mozc-doublesided

Gboard double sided version

This directory contains the firmware and hardware design for Gboard double sided version, which was released on Oct 1, 2024.

This is not an officially supported Google product.

Contents

The directory structure is as follows:

• case/ : STL files for case
• board/ : KiCad schematics and PCB layouts
• firmware/ : Firmware resources for STM32CubeIDE
• gerber/ : Gerber data for PCB production and assembly

Building Gboard double-sided Version

Parts

• Assembled A Type Board: 26 boards (incl. 1 primary board) - See BOM below
• Assembled B Type Board: 26 boards (incl. 1 primary board) - See BOM below
• USB Board: 1 board - See BOM below
• Cable A; JST ZH 1.5mm pitch 8pin 100mm forward double head: 25 units
• Cable B; JST ZH 1.5mm pitch 7pin 100mm forward double head: 1 units
• Pin Header; 1x4 pin 2.54mm pitch 12+mm height, (sample): 52 headers.
• 3D printed case: 26 pcs
• Self tapping screw (M2 10mm): 52 pcs
• Key switch (Cherry MX or compatible): 208 pcs.
• Key caps (For Cherry MX switch): 208 pcs.

A Type Board BOM

Reference	Description	Qty	Note
R1-R2	0402(metric: 1005) Resistor 510 ohm	2
R3-R4	0603(metric: 1608) Resistor 1K ohm	2	Primary board only
J2-J3	JST S8B-ZR	2
J4	JST S7B-ZR	1	Primary board only
U1	STMicro STM32F042F4P6	1
SW1-SW4	Kailh CPG151101S11-1	4
D1-D4	OPSCO Optoelectronics SK6812MINI-E	4
D5-D8	0805(metric: 2012) Small Signal Switching Diode	4
C1	0402(metric: 1005) Capacitor 0.1uF	1

The parts that are only on the primary board are not included in the BOM file (in gerber/ directory), so make sure that you choose one board to be the primary board and solder in the primary board specific parts.

B Type Board BOM

Reference	Description	Qty	Note
R2	0402(metric: 1005) Resistor 510 ohm	1
SW1-SW4	Kailh CPG151101S11-1	4
D1-D4	OPSCO Optoelectronics SK6812MINI-E	4
D5-D8	0805(metric: 2012) Small Signal Switching Diode	4

USB Board BOM

Reference	Description	Qty	Note
U1	1A/3.3V Regulator AMS1117-3.3	1
R1-R2	0402(metric: 1005) Resistor 5.1K ohm	2
R3-R4	0402(metric: 1005) Resistor 22 ohm	2
R5	0402(metric: 1005) Resistor 1.5K ohm	1
J1	JST S7B-ZR	1
J2	USB Type-C 16pin connector	1
C1	0402(metric: 1005) Capacitor 10uF	1
C2	0402(metric: 1005) Capacitor 2.2uF	1
C3-C4	0402(metric: 1005) Capacitor 47pF	2

Hardware

Step 1: Prepare 3d printed parts

The case/ directory of this repository has STL files for the case. The case consists of 26 parts (case00.stl - case25.stl). Each part has a number engraved on the inside. For example, when assembling, you will insert the protrusion of case 0 into the hole of case 1.

We also provide a jig (case/jig.stl) for soldering between the A type boards and B type boards. Please print this too.

Step 2: Prepare PCB

PCB Production and Assembly

First, you need to build 26 A type boards and 26 B type boards, and one USB board. You may be able to use existing gerber data, BOM, and CPL (positions) from gerber/ directory.

Board Type	Gerber	BOM	CPL
A	main_panel.zip	main_panel_bom.csv	main_panel_positions.csv
B	sub_panel.zip	sub_panel_bom.csv	sub_panel_positions.csv
USB	usb.zip	usb_bom.csv	usb_positions.csv

Prepared board data for the A type board and the B type board contains 9 boards in a panel. So, you need to produce 3 panels to build 27 (26 required + 1 spare) boards. You also need one USB board.

Firmware upload

Next, let's burn the prebuilt firmware.

Connect the following 4 pads, SWDIO, SWCLK, GND, and +3.3V with ST-LINK. You can use STM32CubeProgrammer to configure the device and to burn the prebuilt firmware. There's no connector, just holes in the PCB so make sure you keep a secure connection while programming the device.

Once the programmer establishes the connection with the A type board, you need to write the Option bytes. Under the User Configuration section, you will see the BOOT_SEL bit. You need to ensure the bit is unchecked before pushing the Apply button.

Next, you will go to the Erasing & Programming section to burn the prebuilt firmware, firmware/prebuilt/mozc.elf. Select the binary from the Browse button, put 0x08000000 for the Start address, then press the Start Programming button.

You need to burn the same settings and firmware into all the Boards A.

Primary A Type Board Specific Modifications

You need to choose one of the A type boards to be the primary A type board and add three parts to it.

1. J4 JST S7B-ZR connector header
2. R3 0603 Resistor 1K ohm
3. R4 0603 Resistor 1K ohm

Construct the A/B Type Board Pair Modules

You need to prepare 26 pairs of the A type board and B type board. They should be paired as the following picture shows. Each P Connector and each S connector should be connected using the 1x4 pin headers respectively.

Make sure that the IN side of the A type board and B type board face each other.

Also, the distance should be adjusted to fit the case. It will help to print the included jig STL to hold both boards while soldering the pin headers.

Step 3: Insert PCB to case

Primary A/B Pair Module

Connect the primary module and the USB board.

Insert the USB board into case 0.

All Pair Modules

Insert each paired module into a case. You need to ensure the A type board is always placed on the bottom side.

Step 4: Connect the cases together

You need to connect all the UP socket and DOWN socket pairs. Please be careful not to connect the same type of socket, i.e. UP and UP, or DOWN and DOWN together. It will cause a short circuit and destroy the chips when powered on. If you notice a smell or see smoke, disconnect the power immediately. This may prevent damage to the boards.

The below picture shows the connections. Please make sure that module 0 and module 25 are not connected to each other.

Note that this picture is simplified and doesn't reflect the 3d structure of the keyboard. So, module 25 will be placed upside down.

You can use screws to keep the boards tightly connected.

Firmware

Step 1: Environment setup

You need to install STMicroelectronics's official tools to develop STM32.

• STM32CubeIDE - Confirmed with 1.16.1.
• STM32CubeMX - Confirmed with 6.12.1.

Alternatively, you can use Visual Studio Code with the STM32 VS Code Extension, STM32CubeMX, and STM32CubeCLT if your development environment is not on Windows.

• Visual Studio Code - Confirmed with 1.93.0.

• STM32 VS Code Extension - Confirmed with 2.1.0.

• STM32CubeCLT - Confirmed with 1.16.1. You will be asked to specify the path to the VS Code Extension. You may add { "STM32VSCodeExtension.cubeCLT.path": "/opt/ST/STM32CubeCLT_1.16.1" } to .vscode/settings.json.

  You will need the ST-LINK or something equivalent to upload the firmware.

Step 2: Compile and upload

Steps for the STM32CubeIDE:

1. Launch STM32CubeIDE with mozc-doublesided directory as workspace.
2. Start a project via Start new project from STM32CubeMX file (.ioc) to open a configuration dialog.
3. Select firmware/mozc-doublesided.ioc as STM32CubeMX .ioc file and push Finish button to generated required resources.
4. Apply patches. (See the following instructions)
5. Set Release as the active project, from Project > Build Configurations > Set Active > 2 Release. Debug doesn't fit the available memory size.
6. Build, from Project > Build All.

The built binary will be produced at firmware/Release/firmware.elf.

Steps for the Visual Studio Code:

1. Open firmware/mozc-doublesided.ioc by STM32CubeMX and push the GENERATE CODE button. You may need to follow instructions if you are asked to install something required in the process.
2. Launch VSCode and open the folder firmware.
3. Apply patches. (See the following instructions)
4. Select Release or RelWithDebInfo from the build presets. Debug doesn't fit the available memory size.
5. Build from the status bar, or other user interfaces.

The built binary will be produced at build/Release/firmware.elf.

If you saw errors on linking the binary involving STM32F042F6Px_FLASH.ld, you may need a patch to make it work with your installed toolchain.

Try patch < STM32F042F6Px_FLASH.ld.diff.

Steps to apply patches:

In the firmware directory, apply the firmware.diff patch to the generate resources via the following command.

$ patch -p1 < firmware.diff

License

See LICENSE file in this directory.