The Mercutio is a 40% through hole DIY kit with an OLED and rotary encoder. We chose a 40% for our 2nd release because it’s the great divide between useable boards and boards that are too small. Pretty much everyone finds 60% boards useable, you might miss the arrow keys, but it’s an easy problem to solve with layers. Once you get down to 40%, however, you lose numbers and some punctuation. That amount of layering takes some getting used to. Personally, I wanted to see more budget 40% options because I would hate to spend top dollar for a 40%, wait a long time, just to find out I don’t like it. At this price point, we feel we’re providing a very accessible and affordable option for people to “just try out.”

Product Page

The Mercutio has some very minorly complicated parts, but isn’t too difficult altogether. If you have any problems during your build, feel free to stop in to the MechWild Discord Server and ask for assistance. I genuinely love this board and hope that you do as well.

Required Tools and Components

These tools and components are required to complete the project and are not included in the kit. The linked names of the components will generally link to a place where you can buy them.

These tools are not necessary to complete the build, but might make the process a little easier for you or help you correct mistakes if you make them.

Included Components


Note: You will likely have extras of some components. This is normal and is to account for small mistakes.

1x PCB

1x Switch Plate

1x Bottom Plate

50x 1N4148 Diodes


1x ATmega328p

1x 28 Pin IC Socket


2x 6x6mm Reset Button

Boot, Reset

10x M2 10mm Standoffs

3x M2 15mm Standoffs

26x M2x6 Screws

M2x6 Screws

4x Rubber Feet

1x 1.5KOhm Resistor


2x 68 Ohm Resistor

R2, R3

2x 5.6KOhm Resistor

R4, R5

2x Zener Diodes

D47, D48

1x Resettable Fuse


2x 22pF Capacitors

C1, C2

1x .1uF Capacitor


1x 10uF Capacitor


1x 16MHz Oscillating Crystal


1x Rotary Encoder

1x Encoder Knob

1x USB C Port



1x Acryllic Guard

Step 1: Solder USB

 To do this, I recommend having high quality solder and extra flux on hand if possible. The simple summary is:

1. you are going to solder one of the holes on the top of the PCB.
For this one I chose the top right hole

2. you then push the USB port against it lightly (but with enough pressure to hold it there) and reheat the hole you soldered from the underside of the pcb

Before soldering more points on the port, make sure the port is on the top side of the PCB and is flat against the surface.


3. Then flip the PCB over so it is bottom up, and fill the anchor spots with solder for a good mechanical connection

4. Then this is where you especially want high quality solder and/or extra flux. You are going to go through and solder each of the holes. You can get away with feeding a small amount of solder to your soldering iron and dragging it across the pins, then going back and touching up spots if it looks like 2 of the pins are connected (you don’t want this, it wont work that way)

This image shows the base steps for seating it initially:

This image shows soldering the shielding anchors, then doing each of the pins:

And there you go; The hardest part is done now.


Step 2: R4, R5, D48, D47

Next you will do the components to the left of the USB port.

This is R4, R5, D48, and D47 (refer to the table above for the components if you are unsure)

For R4 and R5 the orientation doesn’t matter but it is crucial that you have the correct resistors. PLEASE refer to the table above to ensure you have the correct ones. I like to make sure the brown band of all the resistors is facing to the left, but that doesn’t matter except for looks.

For D47 and D48 the orientation matters. You need to solder it in so that the black band on the diode is on the side closest to the USB port (it should match up with the band on the silkscreen under the diode)

Put all of these components into the board, bend the legs outwards to hold them in place, solder them in from the bottom, and then cut the excess from the legs away to keep the area easy to manage for future components.

Step 3: R1, R2, R3

 Again, orientation doesn’t matter here, but it is crucial that you have the correct resistors. I also do these so that the brown band is on the left.

You’re gonna hear this a lot through the guide, but now we will bend the legs, solder it, and clip the excess.

Step 4: F1

This is the fuse. Orientation doesn’t matter, but I do it with the text facing upwards so that you can see the part number if needed. You will want to seat this as far down as it will sit before the bends (the little knees on the legs) keep it from going further in, then take the legs on the bottom of the board and bend them outwards to hold it in place. From here, fold it downwards towards the top of the board so that it will lay flat on the board. Then go ahead and solder it from the back and clip the legs.

Step 5: C1, Y1, C2, C3

Orientation of these parts doesn’t matter. I do it with the text facing left on C1 and C2 and I put Y1 so that the text is readable when looking at the board normally. You know the drill, bend the legs to keep them in place, solder, and clip.

Please make sure you are putting the capacitors (C1, C2, C3) in the right order. C1 and C2 are brown and C3 is blue.

Once those are in, bend, solder, clip.

Step 6: C4

Orientation matters here. Take the side of the Capacitor (yes, this is also a capacitor) with the white line running the length of it (with a minus sign in the middle of it) and face that towards the top edge of the board (correlating to the solid area on the silkscreen).

Bend the legs, solder, clip.

Step 7: Reset and Boot Buttons

The legs for these types of switches come out of 2 of the sides, not from the corners. Make sure you have it lined up so the legs come out the left and right of the button. Hold them in place, look at the bottom of the board, bend the legs flat against the PCB, then solder into place.

Clip if you’d like, but if you folded them flat enough against the board you shouldn’t need to.

Step 8: U1

Orientation matters here. The socket for the Microcontroller now. One of the short edges has a notch in it. This notch will face to the right. I do the same as I do for the buttons and I bend the legs towards the center of the socket from the bottom, then I solder. 

Same as for the buttons, clip if you’d like, but if you folded them flat enough against the board you shouldn’t need to.

Step 9: D46

Orientation matters here. This is important for testing. D46 is the diode in the top right hand corner of the diode array. Locate it and put the diode in with the black bar on the body of the diode on the left hand side. It should match up with the line on the silkscreen below the diode. 

Bend the legs, solder, clip.

Step 10: OLED

Orientation matters here. Place the 4 pin header that came with the OLED into the board and solder one of the pins to make sure that it is being held in place.

Then make sure the pins are seated all the way and not angled, and go ahead and solder the other pins.

Now you are going to place it in the board, flip the PCB over, and solder the pin furthest from the edge in (It is the end pin that IS CIRCLE and is NOT SQUARE)

The reason we are doing just one pin first is because the OLED is probably all kinds of crooked like this:

To fix this, we will lift one end while reheating the single pin we soldered. Line up the OLED so it looks good from the top, and then clip the legs of the header pins.


Lookin’ good now!

Step 11: Encoder

Some of the pins might be a little bent weird. That’s just because the metal is very thin and from being roughed up in shipping. Bend the pins back into a nice neat line and throw it onto the PCB.

Same as the buttons and IC socket, just bend the pins inwards and solder to finish this off.

Step 12: Insert ATMega328p

Orientation matters here. BE VERY CAREFUL WITH THIS PART.

Any amount of Static Shock could be enough to scramble its brain and stop it from working correctly! Please use appropriate ESD protection!

This is the brain of the entire board. It ships to you preprogrammed, so you will not need to put any additional firmware on it if you do not wish to.

The pins on this microcontroller angle outwards slightly by default. This means you want be able to put it in the socket easily until that is corrected.

To bend the pins inwards slightly, I recommend pushing it against your tabletop or another flat surface very gently and rolling it slowly. You don’t need it to bend inwards, but instead you want it to be closer to straight.

Then you gently place it in the socket, making sure to have the notch facing to the right (same direction as the socket’s notch), and gently apply even pressure across it until it is all the way seated.

MAKE SURE THAT IT IS SEATED COMPLETELYT BEFORE TESTING. If there is too big of a gap it can cause problems that might hurt the components!

Step 13: Test

Now you will plug in your board, wait a second for the OLED to come on (the first boot often takes 4 or 5 seconds before it is ready to use).

After your computer has set up your new device and the OLED is working, test to see that it is working correctly by using the encoder. Clicking it in like a button will mute your computer, and turning it either direction will control the volume.

Step 14: The Rest of the Diodes

Nice and easy. Just pay attention to the orientation of them, and maybe whistle or something. This part is the worst.

Step 15: Stabilizers and Switches

As with all other keyboard builds, your next step will be installing stabilizers onto the PCB. 

Once your stabilizers are in the PCB, you can set it aside for now and insert some switches into the plate. We recommend filling in the corners and installing some switches in the center of the plate.

You can now take this plate+switches assembly and place it on top of the PCB, making sure the switch pins poke through the PCB. From here, you can insert the rest of the switches and be sure to check each switch is fully seated in the plate and both switch pins go through the PCB.

When all your switches are seated in the plate, you can solder them in.

Here are the available layout options to choose from, for your reference while putting the switches onto the PCB:

Step 16: Assemble

Nice and simple. Now we take the bottom of the board and put all the standoffs onto it.

The tall standoffs go in these 3 holes:

The short standoffs go in all the other ones that are for standoffs:

If you are adding aluminum feet and/or rubber feet, do that now.

Then the PCB should slide onto the standoffs, to allow you to screw the plate to the standoffs directly.

If you soldered your switches on already, you will be putting them on together as one piece.

If you millmaxed your PCB or just haven’t bothered putting switches on yet, they will be two pieces like this:

Then once the plate is screwed into place, go ahead and put the protective acrylic piece and encoder knob on there as well:

Step 17: Customize and Enjoy!

Now you have a fully functional and feature packed keyboard to go off and type out your deepest thoughts with. Go ahead and check in to the MechWild Discord server and chat with us using it. Typing on a 40% takes a day or two to really get the hang of, but make sure not to give up as it is oddly satisfying when you get the hang of it. If you have any questions about how to do some things drop into the Discord and ask while trying it out.

If you recognized that I recycled this last step from the BDE build guide, give yourself a pat on the back.

Flashing Instructions

Hold boot button

press and release reset button

wait a few seconds

release boot button



Unplug the board

Press and hold tab

Plug the board in

Wait a few seconds

Release tab