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jives38
10-12-2000, 02:44 AM
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.

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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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