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Stewart, Sandy 443-6113
09-03-1997, 12:10 AM
Dear BIOMCH Listmembers,

Below is a summary of replies to my question concerning the
availability of a device to convert an analog waveform to a video signal,
so that the waveform can be seen at the bottom of the image. The
consensus seems to be to use a PC and A/D board to capture the signal and
display it on the VGA screen, and then convert the VGA output to video
using one of several commercially available VGA-to-video converter boxes
(which appear to be fairly inexpensive). The two video signals can then
be mixed with a conventional video mixer.
My original message follows. Many thanks to all who provided
input.

Sincerely,
Sandy Stewart



************************************************** **********************
* Sandy F.C. Stewart, PhD *
* Hydrodynamics & Acoustics Branch *
* Food & Drug Administration *
* 12721 A Twinbrook Parkway *
* Rockville, MD 20852 *
* *
* 301-443-6113 * fax 301-443-1343 * sxs@cdrh.fda.gov *
************************************************** **********************

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ORIGINAL POSTING:


A colleague has an application for a device that takes an analog
signal (a pressure or flow waveform, for example) and converts it to a
form that can be mixed with a genuine video signal (from a video camera,
for example) so that the waveform is visible down at the bottom of each
frame. Ideally the device would have controls to vary the placement of
the waveform within the video frame and the timing. The waveform would
scroll across to the right, showing n cycles (where n is another
controllable feature), then disappear when it gets to the right side and
start over. Alternatively, the current time could be represented in the
middle of the screen with the waveform itself moving to the left.

The purpose is to synchonize the choice of the frames to use for
flow visualization with features in the pulsatile flow. My colleague is
borrowing a device to do this, but it's on temporary loan.

I believe IPM (Instrumentation for Physiology and Medicine) used
to make such a device but their (admittedly ca. 15 year old) phone number
no longer works.

Any suggestions would be greatly appreciated.

Thanks,
--Sandy Stewart


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SUMMARY OF REPLIES:


Have you taken a look at the Bargain Barn on the ISB web site? We have a
couple of resources there that have been very helpful for other people
searching for equipment. I can place a want ad in the Bargain Barn if
you would like. Why don't you take a look at what is there and see if
that would interest you and send me the ad (in plain text format) if you
are interested. We are hoping it grows into a useful resource. We just
posted it recently. You can find it at:

http://www.kin.ucalgary.ca/isb/bargain/bargain.html

Good luck!

Denise Neptune
denise@zinfandel.kin.ucalgary.ca

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Possibly I underestimate the problem, but it seems quite simple.
a) Use some A/D sofware to display your data on screen
b) Connect a VGA to TV (NTSC or PAL) convertor to the monitor port of
your PC .
c) Mix this video signal with the video of the camera in a video
mixer. There are many types for amateur use, which are quite cheap.
Ask someone from the audiovisual dept. or from a shop for advice.
I hope this will help you further,

At Hof
a.l.hof@med.rug.nl

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This can be done a couple of different ways. One way would be to utilize
multimedia hardware and a PC and overlay the analog waveform on top of
the video image. There are off the shelf boards that allow you to do
this. You also need an A/D board to digitize the analog input. You can
use a variety of programs, such as LabView, to display your waveform.
Depending on how you scale and place your waveform you can place it any
where you want on the screen, and any size.

We have designed custom hardware to do some of these functions, but
unless you are doing something exotic you should be able to use
commercially available products to do this.

Multimedia NTSC video input to VGA: Video Blaster by the same people who
make the Sounds Blaster cards for PC's, several other companoies make
these, I think Matrox makes a combo VGA & NTSC input card.
Analog to Digital (A/D) cards: National Instruments, Data Translation,
Burr Brown, and many others.
Plotting Software: Write your own, LabView by National Instruments, or
other plotting routines.

I have heard of a system that basically uses an oscilloscope and mixes
the trace (the brightest screen portion) with another video signal. This
doesn't seem to have a real cost savings and the data isn't stored for
any post processing as it could be with the PC system.

Good Luck with your development,

Tom Westenburg
Principal Engineer
TWestenburg@USOC.ORG

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As a matter of coincidence, we have been looking for the same thing as
you described in your message. I'm suprised that IPM is out of business,
they had such a neat set of products. Maybe they were purchased by some
larger instrumentation company. Will look into this.

One lead you might wish to pursue is a good audio visual supply firm.
One such company is the AV Blue Book. Our local distributer is Kemmco
sales at 412/327-4904. I will also ask my lab manager to share his
progress with you.

And if your inquirey should turn up any good ideas, I'd appreciate your
forwarding them to us or to the B-Board.

Happy hunting,

James F. Antaki, PhD
antaki@pittsurg.nb.upmc.edu

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I seem to remember seeing a similar system being demonstrated at a
meeting of the Physiological Society in Bristol, UK a couple of years
ago.

I think the name you want is Dr.Margaret Gladden at the
University of Glasgow, UK (Institute of Physiology?) I don't have an
e-mail address for her either... Sorry!

Kenneth Campbell
k.s.campbell@bham.ac.uk

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I know at least one research group that has developped a system like
you describe. They mix the video-signal from one or two (split
screen) camera's with EMG curves and other graphical signals.
You can contact: Roessingh Research and Development
Roessinghsbleekweg 33
NL 7522 AH Enschede, The Netherlands
e-mail: rrd@rrd.nl
tel: +31 53 4875777
I will also forward this question to a collegue in the Netherlands.

Good luck,

Leonard van Schelven
L.J.vanSchelven@ID.AZU.nl

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As an alternative you could do the following: Get your signal using pc
based data-acquistion, and display the signal in the way you want it to.
Then use a video overlay board (should come for less than $500) that gets
video in, overlay video and monitor picture out (usually these cards have
many other fancy features, but this basic one is sufficient I guess).

Success, Jaap
j.harlaar@azvu.nl

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One option is Televeyes. It is a cheapo box ($300 or so?) that merges a
computer screen and a video image that then can be recorded on a vcr. So
for example, you can use a PC data collection system like LabView or
LabNotebook that simulates an oscilliscope and then merge that display
onto part of the video camera image. The televeyes box is generally
called a video effects device and most people use it to add titles to
their home videos or to make a commercial for a cable tv access channel
etc. I got our televeyes box from one of the Macintosh mailorder
catalogs. It works for DOS, Windoze or Mac OS.

We use this device in teaching labs to coordinate EMG or force signals
etc. to their movements.

Rodger

Rodger Kram
rkram@socrates.berkeley.edu

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We've done this sort of thing in a number of ways, but I don't know of
any off the shelf solutions. I'd like to receive any feedback you get.

1. The crude way, just to demonstrate the principle, but can work ok as
a one-off. Put the waveform up on an oscilloscope, and use a video
mixer.

2. When you have demonstrated (using 1. above) what you want to do to an
a-v/electronics boffin, pick him/her up off the floor where he/she is
rolling around laughing at the crudity of your approach, and point in the
direction of the workbench. Will come back with something workable quite
soon. Iterate.

Owen Evans
o.evans@latrobe.edu.au

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I have created a similar device, that records pressure from a
pressure mat with 1024-to 4096 pressure sensors and encodes the resultant
voltage signals onto standard NTSC video, I would be happy to discuss a
modification of the design that could suit your needs or a design to your
colleagues specifications. However, a exceptionally easy way to
accomplish your needs involves two video cameras, an oscilloscope, and a
video mixer or special effects generator. point one of the cameras at the
area of interest, one of the cameras at the oscilloscope, and connect the
outputs of the cameras to the video mixer and use the split screen
function of the mixer. This will give the results that you want, and may
also be the least expensive method to achieve your colleagues needs,
however if they need an integrated device, please email me. I've
attached a abstract on the device for reference.


Sincerely,

Micah Forstein M.S.
forstein@hsc.usc.edu


A LOW COST VIDEO PEDOBAROGRAPH FOR QUALITATIVE MEASUREMENT
OF DYNAMIC PLANTAR PRESSURES

Micah A. Forstein, M.S. , Dan Antonelli, Ph.D., Susan Rethlefsen, P.T.
Sandra W. Dennis, P.T.,MSHCM, Richard Reynolds M.D., Vernon Tolo M.D.
Motion Analysis Laboratory, Department of Orthopaedic Surgery
Childrens Hospital Los Angeles

Introduction

The dynamic measurement of plantar pressure has been of clinical
interest for quite some time. At Childrens Hospital Los Angeles, we
found a need to display qualitative plantar pressure measurements and
dynamic foot contact patterns to supplement the forceplate and foot
switch measurements presently collected during clinical testing. Most
commercially available pedobarographs offer qualitative pressur display,
quantitative data analysis and other features, but at a cost that some
clinical practices are unable to afford. In addition, the number of
options available with the commercially available systems can increase
the time required for operation. At Childrens Hospital Los Angeles, we
are developing a low cost pedobarograph that addresses these issues. The
purpose of this presentation is to introduce participants to a clinically
acceptable, real time qualitative display of the plantar pressures
present during gait.

Methods
In order to meet the low cost criteria, two rules were used to
formulate the design of the pedobarograph:
1) Only stock components could be used. No custom devices could be
utilized.
2) The real time display must use any common TV monitor.
The design consists of three parts: sensors, multiplexers, and the video
display. The sensing elements selected for this project were four
Interlink 8 by 8 matrix force sensitive resistors, making the total of
1024 element within a 16" by 16" square mat. The signals from these
elements were multiplexed using five 16 to 1 analog multiplexers, and
summed using an analog switch. A LM1881 video sync chip, a 16 MHz
crystal oscillator, and ten 16 bit binary counters provided the timing
signals for the multiplexers. The analog signal was conditioned using an
operational amplifier, and overlaid onto the video sync signal. The
composite wave form was displayed in real time on a video monitor and
optionally recorded on video tape.
Each of the sensors was tested to determine if it mapped to a
specified set of video pixels on the video monitor. The sensors were
also tested to determine if the luminance of the video pixels
(representing each sensor) was proportional to the amount of applied
pressure within the sensors range. Initial walking tests were also
conducted to determine if measured plantar pressure followed the expected
pattern. Further testing on the device on clinical subjects is planned,
and the results will be presented.

Results
The total materials cost for the device was approximately $1,500
dollars. The device met the two requirements in that all parts were
commercially available stock components, and displays the information on
a TV monitor. The circuit successfully maps the sensor location to an
area of video pixels, and generates a luminance for each set of video
pixels that is proportional to the applied pressure. The output is
updated every 60th of a second, in real time. During the initial tests,
the expected foot contact pattern and dynamic plantar pressure changes
were successfully identified.

Discussion
The results of the initial tests are promising and show that the
circuit design meets the functional requirements of the device. The aim
of this device is to offer laboratories that presently have force plate
and video capabilities a way to display and record dynamic plantar
pressures with minimal capital investment. This device is not intended
to replace commercially available pedobarographs. Further testing will
help determine the present clinical utility, and possible design
improvements.