EMG Biofeedback Device BME 200300 Fall 2003 Department

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 n 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 n Measure, amplify, and process EMG signal to provide physical and cognitive stimulation

Lissencephaly n n 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 n Device will be in use 24/7 n Easy to learn and operate n Safe for patient and operator n Patient confidentiality is maintained n

Client Requirements EMG electrodes are reusable n Device can distinguish between voluntary and involuntary muscle contractions n Timer to control duration of vibration n

Design Constraints Device must not interfere with other equipment already in use n Fit the design of the patient’s unique chair n Patient has limited body mass and musculature n Limited access to patient n

Basic Circuit Design Simple analog circuit components n Analog circuit contains six stages n Power supplied by two 9 V batteries n High input impedance n Isolated from 120 V wall output for patient safety n

Circuit Stages n 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 n Full Wave Rectifier – Takes absolute value of signal

Circuit Stages n Passive Low Pass Filter – Averages signal n 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 n Timer – Input signal triggers approximately two and half minute countdown n 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 120 V wall voltage

Circuit Schematic Shows exact design of circuit n All components are named and all component values are shown n

Printed Board No ground loop n Accessible Vcc sources n Capacitors in parallel to Vcc sources n – Physical proximity to Op Amp n Custom Pads – Diodes – Potentiometers – Terminals

Construction Solder SMT components to board n Connect board terminals to component n

Carbon-Rubber Electrodes n n 3 electrodes: 2 to input signal, 1 to ground Non-adhesive – non-invasive – reusable – gel required to increase conductivity n Already being used on child for other devices – child’s caregivers are familiar with apparatus – child’s caregivers are comfortable with their safety n Inexpensive

Electrode Attachment n Felt strap fastens around child’s thigh – soft – easily replaceable – fastens with velcro so fit can be adjust – color matches massage pad cover n Electrodes attach to strap with velcro – Will allow consistent results because ensures consistent electrode placement

Massage Pad n Con. AIR HP 08 – 24” x 11” – should not affect ergonomic fit of the chair – two vibration settings, heat option n Can operate independently of circuit

Massage Pad Cover n Removable and washable – maintains sanitation – reduces wear on the pad n 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 n Customize the EMG amplifier to the patient n Test device on patient n Monitor the patient for adaptation towards the device n

Special Thanks To: Paul Victorey John Webster Jeff Schowalter