The first step is to snap off the top and bottom of the PCB.

Use some pliers to gently bend at the perforation until the extra material snaps off.

Please use eye protection when breaking apart printed circuit boards.

Extra Column No More

Pry off the extra column at the far right of the board, as seen from the top side of the PCB.

You can save these key PCBs for use in another project later, such as a five-key macro strip!

Snip Snip

Use diagonal cutters to cut off the four key PCBs of the fifth column as shown, taking care to leave the first PCB in place.

Then, snap off two of the four key PCBs you just removed and reserve them for use with the + and ENTER keys later in the build.

You will eventually wire and solder these loose PCBs back into the numpad matrix.

More Snip Snip

Repeat the previous process to turn the bottom row of four into a spaced out row of three that will accommodate the 2u spacing of the 0 key.

This is the fundamental numpad layout you'll be working with. Next we'll clean up the board edges.

PCBs contain fiberglass which is hazardous to your health. Wear a facemask when filing or sanding the edges.

Edge Cleanup

Use your diagonal cutters to remove some of the excess material where the boards were separated, then file them down with a small metal file or sandpaper.

Be sure not to breathe in the dust!

3D Case

Use the files linked below and print the plate, top, base, and bottom parts.

Keyswitches, Plate, PCBs

Arrange the PCBs as shown, then snap a few keyswitches into place.

Be careful to align the two metal legs of the keyswitch with the sockets of the PCBs.

One Offs

For the 2u spaced keys, snap the keyswitches through the plate, then press the PCBs on from the back.


It's time to wire it all up! There are two sets of wiring tasks here -- one is to connect the key matrix column and row pins to the Feather RP2040 as well as the power, ground and NeoPixel pin. The other wiring task is to re-connect the snapped-off key PCBs to the others.

Note how the NeoPixel data line runs in a snake-like pattern through the grid.

Follow this wiring diagram to make the connections.

Here the plate and keyswitches have been removed to expose the wiring more clearly.

Note: Sometimes the PCB traces that run between the key PCBs can become damaged when neighboring PCBs have been cut, just due to strain on the thin connection. You can repair these with a short jumper wire as shown on the third PCB on the bottom row in the following photograph.


Now that you've wired everything, you can insert all of the keyswitches, and then add the keycaps.

Case Middle

Feed the Feather RP2040 through the case middle section as shown.


Case Top

Place the case top on top of the boards so you can sandwich everything and screw the parts together.

You can start with the three long screws.

Feather Screws, Standoffs

Add the four shorter screws to the Feather mounting holes.

Then, thread the seven hex standoffs onto the screws.

Case Bottom

Set the case bottom in place and then use the smallest screws to attach it to the hex standoffs from below.

You can also add rubber bumper feet as shown for a non-skid experience.

The Numpad 4000 is assembled and ready for coding in CircuitPython.

This guide was first published on Aug 17, 2021. It was last updated on Jun 08, 2021.

This page (Assemble the Numpad) was last updated on Aug 13, 2021.

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