Abstract—In this paper we present an overview on how electrogoniometer measures the angle of elbow joint. A goniometer is a device used to measure the joint’s range of motion. The electrogoniometer in our project uses a slightly different technology for measuring the angle of elbow joint. The electrogoniometer is based upon the working principle of light dependent resistor (LDR) where a light emitting diode (LED) is used as the light source and in between the LDR & LED runs a grayscale sheet that acts as a light attenuator and varies the intensity of light falling on the LDR. Thus the output of the LDR varies as the LED-LDR arrangement (transducer probe) moves across the grayscale sheet. The normal range of motion of the elbow joint is 140 . The⁰ analog output of the LDR is digitized and given to the microcontroller which then converts it into degrees using a look up table and displays it on the LCD screen.

Keywords—Grayscale, range of motion, goniometer, stationary and movable arm, fulcrum, goniometry, kinanthropometry

I. INTRODUCTION

The range of motion of a joint is a description of how much movement exists at the joint. It is measured in degrees using a goniometer. The range of motion of the elbow joint is 140⁰ when the elbow is fully flexed. The most common goniometer used these days is a protractor goniometer which has two arms riveted on a circular protractor. As the patient flexes his elbow, the movable arm is moved by the physician with the forearm of the patient while the stationary arm is hold still. This procedure and the conventional protractor goniometer have the following disadvantages: The mechanical goniometer which is a bulky

apparatus. It does not provide much accuracy.

Patients with severe joint dislocation will find the conventional procedure very painful.

Measuring the angle while holding the protractor in position throughout the measurement is a difficult task for the examiner.

Also holding the arm/ limb in one position for the entire time of procedure is a problem for the patient too.

The electrogoniometer discussed in this paper has been designed in such a way that it overcomes all the disadvantages of the protractor goniometer. The entire project design and its working is explained in two halves, hardware system and the software system

II. HARDWARE SYSTEM

The hardware system of the electrogoniometer consists of the mechanical part and the electronic part. The mechanical part comprises of the transducer probe, the stationary and movable arm, the grayscale sheet and the protractor. The electronic part consists of the microcontroller circuit board, the analog to digital converter, the LCD display, the power supply board and their interfacing with each other.

Fig1. Mechanical part of Electrogoniometer

A. The Mechanical part:

Grayscale sheet

Protractor TransducerProbe

Stationary arm

Screw Fulcrum Pointer Movable arm

ELECTROGONIOMETERPrajakt Badgujar1, Gaurav Molankar2

Department of Biomedical Engineering, Vidyalankar Institute of Technology, University of MumbaiVidyalankar College Marg, Wadala(E), Mumbai – 400 037, India.

1praj1205@rediffmail.com2g_molankar@rediffmail.com

1) Design of the Transducer probe: The transducer probe plays the most significant role in the measurement of the joint angle as it contains the light dependent resistor (detector) and the light emitting diode (source). The enclosure is an aluminum covering which is folded in a narrow manner in order to avoid the effect of the surrounding light on the LDR. There is a gap between the LDR and the

LED through which the grayscale sheet (light attenuator) runs. The transducer probe is attached to the acrylic sheet i.e. the movable arm of the electrogoniometer. This moves the transducer probe as the patient flexes his arm. The stationary arm and the movable arm are attached to the biceps and the forearm of the patient respectively with the help of the Velcro bands.

2) The Grayscale sheet: The semicircular grayscale sheet is nothing but a plastic sheet having different shades of gray. The right end is completely dark and as we move to the left it gradually fades giving us various shades of gray. This linear gradient nature of the grayscale helps us to vary the amount of light falling on the LDR. Thus the grayscale sheet which lies between the LED and the LDR acts a perfect light attenuator giving us a decreasing voltage output of the LDR.

B. The Electronic part:1) Power Supply: This unit supplies 5V DC

voltage to various PCB`s and consists of rectifier, filter and voltage regulator

2) Analog to digital converter (ADC 0808): The output of the LDR from the mechanical part is given to the ADC 0808 (pin 26). The ADC0808 data acquisition component is a monolithic CMOS device with an 8-bit Analog-to-digital converter, 8-channel

multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique.

3) The Microcontroller (P89C51): The P89C51 is a low power, high performance, CMOS 8 bit microcomputer with 64Kbyte code memory and 1Kbyte data memory. The microcontroller controls the operation of the ADC and the LCD display. It converts the digitized ADC values into degrees.

4) LCD: Liquid crystal display displays the measured angle. LCD that we generally use is of 16 x 2 characters, i.e. it has 2 rows and 16 columns.

III. THE SOFTWARE SYSTEM

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IV. CONCLUSIONThe idea of creating a goniometer with a different technology giving accurate readings and overcoming all drawbacks of the protractor goniometer is implemented. It serves main purpose of goniometer i.e. to measure range of motion of joint. It is helpful in determining if a patient is lacking in mobility due to an injury or how well he is recovering after sustaining an injury. The use of more transparent but clear and reusable material for grey scale (which plays most significant role in our project) in future may help getting the required accuracy. The design of the transducer movement and the grayscale sheet was done with respect to only the elbow joint. With some slight changing in this mechanical part we can use it to measure the angle of various other joints.

ACKNOWLEDGEMENT

We owe a great many thanks to great many people who helped and supported us in this project. We are particularly grateful to Dr. Sanjeev Muskawad, our project guide, for his kind guidance and constant support throughout the project. Our deepest thanks and appreciation to the employees of Medirays Corporation, Asangoan for lending a helping hand in the development of the project’s hardware. We express our deep sense of gratitude to Professor Geetha Narayanan for her kind guidance. We would also thank the entire faculty of Biomedical department without whom this project would have been a distant reality.We also extend our heartfelt thanks to our families and well wishers

REFERENCES

[1]. Roger Eston & Thomas Reilly: “Kinanthropometry And Exercise Physiology Laboratory Manual” pp. Ch.4, Pg:79 – 85

[2]. Nancy Berryman Reese, PhD, PT &William D. Bandy, PhD, PT,SCS,ATC: “Joint Range of Motion and Muscle Length Testing”

[3]. Centre for Nanoscale science and Technology: “Goniometer_Manual” pp

[4]. http://academic.scranton.edu/faculty/KOSMAHLE1/courses/PT350/goniomet/gonue.htm: “Introduction to goniometry”

[5]. Roger Eston, Thomas Reilly: Kinanthropometry and Exercise Physiology Laboratory Manual Test, Procedures and Data, Volume 1.Ch.5, Pg:129 - 156

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