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. ![breadboard keyboard with 2 rows and 4 columns of keys](images/breadboard_keyboard_2x5_labeled.jpg "2x5 breadboard 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](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](keybrd_4c_split_with_IOE/keybrd_4c_split_with_IOE.ino) sketch explains how the I/O Expander works on a keyboard. Creative Commons License
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.