Documentation for “Zerocat Mini Machine”
Generated on: Tue, 01 Aug 2023 10:42:37 +0200
Repository: git://
Version: v0.0.0-249-9bbfd9f
Branch: master

Zerocat Mini Machine

A word processing machine of supreme integrity.


Foldable chassis with transparent keyboard, both designed to ease user’s audit and inspection.

Copyright (C) 2021 Kai Mertens
Copyright (C) 2022, 2023 Kai Mertens

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License".

Section #../doc/



Zerocat Mini Machine is a laptop-like, word processing machine of supreme integrity. It uses encrypted Morse code for inter-device data transmission, and focuses on audio rather than wire.

This file is to be as short as possible. It provides information on how to generate the project’s verbose documentation, and how to compile the source code, if any.


It is assumed that you are running a GNU/Linux-libre operating system. We recommend to run GNU Guix System – alternatively, install the GNU Guix package manager.

Get the Sources

Use Git to clone the project’s sources:

    $ git clone git://

Change into the project’s documentation folder:

    $ cd zerocat-mini-machine/doc/

Study this to get started:

    $ cat ../doc/


All paths within the documentation are relative to the location of the documentation source files, which are located in this project’s doc/ folder.


Versions are tagged according to the following pattern:


A tag should be annotated with related change log entries.

The first tag should be: v0.0.0

To checkout a version tag, run:

    git checkout vx.x.x

However, this should be optional.
Using the tip of branch master should be just fine.

Project Environment

Use GNU Make to create a dedicated profile, and an up-to-date profile generation. This allows you to match your environment to the one used by Zerocat, thus yielding for bit-identical results:

    $ make -C ../guix pull

Checkout the profile generation, instantiate channels, create a pure shell that provides nothing but prerequisites:

    $ make -C ../guix environment

To confirm that your project environment is properly set up, run:

    [env]$ make -C ../guix usage

Invocations of make to generate the documentation, compile the sources, etc., should be done from this project environment, only.

To restore the initial environment, later on, when you are done with this project, type:

    [env]$ exit

To remove this project’s handy guix profile, type:

    $ make -C ../guix clean

This will remove symlinks only. If you want to remove the profile from your system, run the GNU Guix Garbage Collector.

To list all available targets, type:

    $ make -C ../guix help

Make Documentation from Project’s Environment

To build the documentation, type:

    [env]$ make -C ../doc

The terminal output should provide a shortcut to the index.html file of the generated HTML documentation. Open this file with your favorite browser.

To get a full list of available targets, type:

    [env]$ make -C ../doc help

To clean-up, type:

    [env]$ make -C ../doc clean

Make Documentation from System’s Shell

To build the documentation in one go, type:

    $ echo "make -C ../doc" | make -C ../guix environment
Section #../doc/


Documentation Files

Documentation source files are written in markdown syntax. They should carry their individual copyright and license notices right below the title giving headline, e.g.:


    Copyright (C) <Year>  <Name-of-Author> <Email-Address>  

    Permission is granted to copy, distribute and/or modify this document
    under the terms of the GNU Free Documentation License, Version 1.3
    or any later version published by the Free Software Foundation;
    with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
    Texts. A copy of the license is included in the section entitled
    "GNU Free Documentation License".



The generated documentation carries a license notice right at top on its title page, with copyright statements generated from git log output.

Sections of the generated documentation are build from selected markdown source files, with their individual copyright and license notice stripped.

In order to enrich the generated documentation ...

... and adapt ../doc/Makefile to produce nice output.

In case more tools are needed, don't forget to update ../guix/manifest0.scm.


To make your image look nice within the documentation, select a landscape layout of 16:9 aspect ratio.

Use ImageMagick to prepare your image, e.g.:

If your image is big, reduce it to a maximal width of 2000 pixel:

    mogrify -resize 2000x <image>

Please clean image files from metadata, before committing, i.e.:

    mogrify -strip <image>

If you embed your image into a markdown documentation file, use this syntax:


   [<path/to/image>]:     <path/to/image>     "title message"

or alternatly:


   [my-image-shortcut]:   <path/to/image>     "title message"

These patterns will guarantee that <img> tags have their src, alt and title attributes properly set within the html output.

Gschem Schematics

Change into folder ../hardware, which ships the project’s gEDA/gaf resource file. Then, using the project environment, invoke gschem.

Within your circuit schematic, you can use specific texts as placeholder objects. They will be replaced with generated values by the documentation build process. When used within the informational fields of a titleblock, use the specified sizes and alignments:

In case you are going to embed images, make sure to use a relative path. Per default, gschem uses absolute paths that might reveal a private username or folder. You can use nano to edit your schematics outside of gschem.

Code Files

Please use this license header for code source files:

    Zerocat Mini Machine --- A word processing machine of supreme integrity.

    Copyright (C) <Year>  <Name-of-Author> <Email-Address>

    This file is part of Zerocat Mini Machine.

    Zerocat Mini Machine is free software: you can redistribute it
    and/or modify it under the terms of the GNU General Public
    License as published by the Free Software Foundation, either
    version 3 of the License, or (at your option) any later

    Zerocat Mini Machine is distributed in the hope that it will be
    useful, but WITHOUT ANY WARRANTY; without even the implied
    PURPOSE. See the GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with Zerocat Mini Machine.
    If not, see <>.

Shell Scripts

If you intend to write shell scripts, use this skeleton to make them work for GNU Guix:


    # Re-exec if we are not using Bash or are using Bash in POSIX mode.
    if [ -z "$BASH" ] || [ "$BASH" = "/bin/sh" ]; then
      bash=`command -v bash`
      if [ -z "$bash" ]; then
        echo "Couldn't find Bash, sorry!"
        exit 1
        exec "$bash" "$0" "$@"

    # We're using Bash now.
    set -o errexit
    set -o nounset
    set -o pipefail

    # Your code goes here ...


Update ../doc/ and list your contributions.

You can use git shortlog to get a starting point for your edit.

Section #../doc/



Go ahead. Fund the project now. Join the future community!

This project depends on funding:

You can help to spread the message using Zerocat’s Handout PDF, which will be updated from time to time – Thank You!

Section #../doc/


Zerocat Mini Machine ships copyrighted work.

Zerocat Mini Machine is free software. It makes use of free software licenses as recognized by Free Software Foundation (FSF), and should be freely distributable:

Files located in folder hardware/, if available, describe hardware of a free design, licensed under:

Authorship, copyright and license information may be provided in more detail on a per-folder and/or per-file basis. Check the sources.

Please send your report if you find the distribution hindered.
See Zerocat Website for contact information.

Section #../doc/



This file tracks changes that are introduced to the project.
However, changes introduced to hardware design files are tracked with:


NOTICE: Anyone modifying the project should provide brief information about the modifications, including the date they were made. Information should be added but never removed from this file. Licensees should provide a brief entry with a date and the nature of the modification for each change. Please use markdown syntax!

Section #../doc/


Let me express my special thanks to:

Section #../doc/


For now, the project has no mechanism to place and track issues, reported by non-project audience. Please send a mail to the author(s), this file will get updated accordingly. Thanks!

These issues are to be clarified, next:

Section #../doc/


Goal Description

The goal of Zerocat Mini Machine is to provide you with a trustworthy, lean, laptop-alike mini machine of a free-design, even down to chip level, easily inspectable, intuitively verifyable on a daily basis.

It helps you to enter words and texts in an intgre way, to store them on simple, trustworthy media, and to produce sound or light output for transmission.

Zerocat Mini Machine focuses on text editing, text encryption, secure file storage, and secure file transfer between Zerocat Mini Machine devices over short and medium distances, avoiding the Internet.

Input of secret words and texts is done by means of the integrated, transparent keyboard. Using microphones instead would not be a good option, as it became hard to find clean, smartphone-free rooms and environments, especially in cities.

The device’s transmission module with loudspeaker and microphone is used in conjunction with high speed, multi channel Morse code – that is Morse code of tenfold frequency, simultaneously send over different frequencies, for example.

For short distances, Internet is not required, and the Mini Machines interact as stand-alone devices. In case of failure or during debugging sessions, the transmission of encrypted base16 data can be recorded with any device, played back with reduced speed, thus making it human readable again.

The transmission module offers wireless transmission via light beam as an alternative. Distances of probably 100m might be manageable with proper weather conditions.

Long distance transmissions without Internet might still be achievable by means of amateur radio stations, using Morse code on short wave. Radio operators manage to run two-way communications well beyond earth’s horizon (40 miles), reaching distances of more than 1000km with proper atmospheric conditions.

Interfaces such as RS232 and SPI should ease interaction with standard laptops or desktop machines, allowing to transmit via e-mail or snail-mail, shipping files on SD cards or SPI flash chips, or simply to transmit via wire.

However, audible Morse code perfectly matches for active voice chat or phone call conversations, set up per smartphones, laptops or desktops, thus supporting standard communication paths as well. Zerocat Mini Machine is meant to be a stand-alone device, but would match and combine with existing technology and transmission paths via Internet or Terrestrial Trunked Radio.

The power consumption of Zerocat Mini Machine is expected to be low enough to make it a portable device. Special requirements might be introduced by the display and transmission modules.

Materials and manufacturing toolchains should be simple enough to support small scale, community driven fab-labs as well as hobbyists. Usage of plastics, resins, paints and glue is greatly reduced in favor of wood, screws, clay and glaze. PCBs might be wired by hand (prototype boards), milled, or ordered from dedicated manufacturers. Optionally, it should be possible to pack kits, giving some extra fun to the end-user and increasing individual value.

Two Blocks of Development

The project shall be split into two major blocks of development, which should be achievable within 12 months, each:

  1. Development of two pairs of functioning prototype devices that are able to communicate with each other per Morse code as sound and light beam.

    This involves:

    a) Fast prototyping with wooden chassis modules, which can easily be adapted, cut, glued, screwed during the process of cahssis and PCB development.

    b) Transformation of the chassis towards glazed pottery. These chassis are expected to be colorful, shiny, sexy, individual, authentic and secure, and best suited to represent a fashion accessoire, making it appealing and attractive for non-tech users. These devices are meant to enter the RYF-compatible web shop, later on.

  2. Implementation of strong cryptography. File storage and data transmission would move forward towards being processed securely and privately. In order to implement strong cryptography, a dedicated level of expertise is required and has to be accumulated, first. Small but essential improvements on the PCBs might be necessary, e.g.: Addition of a random number generator, replacement of inter-modular copper buses by light transmissions, additional input devices – but change of the chassis or module frames is not expected.

Why relying on audible Morse Code?

Zerocat Mini Machine focuses on audible, encrypted Morse code to achieve data transmission, as this old technique has essential advantages over modern ones:

Section #../doc/


Transmission Paths Visualized

                                           data sent as:                                              
          Alice’s                  ---> encrypted Morse code¹ --->               Bob’s                
          Devices                                                               Devices               

                                         ____:          ____:                                         
                     speaker  <)))))))) /…… /          /…… / )))))    ]  microphone                   
                              ·       """""'         """""'           ·                               
                              ·             laptops                   ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·              /····|call|·····/        ·                               
                              ·           __/             __/         ·                               
                              ·          /… /            /… /         ·                               
                              <)))))))) /… /            /… / )))))    ]                               
                              ·        /__/            /__/           ·                               
                              ·            phones                     ·                               
                              ·                                       ·                               
    with internet             ·                                       ·                               
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 
    without internet          ·                                       ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·              /···|TETRA°|····/        ·                               
                              ·           _ /             __/         ·                               
                              ·          /»»/            /»»/         ·                               
                              <)))))))) /»»/            /»»/ )))))    ]                               
                              ·        /__/            /__/           ·                               
                              ·                                       ·                               
                              ·     °Terrestrial Trunked Radio        ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·          /\    |short|    /\          ·                               
                              ·         / ·\···|wave |······\··       ·                               
                              ·         \  /   |radio|   \  /         ·                               
                              ·         _\/_             _\/_         ·                               
                              >))))))) ]……o<            ]……o< ))))    ]                               
                              ·        |___|            |___|         ·                               
                              ·              radios                   ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                              ·                                       ·                               
                           __ ·                                       · __                            
    Mini Machine,         _\ \<)))))))))))))))|sound 50m|)))))))))    ]/ /_      Mini Machine,        
    100% integrity,      / /\ \                                       / /\ \     100% integrity,      
    input + encryption  / /  \ \~~~~~~~~~~~~~~|light² 100m|~~~~~~~~~~/ /  \ \    decryption + display 
         _...._ _______/ /____\/_                                   _\/____\ \_______ _...._          
        /______\\_____/\/\______/                                   \______/\/\_____//______\         
                  · |                                                           | ^                   
                  · |                                                           | ·                   
                  · |                                                           | ·                   
                  · \…………………………………………………………………|wire 1000m|…………………………………………………………/ ·                   
                  ·                                                               ·                   
                  ·                                                               ·                   
                  ·                                                               ·                   
                  ·                                                               ·                   
                  ·                                      cyclist 100km            ·                   
                 SPI          ____          _____                                SPI                  
                  ·          |SD  \        |\   /|           _o                   ·                   
                  ····>      |Card³| --->  | \_/ | --->   _/\/~            ········                   
                  ·          |_____|       |_____|        O " O                   ·                   
                  ·                                                               ·                   
                  ·                                                               ·                   
                  ·                                                               ·                   
                  ·                                                               ·                   
                  ·                                      car 1000km               ·                   
                 SPI          ____          _____         ____                   SPI                  
                  ·          |SD  \        |\   /|       |    | _                 ·                   
                  ····>      |Card | --->  | \_/ | --->  | ___|| \         ········                   
                             |_____|       |_____|       |________|                                   
                                                          O    O

° Terrestrial Trunked Radio, see:

¹ Morse code:

Although computer-based (digital) modes and methods have largely replaced CW [continuous wave, radiotelegraphy using Morse code] for commercial and military applications, many Amateur Radio operators still enjoy using the CW mode—particularly on the shortwave bands and for experimental work, such as Earth–Moon–Earth communication, because of its inherent signal-to-noise ratio advantages. Morse, using internationally agreed message encodings such as the Q code, enables communication between amateurs who speak different languages. It is also popular with homebrewers and in particular with "QRP" or very-low-power enthusiasts, as CW-only transmitters are simpler to construct, and the human ear-brain signal processing system can pull weak CW signals out of the noise where voice signals would be totally inaudible. ---

² Light:

Free-space optical communication (FSO) is an optical communication technology that uses light propagating in free space to wirelessly transmit data for telecommunications or computer networking. "Free space" means air, outer space, vacuum, or something similar. This contrasts with using solids such as optical fiber cable. ---

³ SD-Card:

SD cards operate with a default bus protocol of SD mode. However, if a simpler or slower bus is needed, the card can be configured for SPI mode. While in SPI mode, SD cards operate in one-bit bus widths. [...] ---

Section #../doc/


Features to achieve integrity:

Section #../doc/

Points of Interest

Fantastic, inspiring Projects

Wireless Transmission

Free Space Optical (FSO) Communication

About Morse Code and Amateur Radio

Alternate Display Types

About Keyboards

About Microphones

Electronic Parts

Interfacing SD-Cards in SPI

Looking for Maker Spaces

Section #../doc/


First Block of Development

Estimated time: 12 months
List of milestones: Quite elaborated, budgets per task are missing.
Estimated budget: EUR 49,850.-

  1. Prototype #1: Made of plywood and color

    • Improve existing Chassis | 850.-

      • Improve handle
      • Add a dedicated closure mechanism
      • Exchange mounting screws, make surface as flat as possible
      • Perforate modules (optional?)
      • Apply transparent color
      • Update documentation
    • Power Module | 3,000.-

      • Elaborate circuit schematics
      • Make power module work, using injected DC current
      • Set up power bus towards other modules
      • Add battery bank or large scale capacitors
      • Try a hand-kranked generator, test usability
      • Summarize calculations and measurements
      • Adapt circuits to real life requirements
      • Update documentation
    • Mainboard | 3,000.-

      • Add I²C EEPROMs
      • Add SPI interface
      • Add RS232 interface
      • Set up Makefile for firmware upload (Playground Setup)
      • Make core module accept firmware upload for both controller chips
      • Think about upload switch or HUB, to delegate firmware to correct chip
      • Add high speed communication bus between chips
      • Add LED semaphor to provide feedback while no display, yet
      • Add test buttons for input while no keyboard, yet
      • Write test program, using LEDs and test buttons
      • Refine circuit schematics
      • Update documentation
    • Display | 3,500.-

      • Process basic experiments with some LED7 modules on breadboard
      • Set up display circuit schematics
      • Hands-on display, hook-up busses, wires and decoders
      • Refine circuit schematics
      • Elaborate driver
      • Drive display with text samples
      • Update test program, now using LEDS, display and testbutton
      • Update documentation
    • Keyboard | 3,000.-

      • Fix keyboard, add missing <Enter> key
      • Elaborate keyboard schematics
      • Print temporary keycap paper scheme
      • Grab high speed milling drill, create PCB routes and connectors, manually
      • Assemble keyboard, hook up connector to mainboard
      • Refine circuit schematics
      • Elaborate keyboard driver
      • Update test program, now using keyboard as input device
      • Update documentation
    • Arrange core system (Keyboard, Mainboard, Display, Power) | 1,000.-

      • Refine input/process/display loop
      • Review, refine power requirements
      • Refine test program
      • Refine and improve intermodule busses
      • Refine firmware upload processes
      • Update circuit schematics
      • Update documentation
    • Shell, Applications, Interfaces | 6,500.-

      • Add a shell, to invoke applications
      • Add some applications, e.g.:

        help browser, calculator, word processor, core utilities like sort, cat, tac, basenc, ...

      • Support mainboard’s onboard communication bus

      • Get second controller chip involved
      • Support file storage over mainboard’s SPI interface
      • Support file transfer over mainboard’s RS232 interface
      • Update documentation
  2. Prototype #2: Made of plywood and color | 4,500.-

    • Update CAD files, add functions, create precise cutouts
    • Duplicate the Mini Machine according to CAD files
    • Apply different, transparent color
    • Update documentation
  3. Transmission Circuit Boards | 8,500.-

    • Set up transmission via Light Beam

      • Create circuit boards using lenses, diodes and photo-diodes
      • Mount boards into devices’s modules
      • Try short, straight distances, indoor
      • Try medium, straight distances, outdoor
    • Set up transmission via Sound

      • Adapt circuit boards with speaker, driver circuit, microphones
      • Try short, straight distances, indoor
      • Try medium, straight distances, outdoor
      • Try distances around building’s corner, outdoor
      • Try multi channel morse code (different frequencies in parallel)
      • Try supersonic transmissions
      • Try transmission via laptop chat
      • Try transmission via phone calls
      • Try transmissions by means of radio devices and radio amateurs
    • Refine circuits and drivers, as required

    • Create videos and/or audio files
    • Update documentation
  4. Refine Applications | 4,500.-

    • Refine shell
    • Refine utilities
    • Refine word processor
    • Improve editing and displaying features
    • Support outgoing Morse code via transmission module, light beam
    • Support ingoing Morse code via transmission module, light beam
    • Support outgoing Morse code via transmission module, sound
    • Support ingoing Morse code via transmission module, sound
    • Add test applications
  5. Transformation towards Final Products | 10,500.-

    • Create PCB files
    • Adjust PCB files for home-brewed milling production
    • Setup CNC milling machine or find manufacturer or fab-lab
    • Produce multiple sets of PCBs
    • Adjust CAD files for pottery, take shrinking and glaze into account
    • Replace metal keycaps by caps made of clay and glaze
    • Create template bodies to ease casting
    • Create multiple chassis modules out of clay
    • Apply first heating, document shrinking process precisely
    • Apply glaze, making each chassis unique and authentic
    • Adapt mechanics, insert joints, stand, and closure mechanism
    • Adapt rubber surfaces to minimize shocks
    • Assemble three pairs of devices
    • Design and manufacture sales packages like sleeves, bags or boxes
  6. Finalize Documentation | 1,000.-

    • Run demonstration, outdoor, with audience
    • Create images, videos, audio files
    • Describe use cases
    • Draft cheat sheet
    • Finalize documentation, add credits
    • Create webpage, link results

Second Block of Development

Estimated time: 12 months
List of milestones: To be refined.
Estimated budget: Not yet calculated.

  1. Preparation for Cryptography

    • Research basic concepts
    • Adapt terminology and list of tasks
    • Add random number generator circuit
    • Test random numbers
    • Replace selected copper wires by intermodule light transmission
    • Check power profiles
    • Update circuit schematics
    • Update test boards of wooden prototypes
    • Update documentation
  2. Implement strong Cryptography

    • Add hardened password entry dialog
    • Add key management and verification of keys
    • Support symmetric encryption/decryption of words
    • Support encryption/decryption via key files
    • Support signatures
    • Improve data storage
    • Enrich list of shell applications
    • Update documentation
  3. Test Cryptography

    • Enrich list of test applications
    • Invite hackers and students to attack for testing
    • Summarize results
    • Improve setup
  4. Update Prototype Products

    • Update PCB files
    • Reproduce updated PCBs
    • Exchange selected PCBs on three pairs of prototype products
    • Move one pair of prototype products into RYF¹ compatible webshop
    • Apply for FSF’s RYF Certificate, send one pair of devices
    • Keep one pair of prototype products for long-term maintenance
  5. Finalize Documentation

    • Run demonstration, outdoor, with audience
    • Update documentation
    • Update webpage
    • Launch press release

¹ Respect Your Freedom certification program of the Free Software Foundation (FSF), USA

Section #../doc/

Checklist NGI0


First Check for Eligibility

This project’s proposal...

NGI0 Core

NGI0 Core, Check for Eligibility


NGI0 Entrust

NGI0 Entrust, Check for Eligibility


Project’s Match to Eligibility Checks

This project will cover some important types of activities. As a result, it should indeed be eligible for financial support by NGI0 Entrust and/or NGI0 Core:

Section #../doc/



Chassis, folded


Chassis, set up for operation


Chassis, unfolded to ease user’s inspection.

CAD Animation

Start animation:

CAD Views


View 00


View 01


View 02



Concatenate wooden units.


Inject nails, link units using small stripes of metal.


Cut stripes of plywood.


Add a nice angle.


Glue them onto wooden units.


Test whether the chassis folds together, smoothly.


Cut out some triangles.


Collect former snippets...


...and create small, triangular noses.


Glue noses onto wood units.


Make sure that positive and negative shape will fit together, perfectly.


Apply screws to enforce glued connection.


Prepare PCBs for assemblage.


Bent a wire to get the chassis stand.


Add PCBs and stand, refine tiny cutouts to make the units slip into well defined positions.


Mount handle support, insert raw wire and trim length, ...


...then bent both ends.


Fold chassis, pull out handle.

Section #../doc/

Module 1: Keyboard

CAD Views


View 03


View 04

CAD Views, orthographic


View 05


View 06


View 07

Drill Template


Drill Template and Micro Switch Landing Patterns

Keyboard Layout

    +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+         
    |   ! |   |   " |   |   ? |   |   $ |   |   * |   |   & |   |   / |   |   ( |   |   ) |   |   = |         
    |  1  |   |  2  |   |  3  |   |  4  |   |  5  |   |  6  |   |  7  |   |  8  |   |  9  |   |  0  |         
    +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+         

       +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+      
       |   ' |   |     |   |   É |   |     |   |     |   |     |   |   Ü |   | INS |   |   Ö |   |   + |      
       |  Q  |   |  W  |   |  E  |   |  R  |   |  T  |   |  Z  |   |  U  |   |  I  |   |  O  |   |  P  |      
       +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+      

          +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+             
          |   Ä |   |     |   |     |   |     |   |     |   |   - |   |   ; |   |   : |   |   _ |             
          |  A  |   |  S  |   |  D  |   |  F  |   |  G  |   |  H  |   |  J  |   |  K  |   |  L  |             
          +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+             

     +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+             +-----+        
     |     |   |   \ |   |     |   |   @ |   |     |   | BSP |   |   , |   |   . |             |     |        
     |Shift|   |  Y  |   |  X  |   |  C  |   |  V  |   |  B  |   |  N  |   |  M  |             |Enter|        
     +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+   +-----+             +-----+        

                                        +-----+                       +-----+   +-----+   +-----+             
                                        |  DEL|                       | POS1|   |  UP |   | END |             
                                        |Space|                       | <-- |   | DWN |   | --> |             
                                        +-----+                       +-----+   +-----+   +-----+             

    INS   = Insert
    DEL   = Delete
    POS1  = First Position of Line
    END   = Last Position of Line
    BSP   = Backspace
    UP    = Upwards
    DWN   = Downwards
    Shift = Upper Group
    Enter = Finalize input. This is key #42, which is missing on prototype keyboard.


Notice: Key #42, <Enter>, is missing on prototype images. It should be easy to add this key later on, during an update cycle.

Key Caps


Get some screws.


Use a lathe for the making of key caps.


Cut off cap with metal saw.


Collect 41 key caps.


Clean up caps’ backside to match exact thickness.


Arrange caps nicely, inspired by old ThinkPad keyboard.

Cage and PCB


Cutout an acrylic glass to create a cage.


Print the drill template onto paper.


Drill a first, small diameter according to drill template.


Enlarge diameters, step by step.


Bring the holes to their final diameter, preserving beveled edges.


Test the cage, check whether caps slip in easily.


Prepare for correct size of the PCB.


Cut out the PCB, using a saw.


Grind edges to make it look nice.


Match PCB and Cage and Drill Template, then drill main mounting holes.


Mount PCB and Cage together, then drill PCB mounting holes.


Clean up, refine PCB mounting holes to match sinking screw heads.


Mark landing patterns onto the PCB, using a high speed drill.


Isolate landing patterns manually from rest of PCB surface.


Remove dust, get prepared to solder micro switches into place.


Solder the switches.


PCB fully populated (using different type of switches, but same height).



Populate the cage with all key caps and screws, fix them with tape, flip the cage upside down.


Mount the PCB to the Cage.


Trim the length of mounting screws.


Drill main mounting holes into wood unit.


Mount the keyboard to the wooden chassis.

Section #../doc/

Module 2: Mainboard

CAD View


View 08


View 09

Section #../doc/

Module 3: Display

CAD View


View 10


View 11


View 12

Seven Segment Type with Dot

    One Row of Display (15 Characters)                          
     _   _   _   _   _   _   _   _   _   _   _   _   _   _   _  
    |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| 

Character Set

    1       2       3       4       5       6       7       8       9       0       
             _       _               _       _       _       _       _       _      
      |      _|      _|     |_|     |_      |_        |     |_|     |_|     | |     
      |     |_       _|       |      _|     |_|       |     |_|      _|     |_|     

    A       B       C       D       E       F       G       H       I       J       
     _               _               _       _       _                              
    |_|     |_      |        _|     |_      |_      |       |_|     |         |     
    | |     |_|     |_      |_|     |_      |       |_|     | |     |        _|     

    K       L       M       N       O       P       Q       R       S       T       
                     _                       _       _                       _      
    |_      |       | |      _       _      |_|     |_|      _      |_      |       
    |_      |_      | |     | |     |_|     |         |     |        _|     |       

    U       V       W       X       Y       Z       Ä       Ü       Ö       É       
                             _               _       _                       _      
    | |     | |     |_|      _      |_|      _      |_|     | |      _      |_      
    |_|      _       _      | |      _|      _      | |.    |_|.    |_|.    |_ .    

    '       "       +       -       *       /       =       (       )       \       
     _       _                                                       _              
    |       | |      _|      _               _       _                |     |_      
                      |              _ .     _ .     _      |_                |     

    ?       !       ,       .       ;       :       _       @       &       $       
     _                                                       _       _              
     _|       |      _               _                       _|     |       |_      
    |  .       .      |        .      |.      |.     _      |_|      _|.     _|.

Display Samples

    HELLO, WORLD.                                                                   
    |_| |_  |   |    _   _      |_|  _   _  |    _|                                 
    | | |_  |_  |_  |_|   |      _  |_| |   |_  |_|    .                            

    "HELLO, WORLD!"                                                                 
     _       _                                               _                      
    | | |_| |_  |   |    _   _      |_|  _   _  |    _|   | | |                     
        | | |_  |_  |_  |_|   |      _  |_| |   |_  |_|    .                        

    MORSE CODE                                                                      
     _               _       _           _                                          
    | |  _   _  |_  |_      |    _   _| |_                                          
    | | |_| |    _| |_      |_  |_| |_| |_                                          

     _   _                                                                          
    |_| |_|  _  |   |_                                                              
    |   | | |   |    _|                                                             

     _           _   _                                                              
    |    _   _| |_   _                                                              
    |_  |_| |_| |_  | |                                                             

     _   _       _   _   _   _       _   _   _               _       _              
    |   |_  |_  |    _| |   |_  |_  |   | | |_| |   |       |    _  | |             
    |   |_   _| |   |_| |   |_   _| |   | | | | |   |_     .|_  |_| | |             

     _           _       _       _   _               _                              
    |_          |_|  _   _|  _|  _|   |  _    |  _   _| |_|                         
     _|  _ .|_   _|  _ . _|   | |_            |  _  |_    |                         

     _           _                   _   _   _   _   _                              
    |_| |    _   _|       | |_|   | |_  |_|  _| |_  |_  |_|                         
    |   |    _   _|    .  |   |   |  _|  _| |_  |_|  _|   |                         

    Zerocat Mini Machine                                                            
     _   _           _   _   _       _                   _   _   _               _  
     _  |_   _   _  |   |_| |       | | |    _  |       | | |_| |   |_| |    _  |_  
     _  |_  |   |_| |_  | | |       | | |   | | |       | | | | |_  | | |   | | |_
Section #../doc/

Module 4: Transmission


This module covers two transmission paths, light beam and audio.

Transmission via light beam will require lenses, LED and photo diode driving circuits, additional power considerations, and extra mechanical constructions to protect the beam from direct sunlight. Distances greater than 1km have been managed with stationary equipment, see RONJA project – the distance that a mobile, battery driven device can handle has to be elaborated. It is estimated to 100m.

Transmission via audio will require to integrate speakers, microphones, driving circuits, and probably expertise in analog electronics. The usage of Morse code will hopefully allow to reliably grab signals out of a mix with environmental audio or speech. The managable distance is estimated to 50m.

CAD View


View 13


View 14

Section #../doc/

Module 5: Power

CAD View


View 15


View 16

Section #../doc/



Circuits, build from scratch.

Core PCB and PCB Modules

The hardware consists of five modules, concatenated with each-other. Some modules ship their own controller, some don’t. If a controller is required, a Parallax P8X32A free-design microcontroller is the one that is used. This controller offers reduced complexity in comparison to RISC-V, which is not available as a free-design chip anyway, and Low RISC, which is still more complex and requires to be run on proprietary FPGAs.

Each module controller ships its own on-chip, free-design RAM, which holds the firmware and must be kept powered by means of a small coin battery. The firmware upload process should be managed by the core module in a secure, password protected manner. An I²C EEPROM of proprietary design might be used for powerless firmware backup, optionally. Chips of a proprietary design, such as inverters, gates, buffers and level shifters, will only be used for low level glue logic.

Block Schematics

        | Power Module                         |
        |                                      |
        | P8X32A chips: none                   |
        |                                      |
        | managed array of gold-caps,          |       |
  //====| batteries, incoming DC current,      |<<=====| DC Input
  ||    | supplying all modules,               |       |
  ||    | buffering free-design RAM            |
  ||    +--------------------------------------+
  ||    +--------------------------------------+                     | firmware upload
  ||    | Core Module                  |       |<····················| by corebooted
  ||    |                              | RS232 |                     | laptop
  ||    | P8X32A chips: 2              |       |<········
  ||    |                              ········|        ·
  ++==>>| keyboard driver,                     |        ·
  ||    | word processor, key management,      |        ·
  ||    | password entry, encryption routines, |        ·       | communication
  ||    | interface management, display driver |        ·······>| machine to machine
  ||    |                                      |                | and machine to host
  ||    |············· pin usage ··············|
  ||    | SPI | Kbd  | LED7 | DIPSW | InterCog |
  ||    +--------------------------------------+
  ||       ^     ^      ^       ^
  ||       |     |      |       ·                       | manual runtime
  ||       |     |      |       ························| configuration, i.e.:
  ||       |     |16    |10                             | interactive or repeater mode
  ||       |     /      /
  ||       |     |      |
  ||       |     |      |      +--------------------------------+
  ||       |     |      \------| Display Module                 |
  ||       |     |             |                                |
  ||       |     |             | P8X32A chips: none             |
  ||       |     |             |                                |
  ++=======|=====|===power===>>| managed array of               |
  ||       |     |             | line-oriented 7-segment LEDs   |
  ||       |     |             +--------------------------------+
  ||       |     |       
  ||       |     |             +--------------------------------+
  ||       |     \-------------| Keyboard Module                |
  ||       |                   |                                |
  ||       |                   | P8X32A chips: none             |
  ||       |                   |                                |
  ++=======|=========power===>>| managed array of keys,         |
  ||       |                   | buttons, potis, switches       |
  ||       |                   +--------------------------------+
  ||       |
  ||       |                   +--------------------------------+         | firmware upload
  ||       +-------- SPI------>| Transmission Module    | RS232 |<········| by corebooted
  ||       |                   | sound and light beam   ········|         | laptop
  ||       |                   |                                |
  ||       |                   | P8X32A chips: 1                |
  ||       |                   |                                |
  ++=======|=========power===>>| loudspeaker, microphones,      |
  ||       |                   | kill-switch, potis, buttons,   |
  ||       |                   | lenses, LEDs, photo diodes     |
  ||       |                   +--------------------------------+
  ||       |
  ||       |
  ||       |                   | direct access to:
  ||       +---------SPI------>| SPI flash chip or
  ||       |                   | SD-Card in SPI Mode
  ||       |                   | or buffered SRAM Module
  ||       |
  ::       :
  ::       :
  ||       |                   +--------------------------------+         | firmware upload
  ||       +-------- SPI------>| Experimental Module    | RS232 |<········| by corebooted
  ||       |                   |                        ········|         | laptop
  ||       |                   | P8X32A chips: ?                |
  ||       |                   |                                |
  ++=======|=========power===>>| ...                            |
  ||       |                   |                                |
  ||       |                   +--------------------------------+
  ||       |
  ::       :
  ::       :
  ::       :

Circuit Schematics


Module 5(5), Page 1(1)


Module 4(5), Page 1(1)


Module 3(5), Page 1(1)


Module 2(5), Page 1(2)


Module 2(5), Page 2(2)


Module 1(5), Page 1(1)

Section #../doc/


Example 1: Unknown Helicopter, slowly scanning Berlin


Unknown helicopter, slowly scanning Berlin on a sunday morning

Example 2: Video “CIA vs. Wikileaks – Andy”

Video Title: “CIA vs. Wikileaks – Andy”
Video URL:
Recorded by: C3VOC and FEM
License: CC BY 4.0


Video “CIA vs. Wikileaks – Andy”, cited at 00m11s


Video “CIA vs. Wikileaks – Andy”, cited at 22m54s


Video “CIA vs. Wikileaks – Andy”, cited at 23m04s


Video “CIA vs. Wikileaks – Andy”, cited at 23m34s


Video “CIA vs. Wikileaks – Andy”, cited at 24m14s


Video “CIA vs. Wikileaks – Andy”, cited at 24m24s


Video “CIA vs. Wikileaks – Andy”, cited at 24m34s


Video “CIA vs. Wikileaks – Andy”, cited at 58m24s


Video “CIA vs. Wikileaks – Andy”, cited at 58m35s

Section #../doc/



Image 1: Use wooden prototype as template


Image 2: Perform cutout.


Image 3: Glue pieces together


Image 4: Note measures to learn about shrinking later on


Image 5: First heat applied, no cracks! Shrinking factor: 1.0297

Section #../doc/

GNU Free Documentation License

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    Permission is granted to copy, distribute and/or modify this document
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Section #../doc/


Version 3, 29 June 2007

Copyright (C) 2007 Free Software Foundation, Inc.

Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is not allowed.


The GNU General Public License is a free, copyleft license for software and other kinds of works.

The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program--to make sure it remains free software for all its users. We, the Free Software Foundation, use the GNU General Public License for most of our software; it applies also to any other work released this way by its authors. You can apply it to your programs, too.

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Developers that use the GNU GPL protect your rights with two steps: (1) assert copyright on the software, and (2) offer you this License giving you legal permission to copy, distribute and/or modify it.

For the developers' and authors' protection, the GPL clearly explains that there is no warranty for this free software. For both users' and authors' sake, the GPL requires that modified versions be marked as changed, so that their problems will not be attributed erroneously to authors of previous versions.

Some devices are designed to deny users access to install or run modified versions of the software inside them, although the manufacturer can do so. This is fundamentally incompatible with the aim of protecting users' freedom to change the software. The systematic pattern of such abuse occurs in the area of products for individuals to use, which is precisely where it is most unacceptable. Therefore, we have designed this version of the GPL to prohibit the practice for those products. If such problems arise substantially in other domains, we stand ready to extend this provision to those domains in future versions of the GPL, as needed to protect the freedom of users.

Finally, every program is threatened constantly by software patents. States should not allow patents to restrict development and use of software on general-purpose computers, but in those that do, we wish to avoid the special danger that patents applied to a free program could make it effectively proprietary. To prevent this, the GPL assures that patents cannot be used to render the program non-free.

The precise terms and conditions for copying, distribution and modification follow.


0. Definitions.

"This License" refers to version 3 of the GNU General Public License.

"Copyright" also means copyright-like laws that apply to other kinds of works, such as semiconductor masks.

"The Program" refers to any copyrightable work licensed under this License. Each licensee is addressed as "you". "Licensees" and "recipients" may be individuals or organizations.

To "modify" a work means to copy from or adapt all or part of the work in a fashion requiring copyright permission, other than the making of an exact copy. The resulting work is called a "modified version" of the earlier work or a work "based on" the earlier work.

A "covered work" means either the unmodified Program or a work based on the Program.

To "propagate" a work means to do anything with it that, without permission, would make you directly or secondarily liable for infringement under applicable copyright law, except executing it on a computer or modifying a private copy. Propagation includes copying, distribution (with or without modification), making available to the public, and in some countries other activities as well.

To "convey" a work means any kind of propagation that enables other parties to make or receive copies. Mere interaction with a user through a computer network, with no transfer of a copy, is not conveying.

An interactive user interface displays "Appropriate Legal Notices" to the extent that it includes a convenient and prominently visible feature that (1) displays an appropriate copyright notice, and (2) tells the user that there is no warranty for the work (except to the extent that warranties are provided), that licensees may convey the work under this License, and how to view a copy of this License. If the interface presents a list of user commands or options, such as a menu, a prominent item in the list meets this criterion.

1. Source Code.

The "source code" for a work means the preferred form of the work for making modifications to it. "Object code" means any non-source form of a work.

A "Standard Interface" means an interface that either is an official standard defined by a recognized standards body, or, in the case of interfaces specified for a particular programming language, one that is widely used among developers working in that language.

The "System Libraries" of an executable work include anything, other than the work as a whole, that (a) is included in the normal form of packaging a Major Component, but which is not part of that Major Component, and (b) serves only to enable use of the work with that Major Component, or to implement a Standard Interface for which an implementation is available to the public in source code form. A "Major Component", in this context, means a major essential component (kernel, window system, and so on) of the specific operating system (if any) on which the executable work runs, or a compiler used to produce the work, or an object code interpreter used to run it.

The "Corresponding Source" for a work in object code form means all the source code needed to generate, install, and (for an executable work) run the object code and to modify the work, including scripts to control those activities. However, it does not include the work's System Libraries, or general-purpose tools or generally available free programs which are used unmodified in performing those activities but which are not part of the work. For example, Corresponding Source includes interface definition files associated with source files for the work, and the source code for shared libraries and dynamically linked subprograms that the work is specifically designed to require, such as by intimate data communication or control flow between those subprograms and other parts of the work.

The Corresponding Source need not include anything that users can regenerate automatically from other parts of the Corresponding Source.

The Corresponding Source for a work in source code form is that same work.

2. Basic Permissions.

All rights granted under this License are granted for the term of copyright on the Program, and are irrevocable provided the stated conditions are met. This License explicitly affirms your unlimited permission to run the unmodified Program. The output from running a covered work is covered by this License only if the output, given its content, constitutes a covered work. This License acknowledges your rights of fair use or other equivalent, as provided by copyright law.

You may make, run and propagate covered works that you do not convey, without conditions so long as your license otherwise remains in force. You may convey covered works to others for the sole purpose of having them make modifications exclusively for you, or provide you with facilities for running those works, provided that you comply with the terms of this License in conveying all material for which you do not control copyright. Those thus making or running the covered works for you must do so exclusively on your behalf, under your direction and control, on terms that prohibit them from making any copies of your copyrighted material outside their relationship with you.

Conveying under any other circumstances is permitted solely under the conditions stated below. Sublicensing is not allowed; section 10 makes it unnecessary.

3. Protecting Users' Legal Rights From Anti-Circumvention Law.

No covered work shall be deemed part of an effective technological measure under any applicable law fulfilling obligations under article 11 of the WIPO copyright treaty adopted on 20 December 1996, or similar laws prohibiting or restricting circumvention of such measures.

When you convey a covered work, you waive any legal power to forbid circumvention of technological measures to the extent such circumvention is effected by exercising rights under this License with respect to the covered work, and you disclaim any intention to limit operation or modification of the work as a means of enforcing, against the work's users, your or third parties' legal rights to forbid circumvention of technological measures.

4. Conveying Verbatim Copies.

You may convey verbatim copies of the Program's source code as you receive it, in any medium, provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices of the absence of any warranty; and give all recipients a copy of this License along with the Program.

You may charge any price or no price for each copy that you convey, and you may offer support or warranty protection for a fee.

5. Conveying Modified Source Versions.

You may convey a work based on the Program, or the modifications to produce it from the Program, in the form of source code under the terms of section 4, provided that you also meet all of these conditions:

A compilation of a covered work with other separate and independent works, which are not by their nature extensions of the covered work, and which are not combined with it such as to form a larger program, in or on a volume of a storage or distribution medium, is called an "aggregate" if the compilation and its resulting copyright are not used to limit the access or legal rights of the compilation's users beyond what the individual works permit. Inclusion of a covered work in an aggregate does not cause this License to apply to the other parts of the aggregate.

6. Conveying Non-Source Forms.

You may convey a covered work in object code form under the terms of sections 4 and 5, provided that you also convey the machine-readable Corresponding Source under the terms of this License, in one of these ways:

A separable portion of the object code, whose source code is excluded from the Corresponding Source as a System Library, need not be included in conveying the object code work.

A "User Product" is either (1) a "consumer product", which means any tangible personal property which is normally used for personal, family, or household purposes, or (2) anything designed or sold for incorporation into a dwelling. In determining whether a product is a consumer product, doubtful cases shall be resolved in favor of coverage. For a particular product received by a particular user, "normally used" refers to a typical or common use of that class of product, regardless of the status of the particular user or of the way in which the particular user actually uses, or expects or is expected to use, the product. A product is a consumer product regardless of whether the product has substantial commercial, industrial or non-consumer uses, unless such uses represent the only significant mode of use of the product.

"Installation Information" for a User Product means any methods, procedures, authorization keys, or other information required to install and execute modified versions of a covered work in that User Product from a modified version of its Corresponding Source. The information must suffice to ensure that the continued functioning of the modified object code is in no case prevented or interfered with solely because modification has been made.

If you convey an object code work under this section in, or with, or specifically for use in, a User Product, and the conveying occurs as part of a transaction in which the right of possession and use of the User Product is transferred to the recipient in perpetuity or for a fixed term (regardless of how the transaction is characterized), the Corresponding Source conveyed under this section must be accompanied by the Installation Information. But this requirement does not apply if neither you nor any third party retains the ability to install modified object code on the User Product (for example, the work has been installed in ROM).

The requirement to provide Installation Information does not include a requirement to continue to provide support service, warranty, or updates for a work that has been modified or installed by the recipient, or for the User Product in which it has been modified or installed. Access to a network may be denied when the modification itself materially and adversely affects the operation of the network or violates the rules and protocols for communication across the network.

Corresponding Source conveyed, and Installation Information provided, in accord with this section must be in a format that is publicly documented (and with an implementation available to the public in source code form), and must require no special password or key for unpacking, reading or copying.

7. Additional Terms.

"Additional permissions" are terms that supplement the terms of this License by making exceptions from one or more of its conditions. Additional permissions that are applicable to the entire Program shall be treated as though they were included in this License, to the extent that they are valid under applicable law. If additional permissions apply only to part of the Program, that part may be used separately under those permissions, but the entire Program remains governed by this License without regard to the additional permissions.

When you convey a copy of a covered work, you may at your option remove any additional permissions from that copy, or from any part of it. (Additional permissions may be written to require their own removal in certain cases when you modify the work.) You may place additional permissions on material, added by you to a covered work, for which you have or can give appropriate copyright permission.

Notwithstanding any other provision of this License, for material you add to a covered work, you may (if authorized by the copyright holders of that material) supplement the terms of this License with terms:

All other non-permissive additional terms are considered "further restrictions" within the meaning of section 10. If the Program as you received it, or any part of it, contains a notice stating that it is governed by this License along with a term that is a further restriction, you may remove that term. If a license document contains a further restriction but permits relicensing or conveying under this License, you may add to a covered work material governed by the terms of that license document, provided that the further restriction does not survive such relicensing or conveying.

If you add terms to a covered work in accord with this section, you must place, in the relevant source files, a statement of the additional terms that apply to those files, or a notice indicating where to find the applicable terms.

Additional terms, permissive or non-permissive, may be stated in the form of a separately written license, or stated as exceptions; the above requirements apply either way.

8. Termination.

You may not propagate or modify a covered work except as expressly provided under this License. Any attempt otherwise to propagate or modify it is void, and will automatically terminate your rights under this License (including any patent licenses granted under the third paragraph of section 11).

However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10.

9. Acceptance Not Required for Having Copies.

You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so.

10. Automatic Licensing of Downstream Recipients.

Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third parties with this License.

An "entity transaction" is a transaction transferring control of an organization, or substantially all assets of one, or subdividing an organization, or merging organizations. If propagation of a covered work results from an entity transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work the party's predecessor in interest had or could give under the previous paragraph, plus a right to possession of the Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with reasonable efforts.

You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.

11. Patents.

A "contributor" is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's "contributor version".

A contributor's "essential patent claims" are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, "control" includes the right to grant patent sublicenses in a manner consistent with the requirements of this License.

Each contributor grants you a non-exclusive, worldwide, royalty-free patent license under the contributor's essential patent claims, to make, use, sell, offer for sale, import and otherwise run, modify and propagate the contents of its contributor version.

In the following three paragraphs, a "patent license" is any express agreement or commitment, however denominated, not to enforce a patent (such as an express permission to practice a patent or covenant not to sue for patent infringement). To "grant" such a patent license to a party means to make such an agreement or commitment not to enforce a patent against the party.

If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. "Knowingly relying" means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid.

If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it.

A patent license is "discriminatory" if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.

Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law.

12. No Surrender of Others' Freedom.

If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program.

13. Use with the GNU Affero General Public License.

Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such.

14. Revised Versions of this License.

The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.

Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License "or any later version" applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.

If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program.

Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version.

15. Disclaimer of Warranty.


16. Limitation of Liability.


17. Interpretation of Sections 15 and 16.

If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee.


How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the "copyright" line and a pointer to where the full notice is found.

    <one line to give the program's name and a brief idea of what it does.>
    Copyright (C) <year>  <name of author>

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <>.

Also add information on how to contact you by electronic and paper mail.

If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:

    <program>  Copyright (C) <year>  <name of author>
    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
    This is free software, and you are welcome to redistribute it
    under certain conditions; type `show c' for details.

The hypothetical commands \show w' and \show c' should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an "about box".

You should also get your employer (if you work as a programmer) or school, if any, to sign a "copyright disclaimer" for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see

The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read