## Hardware requirements

#### Required

* single-board computer
  * audio out
  * gpio
* amoled display, min. 320x240, spi. (A hdmi display is not recommended.)

#### Mandatory

* usb otg (file transfer / midi)
* audio in (3.5mm minijack with selectable input)
* speaker
* accelerometer (spi)
* power button
* rechargeable battery
* battery indicator (5 digital out)

#### Shopping list for hacking the OTTO

* 1x Raspberry Pi 3 Model B
* 1x Display
* 1x Usb Audio Adapter (maybe Fe-Pi Raspberry Pi Zero 2 3 B+ Audio Sound Card Module I2S)
* 3x MCP23017 DIP SOP Bidirectional 16-Bit I/O Expander I2C IIC Serial Interface
* 5x KY-040 Rotary Encoder
* 1x MAX9812 Microphone
* 60x pcb push button switch
* 1x ADXL345 3-Axis Digital Acceleration of Gravity Tilt Module
* 1x TEA5767 76-108MHZ FM Stereo Radio Module with Antenna
* 4x DR21A01 DC 5V DPDT Relay Module Polarity reversal switch Board (to switch between audio sources)
* 10x LEDs - you never know when you need them
* different resistors, capacitors, cables, a breadboard, etc.



## Key mapping

This is a general overview of all the required keys and mappings to run the OTTO. Keys or functions not yet implemented are empty or marked with a *.

#### Modifier keys:
| key | action | shift+key | ctrl+key | gpio | osc | midi | comment |
|---|---|---|---|---|---|---|---|
| shift | - | - | - | digital in | - | - |   |
| ctrl  | - | - | - | digital in | - | - | only used on the desktop |

#### Main modes:
| key | action | shift+key | ctrl+key | gpio | osc | midi | comment |
|---|---|---|---|---|---|---|---|
| U |   | revert to preset* | synth | digital in  |   |   |   |
| J |   | revert to preset* | drum sampler  | digital in  |   |   |  |
| T |   | tape erase function* | tape  | digital in  |   |   |   |
| Y |   | signal flow screen*  | mixer | digital in  |   |   |   |

#### Other modes:
| key | action | shift+key | ctrl+key | gpio | osc | midi | comment |
|---|---|---|---|---|---|---|---|
| G |   |   | metronome | digital in  |   |   |   |
| * |   | select sequencer type* | sequencer* | digital in  |   |   |   |


### All the following keys change their behaviour depending on the mode selected (see above):

#### Rotary encoders:

| key | action | shift+key | ctrl+key | gpio | osc | midi | comment |
|---|---|---|---|---|---|---|---|
| Vol +* | master volume +  |   |   | digital in |   |   |   |
| Vol -* | master volume -  |   |   | digital in |   |   |   |
| Q | red +   |   |  | digital in |   |   |   |
| A | red -   |   |  | digital in |   |   |   |
| W | blue +  |   |  | digital in |   |   |   |
| S | blue -  |   |  | digital in |   |   |   |
| E | white + |   |  | digital in |   |   |   |
| D | white - |   |  | digital in |   |   |   |
| R | green + |   |  | digital in |   |   |   |
| F | green - |   |  | digital in |   |   |   |


#### Edits:
| key | action | shift+key | ctrl+key | gpio | osc | midi | comment |
|---|---|---|---|---|---|---|---|
| C* |  | lift all* | lift* | digital in  |   |   |   |
| V* |  | | drop* | digital in  |   |   |   |
| X* |  | | cut*  | digital in  |   |   |   |
| * |  | join* | split* | digital in  |   |   |   |

#### Transport:
| key | action | shift+key | ctrl+key | gpio | osc | midi | comment |
|---|---|---|---|---|---|---|---|
| Z     | record  |   |   | digital in  |   |   |   |
| space | start/stop   |   |   | digital in |   |   | might use 2 digital inputs |
| left arrow | rewind  | skip rewind  |   | digital in  |   |   |   |
| right arrow | forward | skip forward |   | digital in  |   |   |   |
| L     | toggle loop |  |   | digital in  |   |   |   |
| I     | go to loop in  | set loop in |   | digital in  |   |   |   |
| O     | go to loop out | set loop out |   | digital in  |   |   |   |

#### Track:
| key | action | shift+key | ctrl+key | gpio | osc | midi | comment |
|---|---|---|---|---|---|---|---|
| F1 | select track 1 |   |   | digital in  |   |   |   |
| F2 | select track 2 |   |   | digital in  |   |   |   |
| F3 | select track 3 |   |   | digital in  |   |   |   |
| F4 | select track 4 |   |   | digital in  |   |   |   |

#### Sound:
| key | action | shift+key | ctrl+key | gpio | osc | midi | comment |
|---|---|---|---|---|---|---|---|
| 1 |  |   |   | digital in  |   |   |   |
| 2 |  |   |   | digital in  |   |   |   |
| 3 |  |   |   | digital in  |   |   |   |
| 4 |  |   |   | digital in  |   |   |   |
| 5 |  |   |   | digital in  |   |   |   |
| 6 |  |   |   | digital in  |   |   |   |
| 7 |  |   |   | digital in  |   |   |   |
| 8 |  |   |   | digital in  |   |   |   |

#### Other:
| key | action | shift+key | ctrl+key | gpio | osc | midi | implemented |
|---|---|---|---|---|---|---|---|
|   | input select* |   |   | digital out  |   |   | line-in, microphone, radio  |
|   | album* | com* |   | digital in  |   |   |   |
|   | battery status |   |   | 6x digital out  |   |   |  |
|   | musical keys* |   |   | 14x digital in  |   |   | use a (virtual) midi keyboard |
|   | 2nd musical keys* |   |   | 10x digital in  |   |   | use a (virtual) midi keyboard |