Manual for ScopeShapes 0.1.1
Chris Meighan
Copyright (c) 2005 Chris Meighan
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 2 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 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the 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, write to the Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
Please note - ScopeShapes is GPL licenced. However, the version of the PortAudio library bundled with the source code has its own licence (which is broadly similar to the LGPL).
2005
Table of Contents
Introduction
What is ScopeShapes?
How does ScopeShapes work?
- Using ScopeShapes
Connecting up the oscilloscope
The main window
Importing DXF files
Tweaking performance
2. ScopeShapes menus
File menu
Quit
Options menu
Hardware options
3D options
Performance options
Save options on exit
Save options
Help menu
Help contents
About ScopeShapes
3. Keyboard shortcuts
4. Credits
List of Tables
1.1. Main window controls
2.1. Hardware options
2.2. 3D options
2.3. Performance options
3.1. Keyboard shortcuts
Introduction
Table of Contents
What is ScopeShapes?
How does ScopeShapes work?
What is ScopeShapes?
ScopeShapes is a piece of computer software which uses the stereo sound output present on most modern computers to drive the horizontal and vertical axes of any oscilloscope which has an X - Y mode, in order to produce 2D and 3D vector graphic images.
It reads DXF (Drawing eXchange Format) files, as produced by AutoCAD and many other programs, and can switch between up to 10 shapes. It can automatically rotate shapes in 3D space, and morph between different shapes.
How does ScopeShapes work?
Most desktop and laptop computers possess a stereo sound output, usually in the form of a 3.5mm jack socket. It can usually output at a resolution of 16 bits, at up to 44.1KHz. What this is, in effect, is a dual digital to analogue converter, optimised for the audio frequency spectrum.
An oscilloscope in X - Y mode (a function usually used to measure phase difference between two different signals) can be used a vector (as opposed to raster) graphic display by driving the two inputs with analogue voltages of a suitable magnitude. A varying voltage on the X input will drive the beam left or right (according to its polarity), whilst a voltage on the other will drive it up or down.
If we then connect the left and right side of the computer's stereo output to the X and Y inputs respectively (or the other way round, it doesn't really matter), and write some software to drive the outputs according to the geometry of a series of lines, we can draw shapes on the oscilloscope screen. That is the purpose of ScopeShapes.
Chapter 1. Using ScopeShapes
Table of Contents
Connecting up the oscilloscope
The main window
Importing DXF files
Tweaking performance
Connecting up the oscilloscope
As indicated in the introduction, the oscilloscope needs one channel to be connected to the left output of the computer's audio connector, and one to the right.
Exactly how the inputs are labelled will depend on your particular model, but the picture below shows the arrangement for mine, a Hameg HM203-6. Most models are unlikely to vary much from this.
Since most scopes use BNC style connectors, the most convenient way to link it up to the computer (without the use of a soldering iron) is to use a suitably long 3.5mm jack to 2 x phono cable, and 2 BNC to phono adapters. Such things should be readily available in your local Maplin (UK), Radio Shack (US), or local equivalent.
Last but certainly not least, the 'scope should be switched into X - Y mode. This will usually be by pressing a button as on the machine shown above, or by a special setting on the time base control.
Once the software is running, it may be necessary to adjust the Volts/Div controls (usually both channels will be set to the same range). Mine seems to work best at somewhere between 50 and 200mV (millivolts) per division.
The main window
The main ScopeShapes window looks like this (the exact appearance will depend on the platform it is running on).
Before any shapes appear on the oscilloscope screen, it is likely that the sound card's parameters will need to be set up - see Hardware options below.
The large screen shows the shape that is currently (hopefully) showing on the 'scope screen. The ten smaller screens on the right are 'banks', which hold shapes which can be switched into view by clicking on them.
To load a shape into a bank, either click the white 'load' button next to it, or drag a file onto its screen. Any valid ASCII .dxf file will do - don't worry about scale and positioning, it will be automatically normalised to fit the screen. To clear a bank, click on the red 'clear' button below the 'load' button.
[Note] Note
You can specify a list of files on the command line when loading
ScopeShapes, or drag some files onto the program's icon (which
achieves the same thing, anyhow) to have them loaded on startup.
The row of dials underneath the main screen are used to alter various parameters;-
Table 1.1. Main window controls
Transition Speed This affects how quickly one shape 'morphs' into another
when a new bank is selected. X axis and Y axis These control how fast and in which direction the shape
will be rotated about the 3D X and Y axes.
Zoom This moves the viewpoint away or toward the shape.
Further control of the display can be effected via selecting 3D options from the Options menu.
Importing DXF files
[Note] Note
ScopeShapes will only read ASCII (NOT BINARY) DXF files.
First things first - simple is best.
The fundamental weakness in trying to use a soundcard's outputs to generate a graphical display is that it has insufficient bandwidth to do so very effectively. In simpler terms, the signal just can't change at a fast enough rate for complex shapes to be plotted in a reasonably short space of time. What this means is that overly-complex shapes will appear flickery and indistinct.
There is a way around this (sort of) - the Hardware options dialogue allows the speed of the beam to be adjusted, which is something of a trade-off. You can have either a fast-moving beam, which allows complex shapes to be drawn without flicker but which tends to produce distortion and undue oscillations at sharp corner points, or a slow-moving beam, which will only work effectively for simpler shapes, but which minimises distortion. As always, a compromise is usually best.
When producing DXF drawings, try to stick to a few simple shapes, using basic primitives. The following restrictions apply;-
- Blocks and groups are not understood. Reduce everything to basic primitives.
- Only the following DXF entities are supported;-
- LINE
- POLYLINE
- CIRCLE
- ARC
- 3DFACE
However, since most other shapes can be decomposed to these this is unlikely to prove too much of a handicap.
Scale and positioning are unimportant, since these will all be normalised on import so that the shape fits the screen and with other shapes.
Tweaking performance
Performing 3D and 2D transformations, updating the GUI display, and outputting data in real time to the sound system can prove rather processor intensive. To cope with this, there are several options in the Performance options dialogue to reduce CPU load.
Most significantly, turning off real time update of the 10 bank screens can reduce CPU load by more than half. Also, reducing the frame rate, and turning off anti-aliasing (which only affects the GUI display in any case
- you can't anti-alias a vector display!) can also help.
Chapter 2. ScopeShapes menus
Table of Contents
File menu
Quit
Options menu
Hardware options
3D options
Performance options
Save options on exit
Save options
Help menu
Help contents
About ScopeShapes
File menu
[Note] Note
The Mac OS X version has no file menu - the Quit option is on the
ScopeShapes menu (as is standard on OS X).
Quit
Quits ScopeShapes.
Options menu
Hardware options
Controls output to the soundcard.
Table 2.1. Hardware options
Output to soundcard Turns on and off the output to the sound system. Saves
a lot of CPU time if turned off, but then that would
somewhat defeat the purpose of the whole program.
X = Left, Y = Right Changes which side of the stereo output drives which
axis of the scope. Useful if you've got your wires
X = Right, Y = Left crossed (although of course you could just swap the
connectors on the scope).
Mirror X Mirrors the signal for either axis. My system seems to
Mirror Y need the Y axis reversed for some unknown reason.
Device Selects which audio device to use, if there is more
than one available. A device will have to have at
least 2 output channels to be available.
Distance per sample As explained in the section 'Importing DXF files',
there is a trade-off between distortion introduced by
outputting a signal beyond the bandwidth of the audio
output, and introducing too much flicker in the
display by drawing the trace too slowly. This slider
allows a compromise position to be selected.
3D options
Controls the parameters of the 3D display.
Table 2.2. 3D options
Perspective Selects between a wide perspective (more dramatically
foreshortened lines, like looking through a fish-eye lens),
and narrow perspective (flatter-looking, closer to an
isometric drawing).
Performance options
Turns on and off features which affect the CPU load.
Table 2.3. Performance options
Don't update bank The most significant way to reduce CPU load - as
screens such it is enabled by default. When this option is
selected, the display on each bank screen will only
be updated when a new shape is loaded. If not, they
are all updated in real time.
Don't anti alias main Turns off anti-aliasing (smoothing of lines) for the
screen main screen.
Don't anti alias bank Turns off anti-aliasing for the bank screens. screens
Frames per second Selects how often the display will be updated. Lower
frame rates consume less CPU power, but make the
display more jerky, whilst higher rates produce a
smoother image, but consume more CPU power.
Default frames per Selects 20 FPS. second
Save options on exit
If checked, all the options selected will be saved when the program quits, and will be restored when it is next loaded.
Save options
Saves the currently selected options, so that the next time the program is run the same setup will be in operation.
Help menu
Help contents
Launches the interactive help system.
About ScopeShapes
[Note] Note
The Mac OS X version has no about option - it is on the ScopeShapes
menu (as is standard on OS X).
Displays some basic information about ScopeShapes.
Chapter 3. Keyboard shortcuts
The following keys can be used in ScopeShapes;-
Table 3.1. Keyboard shortcuts
1 - 9, 0 Switches into a bank. Banks are numbered from the
top left, and follow down in rows
Z and X Adjust transition speed up or down
Up and Down arrows Adjust X axis rotation speed (these keys are not the
wrong way round, since rotation about he X axis
means movement in the vertical direction).
Left and Right arrows Adjust Y axis rotation speed. Page Up and Page Down Zoom in and out.
Chapter 4. Credits
ScopeShapes was written by Chris Meighan.
It is written in C++ and may be compiled using GCC on Linux and Mac OS X, and MinGW on Microsoft Windows.
The GUI was built using the wxWidgets toolkit.
The sound output code makes use of the PortAudio library.
The installer for the Windows version was compiled using Inno Setup.
The documentation was compiled using the DocBook system with xsltproc. The HTML Help version was compiled using Microsoft HTML Help Workshop command line tools, and Apache FOP was used to generate the PDF version.