Setup

Both sides of the Split Ortho Keyboard contain their own 6x5 diode matrix keyswitch PCB wired to the column and row pins of a TCA8418 keypad matrix expander.

Each TCA8418 takes care of handling keypress decoding and sends the event queue to the QT Py RP2040 over I2C.

Since only one address is possible on the TCA8418 you'll use the two independent I2C buses of the QT Py RP2040.

Wire Columns and Rows

Solder a wire to each column and row pad on the 6x5 PCBs.

Run these to their corresponding column and row pins on the TCA8418.

Repeat this for the second side.

QT Py Prep

In order to plug the STEMMA QT cable into the second I2C bus, solder the STEMMA QT/Qwiic breakout to the SDA, SCL, 3V, and GND pins as shown here.

Note, both sockets on the breakout run to the same on-board I2C bus, so one TCA8418 will plug into the breakout, while the other will plug into the QT Py's on-board STEMMA QT connector.

Case Build

You have two options for the case build -- fully 3D printed or mixed 3D printed with laser cut/CNC acrylic (or other materials).

Download the files from the link below.

3D and 2D fabrication files

3D Files

If you go with the fully 3D build, print the following files in PLA at ~0.2mm layer height and ~10% infill:

sok_plate x2
sok_top x2
sok_base_L
sok_baseR

3D/2D Mix Files

If you opt for a mix of 3D printed and 2D, here are the files you'll use:

3D Printed

sok_qt
sok_mid x2

2D Laser Cut/CNC Milled

sok_curves x2

Frame Prep

Use your soldering iron to press a threaded M3 brass heat set insert into each of the six mounting holes of the base walls. You use these to screw on the top plate later.

If doing the 3D + laser cut frame, insert a second set of inserts on the back side as well so you can screw on the top plate and the back plate.

Base Prep

Screw in M2.5 stand-offs to support the PCB and breakout board as shown.

You can also add rubber bumper feet.

Then, screw the back plate on using M3 screws (only necessary for the hybrid case build).

Switch Plate

To stabilize the keyswitches, snap them into the switch plate. Be sure their header pins are all oriented in the same direction as shown here.

Attach Keys To PCBs

Carefully align all the pins to the sockets and gently, slowly press the keys into place.

This takes patience and massaging, so maybe put on some soothing music and light a good candle first.

Then add your keycaps. (Ignore the photo that shows the caps already in place during the first step.)

Right Side Mounting

On the right side, mount just the TCA8418 and the keyswitch PCB as shown.

Stemma QT Cable Right Side

If you don't think you want to fully disconnect the halves, plug in the STEMMA QT cable as shown. This provides a neater appearance and allows you to push the cable in to adjust the slack.