3.2 KiB
keybrd Tutorial 4 - split keyboard with I/O Expander
When you finish 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 breadboard's four bus strips are used as rows. Two rows (blue buses) are connected to the microcontroller. Two rows (red buses) are connected to the I/O expander.
The I/O expander is a MCP23S17. It has a small notch on one end, which identifies pin 1. In the picture, pin 1 is on the right end.
The MCP23S17 communicates via SPI protocol, where Teensy LC is the master, and MCP23S17 is slave. The Teensy LC and MCP23S17 are connected by 6 jumper wires:
| CONNECTION | Teensy LC | MCP23S17 |
|---|---|---|
| ground | GND | VSS |
| power | 3.3v | VDD |
| Serial Clock | SCK0 | SCK |
| Master Out, Slave In | MOSI0 | SI |
| Master In, Slave Out | MISO0 | SO |
| Chip Select | CS0 | /CS |
A decoupling capacitor suppresses high-frequency noise from the power supply.
MCP23S17's I/O expander address is configured by hardware pins. The MCP23S17 with all address pins grounded has an device address of 0x20.
The MCP23S17's /RESET pin is connected to VDD.
The MCP23S17 I/O expander has two ports. Each port has eight pins. Port B is connected to the matrix's rows. Port A is connected to the matrix's columns.
Building a split keyboard with I/O Expander
Starting with the basic breadboard keyboard described in tutorial_1_breadboard_keyboard.md, add parts as described above. Refer to the MCP23S17 datasheet to locate its pins.
Sketch for split keyboard with I/O Expander
The keybrd_4c_split_with_IOE.ino sketch explains how the I/O Expander works on a keyboard.
keybrd tutorial by Wolfram Volpi is licensed under a Creative Commons Attribution 4.0 International License.
Permissions beyond the scope of this license may be available at https://github.com/wolfv6/keybrd/issues/new.