keybrd/tutorials/tutorial_4_split_keyboard_with_IOE.md

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 has four bus strips used as rows.
Two rows connected to a microcontroller, and two rows connected to a I/O expander.

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.

The microcontroller and I/O expander are connected by 4 jumper wires:
* ground
* power
* Serial CLock signal (SCL)
* Serial DAta signal (SDA)

A decoupling capacitor on the power pin dampens noise coming in through the power wire.

The microcontroller and I/O expander communicate via [I2C](http://en.wikipedia.org/wiki/I%C2%B2C) bus, which consists of two signals: SCL and SDA.
Two resistors pull-up voltage on the SCL and SDA.

I/O expander I2C address is configured by hardware pins.
The MCP23018 with all address pins grounded has an I2C address of ?? todo.

The I/O expander has two ports.  Each port has eight pins.
One port is connected to the matrix's rows.  The other port is connected to the matrix's columns.

## Building a split keyboard with I/O Expander
We will build a split keyboard adding parts to the basic breadboard keyboard described in [tutorial_1_breadboard_keyboard.md](tutorial_1_breadboard_keyboard.md)

todo add schematic

<!-- schematic with IOE power decoupling capacitor
This schematic was written by consulting the I/O expander's datasheet and using the ?? tool. -->

Continuing from the basic breadboard keyboard instructions:

<!--  At some point in the future, Markdown may support starting ordered lists at an arbitrary number. -->

4. Insert the I/O expander

5. Install I/O expander power
 * ground
 * power
 * capacitor

6. Install I2C bus
 * SCL
 * SDA
 * pull-up resistors on SCL and SDA

7. configure I2C address

8. Assemble key matrix as shown in the picture.

9. Connect I/O expander ports to matrix rows and columns

## Sketch for split keyboard with I/O Expander
The [keybrd_4_split_with_IOE_annotated.ino](keybrd_4_split_with_IOE_annotated/keybrd_4_split_with_IOE_annotated.ino)
 sketch explains how the I/O Expander works on a keyboard.

<a rel="license" href="http://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by/4.0/88x31.png" /></a><br /><span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">keybrd tutorial</span> by <a xmlns:cc="http://creativecommons.org/ns#" href="https://github.com/wolfv6/keybrd" property="cc:attributionName" rel="cc:attributionURL">Wolfram Volpi</a> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.<br />Permissions beyond the scope of this license may be available at <a xmlns:cc="http://creativecommons.org/ns#" href="https://github.com/wolfv6/keybrd/issues/new" rel="cc:morePermissions">https://github.com/wolfv6/keybrd/issues/new</a>.
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00			`keybrd Tutorial 4 - split keyboard with I/O Expander`
			`====================================================`
document 2016-05-10 15:05:25 +00:00			`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.`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00
			`## Overview of split keyboard with I/O Expander`
			`The breadboard in this picture models a split keyboard.`
document 2016-05-10 15:05:25 +00:00			`![breadboard keyboard with 2 rows and 4 columns of keys](images/breadboard_keyboard_2x5_labeled.jpg "2x5 breadboard keyboard")`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00
change activeHigh to static, add LED_PinNumber, RowScanner_SPI-ShiftRegisters, keybrd regression tests, remove MCP23018::begin() 2016-06-18 22:32:21 +00:00			`The breadboard has four bus strips used as rows.`
			`Two rows connected to a microcontroller, and two rows connected to a I/O expander.`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00
improve tutorials 2016-05-11 15:25:48 +00:00			`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.`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00
improve tutorials 2016-05-11 15:25:48 +00:00			`The microcontroller and I/O expander are connected by 4 jumper wires:`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00			`* ground`
			`* power`
improve tutorials 2016-05-11 15:25:48 +00:00			`* Serial CLock signal (SCL)`
			`* Serial DAta signal (SDA)`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00
improve tutorials 2016-05-11 18:46:53 +00:00			`A decoupling capacitor on the power pin dampens noise coming in through the power wire.`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00
improve tutorials 2016-05-11 15:25:48 +00:00			`The microcontroller and I/O expander communicate via [I2C](http://en.wikipedia.org/wiki/I%C2%B2C) bus, which consists of two signals: SCL and SDA.`
			`Two resistors pull-up voltage on the SCL and SDA.`

improve tutorials 2016-05-11 18:46:53 +00:00			`I/O expander I2C address is configured by hardware pins.`
			`The MCP23018 with all address pins grounded has an I2C address of ?? todo.`
improve tutorials 2016-05-11 15:25:48 +00:00
			`The I/O expander has two ports. Each port has eight pins.`
			`One port is connected to the matrix's rows. The other port is connected to the matrix's columns.`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00
			`## Building a split keyboard with I/O Expander`
improve tutorials 2016-05-11 18:46:53 +00:00			`We will build a split keyboard adding parts to the basic breadboard keyboard described in [tutorial_1_breadboard_keyboard.md](tutorial_1_breadboard_keyboard.md)`
improve tutorials 2016-05-11 15:25:48 +00:00
improve tutorials 2016-05-11 18:46:53 +00:00			`todo add schematic`

			`<!-- schematic with IOE power decoupling capacitor`
improve tutorials 2016-05-11 15:25:48 +00:00			`This schematic was written by consulting the I/O expander's datasheet and using the ?? tool. -->`

			`Continuing from the basic breadboard keyboard instructions:`

improve tutorials 2016-05-11 18:46:53 +00:00			`<!-- At some point in the future, Markdown may support starting ordered lists at an arbitrary number. -->`

improve tutorials 2016-05-11 15:25:48 +00:00			`4. Insert the I/O expander`

			`5. Install I/O expander power`
improve tutorials 2016-05-11 18:46:53 +00:00			`* ground`
			`* power`
			`* capacitor`
improve tutorials 2016-05-11 15:25:48 +00:00
			`6. Install I2C bus`
improve tutorials 2016-05-11 18:46:53 +00:00			`* SCL`
			`* SDA`
			`* pull-up resistors on SCL and SDA`
improve tutorials 2016-05-11 15:25:48 +00:00
			`7. configure I2C address`

			`8. Assemble key matrix as shown in the picture.`

			`9. Connect I/O expander ports to matrix rows and columns`
initial commit keybrd version 0.3.0 2016-05-09 14:05:08 +00:00
			`## Sketch for split keyboard with I/O Expander`
document 2016-05-10 15:05:25 +00:00			`The [keybrd_4_split_with_IOE_annotated.ino](keybrd_4_split_with_IOE_annotated/keybrd_4_split_with_IOE_annotated.ino)`
			`sketch explains how the I/O Expander works on a keyboard.`
improve tutorials 2016-05-11 15:25:48 +00:00
			<a rel="license" href="http://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by/4.0/88x31.png" /></a><br /><span xmlns:dct="http://purl.org/dc/terms/" property="dct:title">keybrd tutorial</span> by <a xmlns:cc="http://creativecommons.org/ns#" href="https://github.com/wolfv6/keybrd" property="cc:attributionName" rel="cc:attributionURL">Wolfram Volpi</a> is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.<br />Permissions beyond the scope of this license may be available at <a xmlns:cc="http://creativecommons.org/ns#" href="https://github.com/wolfv6/keybrd/issues/new" rel="cc:morePermissions">https://github.com/wolfv6/keybrd/issues/new</a>.