for-split-keyboard

Split Infinitive is a 6x5x2 key ortholinear split keyboard PCB.

The goal of this project is to build a Let's Split keyboard clone with a number of alternative features:

* Designed to be easy to build with minimal soldering experience.
* Supports both 6x5x2 and 12x5x1 layouts and 2U keys in the bottom corners.
* Switch plate cutouts in the PCB so the same PCB can also be used as a switch plate.
* Serial communication over a TRRS cable in split configuration.
* Single sided PCB, so both halves of the keyboard are identical.

![PCB render](pcb.png)

# Bill of Materials (BOM)

* 4 PCBs, 2 for components and 2 as switch plates.
* 60 MX compatible switches.
* 60 1n4148 diodes.
* 1 or 2 Pro Micro controllers with headers or DIP sockets.
* 2 PJ320A 3.5mm TRRS jacks for split configuration.
* TRRS cable and micro USB cable.
* 8 2M standoffs (12mm, depending on required height)
* 16 2M screws
* 60 MX compatible key caps.

## Tools

* Hacksaw blade or similar
* Flat edged file or sanding paper
* Soldering iron and solder

# Ordering PCBs

PCBs can be manufactuered by a variety of online PCB fabricators, the PCB is 114x95mm. You can use [PCBShopper](https://pcbshopper.com/) to search for the best price.

The zip file in the gerber directory contains the gerber files your fabricator will need to make the PCB [for-split.zip](https://github.com/peej/for-split-keyboard/blob/master/gerber/for-split.zip) PCB.

When uploading the gerber zip files, use the default PCB settings. The plate PCB thickness should be 1.6mm for the switches to snap into the plate securely.

# Construction

* You will need 4 PCBs.
* Use the hacksaw blade to remove the 4 support screw holes from the 2 component PCBs.
* Use a hacksaw blade to remove the cutouts for the switch plate PCBs.
* Solder the diodes onto the underside of each PCB.
* Solder on the Pro Micro headers (or a 24 pin DIP socket) onto the underside of each PCB, do not solder on the Pro Micros yet.
  * In split configuration, both PCBs require a Pro Micro so add headers to both PCBs.
  * In non-split configuration, only the master side requires a Pro Micro.
* Solder the PJ320A TRRS sockets onto the underside of each PCB.
  * There are 2 positions per board, use the right position on the left hand PCB and the left position on the right hand PCB.
  * Ensure that the pins will not foul the placement of the switches and still allow the switches to sit flat on the PCB.
  * You may need to slightly bend the pins inwards away from the switch footprint.
* Insert the switches into the plate and then into the top of the PCBs.
  * Insert all the switches and ensure that the pins of each switch are correctly coming through the board and are not bent under the PCB.
  * The top switch that sits underneath the Pro Micro can be inserted in either a north or south facing orientation. North facing helps to prevent it shorting on the Pro Micro components.
* Solder all the switch pins.
* Solder on the Pro Micros, ensure that you get them the correct way around, the chip side should be face down towards the PCB.
* Attach the standoffs to the plate PCB with the screws.
* Connect the halves together with the TRRS cable.
* Flash both Pro Micros with the firmware, see the [QMK documentation](http://qmk.fm/) on how to build and flash the firmware.