Download EMG Biofeedback Device - University of Wisconsin–Madison

EMG Biofeedback
Device
BME 200/300
Fall 2003
Department of Biomedical
Engineering
University of Wisconsin-Madison
Team Members
Tom Chia - BSAC
Jason Ethington - Communicator
Tim Rand –BWIG
Kim Treml - BSAC
Brent Geiger – Team Leader
Client
Arleigh Birchler, MDiv, BSN
Brahms Addition Life and Choice
Advisor
John Webster, Ph.D.
Professor Emeritus
Biomedical Engineering – UW Madison
Abstract
We designed an EMG biofeedback device that will
turn on a vibrating massage pad. The device will
provide a child with Lissencephaly a physical
stimulus triggered by their EMG signal. Through
operant conditioning, the child will learn that he can
use this device to create a pleasurable sensation for
himself. We hope this will provide independence to
the child. The design utilizes three surface
electrodes to detect EMG signals from the child’s
quadriceps. A six stage analog circuit processes the
signal and powers the massage pad for 2.5 minutes
if the EMG signal is sufficiently strong.
Problem Statement
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The goal of the project is to design an
EMG biofeedback device to allow a
patient with Lissencephaly to exhibit
some physical control over their life
Measure, amplify, and process EMG
signal to provide physical and
cognitive stimulation
Lissencephaly
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Malformation of the brain
Occurs during fetal development
Variety of genetic and environmental causes
Symptoms
– Vary and range in severity
– Ex. Mental retardation, poor muscle control,
seizures
Design Criteria
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Voluntary muscle contraction will
activate massage pad
Device will be in use 24/7
Easy to learn and operate
Safe for patient and operator
Patient confidentiality is maintained
Client Requirements
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EMG electrodes are reusable
Device can distinguish between
voluntary and involuntary muscle
contractions
Timer to control duration of vibration
Design Constraints
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Device must not interfere with other
equipment already in use
Fit the design of the patient’s unique
chair
Patient has limited body mass and
musculature
Limited access to patient
Basic Circuit Design
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Simple analog circuit components
Analog circuit contains six stages
Power supplied by two 9V batteries
High input impedance
Isolated from 120V wall output for
patient safety
Circuit Stages
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Instrumentation amplifier
– Amplifies voltage difference across input
electrodes
– Provides high input impedance
– Provides gain for entire circuit
– High and low pass filters determine frequency
range and block DC offset
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Full Wave Rectifier
– Takes absolute value of signal
Circuit Stages
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Passive Low Pass Filter
– Averages signal
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Comparator
– Compares signal to a prescribed reference voltage
– If input signal is greater than reference voltage
then signal is passed to next stage
– Reference voltage manually adjustable
Circuit Stages
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Timer
– Input signal triggers approximately two and half
minute countdown
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Solid State Relay
– Acts as a switch between circuit and massage pad
– Activates massage pad upon active input signal
from timer, deactivates pad when timer
countdown expires
– Optically isolated from 120V wall voltage
Circuit Schematic
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Shows exact design of circuit
All components are named and all
component values are shown
Printed Board
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No ground loop
Accessible Vcc sources
Capacitors in parallel to Vcc sources
– Physical proximity to Op Amp
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Custom Pads
– Diodes
– Potentiometers
– Terminals
Construction
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Solder SMT components to board
Connect board terminals to component
Carbon-Rubber
Electrodes
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3 electrodes: 2 to input signal, 1 to ground
Non-adhesive
– non-invasive
– reusable
– gel required to increase conductivity
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Already being used on child for other devices
– child’s caregivers are familiar with apparatus
– child’s caregivers are comfortable with their
safety
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Inexpensive
Electrode Attachment
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Felt strap fastens around child’s thigh
– soft
– easily replaceable
– fastens with velcro so fit can be adjust
– color matches massage pad cover
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Electrodes attach to strap with velcro
– Will allow consistent results because
ensures consistent electrode placement
Massage Pad
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ConAIR HP08
– 24” x 11”
– should not affect ergonomic fit
of the chair
– two vibration settings, heat
option
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Can operate independently of
circuit
Massage Pad Cover
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Removable and washable
– maintains sanitation
– reduces wear on the pad
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Made of material attractive to children
– aesthetic value
– decreases appearance as a medical
device
– can be changed as child’s interests change
Future Work
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Measure the patient’s EMG signals
Customize the EMG amplifier to the
patient
Test device on patient
Monitor the patient for adaptation
towards the device
Special Thanks To:
Paul Victorey
John Webster
Jeff Schowalter