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SUMMARY OF REPLIES: Infra red photo cells used for triggeringOptotrak or LabView ???

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  • SUMMARY OF REPLIES: Infra red photo cells used for triggeringOptotrak or LabView ???

    Dear BIOMCH-L subscribers,

    Here is a summary of the replies to “Seeking Advice: Infra red photo cells
    used for triggering Optotrak or LabView ???.” We ended up using a simple
    photocell to trigger LabView and a second monitor hooked up to LabView which
    indicated for the subject to go either left or right.

    I have attached the original posting and “slightly” edited versions of the
    replies. Some of the authors also included attachments (Vis, PowerPoint
    schematics, JPEGs) which can be forwarded to whoever is interested.


    I am a mechanical engineer attempting to help a Rehab research group with a
    kinematics/EMG study requiring a few items that I have no knowledge or
    experience with (I have minimal gait lab experience):

    1) External triggering system which will activate LabView (which is
    presently triggering Optotrak). Specifically I would like to use some sort
    of an infra red photo cell (like one sees in heist and burglary movies) that
    when crossed will activate either one or both of the systems. There was a
    posting on BIOMCH-L in 1997 by Michael Slavin at UC Davis: “photocell
    outputting a TTL-compatible voltage change when the beam is broken a few
    steps before the force plate” but I have had no luck locating this
    individual through UC Davis or google.

    2) A lighting system which will indicate to a subject whether to go left or
    right. This system should start a few seconds after the external triggering
    system has been initiated. I’m guessing that this isn’t too difficult, and
    can be done using LabView; I would just like some advice and suggestions on
    specific products.

    Thanks in advance,

    JD Johnston

    %% REPLIES %%%%%

    Two of my fellow students just used a simple photo cell setup to measure
    golf ball velocities.

    16 Sensors: Sharp OPIC IS489, 5V, rise time 0.1 micoseconds, view angle 30°

    1 Light Source: 4.5V Maglite

    -- --

    Not the most accurate method (just one light source rather than fancy red
    light beams like in the burglary movies ;-) ), but pretty unexpensive if I
    remember right. The set up was not influenced by the lights mounted on the
    ceiling of the lab. Sensors were triggered by the shadow of the ball and
    gave a fairly clear signal.

    Nils Betzler

    Sportsengineering Program

    University of Magdeburg, Germany

    -- --

    NOTE: Nils also included two figures of their existing setup. As BIOMCH-L
    does not permit attachments, I can forward these files to whoever is


    I have some experience with photocells and triggering devices. The cheapest
    photocell device that you are talking about can be picked up at RadioShack.
    I don't know if they have those in Canada, but you can go online and find it
    at there website. We had to do some modification to it for a bnc output,
    but this can be done easily by a person with a little electrical engineering
    knowledge. As for the triggering of an event, I have little knowledge with
    Labview or optotrak systems. We use a program call SuperLab Pro. This is a
    very easy program to use to trigger an event.

    Robert D. Catena, M.S.

    Doctoral Student

    Dept. of Human Physiology

    1240 University of Oregon

    122 Eslinger Hall

    Eugene, OR 97403-1240

    Work # (541) 346-1033

    Fax # (541) 346-2841

    -- -- --


    Our walking timer is basically a series of two through-beam IR sensors that
    spans the lab and when someone crosses the beam it sends a signal to the DAQ
    and triggers a counter stop. The triggers we used are about $100 a piece I
    think. Make sure if you get the same type to get a compatible reflector.

    As far as your Left/Right lights, my advice there is to use low current
    using relays attached to an outside power source. That way you can trigger
    the lights directly from the DAQ (DIO) and not have to worry about burning
    out the card.

    Matthew Cowley

    RR&D Center of Excellence

    VA Puget Sound


    -- --

    -- --

    NOTE: Matthew also included a PowerPoint schematic of the timer and a
    LabView VI. As BIOMCH-L does not permit attachments, I can forward these
    files to whoever is interested.


    I did some work a couple of years ago crashing racing cars into a steel
    block at the end of an incline to measure the deceleration but to the cars
    nose deformation. Basically this meant using our system to detect the
    trigger and acquire a sweep of information before and after the trigger was
    detected (an expensive operation if you missed it). This was a simple light
    beam converted to TTL as you suggest. I believe the photocell used was of a
    basic type used for simple home security.

    Simon Gray

    Sales Manager

    -- Cambridge Electronic Design Ltd. --

    -- Tel. [+44] (1223) 420186 --

    -- Fax [+44] (1223) 420488 --

    -- WWW.CED.CO.UK --

    -- --

    P.S. To join the email software upgrade notification list please contact

    P.P.S. We are always interested to hear of published papers mentioning CED
    if you have any that you would like to forward to me I would very much
    appreciate it.


    If you want to build your own sensor you'll need a phototransistor to detect
    the light source and the interruption. For this to trigger the Optotrak you
    need a falling (check this setting though - Optotrak might prefer the rising
    edge) TTL (transistor transistor logic) pulse. You can find the circuits for
    those online and the parts are pretty cheap. It's fairly simple to adapt the
    TTL circuit for the phototransistor as it's a transistor already and shining
    light on it just makes it conduct and removing light will make it stop
    (causing the drop in the TTL pulse).

    As for Labview there's a VI for trigger detection. I think you just hook up
    the trigger to a channel and the VI monitors it for a "pattern". So in the
    case of a TTL pulse you'd use a pattern that matches the failing (or rising)
    edge of the pulse (typically a drop of 2.5 to 0.5V).

    Amy Saari

    Injury Biomechanics Laboratory

    Department of Mechanical Engineering

    University of British Columbia

    6250 Applied Sciences Lane

    Vancouver, BC V6T1Z4

    -- --





    James D. Johnston, MSc

    PhD Candidate

    University of British Columbia

    Division of Orthopaedic Engineering Research

    5th Floor, 828 West 10th Avenue

    Vancouver, BC V5Z 1L8

    phone: 604-839-1174

    fax: 604-875-4851



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