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Biomedical instrumentation system

Chapter 1

INTRODUCTION

1.1 Basic Bio-Medical Instrumentation System:

The basic purpose of a biomedical instrumentation system is to measure the parameter required, and find any deviation in the parameter so that any abnormality can be found easily. The main intention of instrumentation design is that it can be life saving equipments at times. Any abnormalities of vital organs like Heart, if found before it reaches the danger level can be a life saving one.

Measurand:

The physical parameter from the human body that the instrumentation system measure's is called the measurand. The source for the measurand is the human body(skin, muscles, ECG, EEG, etc,.) which generates a various number of vital signals. The measurand may be on the surface of the body or it may be blood pressure in the chambers of heart.

Transducer/Sensor:

A transducer is a device that converts one form of energy to another. It is the basic or most important one in the measurement because of the material and purpose it is made for. Selection of the transducers is very important as it decides the acquisition level of the signal we need. For example, Ecg needs to measured with surface electrodes placed on chest. The primary function of the transducer is to provide a usable output in response to the measurand which may be a specific physical quantity, property or condition. In practice, two or more transducers may be used simultaneously to make measurements of a number of physiological parameters.

Another term ‘SENSOR' is also used for Transducer in the instrumentation of medical equipments. Normally, a sensor converts a physical form of energy to an electrical signal. The sensor must be minimally invasive and interface with the human body with minimum extraction and loss of energy.

Signal Conditioner:

Converts the output of the transducer which acquires the physical parameter in to an electrical quantity or energy which will be suitable for the operation of display or recording system. Signal conditioners may vary in complexity levels of the circuit and applications from a simple resistance network or impedance matching device to multi stage circuits and other complex circuitry. Signal Conditioning includes several functions, most of the mathematical signal processing works like amplifying, filtering, conversion to digital form, etc can be done. They amplify the signals as needed in order to increase the sensitivity of the equipment.

Display System:

Display system is the one which gives a visible form of the signal we acquire may be through graphical representations, charts or graphs or other methods. Although most of the display systems in current use are in visual forms, some are even in audio forms like in doppler method and EMG based bio feedback systems etc. In addition of the above, the processed signal after signal conditioning may be passed on to:

Alarm System -With upper and lower adjustable thresholds to indicate when the measurand goes beyond preset limits.

Data Storage - To store the data for future reference. It may be a hard copy on paper or on magnetic or semiconductor memories.

Data Transmission - using standard interface connections so that information obtained may be carried to other parts of an integrated system or to transmit it from one location to another.

This project involves the work of a, robotic arm controlled using the muscle signals (Electromyogram - EMG). This work is in the field of rehabilitation engineering. This robotic arm is designed to do grasping movement alone. Every muscle fiber has ability to generate action potential which can be recorded and used to control the robotic arm with the help of a Peripheral interface controller- PIC. Such robotic arms controlled using the human EMG signals can be useful for amputated persons at least to a level where they can do their own works like grasping a object, eating etc.

Robotic Arm interfacing with EMG Signal

Table 1.1- Bioelectric Signals

Parameter

Primary Signal Characteristics

Type of Electrode

Electrocardigraphy(ECG)

Frequency range:0.05 to 120 Hz

Signal amplitude:0.1 to 5 µV

Typical Signal:1 µV

Skin Electrode

Electroencephalaography(EEG)

Frequency Range:0.1 to 100 Hz

Signal Amplitude: 2 to 200 µV

Typical Signal:50 µV

Scalp Electrodes

Electromyography(EMG)

Frequency Range:5 to 2000 Hz

Signal Amplitude:0.1 to 5 µV

Needle Electrodes

Electroretinography(ERG)

Frequency Range:dc to 20 Hz

Signal Amplitude:0.5 µV to 1 µV

Typical Signal:0.5 µV

Contact Electrodes

Electro-Oculography

Frequency Range: dc to 100 Hz

Signal Amplitude:10 to 3500 µV

Contact Electrodes

1.2 Description:

Human hand is attached with a sensor which is capable of acquiring the muscle signals. Since the muscle signals EMG is of very low amplitude of mV, it needs to be amplified to a very high level. For this reason only we chose a differential amplifier to amplify the EMG signals to range of several volts. Also we used band pass filter of range 10hz-500hz so that unwanted signals can be remove. A twin T notch filter was used in the circuit in addition to other filters to remove the 50hz power line interference. After acquiring the signals we processed the signal using LABVIEW 9.0, using which we smoothened the signal and was able to find a clear threshold level. Taking the processed signals as input to the PIC, we were able to control the Robotic arm.

1.3 EMG Based Robotic Systems:

Robots are currently used in all kinds of dangerous environment and high end factories where they need everything to be automated. The situation is changing and now as a revolution Robotic arm for amputated persons are increasing steeply. We need to give a cheap and yet sophisticated, robotic arm which can be controlled by the amputated person as he wishes. This will help those people who are living in a life of darkness without being able to do their own work.

Here we describe an EMG based control method of a robotic manipulator as an adaptive human supporting system that consists of a finger control part used in grasping movement. This robotic arm has facility to get input from the processed signal from labview. The grasping movement of the robotic arm is based on the contraction of the person. So as a person contracts his hand the amplitude level increases than when it is in relaxed state, this is the principle which we are using to perform the grasping acting when muscle is contracted.

The assembly consists of a signal processor which smoothens the signal and gives a clear envelop, using which threshold can be detected. Then the PIC programming which says that if the input to PIC is above fixed threshold, then the motor is switched on for a particular time till it can complete an 90 degree movement which finishes the grasping. When the signal is below the threshold the PIC is programmed in such a way that motor returns to its original position. Seeing the speed of rotation needed, angle of rotation and amount of weight to be moved or hold, we used a DC motor of 12V power supply.

Chapter 2

LITERATURE SURVEY

Table 2.1- Literature Survey

Sl.No

Title

Author Name

Description

Advantages

Remarks

1

Myoelectric Brace(Jan 4,1972)

Allan G potter , Lowas

Muscle potential is Transformed into slowly varying control signal .This signal drives hydraulic pump which moves finger support.

Light weight, consumes of minimum power, It is convenient to use.

Power consumption, minimum size.

2

Mechanical Arm(Nov 13,1984)

Alberto Rovetta , Milan Italy

Invention of mechanical arm with four degrees of freedom, controlled by two motor.

This invention helps in controlling the arm movements both in series and in parallel.

No possible theoretical explanations.

Sl.No

Title

Author Name

Description

Advantages

Remarks

3

Electrically driven Artificial Arm(Jun 11,1985)

Stephen C. Johnson; David F. Knutti; R. Todd Johnson

This prosthesis is controlled by the electrical impulse generated from the muscle .The elbow motion is provided by a motor within the prosthesis.

Provide a reliable prosthesis which is cosmetically appearing to amputees.

It can be only use for arms that have undergone amputation.

4

Ultrasonic Motor Prosthetic Arm(Jul 13,2002)

Edwin K. Iversen; James R. Linder; Harold H. Sears

A drive linkage configured to move prosthetic limb. Ultrasonic motor is equalled to drive linkage and power the drive linkage.

It has high torque at low speed.

The result of this research has provided complex multiple degrees of freedom hands, which are too large and complex to be feasible

Sl.No.

Title

Author Name

Description

Advantages

Remarks

5

An EMG controlled Graphic Interface considerig Wearbility(2004)

H. jeong ,J.S. Choi

Human Computer Interaction (HCI) technology using a bioelectric signal such an electromyogram (EMG), an electroencephalogram (EEG) and an electrooculogram(EOG) is considered an alternative to conventional input devices such as a kb.

This device makes it easy to attach the electrodes on a forearm

Future works is to realize the application for controlling mouse position more precisely than the present.

Chapter 3

Theory of Electromyography

Electromyography is a discipline that deals with the detection, analysis and use of electrical signal that emanates from skeletal muscles. The electromyography is studied for various reasons in the medical field. Even a superficial acquaintance with scientific literature will uncover various current applications in fields such as neurophysiology, kinesiology, motor control, psychology, rehabilitation, medicine and biomedical engineering.

The EMG signal is the electrical manifestation of the neuromuscular activation associated with the contracting muscles. The signal represents the current generated by the ionic flow across the membrane of the muscle fibers which propagates through the intervening tissues to reach the detection surface of the electrode located in the environment.

It is an exceedingly complicated signal which is affected by anatomical and physiological properties of muscles and the control scheme of the nervous system, as well as characteristics of the instrumentation used to detect and observe it.

Most of the relationships between the EMG signal and the properties of contracting muscles that are currently in use have evolved serendipitously. The lack of proper description of the EMG signal is probably the greatest single factor that has hampered the development of electromyography in to a precise discipline.

3.1 Applications:

3.2 Muscles:

About 40% of the human body is skeletal muscles and another 10% is smooth muscles of internal organs and cardiac muscles from the heart. Here we are interested in characterizing the function of skeletal muscles. The primary function of skeletal muscles is to generate force. Because of this, they are excitable. Thus skeletal muscles have 2 fundamental properties. They are excitable(able to respond to stimulus) and contractible(able to produce tension).A skeletal muscle consists of numerous fibers with diameters ranging from 10 to 80 µm. Each muscle fiber contains hundreds to thousands of myofibrils .Each myofibril has about 1500 myosin filaments and 3000 actins filaments lying side by side.

Structure of Muscle

3.3 Cell Potential:

The nervous system is comprised of neuron cells. Neurons are the conducting elements of the nervous system and are responsible for transferring information across the body. Only these and muscle cells are able to generate potentials and therefore are called excitable cells. Neurons contain special ion channels that allow the cell to change its membrane potential in response to the stimuli the cell receives.

3.4 Receiving Potential:

All cells in the body have a cell membrane surrounding them. Across this membrane there is an electric charge referred to as the resting potential. This electric impulse is generated by differential ion permeability of the membrane. In the cells, potassium (k+) channels allow diffusion of k+ ions out of the cell while Sodium (Na+) ions diffuse in to the cell. This Na+-K+ pump, which requires ATP to operate, pumps two K+ ions in to the interior of the cell for every 3 Na+ ions pumped out. K+ and Na+ ions are continuously diffusing across the membrane from where they were just pumped, but at a slower rate. Since there are more K+ ions inside the cell than outside, a potential exists.

3.5 Action Potential:

Some cells, such as skin cells are not excitable. Other cells such as nerve and muscle cells are excitable. When a simulating electric field acts on an excitable cell, the Na+ permeability increases, Na+ enters the cell interior and the entering positive charge depolarizes(reduces to approximately zero),the transmembrane potential. Later the K+ permeability increases and K+ ions flow out to counter this effect. The Na+ gates close followed by the K+ gates. Finally, the resting potential is regenerated. The action potential lasts about 1ms in nerves and about 100 ms in cardiac muscle. It propagates in nerves at about 60 m/s and carries sensations from the periphery toward the brain via sensory nerves. Through motor nerves, the brain commands muscles to contract. We can calculate the action potential propagation velocity v=d/t where

d=distance

t=time

Shown here represents the role of voltage-gated ion channels in the action potential. The circled numbers on the action potential correspond to the 4 diagrams of voltage-gated sodium and potassium channels in a neuron's plasma membrane

3.6 Motor Unit:

The most fundamental unit of a muscle is called the Motor Unit. It consists of an alpha-motoneuron and all the muscle fibers that are enervated by the motoneuron's branches. The electrical signal that emanates from the activation of muscle fibers of a motor unit that are in the detectable vicinity of an electrode is called MOTOR UNIT ACTION POTENTIAL (MUAP).This constitutes the fundamental unit of the EMG signal.

A Schematic representation of the genesis of a MUAP is presented above. There are many factors that influence the shape of MUAP. Some of these are

The last two factors have particular importance in clinical applications. Considerable work has been performed to identify morphological modifications in the MUAP shape resulting from modifications in the morphology of the muscle fibers or the motor unit such as regeneration of motoneurons. Although usage of MUAP shape analysis is common practice among neurologists, interpretation of the result is not always straight forward and relies heavily on the experience and disposition of the observer.

To sustain muscle contraction, the motor unit must be activated repeatedly. The resulting sequence of MUAP's is called Motor Unit Action Potential Train(MUAPT).So, EMG signal can be synthesized by linearly summing the MUAPT's as they exist when they are detected by the electrode where mathematically generated MUAPT's are added to yield the signal at the bottom.

3.7 Muscle Contraction:

As an action potential travels along a motor nerve to muscle fibers, it initiates an action potential along the muscle fiber membrane, which depolarizes the muscle fiber membrane and travels with in the muscle fiber. The Subsequent electro-chemical reaction within the muscle fiber then initiates attractive forces between the actin and myosin filaments and causes them to slide together. This mechanism produces muscle contraction.

Tension is developed in the muscle as it contracts. There are 3 types of contraction

Isometric or Static Contraction means a muscle contracts without change in its length. Concentric Contraction occurs when a load is less than the isometric force produced by the muscle and the load shortens the muscle. Eccentric Contraction occurs when the load is greater than the isometric force and elongates the contracting muscle.

CHAPTER 4

EMG ELECTRODES

The basic block of the whole system in which EMG electrodes attached to human hand is acquired and amplified using Instrumentation Amplifier. Then filtering is done to remove 50Hz interference noise and selective frequencies are allowed using wide Band Pass filter. Then filtered signal is fed to a comparator or Analog to Digital Converter which serves as a input for the microcontroller to actuate the six servo motors of a Robotic Arm.

4.2 EMG SENSOR/EMG ELECTRODES:

Different kinds of medical instruments require different types of electrodes. For instance, the ECG requires surface electrodes; the EMG uses either surface electrodes or needle electrodes. Electrodes are actually a type of transducer, which extracts the signals. We can obtain the EMG signal simply by placing a surface electrode on the skin enveloping the muscle or by applying an inserted electrode in the muscle.

ELECTRODE CONFIGURATION

The two electrode configurations are

In the monopolar configuration, one electrode is placed on the particular muscle site. Other one is a reference electrode, which is placed on a site with minimal electric association with the inserted site. The drawback of this monopolar configuration is that it detects not only the signal from the muscle of interest but also unwanted signals from around the muscle of interest.

In the bipolar configuration, two electrodes with a small distance between each other are placed in the muscle to pick up the local signals within the muscle of interest. A differential amplifier amplifies the signals picked up from the two electrodes with respect to the signal picked up by a reference electrode. Because the interference signals from a distant source are essentially equal in magnitude and phase as detected by the two electrodes, the common mode rejection capability of the differential amplifier eliminates the unwanted signals.

TYPES OF ELECTRODES

Electrodes used in EMG can be classified into two types:

SURFACE ELECTRODES

Surface electrodes may be constructed as either passive of active units. In passive units electrodes consist of detection surface that senses the current on the skin through its skin-electrode interface. In the active configuration, the input impedance of the electrode is greatly increased by electronic means, rendering it less sensitive to the impedance of the electrode-skin interface. The electrode impedance can be reduced by applying conducting gel in the skin-electrode interface and can be further reduced by removing the dead surface layer on the skin along with protective oils; this is best done by light abrasion of the skin. Active electrodes are one which can be either resistively or capacitively coupled to the skin. Although the capacitively coupled electrodes have the advantage of not requiring a conductive medium, they have a higher inherent noise level. Also these electrodes do not have long-term reliability. For these reasons they have not yet found a place in electromyography. The disadvantages of surface electrodes are that they cannot effectively detect signal from muscles deep beneath the skin and that because of poor selectivity, they cannot eliminate cross-talk from adjacent muscles

Surface Electrodes are applied inTime-Force relationship of EMG signal, Kinesiological studies of surface muscles, Neurophysiologic studies of surface muscles, Psycho physiological studies, interfacing an individual with external electromechanical devices.

Applications of Needle Electrodes are in manipulating MUAP Characteristics and also in the manipulation of Control properties of motor units (firing rate, recruitment) and find its field in exploratory clinical electromyography.

Wire Electrodes are applied in Kinesiological study of deep muscles, neurophysiologic studies of deep muscles, limited studies of motor unit properties and in Comfortable recording procedure for deep muscles.

Needle and wire electrodes are common in EMG detection. They have diameter in the order of 150 to 25 micrometers. Because of the extremely small surface they are used to pick up action potentials from single motoneurons and are also painless. They are highly non-oxidizing, stiff wire with insulation. Alloys of Platinum, Silver, Nickel and Chromium are preferable. The alloy of 905 Platinum with 10% Iridium offers appropriate combination of chemical inertness.

Table 4.1 - COMPARISON OF ELECTRODES

Attributes

Indwelling

· needle

* fine wire

surface (Ag-AgCl)

surface area

Large area behaves like a string of point electrodes; each 'point' picks up the same signal, slightly delayed in time; the sum is a longer duration waveform.

small area picks up more discrete signals without producing long duration waveform

Pick up zone

limited to 0.5 cm to 1.5 cm; can record only from superficial muscles

necessary for recording from deep muscles

"cross talk" (pickup of signals from adjacent muscles)

more common

less common

Choice of electrode placement

For electrode to detect a muap, it must travel in a direction such that the distance between impulse and electrode changes

Therefore, electrodes should be aligned with expected direction of impulse (or aligned perpendicular to impulses that should be excluded)

SELECTION of Electrode Material

Generally, Noble metals like Gold, Silver, and Platinum are chosen because of their Corrosion resistance. Silver has better mechanical strength. Platinum is used for pacemaker casing. Stainless steel and their alloys are possible alternatives for their low cost and good strength.

4.2.2. CONDUCTIVE GEL:

Many types of electrodes require additional conductive gel to enhance the electrical connection. However, older types of conductive gel contained some ingredients that increased the chance of bacterial growth, such as, polysaccharides and some kind of thickener, which are food for bacteria. Most conductive gel consists of sodium chloride, which provides good electrical contact. However, chloride ion can cause skin irritation.

Antibacterial and antifungal ingredients are added into the conductive gel to prevent bacterial growth. The ingredients, such as, methyl P-Hydroxyl benzoate, zephiran chloride and xylenol have been added to prevent and retard bacterial growth.

Important properties that conductive gel should possess are:

4.2.3 Placement of Electrodes:

EMG ELECTRODES

Electromyogram Sensor is made of Ag/AgCl electrodes and it consists of a 3-pin jack to connect to Instrumentation Amplifier.

Here we have one electrode as a common ground placed on the wrist end of the hand and other two electrodes separated from each other by few inches placed on

CHAPTER 5

INSTRUMENTATION AMPLIFIER

The important features of Instrumentation Amplifier which make it popular in Biomedical Applications are:

The instrumentation amplifier used for this project is LM324.The Instrumentation Amplifier consists of three identical Operational Amplifiers. The first two amplifiers are working in the non-inverting mode but their inverting terminals are not grounded. The feedback loops are connected with the inverting terminals. The third Operational Amplifier will act as Differential Amplifier. The instrumentation amplifier is designed to have high input impedance. All the resistors are Metal Film Military Grade Resistors with tolerance level of 0.1%. All the Capacitors are Tantalum Capacitors with tolerance of 1%. The values of Resistors and the Capacitors are exactly identical to ensure high CMRR. The Values of R, C are chosen such that the Time Period T=2 Seconds. The high input impedance of 10 MegaΩ is provided by resistors R2, R3, and R4. The Capacitors C1, C2, C3 are provided to reduce any DC offset

5.1 LM324 DESCRIPTION:

It consists of four independent high gain frequency compensated operational amplifiers. This LM324 is a product of national semiconductor. The internal circuit consists of so many transistors, resistors and capacitors. Usually an op-amp is a five terminal device. It has two input terminals and one output terminal. One input terminal with a (-) sign is called inverting terminal and other input with (+) sign is called the non-inverting terminal. The other two terminals are power supply terminals.[Appendix 1]

5.2 GAIN CALCULATIONS:

R7=R8 = a R6 ; R9=R10 ; R11=R12= b R9

We assume the input1 as V1, input2 as V2 and the output of the third operational amplifier as V5. Let the output of the amplifiers prior to C4 and C5 be V3 and V4 respectively.

V3 / R6 = 1 + (R7 / R6) V1 - R7V2

V3 / R6 = 1 + (aR6/ R6) V1 - aR6V2

V4 / R6 = 1 + (R8 / R6) V2 - R8V1

V4 / R6 = 1 + (aR6 / R6) V2 - aR6V1

V5 / R9= (V4 - V3) bR9

V5 = (V2 - V1) (1 + 2a) b

Therefore, a net gain of (1 + 2a) b can be achieved and the gain may be easily adjusted without disturbing the circuit symmetry by varying the resistor R6

For this project we have fixed the value of the R6=500 ohm and R7=R8=50K.

R11=R12=50K and R9=R10=10K. Therefore, a=100 and b=5

Hence, substituting back in the formula, we get a net gain of (1+200)5 =1005.

5.3 COMMON MODE REJECTION RATIO CALCULATIONS:

The Common Mode Rejection Ratio (CMRR) is given by the ratio of Differential Gain to the Common Mode Gain. For the value of CMRR to be extremely high, as it is required for EMG signal, the differential gain has to be made as high as possible and common mode gain as low as possible. The Instrumentation Amplifier components were varied by trial and error method to get the best possible CMRR. After meticulous testing we came up with a CMRR of 45,000. The test results are shown below.

5.3.1. DIFFERENTIAL GAIN TEST:

Sinusoidal signal was fed to the two input terminals individually. First, Input1 was given a signal of amplitude 10mV with respect to ground but Input2 grounded. The output was recorded to be 4.5V. The same was done for Input2 with Input1 grounded. Similar result was recorded. Therefore, Differential Gain= Output/Input=4.5V/10mV= 450.

5.3.2. COMMON MODE GAIN:

For common mode common signal was fed for the two Input terminals with respect to the ground. For an input sinusoidal signal of amplitude 2V the output was recorded to be 20mV.

Therefore, Common mode Gain =output/input=20mV/2V=0.01

Thus,

CMRR=Differential Gain/Common Gain=450/0.01=45,000.

CMRR (dB) = 20 log10 (45,000). = 93Db

CHAPTER 6

FILTER

A filter is a device designed to attenuate specific ranges of frequencies, while allowing others to pass, and in so doing limit in some fashion the frequency spectrum of a signal. The frequency range(s) which is attenuated is called the Stop band, and the range which is transmitted is called the Pass band. The EMG signal falls with in the audio frequency range 10Hz to 10 KHz. The prominent frequency range from 10Hz to 5 KHz has to be isolated to be then processed. Hence, Filters play a vital role in signal conditioning part of this project.

6.1. TYPES OF FILTERS

The filters are generally classified into four types:

6.2. FILTERS USED IN THE ELECTROMYOGRAPH:

The inherent noise of the Electrical mains i.e., the 50 Hz signal is first filtered out using a Notch Filter. After the 50 Hz signal is attenuated, the signal is then passed through a band-pass filter and the prominent frequencies between 10 Hz and 500Hz is filtered out.

6.3. NOTCH FILTER:

The notch filter used in the Electromyography is a classic pattern which is generally used for attenuating the electrical hum in the environment. It is a narrow band-reject filter. The Notch filter used for this purpose is a Twin-T type filter. This improves the Q-factor of the filter appreciably.

The above circuit shows a Twin-T notch filter. The resistors R, R1, R2 are military grade resistors with 0.1% tolerance. The capacitors are tantalum capacitors with 1% tolerance level. As an EMG is a precision instrument, the components forming the circuitry should be closely matched. The op-amps in the above circuit are a part of a single IC, LM324. This IC houses 4 identical op-amps.

6.3.1. DESIGN:

The frequency to be notched is given by the formula, f = 1/ (2*pi*R*C)

Where R and C are the values of resistor and capacitor forming the Twin-T network.

The value of capacitance is normally kept low as the cost of a capacitor increase with increase in size. Hence, by fixing the capacitor value, the resistance is calculated.

ng the value of ' values of resistor and capacitor forming the Twin-T network.

een 10 Hz and 5 KHz is filtered out.

By fixing the value of ‘C' as 11nanofarads, the value of R was determined to be

278Kohms for f = 50Hz.

6.3.2. TESTING OF NOTCH FILTER:

The notch filter designed has to be tested for a wide frequency band from 10Hz to 10 KHz. It has to attenuate the design frequency of 50Hz power supply noise. The designed filter can be tested with the help of a Cathode ray oscilloscope. A sinusoidal input of amplitude 20V was fed at the Vi and the frequency was varied from 10Hz to 10 KHz in steps. The output from the terminal Vo was observed on cathode ray oscilloscope. The amplitude of the output had a sharp fall to 50mV at a frequency of 50Hz. As the frequency was increased beyond 50Hz the amplitude again increased. The response was as shown below.

6.4. WIDE BAND PASS FILTER:

The wide band Pass filter is a Butterworth filter. It consists of a high-pass filter followed by a low-pass filter. The high pass filter attenuates the frequency greater than the upper cutoff frequency. The output of the high pass filter is then passed through the low pass filter. The low pass filter attenuates the frequencies less than the lower cutoff frequency.

6.4.1. DESIGN:

The wide band Pass filter is a Butterworth filter. It consists of a high-pass filter followed by a low-pass filter. The cut-off frequencies are 10Hz and 500 Hz. The high pass filter attenuates the frequency greater than the upper cutoff frequency. The output of the high pass filter is then passed through the low pass filter. The low pass filter attenuates the frequencies less than the lower cutoff frequency. Thus, the output of the wide band pass filter has a flat conduction band with the gain remaining constant for almost the whole of the band width.

We first design the Low pass filter. The higher cut-off frequency is2KHz.

Therefore, fh= 500 Hz

fh= 1/ (2 * Pi * R1 * C1)

Let us assume the value of the capacitor C1 = 0.1micro Farads.

i.e.500 Hz = 1/ (2 * Pi * 0.1* 10-6 * R1)

We get, R1=796Ω (820Ω)

For designing the High Pass Filter, let us assume the value of C2 = 0.1µF.

fl = 10 Hz for the High pass filter.

fl = 1/ (2 * Pi * R2 * C2)

.i.e. 10 Hz = 1/ (2 * Pi * R2 * 0.1* 10-6)

We get, R2=1.59MegaΩ

6.4.2. CIRCUIT DIAGRAM:

6.4.3. CHARACTERISTICS:

The output of the wide band pass filter has a flat conduction band with the gain remaining constant for almost the whole of the band width.

The pass band lies between the upper cut off frequency, fh and lower cut off frequency, fl .It is seen from the figure that the gain remains constant through out the pass band and has a sharp rise/fall in the stop bands.

6.4.4. TESTING:

The Wide Band pass Filter was tested with a Cathode Ray Oscilloscope for frequency range of 1Hz to 2 KHz. The gain was found to be constant for the entire bandwidth

CHAPTER 7

LABVIEW

7.1 Description

Labview is a very good and impressing tool for signal processing. We are using labview as a tool for processing of the EMG which we get from the amplifier. Using Labview the signal can be processed to any level we want. The main advantage of this software is that we can see the output visually and it is real time, which makes it a very useful tool. Labview is a tool which has a graphical user interface. It can be interfaced with any hardware using the data acquisition software.

We acquired the signal and after filtering the signals, we send it to the data acquisition system of the labview. Through which signal is sent to labview on real time. Then using the software other filters were used for further processing. Then butterworth smoothening filter of around 200 order was used to get a very clear smoothening, so that the threshold can be found easily. If it had been a hardware smoothing filter the higher order design would have been a complex and a tedious work. The smoothened signal was seen visually in the graph plotted on real time. The final processed signal was taken as a output from the analog output ports Ao1 and Ao0. This output was then sent to the PIC which has an inbuilt A to D converter.

7.1.1 Acquiring signals in LABVIEW:

Using the NI-DAQ provided specially for data acquisition there was no problem in acquiring the input signals. Just the input port in which we are giving the input is needed to be specified in the system designed. Rest of the work will be done by

System itself

7.1.2 Processing Signals:

Almost the processing of signals using the software is easy. Though thorough knowledge of the processing tools which we are going to use is necessary, not much expertise on software is needed. Using the graphical icons and heading by heading subdivision of all mathematical and signal processing tools it is nearly a simple and easy way to process the signals. All the tools have its own settings and ports, these settings are set by the user per the requirement of his development.

7.1.3 Output from Labview:

Output can be taken from labview NI DAQ system. This is a very important point to be noted. It is a unique feature of this software system. Analog or Digital output can be taken from the Data acquisition system, depending on our use. Also the output can be seen in DSO, if output is taken as analog. Only thing needed to take the output port is insert a DAQ Assist from the express output, in the program and specify the ports from which we are going to take the signal. It is a very simple process.

7.2. Steps involved in development of software:

In the software development method, complete the following steps:

7.3 Software development:

7.4 REASONS TO CHOSE LABVIEW:

Output from Labview:

Output from Labview is taken from analog port Ao0. The output will be in such a way that whenever a EMG contraction is detected, there will be a square pulse generated according to the amplitude of EMG contraction. The square pulse is got as a straight DC line of amplitude varying according to EMG by an small circuit. This circuit has a capacitor which changes the negative half to positive, so a DC like wave is obtained. This wave is seen in CRO then sent to the PIC.

CHAPTER 8

PIC MICROCONTROLLER 18F4550

8.1 Introduction

PIC is a family of Harvard architecture microcontrollers made by Microchip Technology, derived from the PIC1640 originally developed by General Instrument's Microelectronics Division. The name PIC initially referred to “Programmable Interface Controller”, but shortly thereafter was renamed “Programmable Intelligent Computer”.

PICs are popular with developers and hobbyists alike due to their low cost, wide availability, large user base, extensive collection of application notes, availability of low cost or free development tools, and serial programming (and re-programming with flash memory) capability.

PIC 18F4550:

Like all Microchip PIC18 devices, PIC18F4550 family are available as both standard and low-voltage devices. Standard devices with Enhanced Flash memory, designated with an “F” in the part number (such as PIC18F4550),accommodate an operating VDD range of 4.2V to 5.5V.Low-voltage parts, designated by “LF” (such as PIC18LF4550), function over an extended VDD range of 2.0V to 5.5V.

Our project uses a standard PIC 18F4550.Hence this microcontroller uses a flash program memory of 24K bytes .It is a 8-bit microcontroller and so they handle data as 8-bit chunks. PICs have a set of registers that function as general purpose ram. Special purpose control registers for on-chip hardware resources are also mapped into the data space. The addressability of memory varies depending on device series and in PIC 18F4550 external code memory is directly addresable which is an exceptional feature compared to baseline and mid line core devices.[Appendix 4]

PICs have a hardware call stack, which is used to save return addresses. The hardware stack is not software accessible on earlier devices, but this changed with the 18F4550 device. Hardware support for a general purpose parameter stack was lacking in early series, but this greatly improved in the 18F4550, making the device architecture more friendly to high level language compilers.

8.2 Core features

All of the devices in thePIC18F 455 series family incorporate a range of features that can significantly reduce power consumption during operation. Key items include:

8.3 Pin Description

The pin details of PIC18F4550 are explained below in detail.

MCLR:

This pin is used to erase the memory locations inside the PIC (i.e. when we want to re-program it). In normal use it is connected to the positive supply rail.

VSS AND VDD

These are the supply pins VDD is the positive supply and VSS is negative supply, or 0v.The maximum supply voltage is 6V and minimum voltage is 2V.

OSC1/CLK1 and OSC2/CLK2:

These pins are where we connect an external clock, which is crystal oscillator so that the microcontroller has some kind of timing.

8.3 I/O PORTS

Depending on the device selected and features enabled, there are up to five ports available. Some pins of the I/O ports are multiplexed with an alternate function from the peripheral features on the device. In general, when a peripheral is enabled, that pin may not be used as a general purpose I/O pin. Each port has three registers for its operation. These registers are:

The Data Latch register (LATA) is useful for read modify- write operations on the value driven by the I/O pins.

8.3.1 PORTA:

PORTA is an 8-bit wide, bi directional port. The corresponding data direction register is TRISA. Setting a TRISA bit (= 1) will make the corresponding PORTA pin an input (i.e., put the corresponding output driver in a high-impedance mode). Clearing a TRISA bit (= 0) will make the corresponding PORTA pin an output (i.e., put the contents of the output latch on the selected pin). Reading the PORTA register reads the status of the pins; writing to it will write to the port latch.

The RA4 pin is multiplexed with the Timer0 module clock input to become the RA4/T0CKI pin. The RA6 pin is multiplexed with the main oscillator pin; it is enabled as an oscillator or I/O pin by the selection of the main oscillator in Configuration Register 1H. When not used as a port pin, RA6 and its associated TRIS and LAT bits are read as ‘0'. RA4 is also multiplexed with the USB module; it serves as a receiver input from an external USB transceiver.

Several PORTA pins are multiplexed with analog inputs, the analog VREF+ and VREF- inputs and the comparator voltage reference output. The operation of pins RA5 and RA3:RA0 as A/D converter inputs is selected by clearing/setting the control bits in the ADCON1 register On a Power-on Reset, RA5 and RA3:RA0 are configured as analog inputs and read as ‘0'. RA4 is configured as a digital input.

8.3.2 PORT B

PORTB is an 8-bit wide, bidirectional port. The corresponding data direction register is TRISB. Setting a TRISB bit (= 1) will make the corresponding PORTB pin an input (i.e., put the corresponding output driver in a high-impedance mode). Clearing a TRISB bit (= 0) will make the corresponding PORTB pin an output (i.e., put the contents of the output latch on the selected pin).

Each of the PORTB pins has a weak internal pull-up. A single control bit can turn on all the pull-ups. This is performed by clearing bit, RBPU.

On a Power-on Reset, RB4:RB0 are configured as analog inputs by default and read as ‘0'; RB7:RB5 are configured as digital inputs. Four of the PORTB pins (RB7:RB4) have an interruption- change feature. Only pins configured as inputs can cause this interrupt to occur. Any RB7:RB4 pin configured as an output is excluded from the interruption- change comparison. Pins, RB2 and RB3, are multiplexed with the USB peripheral and serve as the differential signal outputs for an external USB transceiver RB4 is multiplexed with CSSPP, the chip select function for the Streaming Parallel Port

8.3.3 PORT C

PORTC is a 7-bit wide, bidirectional port. The corresponding data direction register is TRISC. Setting a TRISC bit (= 1) will make the corresponding PORTC pin an input (i.e., put the corresponding output driver in a high-impedance mode). Clearing a TRISC bit (= 0) will make the corresponding PORTC pin an output (i.e., put the contents of the output latch on the selected pin). In PIC18F4550 device, the RC3 pin is not implemented.

PORTC is primarily multiplexed with serial communication modules, including the EUSART, MSSP module and the USB module Pins RC4 and RC5 are multiplexed with the USB module.

Unlike other PORTC pins, RC4 and RC5 do not have TRISC bits associated with them. As digital ports, they can only function as digital inputs. When configured for USB operation, the data direction is determined by the configuration and status of the USB module at a given time.

On a Power-on Reset, these pins, except RC4 and RC5, are configured as digital inputs. To use pins RC4 and RC5 as digital inputs, the USB module must be disabled.

8.3.4 PORT D:

PORTD is an 8-bit wide, bidirectional port. The corresponding data direction register is TRISD. Setting a TRISD bit (= 1) will make the corresponding PORTD pin an input (i.e., put the corresponding output driver in a high-impedance mode). Clearing a TRISD bit (= 0) will make the corresponding PORTD pin an output (i.e., Put the contents of the output latch on the selected pin).

Chapter 9

DRIVER CIRCUIT

9.1 H-Bridge:

An H- bridge circuit is a suitable circuit used in robotic control. It is mostly used in running motors of different types. Usually most of the robots which has forward and reverse spinning motor in its operation use H bridge circuit.[Appendix 3,4]

H-bridge circuit as the name suggests looks like an H representation. It has four switches in it may be solid state or mechanical. S1, S2, S3, S4 are the 4 switches. If S1 and S4 are closed and S2 and S3 are opened the motor runs in forward direction and if the switches are in the other way then the motor runs in reverse direction.

The combination of the switches must not be changed this is because for example, if the switches S2 and S2 are closed at same time then the circuit is shorted thereby destroying the motor. So this should be seen with careful attention. This condition is called as shoot through.

9.2 Operation:

The arrangement in this type of circuit is usually used in reversing the motor's polarity. It can also be used to stop the motor suddenly, which is called as braking. The following table summarizes operation.

9.3 TRUTH TABLE:

Table 9.1 Truth table for H bridge circuit

S1

S2

S3

S4

Current Direction

Effect

1

0

0

1

1 to 2

Motor spins forward

0

1

1

0

2 to 1

Motor spins backward

1

1

0

0

_

Braking Occurs

0

0

0

0

_

Free running

9.4 H Bridge Circuit Diagram:

9.5 L298D (H-BRIDGE IC)

L298 is a motor driver circuit used for control of two motors simultaneously. The current rating for this IC is limited to 600mA, but during operation it operates under much less current only. The case were higher current rating can be used is when high heat sinking is used to keep the temperature down, or else the IC will be damaged. If the IC gets heated up then it is sure that we can not use the IC for running the motor.

The L298 is a standard 16 pin integrated package which has dual line in. The similar type of IC is L293 which has similar configuration. Only difference is it has fly back diodes to minimize inductive voltage spikes.

9.6. Pin Configuration of L298 IC

9.7. Free Wheeling Diodes

A Free Wheeling Diode is a component which is used to prevent damage to circuit when the circuit is reversed.

The current will not reach zero in no time when the inductive load is switched off. This is because magnetic field will store some energy. The free wheeling diode is mostly connected in a way that anode is on minus to the coil. If the coil is switched off then voltage also reverses to keep the current direction.

The free wheeling diode is connected anti-parallel (anode on minus) to the coil. Hence it doesn't conduct normally. If the coil is switched off, the voltage across the coil reverses to maintain the current's direction. Now the diode carries the current until the energy is consumed by the coil's inner resistance.

9.8 Circuit Diagram of L298 D:

CHAPTER 10

Mechanical Arm Operation

10.1 Motors used in the Robot:

10.1.1. Stepper motors:

Stepper motors are easy to handle and use. Robotics is very much dependant of the motors and gearings. Such motors are effective for robotics as it is specific in its task. If we need more torque for operation and speed does not much matters then it can be best choice.

10.1.2. Reasons for selecting Stepper Motor:

In our application the robotic chassis should be rigid and stable as it has to carry the supply battery, robotic and sensor circuitry. Also we need a good accuracy over the angle of rotation, this because we are doing a grasping movement which is done at 90 degree angle only if it exceeds then it may crush object held or damage the robotic arm itself. Hence a Stepper motor will be ideal for this operation as torque and angle is of more concern. Servo controlled motors is a good choice but the cost of motor is more than triple than stepper motor.

10.2. Design of Robotic Arm:

Design of the arm for an grasping movement is a complex work and needs a sound knowledge in the mechanical gears and assemble. But a simple construction can be a one which has two ends one fixed and other connected to rotating part of the Stepper motor. It is connected in a way that the movable end and fixed end is perpendicular to each other.So when the motor runs 90 degree the movable part comes in contact with the fixed end, so that if an object is there in between the ends it can grasp the object, which is the objective and goal of our project.

10.3. Algorithm of motor control:[Appendix 6]

10.4. Motor Rating

Stepper Motor Speed of the motor: 200 revolutions per meter

Voltage Rating of the motor = 12V

Step= 1.8 degree per half step

Current Drawn by the motor on full load = 0.3 A

Power rating of the motor=12 * 0.3=3.6W

Revolutions=200 full steps for a revolution

CHAPTER 11

CONCLUSION AND FUTURE WORKS

The field of biomedical signal processing and rehabilitation engineering seems to hold a very promising future. The field is still in its early stages and extensive research is being held in many institutions around the globe. A future research will be directed at developing techniques to improve the rehabilitation programs for disabled individuals. Improvements will take place in the way in which surface electrodes are mounted on the subject skin and the type of electrodes to be used, for more efficient results. Non-stationary signal processing methods seems to be one of the promising tools in this field. However, Physiological modeling using deep knowledge on the observed physiological system is required to achieve significant progress in the area of biomedical signal processing. Hence, interdisciplinary work groups are necessary to reach this goal.

Research is also being directed at the development of biomedical signal processing algorithms to extract useful information from biomedical signals and relate them to rehabilitation aids and devices. The overall goal is to modify and develop powerful and advanced signal processing algorithms in order to apply them appropriately for the analysis of these signals. Signal processing theory need to be used extensively in order to advance biomedical applications and to push the advancement of biomedical signal processing and rehabilitation engineering theory, design and practice. The interface between the biomedical signal acquisition systems and the rehabilitation device, and the human-machine interface with such system is another promising area of research. In this work, we have modeled such a minimal system, a human-machine interface, in attaining the goal of functional electrical stimulation and rehabilitation.

To Conclude the project, output of EMG was clearly obtained without any interference. Filters designed for the amplifier was perfect by giving a stable gain over the frequency range it allows. Labview based processing is a good way to process and take output clearly. Controlling a stepper motor using PIC and its motor driver circuit was done with basic programming. Finally when a contraction occurs the PIC compares it with threshold level and accordingly it makes the motor run forward or reverse and thus the grasping movement achieved at a low cost.

Future work can be on designing a better stand alone system. Also a better movement other than grasping can be done. This project work being a basic one, a still more sophisticated and fully automatic prostheses can be designed, Such prostheses may include every single finger movement.

APPENDICES

APPENDIX 1

LM 324:

2, 6, 10, 13 - Inverting Input Terminals

3, 5, 9, 12 - Non-inverting Input Terminals

1, 7, 8, 14 - Output Terminals

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