Synchronization

Hi Janet,

This is Al Finch at Indiana State University and I am responding to an
email that Gideon Ariel forwarded to me concerning your question about
synchronizing video cameras, EMG and force plate data.
I have used an Ariel APAS for many years and my students will do 2D &3D
video analyses with force plate or EMG data and we synchronize the data
regularly.

I have made a synchronization device using an LED, 9 volt battery, and
thumb switch and BNC connector for the A/D board. Depressing the thumb
switch activates the LED which can be seen by the cameras, it also
produces a square wave from 0-9 volts which provides a syn timing event
on the analog signal.
Depending on the thumb switch you use you can either ramp up to 9volts
(closure on contact) or have a 9v signal that is chopped or open on the
switch closure. I also have used a microswitch which was imbedded in
the bottom of a box to provide synchronization when the box was lifted
from the ground. All these devices cost less than $20. A commercially
made synchronization unit by Kistler will cost about $900.

To just synchronize multiple video cameras I took a regular camera
strobe light and connected a thumb switch to the discharge plate and
then used a plastic mask in make a small slit aperature to reduce the
intensity of the strobe. I don't use this unit to synchronize to the
A/D because the strobe unit discharge is about 200volts and I could put
a resistor in line but if the resistor didn't step down the voltage then
this would damage the A/D board that is expecting +10volts.

You can set the synchronization time in the trimmer module, in the
digitizer module, or when using the APASview module you can adjust the
synchronization time.

I hope this helps you, in understanding how the Ariel system will
synchronize multiple data streams.

If you have any further questions please feel free to contact me.

Al Finch
Professor Physical Education
Biomechanics Lab
Office: 812-237-3927
Lab: 812-237-4174