Vision Egg Visual stimulus creation and control
with open source software

Introduction

Home Introduction & News
News
Screenshots Views of the demos
Technologies About Python and OpenGL
Platforms Hardware compatibility
Frame rates Frame rates explained
Synchronization Interfacing with other hardware
Calibration Calibrating displays

Documentation

Programmer's Manual Concept overview
Tutorial Simple demo programs explained
Library Reference
FAQ Frequently asked questions

Download and Install

Downloads Get it now!
Installation overview A quick installation summary
Windows Install Step-by-step
Mac OS X Install Step-by-step
Linux install Step-by-step
SGI IRIX install Step-by-step

Miscellaneous

Mailing list Stay up to date
Eye tracking
Labview GUI/Data acquisition interface
The future Potential upcoming changes to be aware of
Develop! How to help the Vision Egg
Other solutions Links to similar stuff
Thanks Credits
VisionEgg @ SourceForge

Synchronization: Interfacing with other hardware

A final timing consideration is synchronization with data acquisition or other hardware. A common paradigm is to trigger data acquisition hardware from the Vision Egg. There are several ways to do this with the Vision Egg.

Perhaps the simplest is to control a digital output on the computer's parallel port so that this value goes from low to high when the first frame of a stimulus is drawn. Support for this is provided for linux and win32. Unfortunately, the parallel port is can only be updated when OpenGL is instructed to swap buffers, not when the monitor actually refreshes. If you need timing accuracy better than your inter-frame interval, the best solution is to ''arm'' the trigger of your data aquisition device (with the parallel port output or a network command) immediately before the stimulus begins and trigger with the vertical sync pulse from the VGA cable itself.

Alternatively, you could begin data acquisition less precisely, digitize the vertical sync pulse going to the monitor along with your usual data, and align the data after the experiment is complete.

Another method, or a method to validate timing, is to use a photo detector on a patch of screen whose brightness might go from dark to light at the onset of the experiment.


Please direct enquires to the Vision Egg mailing list.
The primary author of the Vision Egg is Andrew Straw
This page last modified 27 Jun 2004.
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