Pcas Product Outline

Electrogoniometer Feedback Device University of Pittsburgh Department of Bioengineering Doc. No.: 0428045011 Revision: 1 Pittsburgh, PA 15260 Date: 4/28/2005 Approval: JMW

Circuitry and Electronics Electrogoniometer Feedback Device

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Partner Craig Greiner Partner Zack Mason Partner Richard Stoner Partner Jason Woods CHANGE RECORD:

REV DATE DESCRIPTION OF CHANGE AUTHORIZATION

1 4/25/2005 Initial Index Jason Woods

Distribution List: All project research personnel

0cd48d4017d013c11360b5d54536ccba.doc Page 1 of 7 Electrogoniometer Feedback Device University of Pittsburgh Department of Bioengineering Doc. No.: 0428045011 Revision: 1 Pittsburgh, PA 15260 Date: 4/28/2005 Approval: JMW

CONTENTS

PURPOSE...... 3 SCOPE...... 3 SPECIFICATIONS...... 3 SCHEMATIC...... 4 TESTING...... 5 PROTOTYPE...... 6

Purpose This document was created to aggregate the circuitry and electronics designs and current status.

Scope  This document is to be used as a guide for device-related research and development. It was compiled for the sole use of direction. It is not intended to function as a formal product specification. Documents referenced within may be included in the formal design history file at a later date.  The proposed design solution must undergo validation, review, and complete testing. This document is intended to show the current status of that review and testing.

Specifications

The Smart Kneebrace system is designed around a potentiometer being turned inside the kneebrace as the knee is flexed. This potentiometer will vary a voltage signal between zero and five volts, which then must be inputted to some system that will carry out further actions, ultimately displaying the knee angle on an LCD device. The system’s central components must be a microprocessor capable of analog to digital conversion and hexidecimal to BCD (binary coded decimal) conversion. The PIC16C745 was found to be the most suitable for this application. This microprocessor, manufactured by Microchip, Inc., is capable of 8 bit ADC, has several I/O ports for the output, and has significant amounts of program memory. The microprocessor was programmed in MPASM assembly language using MPLAB IDE v7.1, provided by Microchip, Inc. The program works by accepting an analog voltage signal from pin 2, converting it to a digital number between 0 and 255 (00000000 and 11111111), moving the result of the AD conversion to a lookup table for the BCD conversion, and then outputting the BCD number on pins 21 through 28 (PORTB). The lookup table was made with the following equation in mind:

(5 V / 256 hex #s) * (180 degress / 5 V) = .7 degrees/hex#

This means that for every .7 degrees step in knee angle, the hexidecimal number will increase by one. For code testing purposes, a similar microprocessor, the PIC16C765, was used because they were available to use in Dr. Stetten’s lab and are UV erasable, so errors in the code could be fixed without having to waste a chip.

The output of the BCD conversion is then inputted into two CD4543B, which are BCD to 7 segment decoders. The output of the decoder was then inputted into the appropriate pins of the LCD display, which displays the current knee angle. A LM339 comparator was used to create a square wave inputted into the CD4543B’s and the LCD screen, so that they will be in phase with eachother. Finally, a LM7805 5 V regulator was needed so that the voltage provided by the batteries could be stepped down to the operating voltages of the components.

Schematic

Testing

To test the linearity of the system, the kneebrace with included potentiometer was set at three known angles, 0, 45, and 90 degrees. The voltages were recorded at the analog input of the microprocessor with a voltmeter and then graphed. The system operates very linearly only in the range of 5 to 90 degrees. Below 5 and above 90 degrees, the system fails for unknown reasons, possibly because the potentiometer used in the brace was not designed for this application or the program is confused by rollover in the lookup table. The calculations were redone for angles between 5 and 90 and the output is approximately linear.

Linear Trend Line of Smart Brace Voltage

70 ) s

e 60 e r g

e 50 D (

e l 40 g n

0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Voltage (Volts)

Linear Trend Line of Smart Brace Voltage

70 ) s

e 60 e r g

e y = 19.403x 50 D

e R = 0.9046 l 40 g n

0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Voltage (Volts)

Linear Trend Line of Smart Brace Voltage (Angle > 5o)

70 ) s e

e 60 r g

e 50 D (

e y = 27.907x - 27.379

n R = 0.9709

0 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 Voltage (Volts)

Prototype

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