CHAPTER-1

INTRODUCTIONEnergy harvesting also known aspower harvestingorenergy scavenging is the process by whichenergyis derived from external sources e.g.solar power, thermal energy, wind energy, salinity gradients, and kinetic energy, captured, and stored for small, wireless autonomous devices, like those used inwearable electronicsand wirelesssensor networks. Energy harvesters provide a very small amount of power for low-energy electronics. While the input fuel to some large-scale generation costs money (oil, coal, etc.), the energy source for energy harvesters is present as ambient background and is free. For example, temperature gradients exist from the operation of a combustion engine and in urban areas, there is a large amount of electromagnetic energy in the environment because of radio and television broadcasting.

Over the past two decades, there has been significant interest in converting mechanical energy from human motion into electrical energy. This electrical energy can then be used to Recharge batteries in electronic devices or directly power small scale, Low-power circuits. A number of commercial devices use human power to produce Electricity such as hand-crank generators (for powering Flashlights, radios, and recharging mobile devices), and pedal Generators (that can be used to power larger electrical devices typically generating between 100 and 1000W and can be as high As 1000 W). However, these generators require concentrated human Effort for long periods of time, which might preclude the User from doing other tasks. It is desirable to scavenge or harvest Energy from human movement, while the user is performing His/her everyday activities. Some of the earliest work to harvest energy from human gait Dates back almost 250 years and include the self-winding Watch and closely related modern electromechanical (or so called Electrical) self-winding watches, and various shoe mounted Foot cranks Driven by the potential to power small, portable electronic devices, the first work in self-powered electrical Energy harvesting included electromagnetic vibration in A device carried on the hip, and piezoelectric strain energy Harvesting by a device mounted in the heel of a shoe. This Initial work has lead to substantial interest in gait powered energy Harvesting.CHAPTER-2LITERATURE SURVEY

2.1 INTRODUCTIONEnergy harvesting sources include solar, wind and thermal each with a different optimal size. They either waste much available energy due to impedance mismatch, or they require active digital control that incurs overhead, or they work with only one specific type of source. No more research on the vibration domain. The history of energy harvesting dates back to the windmill and the waterwheel. People have searched for ways to store the energy from heat and vibrations for many decades. One driving force behind the search for new energy harvesting devices is the desire to power sensor networks and mobile devices. Energy harvesting is also motivated by a desire to address the issue of climate change and global warming. Construction cost is high in normal energy harvesting like wind, solar. These systems are not compact. These systems require more storage devices. This paper has investigated the optimal power that can be extracted from human gait over a wide speed range using electromechanical vibration conversion from human movement. Driven by the potential to power small portable electronic devices, more recent research in energy harvesting from gait has focused on 1) increasing the power output 2) energy harvesting from the motion of backpacks during walking, and 3) minimizing energy expenditure by controlling the breaking force.2.2 SALIENT FEATURES OF THE SYSTEM Good output power

Easy Method2.3 OVERALL BLOCK DIAGRAM

Figure.2.1.Overall Block diagramCHAPTER-3 HARDWARE DESIGN DETAILS 3.1 AT89S52 MICROCONTROLLER The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. The device is manufactured using Atmels high-density nonvolatile memory technology and is compatible with the Indus-try-standard 80C51 instruction set and pin out.

3.1.1 Features Compatible with MCS-51 Products

8K Bytes of In-System Programmable (ISP) 4.0V to 5.5V Operating Range

Fully Static Operation: 0 Hz to 33 MHz

Three-level Program Memory Lock

256 x 8-bit Internal RAM

32 Programmable I/O Lines

Three 16-bit Timer/Counters

Eight Interrupt Sources Low-power Idle and Power-down Modes

Interrupt Recovery from Power-down Mode

Watchdog Timer

Dual Data Pointer

Power-off Flag

Fast Programming Time3.1.2 DescriptionThe AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory.

The device is manufactured using Atmels high-density nonvolatile memory technology and is compatible with the Industry-standard 80C51 instruction set and pin out. The Atmel AT89S52 is a powerful microcontroller which provides a highly flexible and cost-effective solution to many embedded control applications.

The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock circuitry.

In addition, the AT89S52 is designed with static logic for operation down to zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue functioning.

The Power-down mode saves the RAM contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset.

3.1.3 Pin Configuration of AT89S52

Figure.3.1.Pin Configuration of AT89S523.1.4 Block Diagram of AT89S52

Figure.3.2. Block Diagram of AT89S523.1.5 Pin DescriptionVCC

Supply voltage pinGND

Ground connection pinPort 0

Port 0 is an 8-bit open drain bidirectional I/O port.Port 1

Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pull-ups and can be used as inputs.Port Pin Alternate Functions P1.0 T2 (external count input to Timer/Counter 2), clock-out P1.1 T2EX (Timer/Counter 2 capture/reload trigger and direction control) P1.5 MOSI (used for In-System Programming) P1.6 MISO (used for In-System Programming) P1.7 SCK (used for In-System Programming)

Port 2

Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the internal pull-ups and can be used as inputs.Port 3

Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the internal pull-ups and can be used as inputs.

RST

Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.ALE/PROG

Address Latch Enable (ALE) is an output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming.

PSEN

Program Store Enable (PSEN) is the read strobe to external program memory. EA/VPP

External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH.XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2

Output from the inverting oscillator amplifier. 3.1.6 Inside a Microcontroller

All the operations within the microcontroller are performed at high speed and quite simply, but the microcontroller itself would not be so useful if there are not special circuits which make it complete. In continuation, we are going to call your attention to them.Read Only Memory (ROM)

Read Only Memory (ROM) is a type of memory used to permanently save the program being executed. The size of the program that can be written depends on the size of this memory.Random Access Memory (RAM)

Random Access Memory (RAM) is a type of memory used for temporary storing data and intermediate results created and used during the operation of the microcontrollers.

The content of this memory is cleared once the power supply is off. For example, if the program performs an addition, it is necessary to have a register standing for what in everyday life is called the sum.Electrically Erasable Programmable ROM (EEPROM)

The EEPROM is a special type of memory not contained in all microcontrollers.

Its contents may be changed during program execution (similar to RAM), but remains permanently saved even after the loss of power (similar to ROM).

It is often used to store values, created and used during operation, which must be saved after turning the power supply off.

A disadvantage of this memory is that the process of programming is relatively slow. It is measured in milliseconds.Special Function Registers (SFR)

Special function registers are part of RAM memory. Their purpose is predefined by the manufacturer and cannot be changed therefore. Since their bits are physically connected to particular circuits within the microcontroller, such as A/D converter, serial communication module etc., any change of their state directly affects the operation of the microcontroller or some of the circuits.Program Counter

Program Counter is an engine running the program and points to the memory address containing the next instruction to execute. After each instruction execution, the value of the counter is incremented by 1.Central Processor Unit (CPU)

As its name suggests, this is a unit which monitors and controls all processes within the microcontroller and the user cannot affect its work. It consists of several smaller subunits. Input/output ports (I/O Ports)

In order to make the microcontroller useful, it is necessary to connect it to peripheral devices. Each microcontroller has one or more registers (called a port) connected to the microcontroller pins.

Why do we call them input/output ports? Because it is possible to change a pin function according to the user's needs. These registers are the only registers in the microcontroller the state of which can be checked by voltmeter.

Oscillator

Figure.3.3.Oscillator circuit of AT89S52

Even pulses generated by the oscillator enable harmonic and synchronous operation of all circuits within the microcontroller. It is usually configured as to use quartz-crystal or ceramics resonator for frequency stabilization.

Timers/Counters

Most programs use these miniature electronic "stopwatches" in their operation. These are commonly 8 or 16 bit SFRs the contents of which are automatically incremented by each coming pulse. Once the register is completely loaded, an interrupt is generated.

If these registers use an internal quartz oscillator as a clock source, then it is possible to measure the time between two events (if the register value is T1 at the moment measurement has started, and T2 at the moment it has finished, then the elapsed time is equal to the result of subtraction T2-T1 ).

If the registers use pulses coming from external source, then such a timer is turned into a counter.Power Supply Circuit

The microcontroller consists of several circuits which have different operating voltage levels, this can cause its out of control performance. In order to prevent it, the microcontroller usually has a circuit for brown out reset built-in.

This circuit immediately resets the whole electronics when the voltage level drops below the lower limit.

Reset pin is usually referred to as Master Clear Reset (MCLR) and serves for external reset of the microcontroller by applying logic zero (0) or one (1) depending on the type of the microcontroller. In case the brown out is not built in the microcontroller, a simple external circuit for brown out reset can be connected to this pin.Serial communication

Parallel connections between the microcontroller and peripherals established over I/O ports are the ideal solution for shorter distances up to several meters.

However, in other cases, when it is necessary to establish communication between two devices on longer distances it is obviously not possible to use parallel connections. Then, serial communication is the best solution.

Today, most microcontrollers have several different systems for serial communication built in as standard equipment.3.1.7 Program

Unlike other integrated circuits which only need to be connected to other components and turn the power supply on, the microcontrollers need to be programmed first.

In order to write a program for the microcontroller, several "low-level" programming languages can be used such as Assembly, C and Basic (and their versions as well). Writing program procedure consists of simple writing instructions in the order in which they should be executed.3.2 POWER SUPPLY

Power supply is a reference to a source of electrical power. A device or system that supplies electrical or other types of energy to an output load or group of loads is called a power supply unit or PSU. The term is most commonly applied to electrical energy supplies, less often to mechanical ones, and rarely to others.

Figure.3.4.Power supplyA 230V, 50Hz Single phase AC power supply is given to a step down transformer to get 12V supply. This voltage is converted to DC voltage using a Bridge Rectifier. The converted pulsating DC voltage is filtered by a 2200f capacitor and then given to 7805 voltage regulator to obtain constant 5V supply. This 5V supply is given to all the components in the circuit. A RC time constant circuit is added to discharge all the capacitors quickly. To ensure the power supply a LED is connected for indication purpose.3.2.1 Bridge rectifierA bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally.

Figure 3.5.Circuit of bridge rectifier

3.2.2 VOLTAGE REGULATORLM7805: 3-Terminal 1A Positive Voltage Regulator

Features Output Current up to 1A

Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V

Thermal Overload Protection

Short Circuit Protection

Output Transistor Safe Operating Area Protection

Figure 3.6.Block diagram of voltage regulator

DescriptionIt employs internal current limiting, thermal shut down and safe operating area protection, making it essentially indestructible. If adequate heat sinking is provided, they can deliver over 1A output current. Although designed primarily as fixed voltage regulators, these devices can be used with external components to obtain adjustable voltages and currents.3.3 ADC 0808The ADC0808, data acquisition component is a monolithic CMOS device with an 8-bit analog-to-digital converter, 8-channel multiplexer and microprocessor compatible control logic. The 8-bit A/D converter uses successive approximation as the conversion technique. The converter features a high impedance chopper stabilized comparator, a 256R voltage divider with analog switch tree and a successive approximation register. The 8-channel multiplexer can directly access any of 8-single-ended analog signals. The device eliminates the need for external zero and full-scale adjustments. Easy interfacing to microprocessors is provided by the latched and decoded multiplexer address inputs and latched TTL TRI-STATE outputs. The design of the ADC0808 has been optimized by incorporating the most desirable aspects of several A/D conversion techniques. The ADC0808 offers high speed, high accuracy, minimal temperature dependence, excellent long-term accuracy and repeatability, and consumes minimal power. These features make this device ideally suited to applications from process and machine control to consumer and automotive applications.3.3.1 Features

Easy interface to all microprocessors

Operates ratio metrically or with 5 VDC or analog span

Adjusted voltage reference

No zero or full-scale adjust required

8-channel multiplexer with address logic

0V to 5V input range with single 5V power supply

Outputs meet TTL voltage level specifications Standard hermetic or molded 28-pin DIP package 28-pin molded chip carrier package ADC0808 equivalent to MM74C949

ADC0809 equivalent to MM74C949-13.3.2 Key Specifications

Resolution 8 Bits

Total Unadjusted Error 12 LSB and 1 LSB

Single Supply 5 VDC3.3.3 Block Diagram of ADC0808

Figure 3.7. Block Diagram of ADC08083.3.4 Pin Diagram of ADC0808

Figure 3.8. Pin Diagram of ADC0808

3.3.5 Functional DescriptionThe device contains an 8-channel single-ended analog signal multiplexer. A particular input channel is selected by using the address decoder. The address is latched into the decoder on the low-to-high transition of the address latch enable signal.3.4 DC-DC CONVERTER

Switching power supplies offer higher efficiency than traditional linear power supplies. They can step-up, step-down, and invert. Some designs can isolate output voltage from the input.The power switch was the key to practical switching regulators. Prior to the invention of the Vertical Metal Oxide Semiconductor (VMOS) power switch, switching supplies were generally not practical.

The inductor's main function is to limit the current slew rate through the power switch. This action limits the high-peak current that would be limited by the switch resistance alone. The key advantage for using an inductor in switching regulators is that an inductor stores energy. This energy can be expressed in Joules as a function of the current by:

E = L I

A linear regulator uses a resistive voltage drop to regulate the voltage, losing power in the form of heat. A switching regulator's inductor does have a voltage drop and an associated current but the current is 90 degrees out of phase with the voltage. Because of this, the energy is stored and can be recovered in the discharge phase of the switching cycle. This results in a much higher efficiency and much less heat.

3.4.1 Switching RegulatorA switching regulator is a circuit that uses a power switch, an inductor, and a diode to transfer energy from input to output. The basic components of the switching circuit can be rearranged to form a step-down, step-up, or an inverter. Feedback and control circuitry can be carefully nested around these circuits to regulate the energy transfer and maintain a constant output within normal operating conditions.Switching regulators offer three main advantages compared to a linear regulators. First, switching efficiency can be much better than linear. Second, because less energy is lost in the transfer, smaller components and less thermal management are required. Third, the energy stored by an inductor in a switching regulator can be transformed to output voltages that can be greater than the input (boost), negative (inverter), or can even be transferred through a transformer to provide electrical isolation with respect to the input. Linear regulators provide lower noise and higher bandwidth; their simplicity can sometimes offer a less expensive solution.There are, admittedly, disadvantages with switching regulators. They can be noisy and require energy management in the form of a control loop. Fortunately the solution to these control problems is found integrated in modern switching-mode controller chips.

3.4.2 EfficiencyOne of the largest power-loss factors for switchers is the rectifying diode. The power dissipated is simply the forward voltage drop multiplied by the current going through it. The reverse recovery for silicon diodes can also create loss. These power losses reduce overall efficiency and require thermal management in the form of a heat sink or fan. To minimize this loss, switching regulators can use Schottky diodes that have a relatively low forward-voltage drop and good reverse recovery. For maximum efficiency, however, we can use a MOSFET switch instead of the diode. This design is known as a 'synchronous rectifier'. The synchronous rectifier switch is open when the main switch is closed, and the same is true conversely. To prevent cross-conduction (both top and bottom switches are on simultaneously), the switching scheme must be break-before-make. Because of this, a diode is still required to conduct during the interval between the opening of the main switch and the closing of the synchronous-rectifier switch (dead time). When a MOSFET is used as a synchronous switch, the current normally flows in reverse (source to drain), and this allows the integrated body diode to conduct current during the dead time. When the synchronous rectifier switch closes, the current flows through the MOSFET channel. Because of the very low-channel resistance for power MOSFETs, the standard forward drop of the rectifying diode can be reduced to a few millivolts. Synchronous rectification can provide efficiencies well above 90%.3.5 LCD3.5.1 Pin Details of LCDVSSGround pinVDDPower supply 5V

VEE

LCD Contrast Adjustment

Control Signals

RS

Register Select

There are 2 very important registers in LCD

Command Code register

Data Register

If, RS=0 Instruction command Code register is selected, allowing user to send command

RS=1 Data register is selected allowing to send data that has to be displayed.

R\W

Read\Write

R\W input allows the user to write information to LCD or read information from it. How do we read data from LCD? The data that is being currently displayed will be stored in a buffer memory DDRAM. This data could be read if necessary.

If, R\W=0, Reading from LCDR\W=1, Writing to LCDE

EnableThe enable Pin is used by the LCD to latch information at its data pins. When data is supplied to data pins, a high to low pulse must be applied to this pin in order for the LCD to latch the data present in the data pins.D0-D7

Data bus 8 bitLED+/LED

Power for Backlighting LEDsWe have to prepare an LCD properly before the character we need, has to be displayed. For this a number of commands have to be provided to the LCD before giving the required data as input.LCD doesnt know about the content (data or commands) supplied to its data bus. It is the user who has to specify whether the content at its data pins are data or commands. For this, if a command is inputted then a particular combination of 0s and 1s has to be applied to the Control lines so as to specify it is a Command on the other hand if a data is inputted at the data lines then an another combination of 0s and 1s has to be applied to the control lines to specify it is Data. The combinations are as follows-

If,Command - RS=0, R\W=0, E=1\0

Data- RS=1, R\W=0, E=1\0

3.5.2 Pin Configuration of the LCD interface

Figure 3.9. Pin Configuration of the LCD interface3.5.3 Programming Steps Before sending Data to be displayed to the LCD, it should be prepared to hold that particular value.

For this certain initializations are to be done as per the Instructions.

Move Value 0X38, 3 times.( Applied max 3 times due to rise time factor)

Move Value 0X06, 1 time.

Move Value 0X0F, 1 time.

After each initializations command function and delay should be called.

After Initialization Move Data to the LCD

Call the Data Function and delay.

3.6 MEMS (Micro Electro-Mechanical Structure)In less than 20 years, MEMS (micro electro-mechanical systems) technology has gone from an interesting academic exercise to an integral part of many common products. But as with most new technologies, the practical implementation of MEMS technology has taken a while to happen. In early MEMS systems a multi-chip approach with the sensing element (MEMS structure) on one chip, and the signal conditioning electronics on another chip was used. The latest generation ADXL2O2E is the result of almost a decades worth of experience building integrated MEMS accelerometers. It is the world's smallest mass-produced, low cost, integrated MEMS dual axis accelerometer. Polysilicon springs suspend the MEMS structure above the substrate such that the body of the sensor (also known as the proof mass) can move in the X and Y axes. Acceleration causes deflection of the proof mass from its centre position. Around the four sides of the square proof mass are 32 sets of radial fingers. These fingers are positioned between plates that are fixed to the substrate. Each finger and pair of fixed plates make up a differential capacitor, and the deflection of the proof mass is determined by measuring the differential capacitance. This sensing method has the ability of sensing both dynamic acceleration (i.e. shock or vibration) and static acceleration (i.e. inclination or gravity).The differential capacitance is measured using synchronous modulation/demodulation techniques. After amplification, the X and Y axis acceleration signals each go through a 32KOhm resistor to an output pin (Cx and Cy) and a duty cycle modulator. The user may limit the bandwidth, and thereby lower the noise floor, by adding a capacitor at the Cx and Cy pin. The output signals are voltage proportional to acceleration and pulse-width-modulation (PWM) proportional to acceleration. Using the PWM outputs, the user can interface the ADXL2O2 directly to the digital inputs of a microcontroller using a counter to decode the PWM.

Figure.3.10.Block Diagram of Accelerometer

3.6.1 The Users Challenge: MEMS sensors, like almost all electronic devices, do not exhibit ideal behavior. While most designers have learned how to handle the non-ideal behavior of op-amps and transistors, few have learned the design techniques used to compensate for non-ideal MEMS behavior. In most cases, this type of information is not available in textbooks or courses, as the technology is quite new. So generally designers must get this type of information from the MEMS manufacturer. Analog Devices, for example, maintains a web site with design tools, reference designs, and dozens of application notes specific to its MEMS accelerometers to ease the users work.

3.7 PIEZOELECTRIC PLATEApiezoelectric plate is a device that uses thepiezoelectric effectto measurepressure, acceleration,strainorforceby converting them to anelectricalcharge.Piezoelectricity, also called the piezoelectric effect, is the ability of certain materials to generate anAC(alternating current)voltagewhen subjected to mechanical stress or vibration, or to vibrate when subjected to an AC voltage, or both. The most common piezoelectric material is quartz. Certain ceramics, Rochelle salts, and various other solids also exhibit this effect.A piezoelectrictransducercomprises a "crystal" sandwiched between two metal plates. When a sound wave strikes one or both of the plates, the plates vibrate. The crystal picks up this vibration, which it translates into a weak AC voltage. Therefore, an AC voltage arises between the two metal plates, with awaveformsimilar to that of the sound waves. Conversely, if an AC signal is applied to the plates, it causes the crystal to vibrate in sync with the signal voltage. As a result, the metal plates vibrate also, producing an acoustic disturbance.

3.7.1 Principle of operationDepending on how a piezoelectric material is cut, three main modes of operation can be distinguished: transverse, longitudinal, and shear.Transverse effect

A force is applied along a neutral axis (y) and the charges are generated along the (x) direction, perpendicular to the line of force. The amount of charge depends on the geometrical dimensions of the respective piezoelectric element. When dimensions apply,

,

Where the dimension in line with the neutral axis is,is in line with the charge generating axis andis the corresponding piezoelectric coefficient.

Longitudinal effect

The amount of charge produced is strictly proportional to the applied force and is independent of size and shape of the piezoelectric element. Using several elements that are mechanically in series and electrically inparallelis the only way to increase the charge output. The resulting charge is,

wheredxxis the piezoelectric coefficient for a charge in x-direction released by forces applied along x-direction.Fxis the applied Force in x-direction [N] andncorresponds to the number of stacked elements.3.7.2 ApplicationPiezoelectric sensors have proven to be versatile tools for the measurement of various processes. They are used forquality assurance,process controland for research and development in many different industries. Although the piezoelectric effect was discovered by Pierre Curiein 1880, it was only in the 1950s that the piezoelectric effect started to be used for industrial sensing applications. Since then, this measuring principle has been increasingly used and can be regarded as amature technologywith an outstanding inherent reliability. It has been successfully used in various applications, such as inmedical, aerospace,nuclearinstrumentation, and as a pressure sensor in the touch pads of mobile phones. In theautomotive industry, piezoelectric elements are used to monitor combustion when developinginternal combustion engines. The sensors are either directly mounted into additional holes into the cylinder head or the spark/glow plug is equipped with a built in miniature piezoelectric sensor.

The rise of piezoelectric technology is directly related to a set of inherent advantages. The highmodulus of elasticityof many piezoelectric materials is comparable to that of many metals and goes up to106N/m. Even though piezoelectric sensors are electromechanical systems that react tocompression, the sensing elements show almost zero deflection. This is the reason why piezoelectric sensors are so rugged, have an extremely high natural frequency and an excellent linearity over a wideamplituderange. Additionally, piezoelectric technology is insensitive toelectromagnetic fieldsandradiation, enabling measurements under harsh conditions. Some materials used (especiallygallium phosphateortourmaline) have an extreme stability even at high temperature, enabling sensors to have a working range of up to1000 C. Tourmaline showspyroelectricityin addition to the piezoelectric effect; this is the ability to generate an electrical signal when the temperature of the crystal changes. This effect is also common topiezo ceramic materials.3.8 RELAY

A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays have two switch positions and they are double throw (changeover) switches.

Relays allow one circuit to switch a second circuit which can be completely separate from the first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no electrical connection inside the relay between the two circuits; the link is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC current to the larger value required for the relay coil. The maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils directly without amplification.

Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example relays with 4 sets of changeover contacts are readily available. For further information about switch contacts and the terms used to describe them please see the page on switches.

Most relays are designed for PCB mounting but you can solder wires directly to the pins providing you take care to avoid melting the plastic case of the relay.

3.8.1 Advantages of relays Relays can switch AC and DC, transistors can only switch DC.

Relays can switch high voltages, transistors cannot.

Relays are a better choice for switching large currents (>5A).

Relays can switch many contacts at once.

3.8.2 Disadvantages of relays Relays are bulkier than transistors for switching small currents.

Relays cannot switch rapidly (except reed relays), transistors can switch many times per second.

Relays use more power due to the current flowing through their coil.

Relays require more current than many ICs can provide.3.9 SUPER CAPACITORSuper capacitors also called ultra capacitors and electric double layer capacitors (EDLC) are capacitors with capacitance values greater than any other capacitor type available today. Capacitance values reaching up to 400 Farads in a single standard case size are available. Super capacitors have the highest capacitive density available today with densities so high that these capacitors can be used to applications normally reserved for batteries. Super capacitors are not as volumetrically efficient and are more expensive than batteries but they do have other advantages over batteries making the preferred choice in applications requiring a large amount of energy storage to be stored and delivered in bursts repeatedly.

3.9.1 Advantages

Power density

Recycle ability

Environmentally friendly

Safe

Light weight

The most significant advantage super capacitors have over batteries is their ability to be charged and discharged continuously without degrading like batteries do. This is why batteries and super capacitors are used in conjunction with each other. The super capacitors will supply power to the system when there are surges or energy bursts since super capacitors can be charged and discharged quickly while the batteries can supply the bulk energy since they can store and deliver larger amount energy over a longer slower period of time.

3.9.2 Super capacitor construction

What makes super capacitors different from other capacitors types are the electrodes used in these capacitors. Super capacitors are based on a carbon (nanotube) technology. The carbon technology used in these capacitors creates a very large surface area with an extremely small separation distance. Capacitors consist of 2 metal electrodes separated by a dielectric material. The dielectric not only separates the electrodes but also has electrical properties that affect the performance of a capacitor. Super capacitors do not have a traditional dielectric material like ceramic, polymer films or aluminum oxide to separate the electrodes but instead have a physical barrier made from activated carbon that when an electrical charge is applied to the material a double electric field is generated which acts like a dielectric. The thickness of the electric double layer is as thin as a molecule. The surface area of the activated carbon layer is extremely large yielding several thousands of square meters per gram. This large surface area allows for the absorption of a large amount of ions. The charging/discharging occurs in an ion absorption layer formed on the electrodes of activated carbon. The activated carbon fiber electrodes are impregnated with an electrolyte where positive and negative charges are formed between the electrodes and the impregnant. The electric double layer formed becomes an insulator until a large enough voltage is applied and current begins to flow. The magnitude of voltage where charges begin to flow is where the electrolyte begins to break down. This is called the decomposition voltage.

The double layers formed on the activated carbon surfaces can be illustrated as a series of parallel RC circuits. As shown below the capacitor is made up of a series of RC circuits where R1, R2 Rn are the internal resistances and C1, C2..., Cn are the electrostatic capacitances of the activated carbons. When voltage is applied current flows through each of the RC circuits. The amount of time required to charge the capacitor is dependent on the CxR values of each RC circuit. Obviously the larger the CxR the longer it will take to charge the capacitor. The amount of current needed to charge the capacitor is determined by the following equation:

In= (V/Rn) exp (-t/ (Cn*Rn))

3.9.3 Equivalent circuit

Super capacitors can be illustrated similarly to conventional film, ceramic or aluminum electrolytic capacitors. This equivalent circuit is only a simplified or first order model of a super capacitor. In reality super capacitors exhibit a non ideal behavior due to the porous materials used to make the electrodes. This causes super capacitors to exhibit behavior more closely to transmission lines than capacitors. Below is a more accurate illustration of the equivalent circuit for a super capacitor.

3.9.4 How to measure the capacitance of a super capacitorThere are a couple of ways used to measure the capacitance of super capacitors.

1. Charge method

2. Charging and discharging method.

Charge method

Measurement is performed using a charge method using the following formula.

C=t/R

t= .632Vo where Vo is the applied voltage.

Charge and Discharge method

This method is similar to the charging method except the capacitance is calculated during the discharge cycle instead of the charging cycle. Discharge time for constant current discharge

t= Cx (V0-V1)/I

Discharge time for constant resistance discharge,t= CRln (V1/V0)

Where t= discharge time, V0= initial voltage, V1= ending voltage, I= current.

3.9.5 Capacitance

Super capacitors have such large capacitance values that standard measuring equipment cannot be used to measure the capacity of these capacitors. Capacitance is measured as per the following method:

1. Charge capacitor for 30 minutes at rated voltage.

2. Discharge capacitor through a constant current load.

3. Discharge rate to be 1mA/F.

4. Measure voltage drop between V1 to V2.

5. Measure time for capacitor to discharge from V1 to V2.

6. Calculate the capacitance using the following equation:

C= I*(T2-T1)

V1-V2

Where V1=0.7Vr, V2=0.3Vr (Vr= rated voltage of capacitor)3.9.6 Life expectancy

The life expectancy of super capacitors is identical to aluminum electrolytic capacitors. The life of super capacitors will double for every 10C decrease in the ambient temperature the capacitors are operated in. Super capacitors operated at room temperature can have life expectancies of several years compared to operating the capacitors at their maximum rated temperature.

L2=L1*2X X=Tm-TaL1= Load life rating of the super capacitor.

L2= expected life at operating condition.

Tm= Maximum temperature rating of the super capacitor.

Ta= Ambient temperature the super capacitor is going to be exposed to in the application.3.9.7 Applications for Super capacitorsSuper capacitors have found uses include:

Computer systems

UPS systems

Power conditioners

Welders

Inverters

Automobile regenerative braking systems

Power supplies

Cameras

Power generatorsCHAPTER-4SOFTWARE ANALYSIS4.1 Introduction The main purpose of using the microcontroller in our project is because high-performance CMOS 8-bit microcontroller with 8K bytes of in-system programmable Flash memory. By combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful microcontroller which provides a highly-flexible and cost-effective solution to many embedded control applications.

The programs of the microcontroller have been written in Embedded C language and were compiled using KEIL, a compiler used for microcontroller programming. The communication between PC and the microcontroller was established MAX 232 standard and those programs were also done in C language.

The following programs are used at various stages for the mentioned functions Serial communication In this program, the various special function registers of the microcontroller are set such that they can send and receive data from the PC. This program uses the serial library to communicate with the ports.

4.2 KEIL compiler The C programming language is a general-purpose, programming language that provides code efficiency, elements of structured programming, and a rich set of operators. C is not a big language and is not designed for any one particular area of application. Its generality combined with its absence of restrictions, makes C a convenient and effective programming solution for a wide variety of software tasks. Many applications can be solved more easily and efficiently with C than with other more specialized languages. The Cx51 Optimizing C Compiler is a complete implementation of the American National Standards Institute (ANSI) standard for the C language. Cx51 is not a universal C compiler adapted for the 8051 target. It is a ground-up implementation dedicated to generating extremely fast and compact code for the 8051 microprocessor. Cx51 provides you the flexibility of programming in C and the code efficiency and speed of assembly language. Since Cx51 is a cross compiler, some aspects of the C programming language and standard libraries are altered or enhanced to address the peculiarities of an embedded target processor.

4.2.1 Support for all 8051 Variants The 8051 Family is one of the fastest growing Microcontroller Architectures. More than 400 device variants from various silicon vendors are today available. New extended 8051 Devices, like the Philips 80C51MX architecture are dedicated for large application with several Mbytes code and data space. For optimum support of these different 8051 variants, Keil provides the several development tools. A new output file format (OMF2) allows direct support of up to 16MB code and data space. The CX51 compiler is a variant of the C51 compiler that is design for the new Philips 80C51MX architecture.

4.3 Compiling with Cx51 This explains how to use Cx51 to compile C source files and discusses the control directives you may specify. These directives allow you to perform several functions.4.3.1 Running Cx51 from the Command Prompt

To invoke the C51 or CX51 compiler, enter C51 or CX51 at the command prompt. On this command line, you must include the name of the C source file to be compiled, as well as any other necessary control directives required to compile your source file.

The format for the Cx51 command line is shown below:

C51 source file _directives_

CX51 source file _directives_

or:

C51 @command file

CX51 @command file

where:

source file is the name of the source program you want to compile.

directives are the directives you want to use to control the function of the

compiler.

Command file is the name of a command input file that may contain sourcefile and directives. A command file is used, when the Cx51 invocation line gets complex and exceeds the limits of the Windows command prompt.

The following command line example invokes C51, specifies the source file

SAMPLE.C, and uses the controls DEBUG, CODE, and PREPRINT.

C51 SAMPLE.C DEBUG CODE PREPRINT

The Cx51 compiler displays the following information upon successful

invocation and compilation.

C51 COMPILER V6.10

C51 COMPILATION COMPLETE. 0 WARNING(S), 0 ERROR(S)

4.4 8051 Derivatives A number of 8051 derivatives are available that provide enhanced performance while remaining compatible with the 8051 core. These derivatives provide additional data pointers, very fast math operations, and reduced instruction sets.

The Cx51 compiler directly supports the enhanced features of the following 8051-based microcontrollers:

Atmel 89x8252 and variants (2 data pointers).

Dallas 80C320, 80C420, 80C520, 80C530, 80C550 an variants (2 data pointers).

Infineon C517, C517A, C509, and variants (high-speed 32-bit and 16-bit binary arithmetic operations, 8 data pointers).

Philips 8xC750, 8xC751, and 8xC752 (maximum code space of 2 KBytes, no LCALL or LJMP instructions, 64 bytes internal, no external data memory).

Philips and Temic support on several device variants 2 data pointers.

The C51 compiler provides you with support for these CPUs through the use of special libraries, library routines, and the MODxxx command-line directives. These directives enable C51 to generate object code that takes advantage of the enhancements mentioned above.

4.5 Atmel 89x8252 and variants The Atmel 89x8252 and variants provide 2 data pointers which can be used for memory access. Using multiple data pointers can improve the speed of library functions like memcpy, memmove, memcmp, strcpy, and strcmp.

The MODA2 control directive instructs the C51 compiler to generate code that uses both data pointers in your program.

The C51 compiler uses at least one data pointer in an interrupt function. If an interrupt function is compiled using the MODA2 directive, both data pointers are saved on the stack. This happens even if the interrupt function uses only one data pointer.

To conserve stack space, you may compile interrupt functions with the NOMODA2 directive. The C51 compiler does not use the second data pointer when this directive is used.CHAPTER-5RESULT

Figure.5.1. Vibration energy conversion from human gait

The mechanical force applied to the piezo plates and accelerometer is converted into electrical energy. This energy is stored in the rechargeable battery via super capacitor. The stored energy is inverted into alternating current using invertor and makes the bulb glow. 5.1 CONCLUSIONAn alternative solution for energy harvesting is proposed in this application. Electrical energy is produced from vibration energy. The boost up level of the electrical energy is given by the controller according to the output from the vibration source. This is carried by the microcontroller. The boosted up energy is given to the load after conversion of DC to AC. The controlling process is done in software using embedded C. The energy produced can also be monitored using LCD. The whole process is implemented in hardware.REFERENCES

[1] J. A. Paradiso and T. Starner, Energy scavenging for mobile and wireless electronics, IEEE Pervasive Comput., vol. 4, no. 1, pp. 1827, Jan./Mar.2005.

[2] R.Amirtharajah andA. P. Chandrakasan, Self-Powered signal processing using vibration-based power generation, IEEE J. Solid-State Circuits, vol. 33, no. 5, pp. 687695, May 1998.

[3] J. Kymissis, C. Kendall, J. Paradiso, and N. Gershenfeld, Parasitic power harvesting in shoes, in 2nd Int. Symp. Wearable Comput. Dig. Papers, 1988, pp. 132139.

[4] A. Khaligh, P. Zeng, and C. Zheng, Kinetic energy harvesting using piezoelectric and electromagnetic technologiesState of the art, IEEETrans. Ind. Electron., vol. 57, no. 3, pp. 850860, Mar. 2010.

[5] P. D. Mitcheson, E. M. Yeatman, G. K. Rao, A. Holmes, and T. C. Green, Energy harvesting from human and machine motion for wireless electronic devices, Proc. IEEE, vol. 96, no. 9, pp. 14571486, Sep. 2008.

[6] L. C. Rome, L. Flynn, E. M. Goldman, and T. D. Yoo, Generating electricity while walking with loads, Science, vol. 309, pp. 17251728, 2005.

[7] J. M. Donelan, Q. Li, V. Naing, J. A. Hoffer, D. J. Weber, and A. D. Kuo, Biomechanical energy harvesting: generating electricity during walking with minimal user effort, Science, vol. 319, pp. 807810, 2008.

[8] T. von Buren, P. D.Mitcheson, T. C. Green, E.M. Yeatman, A. S. Holmes, andG. Troster, Optimization of inertial micropower generators for human walking motion, IEEE Sens. J., vol. 6, no. 1, pp. 2838, Feb. 2006.

[9] S. Adhikari, M. I. Friswell, and D. J. Inman, Piezoelectric energy harvesting from broadband random vibrations, SmartMater. Struct., vol. 19, p. 115005, 2009.

[10] S. Priya and D. J. Inman, Energy Harvesting Technologies. NewYork: Springer, 2009LCD

STORAGE DEVICE

RELAY

AC LOAD

ADC

INVERTER (DC-AC)

SUPER CAPACITOR

ATMEL AT89S52

DC-DC BOOSTER

Accelerometr

Vibration source

Piezo plate

39