fabric around the sides. You'll want to mix your epoxy according to the instructions on the box and get started with the fiberglass right away, as you'll have a limited amount of working time before the resin starts to thicken. Use a spongebrush to apply the epoxy onto the fiberglass, doing your best to massage away any air bubbles. You'll find that the fiberglass becomes transparent once it is saturated with resin. After the entire piece is throughly saturated, you can leave it propped up to dry.

Because I've had limited experience working with fiberglass, I started with the bottom panel, in case I made any mistakes. This proved to be a great decision, as I learned a few things:

1. First, I learned that fiberglass cloth doesn't like to bend around hard edges, and I kept getting air bubbles around the edges; I solved this by letting excess fiberglass hang loose on the sides, then cutting it off once fully cured.
2. Also, it took about 5 layers to get the piece to the strength and thickness that I needed
3. Lastly, I learned that applying layers within a few hours of each other, known as wet-on-wet bonding, leads to a stronger bond between layers.

As I was fiberglassing the cardboard, I had the idea to have the electronic components of the synth rest on a metal panel to give it a sleek look. Armed with practically no metalworking experience, I decided to outsource this portion of the project.

I drafted up a quick model in Fusion 360 using the measurements of the synth and sent it to a magical online service I discovered called Send Cut Send. If you provide them with a model of a metal piece they cut it for you for incredibly cheap, and you can pick from all sorts of different materials and finishes. I chose to go with aluminum as the material for both the plates, and because the back plate was so cheap I ordered an extra one with an anodized finish, just to experiment and see how it would look.

Now, with the exterior shell out of the way, we can focus on one of the most important components of the project: the keys. We’ll be making these out of wood for a luxurious feel, and as usual we’ll need a template to help us out.

I took the measurements of the synthesizer keybed and designed a model of the keys in Fusion 360. Here, I loosely based my model on an existing keyboard I had.

One thing that I learned during the design process is that the group of two black keys on a keyboard (the C# and D# group) are typically spaced further apart than the group of three piano keys (F#-G#-A#), something I had never considered. This means that the black keys aren't just centered on the white keys - they each have their own unique offset.

While designing the template, I also had to take into account the .5 mm washers I would be using in between each key, which cumulatively adds about half an inch to the length of the keybed.

Since I used walnut for the body of the synth, I had plenty of scraps leftover, which I quickly put to use for the black keys. Each black key in this synth is composed of two 1/4" pieces of walnut glued together, so we'll need to cut out 24 pieces total for all the black keys.

If you have the luxury of a CNC machine or laser cutter, you should be able to use the .dxf file from the previous step to cut these all out. If, like me, you don't, you can print out the PDF file from the previous step and trace the black keys onto the piece of walnut. Then use a jigsaw to cut the pieces out. I used a fine-toothed blade to cut the walnut to prevent tearout. Once you have your pieces cut out, you can then apply a dollop of wood glue to each piece, sandwich them together, and clamp them overnight.

You'll likely need to do a heckuvallota sanding to get the keys in shape; I mainly used 60 grit sandpaper, and constantly referenced the printed template to make sure I got the keys to the desired size.

And now the white keys!

Here, I decided to go with oak wood because I knew it would contrast nicely with the darker walnut keys. That, and it was one of my two options at Home Depot - that or poplar. (It was worth doing some research into different wood types, as I found out that poplar is prone to denting and is generally less durable, less dense, and less attractive than oak... poor poplar.)

Again, I used a fine-toothed jigsaw blade to cut these bad boys out, and again used 60 grit sandpaper to sand them to shape. The white keys are more intricate than the black keys, so it was also helpful to use a file to smooth out the right angles.

Before we can start working on the mechanics of the key, there's one more thing we have to do: add a final layer to the back end of the key. This will give the keys the thickness they need for a 1/8-inch steel rod to go through them. There’s no template for this part of the project, as it was all done by hand. You basically need to cut out a small, rectangular piece that will glue onto the back end of each key, as pictured above.

While the glue is setting, cut your steel rod so it's slightly longer than the length of the keybed.

Once the glue is dry, we can use our drill press to make the 1/8 inch hole that the steel rod will go through.

At this point, the keys are functionally done. All that's left before we start to focus on the key mechanism are the aesthetic touches. The black keys all get bevels, not just for aesthetics, but also so they don't get jammed against the white keys when they're pressed. To do this, mark out lines 1 millimeter away from each edge of the black keys, then use an electric sander to add a slight angle to that line.

Also, we need to add a thin coat of fiberglass and epoxy to each key. This really brings out the grain of the wood. Once that has dried, you can start sanding....so much sanding! Start out with a coarser grit, like 100, and work your way up bit by bit until you reach 3000 grit. This will give you a smooth polish.

Before we get to all the yummy electronics, there's still a few more things to do. Namely, we need to secure the steel rod to the bottom panel, add springs beneath the keys while leaving room for the circuit below (more on that in a few steps), and install the aptly-named key stop to prevent the keys from lifting too high.

I started by cutting a piece of wood to the length of the keybed, which was about 40 cm. This piece will hold all the springs that go under each key. I lined this piece up against the keys and marked out where the center of each key was, then drilled holes at these points. I screwed a spring into each hole, and periodically checked to make sure the springs lined up with the top center of each key. I also had to cut a small channel into this piece to fit the electronics.

To create the keys stops, I bought a long, U-shaped metal channel. From this long channel, I cut out 34 small pieces then glued them underneath each key. The remaining metal

The electronics behind the synth can be thought of as two different parts: the Teensy circuit and the Raspberry Pi circuit. On the Teensy side of things, we have 34 switches (one for each key) wired to 34 seperate inputs on the Teensy. These switches are normally open, until you press a key. The Teensy is running a code that continuously scans these switches, and if one is pressed, then a MIDI signal is sent to the Raspberry Pi. The wiring diagram above should give you a rough idea of how the circuit works.

Now, I know what you're thinking - you're saying, "Gabe, why don't I just use multiplexers to reduce the number of GPIO pins I'll have to use on the teensy?"

Great question reader! Definitely valid - in this case using multiplexers would probably be ideal. In my case, I'm new to electronics, and by the time I learned what multiplexers were, I was committed to the wiring I had chosen. If you want a more professional circuit though, you can check out for more information on how to incorporate multiplexers into your project.

Now that we have the wiring diagram for our microcontroller circuit, I needed to create the actual footprint for the circuit that goes under the keys. Unlike a wiring diagram, a footprint is a template that shows where all the components go on a circuit board. I set out to design this template in a program called EasyEDA, with the goal of sending it out to a PCB manufacturer.

It was at this point in the project that I realized I wasn't an electrical engineer. Even a simple circuit like this involves a lot of consideration, as it's not cheap to redo!

And here's a basic run-down of how the circuit works:

Firstly, this is an FPC, meaning the circuit is printed on a flexible material, unlike a traditional PCB (Printed Circuit Board). The circuit consists of a bunch of (fun word alert!) interdigitated pads. These are closely-spaced, exposed copper areas that look like interlocked fingers. Each one of these pads has a rubber dome switch above it that bridges the gap between the copper pads when pressed, closing a circuit.

The FPC also has a small tail coming out of it, with 34 small, rectangular pads at the end - it's designed to fit neatly into the 40-pin ZIF (Zero-Insertion-Force) connector, which we can then wire to the Teensy board.

An important thing to consider: I used EasyEDA because JLCPCB offers a discount to customers who use it. However, it's not the only software out there, and there are many PCB manufacturers to consider. If you live in the U.S, keep in mind that steep tariffs may apply during checkout for any PCB made outside of the U.S.

This was a step that challenged my patience! Here we're putting all the pieces together, and there are many things that can cause issues.

I began by attaching the heat sinks to the Raspberry Pi and then mounting the Pi to the back of the LCD screen. The LCD connects to the Pi using a DSI ribbon cable. Next, I plugged the RaspiAudio HAT onto the Pi’s GPIO header.

We’ll also need to prepare the audio output. Take your 3.5 mm TRS cable, strip the outer jacket, and identify the left, right, and ground wires. Solder these to the tip, ring, and sleeve, respectively.

The most time-consuming part of this step is the connection between the key switch matrix and the Teensy microcontroller. You’ll need to solder 35 traces from the flexible printed circuit (FPC) board to 35 pins on the Teensy (or to a breakout header, depending on your setup). Once that’s done, connect the FPC to the adapter board.

Finally, glue the carbon contact pads inside the rubber dome switches. In the pictures, you’ll see that I originally tried using tiny carbon strips — don’t do that! Use larger pads. Life is too short for small carbon contacts.

When it comes to programming the Teensy Board, you can find pre-existing libraries of code on Github (like the Teensyduino MIDI Library) that will turn your Teensy into a MIDI controller. However, ChatGPT 5 dropped earlier this year, and I was curious to test out what it could do. I took a screenshot of the Teensy board wiring diagram and asked it to write some code:

And voilà! We have some boilerplate; it took a little bit of trial-and-error, but I’ve attached a working version of the code in the files step. To upload this to your Teensy board, simply:

1. Download the Arduino IDE
2. Plug your Teensy board into your laptop via micro USB cable
3. Open the Arduino IDE and select your board from the board dropdown menu
4. Go to Tools>>USB Type and select MIDI
5. Paste the code in
6. Press the upload button

For those of you new to electronics, the Raspberry Pi is a tiny computer that can do many of the same things a regular desktop computer can (like use the internet and play videos). As a matter of fact, if you connect a mouse, keyboard, and monitor to it (like I did in the picture above) it will function like a slightly underpowered desktop computer.

For our synth, we'll be running a special operating system on the Raspberry Pi called Zynthian. Zynthian is an open-source operating system with a sleek user interface and tons of cool synth engines, each with hundreds of amazing presets.

I'll give you a basic walkthrough of how to set up your Raspberry Pi with Zynthian, along with how to troubleshoot a common error. If you want a more complete guide for how to set up Zynthian, check out the Zynthian Wiki. And if you've never used a Raspberry Pi before, check out the official getting started page for the Raspberry Pi.

1. First, start off by going to https://zynthian.org/#software to download the SD Image for Zynthian.
2. While that's downloading, go to https://www.raspberrypi.com/software/ and download the Raspberry Pi Imager - this is what we'll use to etch the Zynthian operating system onto our SD card.
3. Plug your SD Card into your computer
4. Upload the Zynthian .img file into Raspberry Pi Imager and etch it onto your SD (this may take some time to complete.)

You can then eject the SD card and voilà! You now have a synth in the palm of your hand. Plugging this into your Raspberry Pi should lead you to a screen where you can select different synth engines, record audio, and try out different effects.

If, while you are setting up your Zynthian, you get the ominous, slightly haunting error message above, fear not!

Zynthian is programmed to detect an outboard soundcard. If you don't have an audio card setup yet, or if you are using an audio card it doesn't recognize, it will fail to start up. Here's the fix:

1. Because there is no IP address showing up, this means your Raspberry Pi isn't connected to the internet. Connecting it to your home Wi-Fi router via an Ethernet cable should cause the IP address to show on the screen.
2. You will need a separate computer to control Zynthian. With an Ethernet cable, plug this computer into the same router you plugged your Pi into.
3. On your secondary computer, type in HTTP://xxx.xx.x.xx into your browser ( where xxx.xx.x.xx is the IP address showing on the Raspberry Pi screen).
4. This will take you to a login page. The password is “opensynth”. You should now be at a page where you can control various things about your Zynthian, like software, synth engines, and most importantly, hardware setup.
5. Under Hardware, click on Audio. Here you can select the proper sound device (or General USB).

By this point, the hardest steps are behind you. All that's left is painting the body and putting the finishing touches.

As far as the colors go, I was inspired by the peacock blue color of the 1968 Ford Bronco. However, automotive paint isn't cheap, and at over $700 per gallon a gallon I decided it was a bit out of my budget. I chose to go for a couple of $8 cans from Home Depot, using a sea glass turquoise for the top and a matte black for the bottom.

Once that's dried, it's a matter of screwing down the metal plates and finally putting the body together. I used screws to attach the bottom panel, and epoxy to glue down the top panel.

Looking back on this project, there were myriad things I should have done differently. If you're planning on building this, I would entreat you, Dear Reader, to keep the following in mind:

1. Walnut is difficult to bend. Consider using a different type of wood, like White Oak or Birch.
2. For kerf bending, invest in a quality router and tapered router bits. I wasted lots of time using a cheap Dremel rotary tool.
3. CARDBOARD IS NOT A PRACTICAL BUILDING MATERIAL FOR THIS!!! Haha I guess that should go without saying, but filling in corrugated cardboard with epoxy is a pain. An alternative material while still keeping the process the same would be to use foam board instead of cardboard. Just be sure to use foam that won't dissolve in Epoxy. Alternatively, modify the 3D model so you can 3D print this.
4. The metal panels were a bit too thick. The top one makes it difficult to touch the edges of the touch-screen display, and the smaller panel is too thick to allow an ordinary USB-C cable to fit.
5. Cutting out the keys accurately is extremely important. I used a jigsaw, but using a table saw or CNC machine will improve the quality of the finished product tremendously.
6. Speaking of the keys, also consider using a brass sleeve bushing for a better feel in the keys.
7. Consider adding your own touches! I originally intended to add some analog effects but never got around to it.

And just like that, in 24 easy steps, you have a functioning synthesizer! I've included a video of me messing around with one of the infinite sounds available with Zynthian.

Overall, I'm happy with how this turned out. There are certainly things I would have done differently (and still some things I want to work on!), but I learned so much throughout the course of this project, and I hope you picked up something new too.

If you enjoyed this project, consider following me here on Instructables or on my Instagram to see what I make next!