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1.4 +Introduction
1.5 +------------
1.6 +
1.7 +The AcornElectronCartridge distribution provides schematic and circuit layout
1.8 +files for use with KiCad describing a breakout or prototyping cartridge
1.9 +suitable for use with the Acorn Electron microcomputer's Plus 1 expansion
1.10 +unit.
1.11 +
1.12 +The following resources are provided:
1.13 +
1.14 +AcornElectronCartridge.kicad_pcb The circuit board layout
1.15 +
1.16 +AcornElectronCartridge.net The netlist, generated from the schematic
1.17 + and distributed here for convenience
1.18 +
1.19 +AcornElectronCartridge.pro The KiCad project file
1.20 +
1.21 +AcornElectronCartridge.sch The circuit schematic providing the
1.22 + relationships between components
1.23 +
1.24 +AcornElectron.lib Acorn Electron component library
1.25 + containing definitions for the edge
1.26 + connector (used by the schematic editor)
1.27 +
1.28 +AcornElectron.pretty Acorn Electron component footprint library
1.29 + containing definitions of the edge
1.30 + connector (used by the PCB editor)
1.31 +
1.32 +BoardOutline Drawings defining the board outline plus
1.33 + descriptions of the drafting workflow and
1.34 + KiCad import considerations
1.35 +
1.36 +Overview
1.37 +--------
1.38 +
1.39 +The purpose of a cartridge breakout is to route the signals from the cartridge
1.40 +socket to "breakout" connectors that are easily accessed for prototyping
1.41 +purposes. The circuit board is plugged into the cartridge socket and the two
1.42 +sides of the board edge connector make contact with the socket contacts.
1.43 +
1.44 +Preparing the Schematic
1.45 +-----------------------
1.46 +
1.47 +Since the purpose of the board is merely that of routing signals, the
1.48 +schematic is very simple. Connectors corresponding to the two sides of the
1.49 +board edge connector are introduced, together with breakout connectors
1.50 +corresponding to the exposed signals. Each edge connector pin is labelled and
1.51 +a corresponding breakout connector pin is given a matching label. Thus, an
1.52 +association is established between the edge connector pin and the breakout
1.53 +pin.
1.54 +
1.55 +The CvPcb tool in KiCad associates components with footprints. For convenient
1.56 +prototyping, the breakout connectors are associated with headers with 0.1 inch
1.57 +pin spacing (or pitch). The edge connectors are associated with specially
1.58 +designed footprints for the Acorn Electron cartridge provided by the Acorn
1.59 +Electron footprint component library (AcornElectron.pretty).
1.60 +
1.61 +Preparing the Board Outline
1.62 +---------------------------
1.63 +
1.64 +In order to produce a board of the right shape (or indeed of any shape), a
1.65 +board outline must first be produced. The BoardOutline directory contains
1.66 +documentation of the workflow involved in applying measurements used by other
1.67 +cartridges to produce a suitable drawing (cartridge_board_rear.dxf) which can
1.68 +then be used in KiCad (and by subsequent production tools) to establish the
1.69 +correct positions and dimensions of board features such as mounting holes and
1.70 +the edge connector portion of the board.
1.71 +
1.72 +This board outline is exported as DXF (using version 14 in Inkscape) and
1.73 +imported into KiCad to provide the basis of the board itself. The outline is
1.74 +imported into the Edge.Cuts layer, indicating that it shall be used to direct
1.75 +cutting tools to define the shape of the board. In order to align the outline
1.76 +with a grid using 0.127mm (0.05 inch) units, the origin of the outline is
1.77 +positioned at (60.445mm, 127mm). More information about the calculations can
1.78 +be found in the BoardOutline documentation.
1.79 +
1.80 +Preparing the Board Layout
1.81 +--------------------------
1.82 +
1.83 +Each component must be positioned appropriately on the board for it to make
1.84 +any physical sense. The edge connector footprints must be placed on each side
1.85 +of the protruding portion of the board, and the breakout connector footprints
1.86 +must be placed high enough up on the board to be accessible when the cartridge
1.87 +is inserted into the Plus 1. Beyond this, board layout is mostly a matter of
1.88 +routing tracks between connectors and avoiding board features such as mounting
1.89 +holes and the board edges.
1.90 +
1.91 +Design Rules and Production
1.92 +---------------------------
1.93 +
1.94 +It was decided that OSHPark would be used to make the first set of boards.
1.95 +Thus, the design rules for OSHPark were added to the project configuration.
1.96 +Such rules can be found here:
1.97 +
1.98 +http://docs.oshpark.com/services/two-layer/
1.99 +http://docs.oshpark.com/design-tools/kicad/kicad-design-rules/
1.100 +
1.101 +The board uploaded to OSHPark was tagged with oshpark-648KdmKd in this
1.102 +repository. It resides on OSHPark at the following location:
1.103 +
1.104 +https://oshpark.com/shared_projects/648KdmKd
1.105 +
1.106 +Contact, Copyright and Licence Information
1.107 +------------------------------------------
1.108 +
1.109 +The author can be contacted at the following e-mail address:
1.110 +
1.111 +paul@boddie.org.uk
1.112 +
1.113 +Copyright and licence information can be found in the docs directory - see
1.114 +docs/COPYING.txt and docs/gpl-3.0.txt for more information.