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
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
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.
Professor Physical Education