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- 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.
- ![breadboard keyboard with 2 rows and 4 columns of keys]
- (images/breadboard_keyboard_2x4_labeled.jpg "2x5 breadboard 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](http://en.wikipedia.org/wiki/I%C2%B2C) 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:
- 4. 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](connecting_teensy2_to_keyboard.md)
-
- todo these tables might not match the sketch
-
- **Teensy 2.0 pin connections tables**
-
- | Pin Number | Row Column |
- |------------|-------------|
- | 21 | row_R0 |
- | 20 | row_R1 |
- | 0 | col_R0 |
- | 1 | col_R1 |
-
- | Pin Number | I2C |
- |------------|-------------|
- | GND | ground |
- | VCC | power |
- | 5 | SCL |
- | 6 | SDA |
-
- | Pin Number | 4.7K Ohms Pull-up Resistor |
- |------------|-------------|
- | 5 | VCC |
- | 6 | VCC |
-
- 5. 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](connecting_MCP23018_to_keyboard.md)
-
- **MCP23018 I/O expander pin connections tables**
-
- | Pin Number | Row Column |
- |------------|-------------|
- | 3 | row_L0 |
- | 4 | row_L1 |
- | 20 | col_L0 |
- | 21 | col_L1 |
- | 22 | col_L2 |
-
- | Pin Number | I2C |
- |------------|-------------|
- | 1 | ground |
- | 11 | power |
- | 12 | SCL |
- | 13 | SDA |
-
- | Pin Number | Jump to Pin |
- |------------|-------------|
- | 11 | 16 |
- | 1 | 15 |
-
- 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](keybrd_4_split_with_IOE_annotated/keybrd_4_split_with_IOE_annotated.ino)
-
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