Perplexity

Overview

Perplexity is a 34-36 key split keyboard with a lot of features:

• Support for MX and Choc switches, with the correct spacing for each switch (break away the extra parts if using MX)
• Support for Pro Micro or MCP23017 on secondary half
• Support for either TRRS or USB-C connection between halves using I2C or serial
• Support for SSD1306 OLED displays
• Many different options for thumb cluster (variants of Absolem and Ferris thumb clusters)
• Third thumb cluster key is removable
• Support for extra tact switches or LEDs

Viewer

The Perplexity Viewer allows you to show and hide the different sets of thumb cluster positions to assist in choosing which layout you will use.

Download PCB files

Download the gerber files and KiCad project, licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Options

Other than the keyboard layouts, here are all of the options and how to use them:

Controller

On the secondary half, you can solder an MCP23017 IO expander chip instead of a Pro Micro. You will need to use I2C instead of a serial connection between the two halves.

Connection

Protocol

By default, the PCB uses a serial connection between the two halves. If you need to change it to I2C, you can solder the jumper next to the footprint for the TRRS connector and solder two 2.2k resistors in the resistor footprints.

Connector

You can use either a PJ-320A TRRS connector or a TYPE-C-31-M-12 connector. However, you cannot use the Type-C connector if you want to use the DIP switch.

LEDs/tact switches

Underneath the third column, there are footprints for two SMD tact switches or two SMD LEDs (0805 package). To use the tact switches, you will need to solder diodes to the two rotated footprints nearest to the tact switches. To use the LEDs, you will need to solder 220 ohm resistors (also 0805 package) to the resistor footprints located near the bottom switch in the fourth column.

DIP switch

Next to the USB Type-C connector footprint, there is a footprint for a single SMD DIP switch (part number DSIC01LSGET on LCSC). This can be used in QMK, it does not function as a power switch.

OLED

An SSD1306 OLED display can be placed over the controller. To connect it, solder the jumpers on the opposite side of the PCB as you are soldering the OLED.

Reset switch

There are two options for positioning a reset switch; the first is on the bottom side of the board under the controller, and the second is below the USB-C footprint. The two positions use different footprints. If you use the footprint below the USB-C footprint, you need to cut off one of the mounting pins on the switch, and you cannot use some thumb key positions. The switch is not necessary on a half that uses an MCP23017.