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1. INTRODUCTION
1.1 Human transporter:
A Human transporter (HT) system is an eco-friendly e-bike which mainly aims to transport a person for small distant paths designed in an innovative way. The project is proposed to present a completely different and a lot interesting way to get around the surroundings.
Human transporter basically aimed to drive a normal human being (with an avg wt. of 75kg) through short distances, for that purpose the components used are 2 high torque DC gear motors (embedded with efficient wheel set) which are supplied by a battery (or more specifically UPS) through some stabilization circuitry and a caster wheel as the third wheel at the centre to balance the vehicle. That was the mechanical side of the Human transporter, now to control all its operations the ATMEL`s an 8-bit microcontroller is used for interfacing with all the parts of the human transporter. Additionally a pair of TSOP (the IR sensors) is used to protect the transporter to collide with any wall or any obstruction in its path (obstacle avoidance technique), an LCD display to inform the user about various things (like direction indicator, low battery warnings……..). The physical appearance of the human transporter is similar to a normal hand truck set straight up, with a T-shaped handle bar and the aluminum base box containing the battery and control circuit.
This project is mainly determined to introduce a dual mode drive for the human transporter, namely the manual mode and the auto-mode. Manual mode is a default way for driving the human transporter, where we control the human transporter using the keypad on the handle bar. There are four keys to drive the vehicle in four directions correspondingly, the basic principle is the differential drive technique where the rotation of alternate wheels is the key part to steer the human transporter in all the directions. On the other side, the auto mode deals with driving the human transporter automatically following a pre-fetched path, this is rather used in industrial processes where a specific transportation of a material is repeatedly done, instead of transporting a human. Along
with these things there is an additional feature of obstacle avoidance; using this feature the human transporter is capable of driving safe without any collision, this is made possible by making use the IR sensors. The technical details about the peripherals along with the working principle are covered in the further chapters.
2. PROJECT DESCRIPTION
This chapter deals with the physical description and the principle of operation of the device in detail theoretically. Description starts with the basic block diagram of the human transporter with a detailed explanation of each block and then about each part of the block along with the total specifications and various technical data about each of them.
The following schematic shows the block diagram of the human transporter
2.1(a) Block diagram
2.1(b)HARDWARE COMPONENTS:
2.2 POWER SUPPLY
2.2 VOLTAGE REGULATOR
2.4 VOICE RECOGNITION
2.5 MICRO CONTROLLER
2.6 DRIVER CIRCUIT
2.7 LCD
2.8 KEYPAD
2.9 MOTOR
2.2 Power supply:
The main task of HT is to drive the high torque motors and to provide a digital voltage level to drive various ICs, and hence the power supply is provided from a DC battery source. In order to build up enough current and supply sufficient voltage we use a parallel combination of two batteries of rating 12V, 8Ahr so that a cumulative current of 16Ahr and a constant 12V voltage is produced. These batteries can be recharged after they are used each and every time.
The parallel combination of the two batteries is connected to a Voltage regulator circuit which produces a constant 5V output which helps in driving the digital ICs of the circuit. On the other hand the motors are supplied by 12V, 16Ah through a driver circuit which is directly connected to the parallel combination of the batteries.
2.3 VOLATGE REGULATOR:
2.3.1 Voltage regulator:
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. It may use an electromechanical mechanism, or passive or active electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.
With the exception of passive shunt regulators, all modern electronic voltage regulators operate by comparing the actual output voltage to some internal fixed reference voltage. Any difference is amplified and used to control the regulation element in such a way as to reduce the voltage error. This forms a negative feedback control loop; increasing the open-loop gain tends to increase regulation accuracy but reduce stability (avoidance of oscillation, or ringing during step changes). There will also be a trade-off between stability and the speed of the response to changes. If the output voltage is too low (perhaps due to input voltage reducing or load current increasing), the regulation element is commanded, up to a point, to produce a higher output voltage - by dropping less of the input voltage (for linear series regulators and buck switching regulators), or to draw input current for longer periods (boost-type switching regulators); if the output voltage is too high, the regulation element will normally be commanded to produce a lower voltage. However, many regulators have over-current protection, so that they will entirely stop sourcing current (or limit the current in some way) if the output current is too high, and some regulators may also shut down if the input voltage is outside a given range (see also: crowbar circuits).
2.3.2 Measures of regulator quality:
The output voltage can only be held roughly constant; the regulation is specified by two measurements:
• load regulation is the change in output voltage for a given change in load current (for example: "typically 15mV, maximum 100mV for load currents between 5mA and 1.4A, at some specified temperature and input voltage").
• line regulation or input regulation is the degree to which output voltage changes with input (supply) voltage changes - as a ratio of output to input change (for example "typically 13mV/V"), or the output voltage change over the entire specified input voltage range (for example "plus or minus 2% for input voltages between 90V and 260V, 50-60Hz").
Other important parameters are:
• Temperature coefficient of the output voltage is the change in output voltage with temperature (perhaps averaged over a given temperature range), while...
• Initial accuracy of a voltage regulator (or simply "the voltage accuracy") reflects the error in output voltage for a fixed regulator without taking into account temperature or aging effects on output accuracy.
• Dropout voltage - the minimum difference between input voltage and output voltage for which the regulator can still supply the specified current. A Low Drop-Out (LDO) regulator is designed to work well even with an input supply only a Volt or so above the output voltage.
• Absolute Maximum Ratings are defined for regulator components, specifying the continuous and peak output currents that may be used (sometimes internally limited), the maximum input voltage, maximum power dissipation at a given temperature, etc.
• Output noise (thermal white noise) and output dynamic impedance may be specified as graphs versus frequency, while output ripple noise (mains "hum" or switch-mode "hash" noise) may be given as peak-to-peak or RMS voltages, or in terms of their spectra.
In older electromechanical regulators, voltage regulation is easily accomplished by coiling the sensing wire to make an electromagnet. The magnetic field produced by the current attracts a moving ferrous core held back under spring tension or gravitational pull. As voltage increases, so does the current, strengthening the magnetic field produced by the coil and pulling the core towards the field. The magnet is physically connected to a mechanical power switch, which opens as the magnet moves into the field. As voltage decreases, so does the current, releasing spring tension or the weight of the core and causing it to retract. This closes the switch and allows the power to flow once more.If the mechanical regulator design is sensitive to small voltage fluctuations, the motion of the solenoid core can be used to move a selector switch across a range of resistances or transformer windings to gradually step the output voltage up or down, or to rotate the position of a moving-coil AC regulator.
Early automobile generators and alternators had a mechanical voltage regulator using one, two, or three relays and various resistors to stabilize the generator's output at slightly more than 6 or 12 V, independent of the engine's rpm or the varying load on the vehicle's electrical system. Essentially, the relay(s) employed pulse width modulation to regulate the output of the generator, controlling the field current reaching the generator (or alternator) and in this way controlling the output voltage produced. The regulators used for generators (but not alternators) also disconnect the generator when it was not producing electricity, thereby preventing the battery from discharging back into the generator and attempting to run it as a motor. The rectifier diodes in an alternator automatically perform this function so that a specific relay is not required; this appreciably simplified the regulator design.
More modern designs now use solid state technology (transistors) to perform the same function that the relays perform in electromechanical regulators.
2.3.3 Active regulators:
Active regulators employ at least one active (amplifying) component such as a transistor or operational amplifier. Shunt regulators are often (but not always) passive and simple, but always inefficient because they (essentially) dump the excess current not needed by the load. When more power must be supplied, more sophisticated circuits are used. In general, these active regulators can be divided into several classes:
• Linear series regulators
• Switching regulators
• SCR regulators
2.3.3(a) Linear regulators:
Linear regulators are based on devices that operate in their linear region (in contrast, a switching regulator is based on a device forced to act as an on/off switch). In the past, one or more vacuum tubes were commonly used as the variable resistance. Modern designs use one or more transistors instead, perhaps within an Integrated Circuit. Linear designs have the advantage of very "clean" output with little noise introduced into their DC output, but are most often much less efficient and unable to step-up or invert the input voltage like switched supplies.
Entire linear regulators are available as integrated circuits. These chips come in either fixed or adjustable voltage types.
2.3.3(b) Switching regulators:
Switching regulators rapidly switch a series device on and off. The duty cycle of the switch sets how much charge is transferred to the load. This is controlled by a similar feedback mechanism as in a linear regulator. Because the series element is either fully conducting, or switched off, it dissipates almost no power; this is what gives the switching design its efficiency. Switching regulators are also able to generate output voltages which are higher than the input, or of opposite polarity something not possible with a linear design.
Like linear regulators, nearly-complete switching regulators are also available as integrated circuits. Unlike linear regulators, these usually require one external component: an inductor that acts as the energy storage element. (Large-valued inductors tend to be physically large relative to almost all other kinds of component, so they are rarely fabricated within integrated circuits and IC regulators with some exceptions.
2.3.4 Comparing linear vs. switching regulators:
The two types of regulators have their different advantages:
1. Linear regulators are best when low output noise (and low RFI radiated noise) is required
2. Linear regulators are best when a fast response to input and output disturbances is required.
3. At low levels of power, linear regulators are cheaper and occupy less printed circuit board space.
4. Switching regulators are best when power efficiency is critical (such as in portable computers), except linear regulators are more efficient in a small number of cases (such as a 5V microprocessor often in "sleep" mode fed from a 6V battery, if the complexity of the switching circuit and the junction capacitance charging current means a high quiescent current in the switching regulator).
5. Switching regulators are required when the only power supply is a DC voltage, and a higher output voltage is required.
6. At high levels of power (above a few watts), switching regulators are cheaper (for example, the cost of removing heat generated is less).
In order to drive various chips of the HT circuit we need a constant 5V of voltage. This 5V of regulated output is generated by using LM7805 voltage regulator IC which is easily available, low cost and very simple to use. The input may be given from a battery of some DC volts with respect to ground and the output generated will be a constant 5V supply.