1 Introduction
2 ------------
3
4 The AcornElectronCartridge distribution provides schematic and circuit layout
5 files for use with KiCad describing a breakout or prototyping cartridge
6 suitable for use with the Acorn Electron microcomputer's Plus 1 expansion
7 unit.
8
9 The following resources are provided:
10
11 AcornElectronCartridge.kicad_pcb The circuit board layout
12
13 AcornElectronCartridge.net The netlist, generated from the schematic
14 and distributed here for convenience
15
16 AcornElectronCartridge.pro The KiCad project file
17
18 AcornElectronCartridge.sch The circuit schematic providing the
19 relationships between components
20
21 AcornElectron.lib Acorn Electron component library
22 containing definitions for the edge
23 connector (used by the schematic editor)
24
25 AcornElectron.pretty Acorn Electron component footprint library
26 containing definitions of the edge
27 connector (used by the PCB editor)
28
29 BoardOutline Drawings defining the board outline plus
30 descriptions of the drafting workflow and
31 KiCad import considerations
32
33 Overview
34 --------
35
36 The purpose of a cartridge breakout is to route the signals from the cartridge
37 socket to "breakout" connectors that are easily accessed for prototyping
38 purposes. The circuit board is plugged into the cartridge socket and the two
39 sides of the board edge connector make contact with the socket contacts.
40
41 Preparing the Schematic
42 -----------------------
43
44 Since the purpose of the board is merely that of routing signals, the
45 schematic is very simple. Connectors corresponding to the two sides of the
46 board edge connector are introduced, together with breakout connectors
47 corresponding to the exposed signals. Each edge connector pin is labelled and
48 a corresponding breakout connector pin is given a matching label. Thus, an
49 association is established between the edge connector pin and the breakout
50 pin.
51
52 The CvPcb tool in KiCad associates components with footprints. For convenient
53 prototyping, the breakout connectors are associated with headers with 0.1 inch
54 pin spacing (or pitch). The edge connectors are associated with specially
55 designed footprints for the Acorn Electron cartridge provided by the Acorn
56 Electron footprint component library (AcornElectron.pretty).
57
58 Preparing the Board Outline
59 ---------------------------
60
61 In order to produce a board of the right shape (or indeed of any shape), a
62 board outline must first be produced. The BoardOutline directory contains
63 documentation of the workflow involved in applying measurements used by other
64 cartridges to produce a suitable drawing (cartridge_board_rear.dxf) which can
65 then be used in KiCad (and by subsequent production tools) to establish the
66 correct positions and dimensions of board features such as mounting holes and
67 the edge connector portion of the board.
68
69 This board outline is exported as DXF (using version 14 in Inkscape) and
70 imported into KiCad to provide the basis of the board itself. The outline is
71 imported into the Edge.Cuts layer, indicating that it shall be used to direct
72 cutting tools to define the shape of the board. In order to align the outline
73 with a grid using 0.127mm (0.05 inch) units, the origin of the outline is
74 positioned at (60.445mm, 127mm). More information about the calculations can
75 be found in the BoardOutline documentation.
76
77 Preparing the Board Layout
78 --------------------------
79
80 Each component must be positioned appropriately on the board for it to make
81 any physical sense. The edge connector footprints must be placed on each side
82 of the protruding portion of the board, and the breakout connector footprints
83 must be placed high enough up on the board to be accessible when the cartridge
84 is inserted into the Plus 1. Beyond this, board layout is mostly a matter of
85 routing tracks between connectors and avoiding board features such as mounting
86 holes and the board edges.
87
88 Design Rules and Production
89 ---------------------------
90
91 It was decided that OSHPark would be used to make the first set of boards.
92 Thus, the design rules for OSHPark were added to the project configuration.
93 Such rules can be found here:
94
95 http://docs.oshpark.com/services/two-layer/
96 http://docs.oshpark.com/design-tools/kicad/kicad-design-rules/
97
98 The board uploaded to OSHPark was tagged with oshpark-648KdmKd in this
99 repository. It resides on OSHPark at the following location:
100
101 https://oshpark.com/shared_projects/648KdmKd
102
103 Contact, Copyright and Licence Information
104 ------------------------------------------
105
106 The author can be contacted at the following e-mail address:
107
108 paul@boddie.org.uk
109
110 Copyright and licence information can be found in the docs directory - see
111 docs/COPYING.txt and docs/gpl-3.0.txt for more information.