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Download EMG Biofeedback Device - University of Wisconsin–Madison
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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 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 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 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 EMG electrodes are reusable Device can distinguish between voluntary and involuntary muscle contractions Timer to control duration of vibration Design Constraints 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 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 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 Full Wave Rectifier – Takes absolute value of signal Circuit Stages Passive Low Pass Filter – Averages signal 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 Timer – Input signal triggers approximately two and half minute countdown 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 Shows exact design of circuit All components are named and all component values are shown Printed Board No ground loop Accessible Vcc sources Capacitors in parallel to Vcc sources – Physical proximity to Op Amp Custom Pads – Diodes – Potentiometers – Terminals Construction Solder SMT components to board Connect board terminals to component Carbon-Rubber Electrodes 3 electrodes: 2 to input signal, 1 to ground Non-adhesive – non-invasive – reusable – gel required to increase conductivity Already being used on child for other devices – child’s caregivers are familiar with apparatus – child’s caregivers are comfortable with their safety Inexpensive Electrode Attachment Felt strap fastens around child’s thigh – soft – easily replaceable – fastens with velcro so fit can be adjust – color matches massage pad cover Electrodes attach to strap with velcro – Will allow consistent results because ensures consistent electrode placement Massage Pad ConAIR HP08 – 24” x 11” – should not affect ergonomic fit of the chair – two vibration settings, heat option Can operate independently of circuit Massage Pad Cover Removable and washable – maintains sanitation – reduces wear on the pad Made of material attractive to children – aesthetic value – decreases appearance as a medical device – can be changed as child’s interests change Future Work 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