keybrd Tutorial 4 - split keyboard with I/O Expander

After reading this tutorial you will be able to be able to modify a 2-matrix keybrd sketch to suite your own split keyboard design.

Overview of split keyboard with I/O Expander

The breadboard in this picture models a split keyboard.

The right matrix is connected to a microcontroller. The left matrix is connected to a I/O expander.

There is a total of 4 matrix rows, each on a dedicated power rail.

The microcontroller and I/O expander communicate by I2C via 4 jumper wires:

• ground
• power
• Serial CLock input (SCL)
• Serial DAta I/O (SDA)

The two resistors near the microcontroller pull-up voltage on the SCL and SDA pins.

The I/O expander has a small notch on one end, which identifies the end with pin 1. In the picture, pin 1 is on the right end.

Building a split keyboard with I/O Expander

The split keyboard is built on the Basic Breadboard Keyboard described in tutorial_0_keybrd_breadboard.md > Building a Basic Breadboard Keyboard

Follow these instructions to add a second matrix to the Basic Breadboard Keyboard:

1. Insert I2C jumper wires and pull-up resistors connecting to Teensy2.
   • follow the I2C and pull-up resistors tables (below) and consult Teensy pinout diagram in Connecting Teensy 2.0 to a Keyboard

todo these tables might not match the sketch

Teensy 2.0 pin connections tables

1. Insert jumper wires to connect MCP23018 I/O expander
   • follow pin connections tables (below) and consult pinout diagram in Connecting MCP23018 I/O Expander to a Keyboard

MCP23018 I/O expander pin connections tables

todo add capacitor

Sketch for split keyboard with I/O Expander

An annotated sketch for the split keyboard with I/O Expander is on keybrd_4_split_with_IOE_annotated.ino