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  • summary: timers

    Biomechers:
    Last week I inquired about low cost timers -- ones that have .001 s
    precision and can be hooked up to a variety of stop/start/reset
    inputs. In summary, the three basic replies were 1) modify a typical
    stopwatch, 2) build it yourself from scratch, and 3) buy a ready
    made device. Relevant replies in each category are below.
    I want to thank all those who responded -- your help was quite
    valuable.

    Modify a stopwatch:
    --------------------------------------------------------
    [As a point of note, this is what I had originally intended to do,
    but wanted more precision than the .01 s afforded by all the
    stopwatches I found. I contacted Casio and Accusplit and both
    companies mentioned that they do not make timers with .001
    precision. I also contacted Seiko -- timers for the 2002 Winter
    Olympics -- but they did not get back to me. I was unable to
    contact Swatch -- timers for the Sydney Olympics -- because
    their website was so slow/bad.]

    --How about using cheap stop watches and using a transistor to short
    out the relevant switch when activated? We have used such devices
    here without any problems.

    --This month's issue of The Physics Teacher has an article entitled: A
    Stopwatch-Based Photogate Timer. It describes how to build something
    similar to what you want. Here is the full biobliographic information
    for the article:
    Wooten, A. (Oct. 2000). A stopwatch-based photogate timer. The Physics
    Teacher, v. 38, pp. 405-407.
    [I have yet to check out this article, but certainly will]

    --We have made these by buying an off the shelf stopwatch for about 7UK and
    replacing the start stop switch a connector for an external cable. With
    some fiddling an appropriate electical signal of a few volts or an
    electronic switch (available as an ic for less than about a pound) can be
    used to control the stop watch. Trial and error is the best way of finding
    what is required as a trigger - if you keep below 5 volts you are unlikely
    to destroy the watch. This saves the much more complex task of constructing
    the timer/output circuitry.

    --------------------------------------------------------
    Build it Yourself (There was some level of disagreement here about
    what this might cost):

    --I'd encourage you to do it yourself. I've made timers like this
    before. It is a pretty basic digital project and you could find all
    you needed to know from beginner level electronics books (the type
    that take about an hour to read and are available at most electronics
    retailers). You could do the lot on a budget of about $20 too.
    I live in Australia so can't really point you to any good local
    resources but please feel free to get in touch if you want to.

    --I developed a timer used to control the signal output one year ago. This
    small timer system can be controlled both manually and electronically. The
    basic idea of this timer development is to use a Monostable/Astable
    Multivibrator (CD4047) to generate a basic clock frequency; and use several
    Decade Counters/Dividers (CD4017) to get the timing accuracy you want. All
    manual or electric control, and input or output of the timer can be built
    up based on this basic structure of the timer. The cost (not include the
    labor) should be within $400USD. Also, it might be possible to use some
    kind of software package (LabView) combining with other I/O device to
    realise the function you need if you have these facilities. But, I have no
    experience of this approach.

    --I was interested to read your reply [referring to response above].
    Especially with regard to the cost of the project. I have made timers
    based on a 555 IC, a few latches (flip/flops), logic gates and a counter
    for a price of around $20. There is really no limit to the potential number
    of triggers (processed with a few logic gates) so I can't see why you'd ever
    need to spend more.

    --I constructed photoelectric timing system with a couple of off the shelf
    products. I purchased a digital clock from Kessler-Ellis (Keptrol counter -
    KP8A3A2A) for about $420.00 and Photocells from Cutler-Hammer (CH14150AD17 -
    photocells (purchase 2) and CH6200A6501 - reflectors - total price about
    $116.00). Then I purchased 3 power supply's from Radio Shack to power it
    all. We attach the photocells to some old tripods and use this for
    primarily gait analysis. It works well but the cost is probably a wash.

    --We used Microsoft Visual Basic to construct a timer on a PC for use with a
    mountaineering reaction time project we are involved with. It was easy to
    construct and uses the PC's in built timer. It wouldn't be hard to find a
    way of externally triggering it - at the moment it is triggered using the
    mouse or keyboard.

    -------------------------------------------------------------------------
    Buy it Off-The-Shelf:

    --I use timers from FarmTek - they're located in Texas [http://farmtek-fti.com]
    The timer works via infrared detectors and are used in rodeo competition...
    we use them in crash testing and the accuracy has been excellent... I'm not
    sure about the cost however. [Systems range from about $550USD to $1000+.
    They look pretty interesting, but a little more money that what I wanted to
    spend]. I noticed your reference to Lafayette instruments and I have never
    heard of them. I tried to find them on the web without success... if you can
    forward me a website I'd appreciate it. [Lafayette makes a lot of motor
    behavior research equipment, like reaction time apparatus; find them at
    http://www.Lafayetteinstruments.com or
    http://www.licmef.com]

    [I searched the web for companies making what I wanted but came up with
    only a few choices. Aside from those mentioned above (FarmTek and
    Kessler-Ellis (http://www.kep.com), there is Newtest (www.newtest.com?)
    and a couple of companies making reaction time devices for auto drag
    racing. These did not seem general purpose enough for my needs.]

    I guess I am off to Radio Shack. . . .
    Thanks again for all those who responded.

    Jeff Ives, Ph.D.
    Dept. of Exercise & Sport Sciences Phone: 607-274-1751
    Ithaca College Fax: 607-274-1943
    Ithaca, NY 14850 USA Email: jives@ithaca.edu

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