This is the documentation for the HobECAD is an ECAD (Electronic Computer Aided Design) system for the electronics hobbiest.

HobECAD Documenation

Table of Contents

• Table of Contents
• Introduction
• HobECAD Modes
• Command Line Options
• Mouse Operations
• Keyboard Operations
• Glyphs
• Schematic Capture Mode
• File Formats
  • .sc and .pcb Format
  • Font Format
  • .ptl Format
  • .pkg Format
  • .prt Format
• Summary

Introduction

Both the schematic capture and printed circuit board layout are implemented by the same drawing program called HobECAD. The HobECAD program basically implements a grid on which you can draw special symbols, text, and either thick or thin lines that are constrained to be horizontal, vertical, or diagonal.

For now, everything in is controled via the keyboard and mouse; there are no screen buttons or controls. (The eventual solution to this problem is to upgrade to a window toolkit that supplies buttons and controls.)

HobECAD Modes

There are two modes that hobecad can be operated in; the two modes are:

Schematic Capture Mode

Schematic capture mode is entered by specifying a suffix of .sc on the file name when it is created. In schematic capture mode, there are two layers that you can draw into; the two layers are:

Wire Layer (black):

The wire level uses lines to represent wires that interconnect electrical components. This layer is also used to label the pins of components.

Component (brown):

The component layer is used to represent the components of the circuit. Since some components are basically represented by a box with some text inside, drawing these lines in a different layer distinguishes them from wires.

When a schematic is printed out to a printer, all layers will be printed in a single color (black). The reason for keeping the component and wire layers separate is because the consistency checker needs a way to distinguish between lines the represent wires interconnecting components and lines that are used represent integrated circuits (e.g. flip-flops, counters, etc.)

Printed Circuit Board Layout Mode

PCB layout mode is entered by specifying a suffix of .pcb on the file name when starting HobECAD. In PCB layout mode, there are three layers that you can draw into; the three layers are:

Front (green):

This layer corresponds to the front (component side) copper layer on a printed circuit board. If you are laying out a single sided printed circuit board, the front layer is not used.

Back (red):

This layer corresponds to the back (solder side) copper layer on a printed circuit board.

Artwork (black):

This layer corresponds to the black artwork that is frequently applied to the component side of the printed circuit board to aid in component placement.

Other than the number and color of the layers, the HobECAD program behaves the same in both schematic capture and printed circuit board layer mode.

The reason for using a .05 inch grid, rather than the much more sensible metric system, is because .1 inch is the most common spacing between pins on a integrated circuit in a dual in-line package (DIP).

Command Line Options

The hobecad command line options are:

-c cell_size

The cell_size can be either 10 or 15 pixels square at the moment. 15 is the default cell size.

-d mono|gray|color

Force the display into monochrom, grey scale, or color mode. Do not use this option.

-D

This causes HobECAD to write out any files in debug format. Debug format stores all symbols in absolute coordinates rather than relative coordinates. For someone who understnads the file format, it is possible to grep for symbols in the .sc and .pcb files.

-g gerber_base

This option causes the generation of several files:

gerber_base.drl

This is a drill file in Excellon drill file format. The drill sizes are specified in gerber_base.tol .

gerber_base.gal

This is the artwork of the printed circuit board in RS-274X file format.

gerber_base.gbl

This is the back side of the printed circuit board in RS-274X file format (i.e. Gerber file format with embedded aperture specification.)

gerber_base.gtl

This is the front side of the printed circuit board in RS-274X file format.

gerber_base.gml

This is the mask layer of the printed circuit board in RS-274X file format.

gerber_base.tol

This is the drill size specification file. There does not appear to be any standard format for this file.

Mouse Operations

Either a 1, 2, or 3-button mouse can be used. The three mouse buttons are:

Left

The left button is used move the insertion point, draw lines, and delete lines.

Move Insertion Point

The character insertion point represented by a small hallow square that is the color of the current layer. It is moved by placing the at the desired new location and clicking the left button.

Draw Lines

Lines are drawn by placing the cursor to the desired starting point pressing down on the left mouse button, moving the cursor to the desired end point (while keeping the left mouse button depressed) and releasing the left mouse button. Lines are constrained to be vertical, horizontal, or diagonal.

Erase Lines

Lines are erased the same way they are drawn. The cursor is positioned at one end of the line, the left mouse button is depressed, the cursor is moved to the other end of the line, and the left mouse botton is released.

The middle button is used to switch between layers. The cycle order is front layer, back Actually, line drawing is done in an exclusive OR mode. As you draw a line, it complements the state of the prevoius line.

Middle

The middle button is used to switch between layers. The cycle order is front layer, back layer, artwork layer and then it repeats. The current layer is indicated by the color of the insertion cursor.

Right

The right button is used to toggle the thickness of lines. There are two line thicknesses -- thick and thin.

Left and Middle

By clicking on both the left and middle buttons at the same time you will either insert or delete a via. A via is hole through the printed circuit board that is is used to connect a trace from the back side to the front side. If there is no via present under the cursor when both the left and middle buttons are depressed, it will be inserted; otherwise, the via under the cursor will be deleted. In schematic capture mode, wire connection dots are drawn instead of printed circuit vias.

Keyboard Operations

Whenever you type at the keyboard, printing characters are inserted into the current layer. If the cursor is in the middle of some characters, the new ones are inserted into the middle. Characters are never moved over a via.

The following non-printing characters are supported by hobecad:

Delete

The delete character will delete the character to the left of the cursor. Any characters at the cursor or to the right will be moved left one character. If the characters are bounded on he right a via, the cursor stays in it current position and any characters to its left are moved one position to the right.

Escape

The current schematic or printed circuit board layout is written out to disk and hobecad terminates execution.

Control-@

Set the mark. The mark is used as one corner in a wipe operation (see Control-W).

Control-D

All special symbols at the current cursor location are deleted. Whereas the Delete key deletes to the left, the control-D key deletes to the right.

Control-H

Delete a character.

Control-L

Control-L will change the current insertion layer. The cursor color changes to indicate what insertion layer is currently selected.

Control-O

Toggle over-line mode for characters. In over-line mode, the characters drawn have a line drawn over them. Overlined characters are standarad notation for active low logic signals. {Currently, there is no cursor feedback concerning overline mode; this needs to be fixed.}

Control-P

Put in component pads. The string over the characters has the form "[#][A-Z]+[0-9]+[<>^]?offset". The first digit specifies the hole width; this is usually a 1 or 2. The next characters specify the component name (e.g. R1, U23, C17). The characters ">", "^", and "<" specify the direction of the components. The pads pivit around the pivit pad in the package file (i.e. the pad marked with a "*" in the .pkg file.) Finally, the whole pad can be offset by an optional offset of the form ";X:Y" where X and Y are signed decimal numbers. For example ";+0:+.01" will move the whole pad up one hundredth of a inch in the Y direction from the grid location.

Control-Q

Print out information about the symbol underneath the curser.

Control-R

Using the text underneath the cursor as a path to a .pcb or .sc file, read it into the clipboard. Use contorl-Y to "yank" it onto the screen.

Control-S

Change the character spin mode to the right by 90 degrees. This should also change text entry direction, but it does not. There is no visible cursor feedback that characters are being entered in a rotated direction.

Control-T

Control-T will toggle line thickness between thick and thin. A cursor will change from a thin box to a thick box to indicate the line thickness mode.

Control-V

In printed circuit board layout mode, the control-V character is used to insert or delete vias. If there is a via at the cursor, control-V will delete it; otherwise, control-V will insert a via at the cursor. In schematic capture mode, control-V is used to insert and delete wire connection dots. If there there is a connection dot at the cursor, Control-V will delete it; otherwise, control-V will insert a connection dot at the cursor.

Control-W

This will copy a rectangular region from the main window into a internal clipboard and delete the rectangular region from the main window. One corner of the rectangual region is specified by the mark (Control-@) and the other corner is specified by the current cursor position. Afterwards, the cursor is moved to the lower left corner of the wiped region so that the region can be copied back in using a yank command (Control-Y).

Control-X

If the cursor is on top of a bunch of characters, the characters are treated as a special symbol which is inserted at the cursor. Special symbols can span multiple cells and are used to represent electrical symbols such as diodes, resistors, and transistors. An additional character can be tacked onto the end of the symbol name to change its orientation:

^

Symbol will point up.

>

Symbol will point right.

<

Symbol will point left.

{none}

Symbol will point down.

The glyphs are documented in the section below:

Control-Y

The clip-board is merged back into the main window at the cursor. This command can be performed multiple times. {Currently, the characters are copied (not merged) from the clip-board; this a bug that needs to be fixed.}

Glyphs

The following glyphs can be used in schematics:

and

and2

buffer

bufferboth

bufferbubbleleft

bufferbubbleright

bufferleft

bufferright

capacitor

coil

diode

driver

fuse

inverter1

inverter2

nand

nor

not

npn

npn2

opamp

or

plug

pnp

pnp2

potentiometer

rail

resistor

zener

Schematic Capture Mode

The basic idea behind schematic capture mode is that you draw your circuit as a set of one or more schematic capture files. These schematic capture files are `read' by HobECAD to extract a wire list. The wire list can be used as an aid to layout the printed circuit board and to verify that the printed circuit board layout is a faithful rendition of the schematics.

Do you have to have schematics for your printed circuit board? No, but it is surprising how many errors in your board you will catch if you take the time to draw the schematics. Furthermore, taking the time to draw the schematics will leave behind useful documentation for future reference.

The basic `trick' behind schematic capture mode is that you draw your schematic in two layers -- the wire layer and the annotation layer. Currently, the wire layer is black and the annotation layer is brown, but these color selections are likely to change in the future. By drawing your schematic in two layers, HobECAD can successfully distinguish wires from component boxes and generate a correct wire list. When the final schematic is produced, both layers are output in black to produce a traditional black-and-white electrical schematic.

The `rules' for drawing a schematic are listed below:

Connected Wires

Connected wires are drawn in the wire layer (currently black.) Joined wires are indicated by placing a connector dot at the junction of the two wires. Alternaively, if three wires all end at the same location, HobECAD assumes that they are connected together. Some examples are shown below:

Crossing Wires

Wires that cross over one another are represented by just having straight lines cross over one another in the wire layer (currently black.) No connector dot is present. A couple of examples are shown below:

Labeled Wires

Unterminated horizontal or vertical wires that end in a label are called `labeled wires'. Labeled wires are how you connect wires between multiple schematic diagrams. All wires with the same label are connected together by HobECAD. By the way, the labels strings must be in the wire layer (i.e. black.) labeled wires including overbar labels are shown below:

Note that some of the labels in the examples above have a line drawn over them. These labels are called `overbar labels'. Overbar labels are quite common in digital circuits where they indicate an `active low' signal. Overbar labels ard drawn using the control-O `overbar toggle control'. Each time you type control-O, it will toggle label insertion between overbar mode or non-overbar mode. Currently, there is no feedback in the cursor block to indicate whether or not HobECAD is in overbar mode or not (this is bug!)

Labeled Components

It is also possible to insert a component directly into a schematic. If there is exactly one label `next' to the component, the label is taken as component name. The component lead names are assumed. Some examples are shown below:

Labeled Component Leads

It is also possible to insert a component into a schematic and explicitly label each of the component leads. The rule is that HobECAD will find the label closest to each component lead and use that as the component lead name. The remaining label that is `next' to the component is used as the component name. Some examples are shown below:

Note that the operational amplifier has a couple of labels in the annotation layer (shown in brown). HobECAD completely ignores labels in the annotation layer. Thus the component leads for the operational amplifier are labeled `1', `2', and `6'; the annotation labels of `+' and `-' are completely ignored.

Component Boxes

With one exception, all lines and labels drawn in the annotation layer (i.e. brown layer) are ignored by HobECAD. The only exception is a component box. A component box is a rectangular box drawn in the annotation layer that encloses a single black label. The black label is component name and any black wires that terminate at the edge of the box must be labeled in black as component leads. Some example component boxes are shown below:

Please note that anything in brown enclosed in the componet box is ignored by HobECAD. Further note that for `U3' that there is a brown `A' afterwards that is ignored by HobECAD. Finally, note that the wires for `U3' on the left have wires that are quite close to one another; HobECAD is smart enough to figure out which component lead names are attached to which components by figuring out whether a vertical sequence of labels is `on top' or `on bottom'.

File Formats

The file formats are:

• .sc and .pcb Format
• Font Format
• .ptl Format
• .pkg Format
• .prt Format

.sc and .pcb Format

Font Format

.ptl Format

    # Comment start with a sharp ('#') character.
    # Blank lines are ignored.
    component_name1: part_name1
    #...
    component_namen: part_namen
								

.pkg Format

    # Comment start with a sharp ('#') character.
    # Blank lines are ignored.   The first non-comment
    # line is the header and must be exactly:
    H Packages 1 0

    P package_name
    L x1 y1 lead_name1 [*]
    #...
    L xn yn lead_namen

    #...

    P package_name
    L x1 y1 lead_name1 [*]
    #...
    L xn yn lead_namen

    # The last line must be and end rerord:
    E
								

    P DIP8 # 8-pin Dual In-line Package
    L 0 6 5
    L 0 4 6
    L 0 2 7
    L 0 0 8
    L 6 0 1*
    L 6 2 2
    L 6 4 3
    L 6 6 4

								

.prt Format

    # Comment start with a sharp ('#') character.
    # Blank lines are ignored.   The first non-comment
    # line is the header and must be exactly:
    H Parts 1 0

    P part_name package_name
    L physical_lead_name1 logical_lead_name1 signal_type1
    #...
    L physical_lead_namen logical_lead_namen signal_typen

    #...

    P part_name package_name
    L physical_lead_name1 logical_lead_name1 signal_type1
    #...
    L physical_lead_namen logical_lead_namen signal_typen

    # The last line must be and end rerord:
    E
								

Summary

With the growing proliferation of surface mount components, the fundamental design choice of putting all components on a .05 inch grid is becoming suspect. However, as of the late 1990's, HobECAD still meets my goal of being a schematic capture and layout program for electonics hobbiests. Professional electrical engineers should purchase and utilize full featured schematic capture and layout products.