22-10-2016, 04:15 PM
HAND THERAPIST: A REHABILITATION APPROACH BASED ON WEARABLE TECHNOLOGY AND VIDEO GAMING
1460621707-repforcea0275.docx (Size: 1.24 MB / Downloads: 5)
OBJECTIVE:
To design a hand therapist for the rehabilitation approach based on wearable technology and video gaming.
Methodology:
This project is designed with the following components,
• Flexibility sensors,
• Amplifiers,
• Accelerometer sensor,
• Interfacing circuit,
• Microcontroller,
• LCD display,
• RS232,
• PC.
Working principle:
Hand impairment after stroke is quite debilitating. Present hand rehabilitation approaches, although useful, are still limited as they often require the constant help of a technician or caregiver and also because they are based on repetitive training which may be de motivating. More advanced approaches are in development including the use of robotized systems.. Here, we show the proof-of-concept of a hand rehabilitation system, dubbed “hand therapist”, inspired in video gaming devices and software which is comprised of the flexibility sensors, accelerometer sensor and Unity3D, a video game development engine. With this approach we aim at a solution that combines performance, low-cost and engagement/motivation in hand therapy.
Here two flexibility sensors are fixed in the two hand fingers to identify the force associated with it and accelerometer sensor is fixed in the hand to detect the movement of it. All the sensors are interfaced with the microcontroller through the amplifier and interfacing circuit. Microcontroller is already programmed for the task needed for the proposed work. From where PC is interfaced with it through the RS232 serial communication. In PC we can easily monitor the whole hand movements and force associated with it. And also in PC video game is created in Unity 3D for hand training in which the user must grab, hold, transport and drops a cube in several increasingly difficult puzzle levels. In the game the user sees virtual hands/arms that replicate the user’s movements such that the user can feel more immersed in the game.
FLEXI FORCE SENSOR:
INTRODUCTION:
This manual describes how to use Tekscan's Flexi Force Sensors. These sensors are ideal for designers, researchers, or anyone who needs to measure forces without disturbing the dynamics of their tests. The Flexi Force sensors can be used to measure both static and dynamic forces (up to 1000 lbf.), and are thin enough to enable non-intrusive measurement.
The Flexi Force sensors use a resistive-based technology. The application of a force to the active sensing area of the sensor results in a change in the resistance of the sensing element in inverse proportion to the force applied.
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GETTING ASSISTANCE:
Tekscan, Inc. will provide technical assistance for any difficulties you may experience using your Flexi Force system. Write, call or fax us with any concerns or questions. Our knowledgeable support staff will be happy to help you. Comments and suggestions are always welcome.
OVERVIEW:
This section outlines Sensor Construction and Application.
SENSORS:
The Flexi Force sensor is an ultra-thin and flexible printed circuit, which can be easily integrated into most applications. With its paper-thin construction, flexibility and force measurement ability, the Flexi Force force sensor can measure force between almost any two surfaces and is durable enough to stand up to most environments. Flexi Force has better force sensing properties, linearity, hysteresis, drift, and temperature sensitivity than any other thin-film force sensors. The "active sensing area" is a 0.375” diameter circle at the end of the sensor. The A201 sensor is available in the following force ranges:
.. Sensor A201-1 (0-1 lb. force range)
.. Sensor A201-25 (0-25 lb. force range)
.. Sensor A201-100 (0-100 lb. force range)*
* In order to measure forces above 100 lbs. (up to 1000 lbs), apply a lower drive voltage and reduce the resistance of the feedback resistor (1k.. min.). See the sample drive circuit below. The sensors are constructed of two layers of substrate. This substrate is composed of polyester film. On each layer, a conductive material (silver) is applied, followed by a layer of pressure sensitive ink. Adhesive is then used to laminate the two layers of substrate together to form the sensor. The silver circle on top of the pressure-sensitive ink defines the “active sensing area.” Silver extends from the sensing area to the connectors at the other end of the sensor, forming the conductive leads.
Flexi Force sensors are terminated with a solder able male square pin connector, which allows them to be incorporated into a circuit. The two outer pins of the connector are active and the center pin is inactive. The length of the sensors can be trimmed by Tekscan to predefined lengths of 2”, 4” and 6” or can be trimmed by the customer. If the customer trims the sensor, a new connector must be attached. This can be accomplished by purchasing staked pin connectors and a crimping tool. A conductive epoxy can also be used to adhere small wires to each conductor.
The sensor acts as a variable resistor in an electrical circuit. When the sensor is unloaded, its resistance is very high (greater than 5 Meg-ohm); when a force is applied to the sensor, the resistance decreases. Connecting an ohmmeter to the outer two pins of the sensor connector and applying a force to the sensing area can read the change in resistance. Sensors should be stored at temperatures in the range of 15°F (-9°C) to 165°F (74°C)
APPLICATION:
There are many ways to integrate the Flexi Force sensor into an application. One way is to incorporate it into a force-to-voltage circuit. A means of calibration must then be established to convert the output into the appropriate engineering units. Depending on the setup, an adjustment could then be done to increase or decrease the sensitivity of the sensor.
An example circuit is shown below. In this case, it is driven by a -5 V DC excitation voltage. This circuit uses an inverting operational amplifier arrangement to produce an analog output based on the sensor resistance and a fixed reference resistance (RF). An analog-to-digital converter can be used to change this voltage to a digital output. In this circuit, the sensitivity of the sensor could be adjusted by changing the reference resistance (RF); a lower reference resistance will make the sensor less sensitive, and increase its active force range.
SENSOR LOADING CONSIDERATIONS:
The following general sensor loading guidelines can be applied to most applications, and will help you achieve the most accurate results from your tests. It is important that you read the Sensor Performance Characteristics section for further information on how to get the most accurate results from your sensor readings.
SENSOR LOADING:
The entire sensing area of the Flexi Force sensor is treated as a single contact point. For this reason, the applied load should be distributed evenly across the sensing area to ensure accurate and repeatable force readings. Readings may vary slightly if the load distribution changes over the sensing area.
Note that the sensing area is the silver circle on the top of the sensor only.
It is also important that the sensor be loaded consistently, or in the same way each time.
If the footprint of the applied load is smaller than the sensing area, the load should not be placed near the edges of the sensing area, to ensure an even load distribution.
It is also important to ensure that the sensing area is the entire load path, and that the load is not supported by the area outside of the sensing area. If the footprint of the applied load is larger than the sensing area, it may be necessary to use a "puck." A puck is a piece of rigid material (smaller than the sensing area) that is placed on the sensing area to ensure that the entire load path goes through this area. The puck must not touch any of the edges of the sensing area, or these edges may support some of the load and give an erroneous reading.
The Flexi Force sensor reads forces that are perpendicular to the sensor plane. Applications that impart "shear" forces could reduce the life of the sensor. If the application will place a "shear" force on the sensor, it should be protected by covering it with a more resilient material. If it is necessary to mount the sensor to a surface, it is recommended that you use tape, when possible. Adhesives may also be used, but make sure that the adhesive will not degrade the substrate (polyester) material of the sensor before using it in an application. Adhesives should not be applied to the sensing area; however, if it is necessary, ensure that the adhesive is spread evenly. Otherwise, any high spots may appear as load on the sensor.
SATURATION:
The Saturation force is the point at which the device output no longer varies with applied force. The saturation force of each sensor is based on the maximum recommended force specified by Tekscan, which is printed on the system packaging or the actual sensor, along with the "Sensitivity." The saturation value is based on using the circuit and the values shown in the example circuit in the ‘Application’ section. In this example, the saturation force (maximum force) of each sensor is related to the RF (reference resistance), and can be altered by changing the sensitivity. The sensitivity of the sensor would be adjusted by changing the reference resistance (RF); a lower reference resistance will make the system less sensitive, and increase its active force range. It is essential that the sensor(s) do not become saturated during testing.
CONDITIONING SENSORS:
Exercising, or Conditioning a sensor before calibration and testing is essential in achieving accurate results. It helps to lessen the effects of drift and hysteresis. Conditioning is required for new sensors, and for sensors that have not been used for a length of time. To condition a sensor, place 110% of the test weight on the sensor, allow the sensor to stabilize, and then remove the weight. Repeat this process four or five times. The interface between the sensor and the test subject material should be the same during conditioning as during calibration and actual testing. IMPORTANT! Sensors must be properly conditioned prior to calibration and use.
CALIBRATION:
Calibration is the method by which the sensor’s electrical output is related to an actual engineering unit, such as pounds or Newtons. To calibrate, apply a known force to the sensor, and equate the sensor resistance output to this force. Repeat this step with a number of known forces that approximate the load range to be used in testing. Plot Force versus Conductance (1/R). A linear interpolation can then be done between zero load and the known calibration loads, to determine the actual force range that matches the sensor output range.
CALIBRATION GUIDELINES:
The following guidelines should be considered when calibrating a sensor:
.. Apply a calibration load that approximates the load to be applied during system use, using dead weights or a testing device (such as an MTS or Instron). If you intend to use a "puck" during testing, also use it when calibrating the sensor. See Sensor Loading Considerations for more information on using a puck.
.. Avoid loading the sensor to near saturation when calibrating. If the sensor saturates at a lower load than desired, adjust the "Sensitivity."
.. Distribute the applied load evenly across the sensing area to ensure accurate force readings. Readings may vary slightly if the load distribution changes over the sensing area.
Note: Read the Sensor Performance Characteristics section before performing a Calibration.
SENSOR PERFORMANCE CHARACTERISTICS:
There are a number of characteristics of sensors, which can affect your results. This section contains a description of each of these conditions, and recommendations on how to lessen their effects.
REPEATABILITY:
Repeatability is the ability of the sensor to respond in the same way to a repeatedly applied force. As with most measurement devices, it is customary to exercise, or "condition" a sensor before calibrating it or using it for measurement. This is done to reduce the amount of change in the sensor response due to repeated loading and unloading. A sensor is conditioned by loading it to 110% of the test weight four or five times. Follow the full procedure in the Conditioning Sensors section.
LINEARITY:
Linearity refers to the sensor’s response (digital output) to the applied load, over the range of the sensor. This response should ideally be linear; and any non-linearity of the sensor is the amount that its output deviates from this line.
HYSTERESIS:
Hysteresis is the difference in the sensor output response during loading and unloading, at the same force. For static forces, and applications in which force is only increased, and not decreased, the effects of hysteresis are minimal. If an application includes load decreases, as well as increases, there may be error introduced by hysteresis that is not accounted for by calibration.
DRIFT:
Drift is the change in sensor output when a constant force is applied over a period of time. If the sensor is kept under a constant load, the resistance of the sensor will continually decrease, and the output will gradually increase. It is important to take drift into account when calibrating the sensor, so that its effects can be minimized. The simplest way to accomplish this is to perform the sensor calibration in a time frame similar to that which will be used in the application.
TEMPERATURE SENSITIVITY:
In general, your results will vary if you combine high loads on the sensor with high temperatures. To ensure accuracy, calibrate the sensor at the temperature at which it will be used in the application. If the sensor is being used at different temperatures, perform a calibration at each of these temperatures, save the calibration files, then load the appropriate calibration file when using the sensor at that temperature.
SENSOR LIFE / DURABILITY:
Sensor life depends on the application in which it is used. Sensors are reusable, unless used in applications in which they are subjected to severe conditions, such as against sharp edges, or shear forces. FlexiForce sensors have been successfully tested at over one million load cycles using a 50 lb. force. Rough handling of a sensor will also shorten its useful life. For example, a sensor that is repeatedly installed in a flanged joint will have a shorter life than a sensor installed in the same joint once and used to monitor loads over a prolonged period. After each installation, visually inspect your sensors for physical damage. It is also important to keep the sensing area of the sensor clean. Any deposits on this area will create uneven loading, and will cause saturation to occur at lower applied forces.
ACCELEROMETER:
Accelerometers are sensors or transducers That measure acceleration. Accelerometers generally measure acceleration forces applied to a body by being mounted directly onto a surface of the accelerated body. Accelerometers are useful in detecting motion in objects. An accelerometer measures force exerted by a body as a result of a change in the velocity of the body. A moving body possesses an inertia which tends to resist change in velocity. It is this resistance to change in velocity that is the source of the force exerted by the moving body. This force is directly proportional to the acceleration component in the direction of movement when the moving body is accelerated. The motion is detected in a sensitive portion of the accelerometer. This motion is indicative of motion in the larger object or application in which the accelerometer is mounted. Thus, a sensitive accelerometer can quickly detect motion in the application. Accelerometers have uses in many commercial, military, and scientific applications including inertial navigation, vehicular safety systems such as airbags, ride comfort control, platform stabilization, tilt sensing, and vibration monitoring. Accelerometers find use in automobile suspension systems, vehicle air bag systems, anti-lock brake systems (ABS), vibrometers, and computer hard disc drives, smart detonation systems for bombs and missiles and machine vibration monitors. A disk drive employs an accelerometer to detect disturbances affecting an actuator arm while attempting to maintain a head over a centerline of a track. The output of the accelerometer is used as a feed-forward compensation signal in a servo control system to effectively reject the disturbance. Accelerometers have been employed to help determine the acceleration or deceleration of a ship or plane, to monitor the forces being applied to an apparatus or device, such as a car, train, bus, and the like. Accelerometers are used as a GPS-aid to obtain position information when the GPS receivers lose their line-of-sight with the satellites. Accelerometers are widely used to monitor the vibration of electrical motors, pumps and the like in industrial applications, especially in continuous production operations. Changes in vibration levels, particularly in rotating machinery, provide an advance warning of problems such as excessive wear or an approaching bearing failure. Electromechanical accelerometers have been used in washing machines to detect an unbalanced load by sensing the sharp accelerations and decelerations of the spinning tub as it rocks back and forth. An accelerometer can measure changes in a patient's physical activity. The physical changes are detected by the accelerometer and algorithmically interpreted by circuitry within the pulse generator to produce a modified therapy that is correct for the current activity level. The accelerometer is placed within the implantable medical device. Accelerometers are also used to detect and record environmental data. In particular, accelerometers are often used in seismic applications to gather seismic data. In the area of oilfield investigation and earth formation characterization, accelerometers may be deployed in wire line applications, logging while drilling applications, or using coiled tubing.
Typical accelerometer sensors include a pendulous reaction mass, often referred to as a proof mass, suspended from a stationary frame by, for example, a flexural suspension member or some other form of pivot mechanism. An accelerometer may be viewed as a mass-spring transducer housed in a sensor case with the sensor case attached to a moving object whose motion is inferred from the relative motion between the mass and the sensor case. The relative displacement of the mass is directly proportional to the acceleration of the case and therefore the moving object. The heart of an accelerometer is a mechanical proof-mass. Pendulous accelerometers, for example, vibrating beam accelerometers, capacitive accelerometers, capacitive rebalance accelerometers, and translational mass accelerometers comprise a reaction mass. The proof-mass is connected to a substrate by a suspension. Under an applied acceleration, the proof-mass moves with respect to the substrate. The accelerometer is attached to the moving object, and as the object accelerates, inertia causes the proof mass to lag behind as its housing accelerates with the object. The force exerted on the proof mass is balanced by the spring, and because the displacement allowed by the spring is itself proportional to applied force, the acceleration of the object is proportional to the displacement of the proof mass. In a typical accelerometer sensor mechanism the pendulous reaction mass is suspended on a flexural suspension member inside an external support frame. Isolation is typically provided by mounting the supporting frame itself inside an isolation feature supported from a final exterior frame which provides mounting both to sensor covers and to the accelerometer housing. In an accelerometer, acceleration is usually measured at a measurement point in the accelerometer, along a sensitive axis of the accelerometer. Generally, the magnitude of an applied acceleration is communicatively coupled to external instruments or circuits as an electrical impulse having amplitude proportional to the magnitude of the applied acceleration. The electrical impulse comprises the measured acceleration and is processed by the external circuits as required for a variety of applications. The electrical impulse output of an accelerometer is proportional to the acceleration, applied at the measurement point along the sensitive axis of the accelerometer. A sense-element may be operated either open-loop, or placed into a force-feedback loop. Enclosure of a sense-element in a force-feedback loop is commonly called force-balancing or force-rebalancing. Accelerometers require either a frequency or voltage reference. Voltage references hardened against radiation are not available so that frequency referenced accelerometers are preferred for strategic applications. Frequency based accelerometers include silicon micro machined devices and quartz devices. An accelerometer generates an output signal which has amplitude which is related to the acceleration that is applied to the accelerometer. It is often necessary to calibrate the accelerometer, that is, to determine the amplitude of its output signal as a function of the magnitude of the applied acceleration and of its frequency. The process of calibrating an accelerometer consists of computing a constant of proportionality, referred to as a scale factor of the accelerometer. The scale factor of an accelerometer precisely relates the amplitude of the electrical impulses comprising the measured acceleration to the magnitude of a corresponding acceleration applied at the measurement point, along the sensitive axis of the accelerometer.
Various accelerometers capable of measuring acceleration are being developed. The accelerometers are mainly fabricated through the semiconductor process, and classified into piezoelectric, piezor esistant and capacitance accelerometers. Often piezoelectric materials, piezo resistive materials, or air-gap capacitors are used in conjunction with an electrical position-sense interface to detect proof-mass displacements. Piezoelectric based electronic accelerometer suffers from several major drawbacks when faced with the continuing stricter demands of the industry. Higher performance piezoelectric accelerometers require power at the sensor head. Also, multiplexing of a large number of sensors is not only cumbersome but tends to occur at significant increase in weight and volume of an accelerometer array. Capacitance accelerometers employ a capacitor between the mass and a support structure, and measure the variable capacitance between the two. An acceleration of the mass causes a change in the space between moving and fixed plates of the capacitor. The change in the space or displacement of the moving plate relative to the fixed plate is inversely proportional to the charge on the capacitor. In general, capacitive accelerometers change electrical capacitance in response to acceleration forces and vary the output of an energized circuit. A capacitive accelerometer shows a small level of characteristic change according to temperature variation, allows a field effect transistor of a high integrity to constitute a signal processing circuit without additional processes, and can be prepared at low cost. Capacitive accelerometer systems generally include sensing elements, such as capacitors, oscillators, and detection circuits. Angular accelerometers are employed to measure the second derivative of angular rotation with respect to time. In some machine controlled applications, a measurement of angular acceleration is often needed as a direct input to a control system. Rotary accelerometers may be used to provide closed loop motion control of a load through the use of feedback techniques. The acceleration signal from an accelerometer may be used to electronically simulate larger, smaller or varying system inertia. Pendulous gyroscopic accelerometer is a type of high precision accelerometers based on a rebalance mechanism. An unbalance is created, for example by adding a pendulous mass along a spin axis. An input acceleration creates a torque, which is counterbalanced by a torque in the opposite direction resulting from the rotation of the gyroscope about its input axis. The velocity of rotation of the gyroscope is used to determine the acceleration being sensed by the accelerometer. Linear accelerometers measure linear acceleration along a particular sensing axis. Linear accelerometers are frequently employed to generate an output signal (e.g., voltage) proportional to linear acceleration for use in a vehicle control system. A multi-axis accelerometer device can measure acceleration along multiple sensitive axes. This can be a combination of one or more accelerometers, with one or more axes of sensitivity each, and a common frame of reference with respect to which each of these accelerometers and their respective measurement points and sensitive axes remains fixed at all times. Optical accelerometers or displacement devices operate through a connection of an optical element to a mass usually positioned inside of housing. As a force acts on the mass, the mass moves within the housing, thereby imparting a stress to the optical element indicative of the force. The optical element in such devices is typically an optical fiber, perhaps containing a fiber Bragg grating (FBG). Thermal accelerometers are known that comprise an enclosure in which a central filament is disposed that is connected to a power supply member delivering electricity, and that lies between two detector filaments connected to a member for comparing the temperatures of the detector filaments. A resonant accelerometer is a sensor that responds to an acceleration force by producing a frequency shifted output signal. Quartz-based resonant accelerometers have been used in many commercial applications, including navigation-grade precisionaccelerometers.
Silicon micro machined acceleration sensors are beginning to replace mechanical acceleration switches. Micro accelerometers typically include a sensor for sensing a proof mass and movements thereof. Micro-accelerometers can be classified as an electric capacity sensing type, a piezo resistance sensing type, a piezoelectricity sensing type and an optical sensing type accelerometer according to the constructions and sensing methods thereof. Advancements in micromachining and other micro fabrication techniques and associated processes have enabled manufacture of a wide variety of micro electromechanical (MEMS) devices. MEMS devices indicate micro scale mechanical devices that are electrically controlled and measured, in which the MEMS is a technique for fabricating mechanical and electrical devices through the semiconductor process. One advantage of micro fabricated sensors is the possibility of large scale production and ensuing lower costs. Another advantage is the small size and weight of the accelerometer. An MEMS accelerometer includes, among other component parts, a proof mass that is resiliently suspended by one or more suspension springs. The proof mass moves when the MEMS accelerometer experiences acceleration. The motion of the proof mass may then be converted into an electrical signal having a parameter magnitude that is proportional to the acceleration. Another type of MEMS accelerometer that is used to sense acceleration is commonly referred to as a teeter-totter capacitive acceleration transducer, or a teeter totter accelerometer. A typical teeter totter accelerometer includes an unbalanced proof mass suspended over a substrate using a fulcrum or other axis. Micro machined structures are frequently used as sensors or actuators and micro machined accelerometers. Among micro machined accelerometers, the differential capacitor type is typically used. A differential-capacitor based accelerometer typically includes a micro machined sensor and its excitation and readout electronics. The micro machined sensor typically includes several primary micro machined elements; a movable mass, support springs, and capacitor plates for sensing the displacement of the movable mass. Often, additional actuator plates are provided to implement a self-test function. The sensitivity of a micro machined accelerometer is determined by a variety of factors, including spring constant, mass of certain elements (e.g., proof mass), sense and parasitic capacitances, and electronic gain.
An accelerometer is a device that measures proper acceleration. Most accelerometers do not display the value, but supply it to other devices. Single- and multi-axis models are available to detect magnitude and direction of the acceleration as a vector quantity, and can be used to sense orientation, acceleration, vibration, shock, and falling. Micro machined accelerometers are increasingly present in portable electronic devices and video game controllers, to detect the position of the device or provide for game input.
An accelerometer measures proper acceleration, which is the acceleration it experiences relative to freefall and is the acceleration felt by people and objects. Put another way, at any point in space time the equivalence principle guarantees the existence of a local inertial frame, and an accelerometer measures the acceleration relative to that frame.[1] Such accelerations are popularly measured in terms of g-force.
An accelerometer at rest relative to the Earth's surface will indicate approximately 1 g upwards, because any point on the Earth's surface is accelerating upwards relative to the local inertial frame (the frame of a freely falling object near the surface). To obtain the acceleration due to motion with respect to the Earth, this "gravity offset" must be subtracted and corrections for effects caused by the Earth's rotation relative to the inertial frame.
For the practical purpose of finding the acceleration of objects with respect to the Earth, such as for use in an inertial navigation system, knowledge of local gravity is required. This can be obtained either by calibrating the device at rest,[3] or from a known model of gravity at the approximate current position. Another, far less common, type of MEMS-based accelerometer contains a small heater at the bottom of a very small dome, which heats the air inside the dome to cause it to rise. A thermocouple on the dome determines where the heated air reaches the dome and the deflection off the center is a measure of the acceleration applied to the sensor.
Most micromechanical accelerometers operate in-plane, that is, they are designed to be sensitive only to a direction in the plane of the die. By integrating two devices perpendicularly on a single die a two-axis accelerometer can be made. By adding an additional out-of-plane device three axes can be measured. Such a combination always has a much lower misalignment error than three discrete models combined after packaging. Micromechanical accelerometers are available in a wide variety of measuring ranges, reaching up to thousands of g's. The designer must make a compromise between sensitivity and the maximum acceleration that can be measured.
Applications:
Accelerometers can be used to measure vehicle acceleration. They allow for performance evaluation of both the engine/drive train and the braking systems. Useful numbers like 0-60 mph, 60-0 mph and 1/4 mile times can all be found using accelerometers. Accelerometers can be used to measure vibration on cars, machines, buildings, process control systems and safety installations. They can also be used to measure seismic activity, inclination, machine vibration, dynamic distance and speed with or without the influence of gravity. Applications for accelerometers that measure gravity, wherein an accelerometer is specifically configured for use in gravimeter, are called gravimeters.
Notebook computers equipped with accelerometers can contribute to the Quake-Catcher Network (QCN), a BOINC project aimed at scientific research of earthquakes.[4]Accelerometers are also increasingly used in the biological sciences. High frequency recordings of bi-axial [5] or tri-axial acceleration [6] (>10 Hz) allows the discrimination of behavioral patterns while animals are out of sight. Furthermore, recordings of acceleration allow researchers to quantify the rate at which an animal is expending energy in the wild, by either determination of limb-stroke frequency[7] or measures such as overall dynamic body acceleration[8] Such approaches have mostly been adopted by marine scientists due to an inability to study animals in the wild using visual observations, however an increasing number of terrestrial biologists are adopting similar approaches. This device can be connected to an amplifier to amplify the signal.
Amplifier:
Generally, an amplifier is any device that will convert a signal with a small amount of energy into a similar signal with a larger amount of energy. In popular use, the term today usually refers to an electronic amplifier, often as in audio applications. The relationship of the input to the output of an amplifier — usually expressed as a function of the input frequency — is called the transfer function of the amplifier, and the magnitude of the transfer function is termed the gain
.General characteristics of amplifiers
Most amplifiers can be characterized by a number of parameters.
Gain
The gain is the ratio of output power to input power, and is usually measured in decibels . (When measured in decibels it is logarithmically related to the power ratio: G(dB)=10log(Pout/Pin)).
Output dynamic range
Output dynamic range is the range, usually given in dB, between the smallest and largest useful output levels. Since the lowest useful level is limited by output noise, this is quoted as the amplifier dynamic range.
Bandwidth and rise time
The bandwidth (BW) of an amplifier is usually defined as the difference between the lower and upper half power points. This is therefore also known as the -3 dB BW. Bandwidths for other response tolerances are sometimes quoted (-1 dB, -6 dB etc.).
A full-range audio amplifier will be essentially flat between twenty hertz to about twenty kilohertz (the range of normal human hearing.) In minimalist amplifier design, the amp's usable frequency response needs to extend considerably beyond this (one or more octaves either side) and typically a good minimalist amplifier will have -3 dB points < 10 and > 65 kHz. Professional touring amplifiers often have input and/or output filtering to sharply limit frequency response beyond 20-20 kHz; too much of the amplifier's potential output power would otherwise be wasted on infrasonic and ultrasonic frequencies, and the danger of AM radio interference would increase. Modern switching amplifiers need steep low pass filtering at the output to get rid of high frequency switching noise and harmonics.
The rise time of an amplifier is the time taken for the output to change from 10% to 90% of its final level when driven by a step input.
Many amplifiers are ultimately slew rate limited (typically by the impedance of a drive current having to overcome capacitive effects at some point in the circuit), which may limit the full power bandwidth to frequencies well below the amplifiers frequency response when dealing with small signals.
For a Gaussian response system (or a simple RC roll off), the rise time is approximated by:
Tr * BW = 0.35, where Tr is in seconds and BW is in Hz.
Settling time and aberrations
Time taken for output to settle to within a certain percentage of the final value (say 0.1%). This is usually specified for oscilloscope vertical amplifiers and high accuracy measurement systems.
Slew rate
Slew rate is the maximum rate of change of output variable, usually quoted in volts per second (or microsecond).
Noise
This is a measure of how much noise is introduced in the amplification process. Noise is an undesirable but inevitable product of the electronic devices and components. It is measured in either decibels or the peak output voltage produced by the amplifier when no signal is applied.
Efficiency
Efficiency is a measure of how much of the input power is usefully applied to the amplifier's output. Class A amplifiers are very inefficient, in the range of 10–20% with a max efficiency of 25%. Class B amplifiers have a very high efficiency but are impractical because of high levels of distortion (See: Crossover distortion). In practical design, the result of a tradeoff is the class AB design. Modern Class AB amps are commonly between 35–55% efficient with a theoretical maximum of 78.5%. Commercially available Class D switching amplifiers have reported efficiencies as high as 97%. The efficiency of the amplifier limits the amount of total power output that is usefully available. Note that more efficient amplifiers run much cooler, and often do not need any cooling fans even in multi-kilowatt designs.
Linearity
An ideal amplifier would be a totally linear device, but real amplifiers are only linear within certain practical limits. When the signal drive to the amplifier is increased, the output also increases until a point is reached where some part of the amplifier becomes saturated and cannot produce any more output; this is called clipping, and results in distortion.
Some amplifiers are designed to handle this in a controlled way which causes a reduction in gain to take place instead of excessive distortion; the result is a compression effect, which (if the amplifier is an audio amplifier) will sound much less unpleasant to the ear. For these amplifiers, the 1 dB compression point is defined as the input power (or output power) where the gain is 1 dB less than the small signal gain.
Linearization is an emergent field, and there are many techniques, such us feed forward, pre distortion, post distortion, EER, LINC, CALLUM, Cartesian feedback, etc., in order to avoid the undesired effects of the non-linearity.
Signal conditioning unit:
The signal conditioning unit accepts input signals from the analog sensors and gives a conditioned output of 0-5V DC corresponding to the entire range of each parameter. This unit also accepts the digital sensor inputs and gives outputs in 10 bit binary with a positive logic level of +5V. The calibration voltages* (0, 2.5 and 5V) and the health bits are also generated in this unit.
Microcontrollers are widely used for control in power electronics. They provide real time control by processing analog signals obtained from the system. A suitable isolation interface needs to be designed for interaction between the control circuit and high voltage hardware. A signal conditioning unit is which provides necessary interface between a high power grid inverter and a low voltage controller unit.
Microcontroller:
PIC microcontroller:
Microcontroller is a general purpose device, which integrates a number of the components of a microprocessor system on to single chip. It has inbuilt CPU, memory and peripherals to make it as a mini computer. A microcontroller combines on to the same microchip:
The CPU core
Memory(both ROM and RAM)
Some parallel digital i/o
Microcontrollers will combine other devices such as:
A timer module to allow the microcontroller to perform tasks for certain time periods.
A serial i/o port to allow data to flow between the controller and other devices such as a PIC or another microcontroller.
An ADC to allow the microcontroller to accept analogue input data for processing.
Microcontrollers are:
Smaller in size
Consumes less power
Inexpensive
Micro controller is a standalone unit ,which can perform functions on its own without any requirement for additional hardware like i/o ports and external memory.
The heart of the microcontroller is the CPU core. In the past, this has traditionally been based on a 8-bit microprocessor unit. For example Motorola uses a basic 6800 microprocessor core in their 6805/6808 microcontroller devices.
In the recent years, microcontrollers have been developed around specifically designed CPU cores, for example the microchip PIC range of microcontrollers.
INTRODUCTION TO PIC:
The microcontroller that has been used for this project is from PIC series. PIC microcontroller is the first RISC based microcontroller fabricated in CMOS (complementary metal oxide semiconductor) that uses separate bus for instruction and data allowing simultaneous access of program and data memory.
The main advantage of CMOS and RISC combination is low power consumption resulting in a very small chip size with a small pin count. The main advantage of CMOS is that it has immunity to noise than other fabrication techniques.
PIC (16F877):
Various microcontrollers offer different kinds of memories. EEPROM, EPROM, FLASH etc. are some of the memories of which FLASH is the most recently developed. Technology that is used in pic16F877 is flash technology, so that data is retained even when the power is switched off. Easy Programming and Erasing are other features of PIC 16F877.
PIC START PLUS PROGRAMMER:
The PIC start plus development system from microchip technology provides the product development engineer with a highly flexible low cost microcontroller design tool set for all microchip PIC micro devices. The pic start plus development system includes PIC start plus development programmer and mplab ide.
The PIC start plus programmer gives the product developer ability to program user software in to any of the supported microcontrollers. The PIC start plus software running under mplab provides for full interactive control over the programmer.
SPECIAL FEATURES OF PIC MICROCONTROLLER:
CORE FEATURES:
• High-performance RISC CPU
• Only 35 single word instructions to learn
• All single cycle instructions except for program branches which are two cycle
• Operating speed: DC - 20 MHz clock input
DC - 200 ns instruction cycle
• Up to 8K x 14 words of Flash Program Memory,
Up to 368 x 8 bytes of Data Memory (RAM)
Up to 256 x 8 bytes of EEPROM data memory
• Pin out compatible to the PIC16C73/74/76/77
• Interrupt capability (up to 14 internal/external
• Eight level deep hardware stack
• Direct, indirect, and relative addressing modes
• Power-on Reset (POR)
• Power-up Timer (PWRT) and Oscillator Start-up Timer (OST)
• Watchdog Timer (WDT) with its own on-chip RC Oscillator for reliable
Operation
• Programmable code-protection
• Power saving SLEEP mode
• Selectable oscillator options
• Low-power, high-speed CMOS EPROM/EEPROM technology
• Fully static design
• In-Circuit Serial Programming (ICSP) via two pins
• Only single 5V source needed for programming capability
• In-Circuit Debugging via two pins
• Processor read/write access to program memory
• Wide operating voltage range: 2.5V to 5.5V
• High Sink/Source Current: 25 mA
• Commercial and Industrial temperature ranges
• Low-power consumption:
< 2mA typical @ 5V, 4 MHz
20mA typical @ 3V, 32 kHz
< 1mA typical standby current
PERIPHERAL FEATURES:
• Timer0: 8-bit timer/counter with 8-bit prescaler
• Timer1: 16-bit timer/counter with prescaler, can be incremented during sleep
Via external crystal/clock
• Timer2: 8-bit timer/counter with 8-bit period register, prescaler and postscaler
• Two Capture, Compare, PWM modules
Capture is 16-bit, max resolution is 12.5 ns,
Compare is 16-bit, max resolution is 200 ns,
PWM max. Resolution is 10-bit
• 10-bit multi-channel Analog-to-Digital converter
• Synchronous Serial Port (SSP) with SPI. (Master Mode) and I2C.
(Master/Slave)
• Universal Synchronous Asynchronous Receiver Transmitter (USART/SCI) with
9- bit address detection.
• Brown-out detection circuitry for Brown-out Reset (BOR)
ARCHITECTURE OF PIC 16F877:
The complete architecture of PIC 16F877 is shown in the fig 2.1. Table 2.1 gives details about the specifications of PIC 16F877. Fig 2.2 shows the complete pin diagram of the IC PIC 16F877.