90 lines
3.1 KiB
Markdown
90 lines
3.1 KiB
Markdown
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keybrd Tutorial 4 - split keyboard with I/O Expander
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====================================================
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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.
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## Overview of split keyboard with I/O Expander
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The breadboard in this picture models a split keyboard.
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![breadboard keyboard with 2 rows and 4 columns of keys]
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(images/breadboard_keyboard_2x4_labeled.jpg "2x5 breadboard keyboard")
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The right matrix is connected to a microcontroller.
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The left matrix is connected to a I/O expander.
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There is a total of 4 matrix rows, each on a dedicated power rail.
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The microcontroller and I/O expander communicate by [I2C](http://en.wikipedia.org/wiki/I%C2%B2C) via 4 jumper wires:
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* ground
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* power
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* Serial CLock input (SCL)
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* Serial DAta I/O (SDA)
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The two resistors near the microcontroller pull-up voltage on the SCL and SDA pins.
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The I/O expander has a small notch on one end, which identifies the end with pin 1.
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In the picture, pin 1 is on the right end.
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## Building a split keyboard with I/O Expander
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The split keyboard is built on the Basic Breadboard Keyboard described in
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tutorial_0_keybrd_breadboard.md > Building a Basic Breadboard Keyboard
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Follow these instructions to add a second matrix to the Basic Breadboard Keyboard:
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4. Insert I2C jumper wires and pull-up resistors connecting to Teensy2.
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* follow the I2C and pull-up resistors tables (below) and consult Teensy pinout diagram in
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[Connecting Teensy 2.0 to a Keyboard](connecting_teensy2_to_keyboard.md)
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todo these tables might not match the sketch
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**Teensy 2.0 pin connections tables**
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| Pin Number | Row Column |
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|------------|-------------|
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| 21 | row_R0 |
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| 20 | row_R1 |
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| 0 | col_R0 |
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| 1 | col_R1 |
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| Pin Number | I2C |
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|------------|-------------|
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| GND | ground |
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| VCC | power |
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| 5 | SCL |
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| 6 | SDA |
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| Pin Number | 4.7K Ohms Pull-up Resistor |
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|------------|-------------|
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| 5 | VCC |
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| 6 | VCC |
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5. Insert jumper wires to connect MCP23018 I/O expander
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* follow pin connections tables (below) and consult pinout diagram in
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[Connecting MCP23018 I/O Expander to a Keyboard](connecting_MCP23018_to_keyboard.md)
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**MCP23018 I/O expander pin connections tables**
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| Pin Number | Row Column |
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|------------|-------------|
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| 3 | row_L0 |
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| 4 | row_L1 |
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| 20 | col_L0 |
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| 21 | col_L1 |
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| 22 | col_L2 |
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| Pin Number | I2C |
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|------------|-------------|
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| 1 | ground |
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| 11 | power |
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| 12 | SCL |
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| 13 | SDA |
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| Pin Number | Jump to Pin |
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|------------|-------------|
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| 11 | 16 |
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| 1 | 15 |
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todo add capacitor
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## Sketch for split keyboard with I/O Expander
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An annotated sketch for the split keyboard with I/O Expander is on
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[keybrd_4_split_with_IOE_annotated.ino](keybrd_4_split_with_IOE_annotated/keybrd_4_split_with_IOE_annotated.ino)
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