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jeng28
04-21-1997, 09:17 AM
Summary of A/D system set-up with Optotrak System

Thanks to all who replied to my question regarding the sychronization and
A/D collection of data along with the Optotrak System. The general
consensus was that a second PC would be required to collect Optotrak data
and A/D data via LabView software (however, see the last individual reply
for a possible way around this). Several people mentioned you could output
the Optotrak synchronisation pulse to LabView or other similar products
(e.g., AMLAB, HPVEE) running on a second PC or MAC. The Optotrak 16
channel A/D system combined with a multiplexer system was the least
expensive solution, however, it was agreed that if you could afford the
dual PC system, that this system would have superior advantages in
flexibility.

Here is the original posting with some of the individual replies:

"I am investigating the feasibility of setting up an Optotrak Position
Sensor System with a 64 channel A/D system. Can anyone tell me what
advantages/disadvantages there might be to the following two systems? The
A/D board would be used to collect data from 2 forceplates plus EMG.

1. Opotrak Acquisition Unit (ODAU II, 16 channel A/D converter and software
which also enables synchronized collection with the Optotrak position data)
plus the National Instruments AMUX-64T (front-end analog multiplexer that
quadruples the number of analog input signals that can be digitized)

VERSUS

2. National Instruments 64 channel A/D board (e.g., AT-MIO-64E-3) using
LabView software for Windows. Thus, you would have to somehow use one of
the Optotrak output s to create a synchronized system. Has anyone done
this? Would a second PC be required for this set-up or could this somehow
run in conjunction with the Optotrak software? It seems to me that this
second system using a true 64 channel A/D board plus LabView software would
be more flexible in the long run but perhaps it is not feasible within one
PC."

>From Bob Singerman case western reserve university rbjs@falstaff.cwru.edu

i've been using the optotrak 3020 for about a year now ...a sync pulse is
supplied at onset of data collection...i have collected analog data both
with their system and with a separate parallel system by using one of
external a-to-d channels to sample optotrak
sync pulse...works fine

>From Michael Slavin

Does Optotrak have the capability to output or read in a sync signal (e.g.
TTL hi-lo)? Our Motion Analysis system does, and this makes triggering in
either direction fairly simple,
so that data collection starts at the same time on both systems. I would
be surprised if there is not provision for this since it is such a common
need. At worse, it would require you monitor the voltage on your keyboard
or wherever you start the acquisition from. In our gait lab, we often use
a photocell outputting a TTL-compatible voltage change when the beam is
broken a few steps before the force plate, to trigger both systems
simultaneously. I have no real familiarity with the AMUX boards and only
know that, depending on the type of acquisition (e.g. differential vs.
single-ended), they can sometimes be tricky to get to behave. But they do
provide a lot more channels for
relatively little investment. We use LabVIEW (for Macintosh) and there is
a learning curve like any language (flatter if you're not a visual
person!). I have used the input trigger (both hardware and software
analog), the counters to time things and the pulse output to trigger other
systems. It takes some learning but works well now and is pretty
software-flexible. Anyway, I vote for a separate DAQ system using LabVIEW.
The synchronization (triggering) should be a relatively minor issue. You
will have much more flexibility to use it to acquire other types of data,
write your own vi's (programs), etc. You may still want the AMUX on top of
a 16-channel board (for cost). Some of this assumes you do not need high
SR's (for biomechanics, above 1000 hz or so) since 64 channels at 1000 hz
might pose a problem for some systems. You might want to compare
Optototrak SW/card vs LabVIEW SW/card if this is an issue.

>From Hans Hoffman hhoffman@BIOMED.MED.YALE.EDU

Using an AD board and optotrac at the same time is possible with one PC.
We use a Kiethley Metrabyte DAS1600 board in conjunction with optotrac to
collect quasistatic load/displacement data. Optotrac collection is
triggered by an AD board digital output through the serial port. Windows
95 allows us to have separate applictions running for the two systems.
But, as I said, our application collects only discrete points of a
quasistatic system so we actually take AD board and optotrac data
consecutively. By using optotrac to trigger the AD board collection in DMA
mode, however, I think concurrent collection would be possible.

Thanks also to the following people who took the time to reply,

J Greg Anson School of Physical Education, Otago
Andrew Brammall Summit Medical and Scientific
Lesley Brown Dept of Exercise and Movement
Science, U. Oregon
John Crevani
Peter Keir UCSF Ergonomics Program
Peter F. Meyer NeuroMuscular Research Center, Boston
University

Regards, Janice Eng

__________________________________________________ __________________
Janice Eng, PhD, PT
Assistant Professor
School of Rehabilitation Sciences
Faculty of Medicine
University of British Columbia
T325 - 2211 Wesbrook Mall
Vancouver, British Columbia, Canada
V6T 2B5
Tel: (604) 822-7571
Fax: (604) 822-7624
E-Mail: JENG@REHAB.UBC.CA