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EMG Biofeedback Device
BME 200/300
Final Design Report
12-10-03
Team Members:
Tom Chia
Jason Ethington
Kim Treml
Tim Rand
Brent Geiger
Client:
Arleigh Birchler, MDiv, BSN
Advisor:
John Webster, Ph.D.
Professor Emeritus
Department of Biomedical Engineering
University of Wisconsin - Madison
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Abstract
The following report outlines a design of an electromyogram (EMG) controlled
massaging pad intended for use by a child with lissensephaly. The device was designed
using criteria and constraints suggested by a client familiar with lissensephaly. The final
design consists of an electrode attachment device, an analog circuit to amplify and
process the patient’s EMG signal and a massaging pad to provide positive tactile
stimulation to the patient. A prototype circuit was built and tested and the design
functions properly. The circuit was constructed on a printed circuit board to consolidate
the circuitry, however future work is needed to complete the final printed circuit board
design.
Problem Statement
The purpose of this project is to design a device that will serve as an EMG
biofeedback device to activate a vibrating pad. A child with Lissencephaly will use this
device to activate the pad by flexing a muscle in his thigh. The vibrations will provide a
pleasurable tactile sensation at his command, providing him some control over his life
which he currently lacks. An EMG signal of a chosen magnitude will activate the pad and
the pad will deactivate after a chosen time period.
Motivation
The child with Lissencephaly currently has no control over his life. This device
will give him a way to take some control. By allowing him to activate the pad on his own
the child will be given freedom that he currently lacks. Our device will also allow us to
observe whether the child is capable of simple operant conditioning; should the child
associate flexing his muscle with activating the massage pad it will demonstrate a
capacity for cognitive activity.
We would observe this association through a deliberate increase in the flexing of
the targeted muscle. This could provide a basis for further learning. The device could be
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modified to give more options to the child. For example, a component of the circuit could
be added so that the child could also turn the device off with a second flex. This process
of learning would serve to improve the quality of the patient’s life
Lissencephaly
Lissencephaly is a brain disorder exhibited when the brain fails to correctly
develop. Lissencephaly is also referred to as smooth grey matter due to the smooth
appearance of the brain in patients with this condition (Figure 1). During development,
nerve cells are not able to reach the outer cortex of the brain, which in turn prevents cells
from making necessary connections. The deficiency in development also accounts for the
lack of ridges normally present [1].
Symptoms of Lissencephaly can vary from case to
case. Some of the common problems experienced are
difficulties eating, loss of bodily control, severe mental
retardation, regular seizures and reoccurring pneumonia.
The severity of these symptoms varies greatly. The
lifespan of a person with Lissencephaly is projected at
around two years, but since the disorder is quite rare and
provides few recorded cases the lifespan is difficult to
gauge [1].
Figure 1:
(above) A normally
developed brain.
(below) A brain from a
patient with Lissencephaly.
Notice the smooth
appearance of thisbrain[2]
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Design Problem
The EMG biofeedback device needs to detect a proper EMG signal and then
activate the massage pad for a predetermined amount of time. There are three major
components to the EMG biofeedback device; the EMG electrodes, the EMG amplifier
circuit and the massage pad.
Either needle or surface electrodes can measure EMG signals. We will be using
the less invasive surface electrode. Surface electrodes are often composed of a Ag+/AgCl
disk and an adhesive attached to the skin [3]. However, the client has specified that the
EMG electrodes need to be reusable. Reusable EMG electrodes are already in use with
the child for his apnea monitor. The EMG pads need to be easily attached to the child’s
body, reusable, and require minimal training for application. A total of three EMG
electrodes will need to be attached to the patient’s body.
Figure 3: Patient’s actual chair
Figure 2: Schematic of chair
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The EMG circuit needs to detect a proper EMG signal and respond by activating
the massage pad. A proper EMG signal is defined as a voluntary muscle contraction. This
patient will occasionally have seizures which result in involuntary muscle contractions.
Therefore, the device will need to distinguish between voluntary and involuntary muscle
contractions. Once a proper EMG signal is detected the massage pad will be activated by
a timer for a predetermined amount of time.
The final component in the EMG biofeedback device is a massaging pad. The pad
is the device that will deliver the pleasurable stimulus to the patient. There is a wealth of
small vibrating devices available through retail, ranging in function from full back
massage devices that fit inside a chair to simple massage pad motors. The massage pad
used in our biofeedback device must fit the unique shape and size of the patient’s chair.
Figure 2 is a schematic of the chair with its dimensions and figure 3 is an actual picture of
the chair.
More detailed discussion of each component in the EMG biofeedback device is
found in the latter parts of this report. Overall, the entire device must be safe and reliable
for years of use by the child and his caretakers. The controls on the device also need to be
easy to learn and operate. Finally, throughout the design process the patient’s
confidentiality must be maintained. At no time can the patient’s name, personal
information, and/or pictures of the patient be released to the public.
Design Constraints
Designing our device specifically for this patient introduced a number of design
constraints. The first constraint was that our device must not interfere with any of the pre-
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existing equipment already in use with the patient. This includes his apnea monitor,
feeding tube, and oxygen tank.
The EMG amplifier designed for this project also needs to be designed for the
patient’s limited musculature. Most EMG amplifiers are designed assuming that the
subject has normal muscle tone; however for this project that assumption is not valid. To
further complicate matters, the team’s access to the patient for testing and EMG
measurements is very limited. For privacy reasons, the mother of the child has not given
the team permission to work directly with him. Instead all matters involving the child
must first go through our client, Arleigh Birchler. Additional design specifications and
constraints can be found in appendix A.
Proposed Solutions
All of our proposed design solutions include the same circuitry and electrodes,
components that provide little area for variation. As mentioned previously, reusable
carbon rubber electrodes will be used and placed on the child’s thigh per the request of
our client. The quadriceps is the best option for electrode placement because it is a large
muscle that the child can easily isolate and signal. Also, the thigh is not highly prone to
involuntary muscle contractions. Our design proposals vary in size, shape and application
of the vibrating pad. We will describe our best design solution in detail later in the report.
The first alternative design is to use a portable, prefabricated massage cushion for
the vibrating pad. The model of the massage cushion is the Homedics BK-150 Back
Master and measures 19” x 16” x 3.25”. Even though the BK-150 is smaller then many of
the other massage pads on the market, it is still too wide to fit perfectly in the child’s
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chair. Also, this solution leaves little opportunity to modify the padding or change the
location of the vibrating motors.
A second alternative design is a pad that wraps around the child. It is assembled
from different parts including a small vibrating motor, and padding. It will be built into a
pad that can be wrapped around the child’s waist as opposed to attached to his chair. The
form of this design is similar to a wide belt. A Velcro™ piece attaches the two ends of
the pad in front of the child. A drawback to this design comes from the additional
equipment already in use. The apnea monitor and feeding tube would most likely
experience some interference from the front portion of the pad.
Table 1: Design Matrix
Cost
Simplicity
Durability
Ergonomics (x3)
Total
Homedics BK-150
3
Modified/Customized
1
Wraparound
2
$25.00
$25.00 plus costs to modify
and cost in time
similar to Modified pad
plus fastening pieces
3
1
1
requires only the
modification to connect to
EMG circuit
requires disassembly and
reassembly of pad and
modification to connect to
EMG circuit
requires disassembly and
reassembly of pad and
modification to connect
to EMG circuit
2
1
1
durability assured without
testing
would have to test for
durability of pad components
would have to test for
durability of pad
components
3
9
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no chance for modification
can be very specifically
designed for child
marginal opportunity for
specification
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In order to decide which massage pad design alternative would be best we ranked
the solutions on the criteria of cost, simplicity of production, durability and
ergonomics/comfort (Table 1). The child will be sitting with the pad behind him at all
times, so we deemed ergonomics the most important criteria weighing it three times
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higher than the others. Each design option was ranked with a 1, 2, or 3; 3 being the best,
depending on how well it fit each criterion in relation to the other alternatives.
Modification of the ConAIR HP08 to create a custom fit for the child received the largest
total points making it our best design option.
EMG Circuit Design
The final circuit design contains seven main components. A functional block
diagram outlining the basic circuit design is shown below.
Input Electrodes
Instrumentation
Amplifier
Rectifier
Ground
Timer
Comparator
Solid State Relay
Massage Pad
Low Pass Filter
Figure 4: Block diagram of circuit design
Power is supplied to the integrated circuit (IC) components by two nine volt
batteries. Due to certain specifications of the IC components, two voltage regulators were
necessary to drop the power supply voltage from 9V to 7V. Attached in appendix B is the
precise circuit schematic. All components are named and all their values are shown.
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Two carbon patch input electrodes measure the potential difference created when
the patient contracts his/her muscle group. A third electrode is attached to ground to and
serves as a reference voltage. The potential difference created by the patient’s EMG
signal is then input into an instrumentation amplifier.
The instrumentation amplifier has high input impedance so it does not draw any
current from the patient. A differential amplifier then amplifies the potential difference
across the two electrodes and has a gain of 13. This value is determined by one external
resistor, R1 on the circuit schematic.
The signal is then passed through a passive high pass filter with a low corner
frequency of 1.6 Hz. This filter blocks any DC offset present in the signal. The final stage
of the instrumentation amplifier is an active low pass filter that has a gain of 158 and a
2027 Hz corner frequency. Overall, the gain of the entire circuit is about 2050.
The next stage of the circuit is a precision full wave rectifier [4]. The rectifier
takes the absolute value of the amplified signal. After the rectifier is a passive low pass
filter. The low pass filter serves to effectively average the signal.
At this point in the circuit the EMG input signal has been processed from a signal
similar to high frequency noise, to essentially a DC signal with amplitude proportional to
the strength of the patient’s muscle contraction. This signal now can be easily compared
to a set threshold voltage.
The next stage in the circuit, a comparator, performs the threshold operation. The
threshold voltage, or reference voltage, can be manually controlled via a potentiometer
that feeds the positive input of the comparator. The reference voltage set on the
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comparator stage of the circuit determines the strength of muscle contraction needed to
trigger the timer device.
If the signal is strong enough, the comparator outputs positive saturation (+7V) to
the timer stage of the circuit. However, if the amplitude of the input signal is not greater
than the set reference voltage then the output of the comparator will stay at negative
saturation (-7V).
A 555 timer IC component was used to establish a specific time to trigger the
massage pad. The input to the timer determines whether the output is either high or low.
A high output passes the signal to the next stage of the circuit and triggers a timed
countdown, while a low output gives no input to the next circuit stage. If the timer
receives a positive signal from the comparator the output will be high for about two and
half minutes. The time constant of the timer stage is determined by the product of the
values of R9 and C10 on the circuit schematic.
After the duration of one time constant, the output of the timer will return to low.
The high output of the timer is about 7 volts and is sent to the next stage of the circuit, a
solid state relay device.
The relay serves as a switch that safely activates the massage pad unit upon
receiving a high input from the timer. The relay is optically isolated so that there is no
opportunity for the high voltage and current supplied by a wall outlet to reach the patient.
The final stage is the massage pad unit. The pad contains a transformer that steps
down the 120 volt wall voltage to 12 volts for pad operation. One of the massage pad
cord wires was severed and the two output wires of the relay device were attached across
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the severed lead to complete the design. See appendix B for an exact schematic of the
circuit design.
Circuit Board
A circuit board was drawn to match specifications laid out in the circuit
schematic. Guidelines for drawing a circuit board were used [5]; thicker traces for power
supply and ground, no closed-loop ground trace, and sufficient spacing for traces and
pads. PCB Express was the program used to draw and order the circuit boards used in the
final design.
Most of the components for the schematic were ordered as SMT (surface mount)
components through Digi-Key. Custom “footprints” were drawn for components that
were unavailable in SMT, requiring common “push-through” parts such as diodes, wire
terminals, potentiometers and capacitors used with the voltage regulators. Components
were attached to the circuit board in the final design using a simple soldering procedure.
The design of the circuit board condensed the circuitry in to as little space as
possible. The remainder of the board was used as space for the battery casing. These
batteries were used to power the circuitry components independent of the wall source,
which powered the vibrating pad. See appendix C for printed circuit board design.
Consolidated Circuitry
A black plastic box was selected to house the various electrical components
separate from the pad. This protects the components from damage, and protects a user
from accidental electrical exposure. The physical dimensions of the box were
approximately 3” × 3” × 6”. The limited volume was used to contain the circuitry,
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batteries, and SSR in a protected compartment. The three components needed to be as
compact as possible, and this was mostly accomplished through condensing the circuitboard design.
The circuit board was mounted inside the black box using four bolts attached to
the corners. The SSR was attached alongside the circuit board. Openings in the black box
would have been drilled for the electrode leads, and the massage pad wire fed in series
through the SSR. These holes were not completed in the prototype due to the unfunctional operation of the circuitry upon assembly.
Figure 5: Printed circuit board mounted in black box.
Massage Pad
The massage pad is the second major component of the biofeedback device,
which provides a stimulating and pleasurable feedback. We chose the ConAIR HP08, an
off-the-shelf massage pad to modify for the project. This particular pad was chosen
because its dimensions (11 ½“ x 24”) match the child’s unique chair. In addition, the pad
is less than one inch thick so it should not disturb the comfortable fit of the chair that the
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child is accustomed to. The ConAIR HP08 offers two massage intensities and a heat
option that can be adjusted to create the most pleasurable sensation for the child.
To improve the quality and functionality of the pad we created a fabric cover
similar to a pillow case to put over the pad (Figure 6). The cover serves many functions.
Made with a fabric with a child friendly pattern, it appears less like a medical device than
the plain massage pad would and new covers can be made as the child’s interests change.
More importantly, the cover is removable and washable to increase sanitation since the
child will be sitting on it twenty-four hours a day, seven days a week. Finally, the cover
will reduce the amount of wear on the pad increasing its useful life.
Figure 6: Modified massage pad with protective cover.
Electrodes
Electrodes and means of attaching them are the final component of the full design.
We chose to use carbon-rubber electrodes to fulfill the request of our client that they be
reusable and inexpensive. The child is already using carbon-rubber electrodes on other
devices so he and his caretakers are already familiar with them. Moreover, the carbon-
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rubber electrodes are an excellent choice because they are non-invasive. They simply rest
on the skin rather than penetrate it or adhere to it. With the addition of a thin layer of
conductive gel they work nearly as well as an adhesive electrode.
The electrodes will be attached to the child with a soft, felt strap that will
Velcro™ around the child’s thigh and can be adjusted for a perfect fit as the child grows
(Figure 7). The strap is washable for the same reason as the massage pad cover. The
electrodes can also be removed from the strap for washing. The electrodes attach to the
strap with Velcro™ to assure simple replacement in the correct position after they have
been removed. This is important because the electrodes must be in approximately the
same place each time in order to obtain consistent results.
Figure 7: Electrode attachment device.
Ethics
Our project has presented us with some important ethical considerations. These
considerations stem from the fact that our device is designed for a specific patient rather
than the general public. Of utmost importance was honoring the client’s request that all
sensitive patient information be kept confidential. All operating components of our
design must be safe for use within specific design parameters for this patient. Additional
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technical support could be necessary, but is possible with such exclusive patient use. All
possible emphasis was placed on meeting these ethical requirements.
Conclusion
The EMG biofeedback project has been very successful in proving that an EMG
signal can be obtained, amplified, and used to control the activation of a massage pad.
Our large degree of accomplishment shows that a project of this sort can be completed to
the given specifications. There are, however, a number of steps that need to be taken
before this prototype can be implemented with the child.
The first step towards completion is an accurate measurement of the child’s EMG.
This measurement needs to include measurements in multiple locations to find an ideal
position on the body. From these measurements the EMG amplifier can be calibrated to
properly amplify his biological signal to proper amplitude to activate the massage pad.
Voluntary and involuntary EMG signals will also need to be measured. These
measurements could allow the design of an IC to distinguish between a conscious versus
involuntary muscle contraction, such as during a seizure.
The patient will finally need to be monitored to see if he is adapting to the device.
This will be the ultimate test of this project’s success. If client’s predictions are correct,
the patient will eventually condition himself to understand that a particular muscle
contraction will elicit a pleasurable stimulus.
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References
[1] Dobyns, William. Lissencephaly: Information for Parents. 1991. Online:
http://www.Lissencephaly.org/about/lissen.htm
[2] Lissencephaly Newsgroup. Acessed: Oct 2003.
http://groups.yahoo.com/group/Lissencephaly/
[3] Webster, John. Bioinstumemtation. New York: John Wiley and Sons, 2004. Chapter 2
[4] Medical Instrumentation – Application and Design. 3rd Ed. John G. Webster – Editor.
John Wiley and Sons Inc. NY 1998.
[5] Victorey, Paul. Personal consultation. Oct-Dec 2003.
Sources Consulted
Webster, John. Personal consultation. Oct-Dec 2003
Birchler, Arleigh. Personal consultaion. 12 Sept. 2003
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Appendix A
Product Design Specification:
EMG Biofeedback Device
Team Members:
Brent Geiger – Leader
Jason Ethington – Communications
Tom Chia – BSAC
Kim Treml – BSAC
Tim Rand – BWIG
Advisor: John G. Webster
Revision date – December 7, 2003
Function: An EMG biofeedback device will allow a child with Lissencephaly to exhibit
some control over his life.
Client Requirements: Client would like the device to serve as a learning tool for the
child. The device will consist of four components: electrodes, amplifier, information
processor, and massage pad.
Electrodes
Two/three carbon patch electrode placed on skin on child’s thigh muscle. The
electrodes must not be intrusive or irritating to the child. They must require little
skill to attach and remove.
Amplifier
A basic EMG amplification circuit will be used.
Information Processor
This stage must distinguish between voluntary and involuntary muscle
contractions by establishing a baseline. The amplified EMG signal will trigger the
massage pad. This stage will control the duration of vibrations, and record how
many voluntary contractions occur in a certain time period. The processor will
terminate the massage after a specified time period. It should regulate massage
pad to eliminate over stimulation by child.
Massage Pad
The massage pad must fit in the child’s chair. The pad should be comfortable for
the child and not change the environment to which he has became accustomed to.
The massage must not be too strong and must not cause the child any discomfort.
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Design Requirements:
Physical and Operational Characteristics
a. Performance requirements
Must be able to perform at any given time 24/7. Massage mechanism will be
activated 5-6 times a day. Must be easy to operate and have minimal learning
curve for operator.
b. Safety
Must not harm patient in any way. Device will not have any sharp areas, exposed
wires, or abrasive material. EMG pads will not draw current from the patient’s
body. Massage pad vibration will be noticeable, but not cause pain. Entire device
must not interfere and be compatible with current devices he is hooked up to.
c. Accuracy and Reliability
Massage feedback must trigger every time an intentional muscle contraction is
performed. Device must accurately distinguish between involuntary (C-posturing)
and voluntary muscle contractions. Vibrational feedback must only be turned on
for 5 minutes each time a voluntary muscle contraction is detected.
d. Life in Service
Must be in service for as long as patient is able to utilize the device. Proper
operation should be checked for each week. Major calibration checked for every 6
months.
e. Shelf Life
The shelf life of our product will be five years stored at room temperature in a dry
location.
f. Operating Environment
This device will be used in a home environment. It will be subjected to constant
pressure caused by the patient sitting on top of the vibrating pad. The device may
be subjected to fluids and dust caused by everyday use. This device will be
handled by a nurse or caretaker for the patient.
g. Ergonomics
The patient will be sitting on this device for most of the day so it is important that
the device does not change the current environment as to annoy or agitate the
patient. The device must as comfortable as the chair that the patient currently
uses. A washable, protective pad will cover the massage pad to minimize wear
and increase sanitation.
h. Size
The device must fit in the current chair of the patient. The bottom of the chair is
11.5”x11.5”. The device must fit between two side guards that are 9.5” apart and
8” above the bottom on the back of the chair. The back of the chair is 15” tall.
i. Weight
The information processor should be no more than 5 pounds so that it is easy to
transport with the child. The electrodes and device used to hold them in place
should be just a few ounces so that they do not inhibit or encumber the child.
There are no weight specifications for the massage pad because we will assume
whichever model we use is already at a suitable weight.
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j. Materials
There are no restrictions on materials.
k. Aesthetics, Appearance, and Finish
The massage pad must be soft and comfortable. The apparatus for applying the
electrodes must also be comfortable so that it does not bother the child in any
way. The massage pad cover has been designed with a colorful pattern that is
child orientated.
Production Characteristics
a. Quantity
One. Child’s guardian gets to keep prototype if she wishes.
b. Target Production Cost
$100-$200. More if digital microcomputer processors are incorporated into
design.
Miscellaneous
a. Standards and Specifications
Human subjects testing approval may be required. Approval from child’s doctors
and mother also required.
b. Customer
Confidentiality is of utmost importance for both the child and the child’s mother.
No information whatsoever regarding their whereabouts can be disclosed.
c. Patient-related concerns
Child’s EMG signal may be somewhat irregular, amplifier must be able to
properly amplify signal. Device must fit into child’s chair. Device must be able to
be cleaned periodically due to constant contact with child. Child could possibly
find device uncomfortable and irritable. Again, all patient information must be
held in confidence.
d. Competition
Lissencephaly is an extremely rare. There are no devices designed for this
purpose.
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