wireless control of powered wheelchair using tongue report,tongue drive system report,tds...

TDS 2013 – 2014

Department of Electronics and Communication, Sir MVIT

CHAPTER 1

INTRODUCTION

Tongue Drive system (TDS) is a tongue-operated unobtrusive assistive technology, which can

potentially provide people with severe disabilities with effective access and environment

control. It translates user’s intentions in to control commands by detecting and classifying their

voluntary tongue motion utilizing a small permanent magnet, secured on the tongue, and an

array of magnetic sensors mounted on a headset outside the mouth or an orthodontic brace

inside. Customized interface circuitry had been developed and four control strategies to drive

a powered wheel chair (PWC) using an external TDS prototype is implemented.

Persons with severe disabilities as a result of causes ranging from traumatic brain and spinal

cord injuries (TBI/SCI) to amyotrophic lateral sclerosis (ALS) and stroke generally find it

extremely difficult to carry out daily tasks without receiving continuous help. These individuals

are completely dependent on wheeled mobility for transportation inside and out of their homes.

Many of them use electrically powered wheelchairs (PWC) that are the most helpful tools

allowing individuals to complete daily tasks with greater independence, and to access school,

work, and community environments. Unfortunately, the default method for controlling PWCs

is by operating a joystick, which requires a certain level of physical movement ability, which

may not exist in people with severe disabilities.

The magnetic sensors are nothing but hall-effect sensors. A Hall Effect sensor is a transducer

that varies its output voltage in response to changes in magnetic field. In its simplest form, the

sensor operates as an analogue transducer, directly returning a voltage. This Project consists of

a Microcontroller Units, Wheel chair and Hall Effect sensor. Wheel chair is made up of High

torque Geared DC Motors, the Motors Directions can be changed through the set of instructions

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given from the Hall Effect sensor and the action of these Instructions is already loaded into the

Microcontroller using Embedded C programming.

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CHAPTER 2

LITERATURE SURVEY

2.1 EXISTING ASSISTIVE TECHNOLOGIES

2.1.1 SIP – AND – PUFF WHEELCHAIR

The Sip-and-Puff system is a method of sending signals to a device using air pressure. The

signals are conveyed by "sipping", or inhaling, and “puffing", or exhaling, into a wand as

demonstrated in Figure 2.1. The system is used for a variety of purposes, ranging from basic

wheelchair commands to sports, like hunting.

When used for controlling an electric wheelchair there are typically four different inputs from

the user used in various patterns described as follows. An initial hard puff will enable the chair

to move forward, while a hard sip will stop the wheelchair. Conversely, an initial hard sip will

enable the wheelchair to move backward, while a hard puff will stop the wheelchair. A

continuous soft sip or soft puff will enable the wheelchair to move left or right, respectively,

depending on how long the user blows into the wand.

The main problem with this mode of control is the range in breathing capability across the

spectrum of consumers. The system is calibrated to respond to hard and soft puffs and sips, and

for individuals that have problems controlling their breathing, achieving the hard puffs or sips

with consistency can be difficult

Fig 2.1 Sip – and – Puff System

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2.1.2 HUMMING AND SPEECH RECOGNITION

Another alternative is powering the chair through speech or humming. A version for this option

is being constructed at George Mason University in Virginia (prototype miniature shown in

Figure 2.2). The configuration on this prototype is two digital signal processors mounted on a

custom printed circuit board to perform humming and speech recognition.

The main problem with this method is that many people have difficulty with speech recognition

software in general, because speech recognition varies due to many documented reasons

including: accent, pronunciation, articulation, roughness, nasality, pitch, volume, and speed.

Furthermore, speech is distorted by a background noise, echoes, and electrical characteristics

that cannot always be recognized and filtered out by the system. The humming recognition

attempts to compensate for the lack of accuracy in the speech recognition but limits the quantity

of commands the system can be programmed for.

Fig 2.2 Small Scale Prototype of George Mason University’s Humming and Speech

Recognition Wheelchair System

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2.1.3 HEAD/CHIN CONTROLLED SYSTEM

The Head or chin controls are very invasive alternatives to a joystick. The system requires

constant pressure to be applied to the sensor. The sensor is either a ball placed near the chin or

a pad placed at the lower back of the head (Figure 2.3).

In head control devices, switches are mounted in the headrest and activated by head

movements. Ideally the system has six commands: mode, power (on-off/emergency stop), and

the four directional controls. By being in proximity to the switch in the centre pad, the patient

moves the wheelchair forward. Activating the side pads moves the chair in the corresponding

direction. A reset switch toggles between the forward and reverse functions. Some new head

controllers can detect the position and movement of the head using ultrasonic transducers or

RF, and translate those movements into proportional control of the wheelchair.

Chin control is usually considered in a separate category from head control, but a chip-mounted

joystick requires head movement (Figure 2.4). The chin sits in a cup-shaped joystick handle

and is usually controlled by neck flexion, extension and rotation. This system is designed for a

user with good head control.

A major problem with this mode of control is the need for constant pressure. For users that lack

trunk control, or abdominal control, common compensation is to lean to one side, using the

limits of their neck rotation to the left or right to stabilize their head. The strain this puts on a

person’s neck can be hazardous to their health over time, so this method is not recommended

for people with decreased trunk function. Another problem with this system is the lack of

stability. When the wheelchair rides on uneven roads, a person with any difficulty holding their

head in a constant position will inevitably hit the joystick in unintentional directions as their

head sways to the movement of the uneven ride. The only way to stop the cycle of unintentional

movement is to completely stop the wheelchair by letting go of the joystick and waiting for the

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rocking to stop. Therefore, this system is not meant for people with decreased control of the

neck or abdomen.

Fig 2.3 Head Controlled System Fig 2.4 Chin Controlled System

2.1.4 BRAIN WAVE POWERED SYSTEM

Another alternative is powering the chair through brainwaves. A version for this option is being

constructed at California State University Northridge.

The technology used in the referenced project is an Emotive EPOC EEG

(electroencephalography) headset to decipher user’s brainwave inputs as commands for the

wheelchair (image of headset in Figure 2.5). The EPOC headset monitors three separate inputs:

facial expressions, head positions and brain sensing. The main use for the referenced project

was the brain sensing aspect. The headset with a set of EEG electrodes needs to be tuned to

optimize its functionality. Signatures of the waveforms will be identified and analysed, and

then used to create a movement command in steering an intelligent wheelchair. The project

requires a non-invasive brain-computer interface (BCI), which learns by repetition.

The main problems with this method are the sensor headset shown in Figure 2.5, the cost, and

the BCI interface. Consumer reviews claim that the Emotiv headset’s fragile, hard-to-handle

nature is disappointing for its high price of $299. To make the entire system work, the user

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must purchase the software separately, which brings the cost up by another $500. In addition,

the reviews found the thought-sensing functionality of the “sensor-stuffed EPOC headgear” to

be a bit too random and inaccurate to actually be useful. Furthermore, the sensor pads must be

wet separately and then placed in the headset slots each time the headset is used. Because of

the clunky hardware issues and the cost of the headset being almost as expensive as the

wheelchair itself, consumers are already looking for alternatives. The most important drawback

is that the BCI learning interface is difficult to control. The user may become distracted and

not think “stop” or might think “go” when they do not mean to, causing the wheelchair to react

unexpectedly. This could lead to many embarrassing and even dangerous situations for a

consumer.

Fig 2.5 Emotiv EPOC EEG Sensor (EMOTIV)

2.2 OUR PROPOSED SOLUTION

We proposed a simpler solution than the common joystick to solve this problem. Our focus is

purely on extreme cases, for example on quadriplegic individuals or individuals that cannot use

joysticks. Our goal in this project was to create a design that can easily adapt to a common

electric, joystick controlled wheelchair.

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In our system, we are controlling the wheelchair using our tongue. Controlling a wheelchair

using our tongue has several advantages.

Muscle fibers in tongue are similar to heart muscle fibers.

Low rate of perceived exertions

Directly connected to brain

Hidden inside mouth will give a certain degree of privacy

REQUIREMENTS:

There were three types of requirements: first the constraint requirements, which were limits set

on the project due to resource or time constraints; second were user or consumer requirements,

which are set by asking those currently in a wheelchair what they would want or need in an

alternative control system design; the final requirement set was the engineering requirements,

which set goals or limits on the project design based on the previous requirement sets and what

is physically possible with current tools and budget at our disposal. The requirements listed

below were known requirements when we began constructing our project.

Constraint Requirements:

The new alternative control system shall cost a maximum of $100 to prototype and

build.

All major components shall be easily assessable (may be ordered on the internet.)

Consumer Requirements:

The system shall be non-invasive.

The system shall be made for persons with quadriplegia.

The system shall to be easy to operate.

The system shall to be safe. (Incorporate emergency stops.)

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Engineering Requirements:

The portion of the system mounted on the wheelchair shall run off a common

wheelchair battery (12V VDC, 50 Amp-hours).

Wireless shall not have interference with other devices.

Table 2.1 shows the advantages of our proposed solution over existing solutions.

Table 2.1 Proposed solution compared to existing solutions

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CHAPTER 3

THE BASIC PRINCIPLE

Our proposed Tongue Drive System consists of 4 Hall Sensors that can be placed outside the

mouth. A small permanent magnet is placed on the tongue. The Hall Sensors are interfaced to

a microcontroller. When the magnet placed on the tongue moves towards a particular Hall

Sensor, the microcontroller takes a decision to move the wheel chair in a particular direction

which is sent wirelessly to another microcontroller to which motors are interfaced. For

example, when the magnet placed on tongue is moved towards sensor S1as shown in the figure,

the wheelchair moves in the forward direction. Similarly when it is moved towards the sensors

S2, S3 and S4 the wheelchair moves back, left and right respectively.

Fig 3.1 Basic principle of TDS

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CHAPTER 4

SYSTEM DESIGN

4.1 BLOCK DIAGRAM

4.1.1 TRANSMITTER BLOCK DIAGRAM

Fig 4.1 Transmitter Block Diagram

Figure 4.1 shows the block diagram of the transmitter. There are four Hall Effect Sensors which

are interfaced to the microcontroller. Hall Effect Sensors are transducers whose output voltage

varies in response to the change in magnetic field. We are using four Hall Effect Sensors to

control the direction of the powered wheelchair. When a magnet is brought near a particular

Hall Effect Sensor, the sensor gets activated. When the magnetic field is removed, the Hall

Effect Sensor gets deactivated. Based on which Hall Effect Sensor is activated, the

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microcontroller takes a particular decision regarding which direction the wheelchair should go.

The RF transmitter sends that particular decision to the receiver circuitry.

4.1.2 RECEIVER BLOCK DIAGRAM

Fig 4.2 Receiver Block Diagram

Figure 4.2 shows the block diagram of the receiver part of our project. The decision transmitted

by the transmitter circuitry is received through the RF receiver which is interfaced to the

microcontroller as shown in the figure. The motors are connected to the microcontroller using

an H – Bridge motor driver. The motor driver is used to control the directions of both the motors

used. Based on the decision transmitted, the wheelchair is moved in a specific direction by

controlling the motor’s direction. To prevent the wheelchair from ramming into obstacles such

as walls, we have connected a proximity sensor to the microcontroller to detect the obstacles.

Based on the proximity sensor output, the microcontroller takes decision whether or not to

emergency stop the wheelchair.

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4.2 CIRCUIT DIAGRAM

4.2.1 TRANSMITTER CIRCUIT DIAGRAM

Fig 4.3 Transmitter Circuit Diagram

Figure 4.3 shows the circuit diagram of the transmitter of our project. We are using 4 Hall

Effect Sensors in our project and they are connected to pins P1.0, P1.1, P1.2 and P1.3 of

ATMEL AT89S52 microcontroller. We have therefore configured Port 1 as the input port. The

output of Hall Effect sensor is very less to be detected by the microcontroller (which required

5V at its pins). To alleviate this problem, we have used pull – up resistors with each Hall Effect

Sensors to pull up the output voltage of each sensor to 5V. The pull – up resistors used in our

project are of 1kΩ value and they are connected between the output and VCC terminals of the

Hall Effect Sensors. Without any magnetic field, the output of all Hall Effect Sensors are pulled

up to VCC (5V). When a magnet is brought near a particular Hall Effect Sensor, the Hall

Sensors gets activated and the output gets pulled down to ground (0V). Pins P0.1, P0.2, P0.3,

and P0.4 are connected to the RF Transmitter (which transmits bit patterns) for transmitting

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the controlling decisions of the wheelchair. We have therefore configured Port 0 as the output

port.

4.2.2 RECEIVER CIRCUIT DIAGRAM

Fig 4.4 Receiver Circuit Diagram

Figure 4.4 shows the circuit diagram of the receiver of our project. The RF receiver is connected

to pins P2.0, P2.1, P2.2 and P2.3 of the ATMEL AT89S52 microcontroller. The RF receiver

receives the decisions for controlling the wheelchair which were transmitted by the RF

transmitter using bit patterns. Therefore, we configure Port 2 as input port. Pins P1.0, P1.1,

P1.2 and P1.2 of the microcontroller are connected to pins A1, A2, B1 and B2 of the H – bridge

driver which is used to control the direction of the motors of the powered wheelchairs. Since

we are using two motors, we need two H – bridge drivers. Hence, we are using L293d where

A1 and A2 is the control pins of motor A whereas B1 and B2 are controls pins of motor B.

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Since we are using both the H – bridge drivers in L293d IC, we connect both enable pins of the

IC to VCC (5V). The output pins of the H – bridge drivers are connected to the motors. Another

feature which we have incorporated into our project is the ability of the wheelchair to stop in

case the wheelchair rams into obstacles. For this, we have connected a proximity sensor to pin

P2.4 of the microcontroller. The proximity sensor gives an output voltage of 5V in case it

comes near any obstacles. Thus, we have programmed the microcontroller in such a way that

the wheelchair stops if it encounters any obstacles. Also, once the proximity sensor is activated

(the wheelchair stops), the forward, left and right motion of the wheelchair is inhibited and the

only movement allowed then is the backward motion so that the user can come out the situation.

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CHAPTER 5

HARDWARE

5.1 MICROCONTROLLER (ATMEL AT89S52)

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 Atmel’s high-

density non – volatile memory technology and is compatible with the industry-standard 80C51

instruction set and pinout. The on-chip Flash allows the program memory to be reprogrammed

in-system or by a conventional non – volatile memory programmer. 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 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.

5.1.1 FEATURES OF AT89S52

• 8K Bytes of In-System Reprogrammable Flash Memory

• Endurance: 100,000 cycles per byte

• Fully Static Operation: 0 Hz to 33 MHz

• Three-level Program Memory Lock

• 256 x 8-bit Internal RAM

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• 32 Programmable I/O Lines

• Three 16-bit Timer/Counters

• Eight Interrupt Sources

• Watchdog Timer

• Low-power Idle and Power-down Modes

5.1.2 PIN DESCRIPTION

Fig 5.1 Pin Diagram of AT89S52

Port 0:

Port 0 is an 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink eight

TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs.

Port 0 may also be configured to be the multiplexed low order address/data bus during accesses

to external program and data memory. In this mode P0 has internal pull-ups.

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Port 0 also receives the code bytes during Flash programming, and outputs the code bytes

during program verification. External pull-ups are required during program verification.

Port 1:

Port 1 is an 8-bit bi-directional 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. As inputs, Port 1 pins that are externally being

pulled low will source current (IIL) because of the internal pull-ups. Port 1 also receives the

low-order address bytes during Flash programming and verification.

Port 2:


sink/source four TTL inputs.

Port 3

Table 5.1 Port 3 pin details


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. As inputs, Port 3 pins that are externally being

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pulled low will source current (IIL) because of the pull-ups. Port 3 also serves the functions of

various special features of the AT89S52 as listed in Table 5.1.

XTAL1: Input to the inverting oscillator amplifier and input to the internal clock operating

circuit.

XTAL2: Output from the inverting oscillator amplifier.

5.1.3 CIRCUIT DIAGRAM

Fig 5.2 Circuit Diagram of AT89S52

As shown in Figure 5.2 the mother board of AT89S52 has following sections: Power Supply,

AT89S52 IC, Oscillator, Reset Switch and I/O ports. Let us see these sections in detail.

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1) POWER SUPPLY

This section provides the clean and harmonic free power to IC to function properly. The output

of the full wave rectifier section, which is built using two rectifier diodes, is given to filter

capacitor. The electrolytic capacitor C1 filters the pulsating dc into pure dc and given to Vin

pin-1 of regulator IC 7805.This three terminal IC regulates the rectified pulsating dc to constant

+5 volts. C2 & C3 provides ground path to harmonic signals present in the inputted voltage.

The Vout pin-3 gives constant, regulated and spikes free +5 volts to the mother board.

The allocation of the pins of the AT89S52 follows a U-shape distribution. The top left hand

corner is Pin 1 and down to bottom left hand corner is Pin 20. And the bottom right hand corner

is Pin 21 and up to the top right hand corner is Pin 40. The Supply Voltage pin VCC is 40 and

ground pin VSS is 20.

2) OSCILLATOR

If the CPU is the brain of the system then the oscillator, or clock, is the heartbeat. It provides

the critical timing functions for the rest of the chip. The greatest timing accuracy is achieved

with a crystal or ceramic resonator. For crystals of 2.0 to 12.0 MHz, the recommended

capacitor values should be in the range of 15 to 33pF.

Across the oscillator input pins 18 & 19 a crystal x1 of 4.7 MHz to 20 MHz value can be

connected. The two ceramic disc type capacitors of value 30pF are connected across crystal

and ground, stabilizes the oscillation frequency generated by crystal.

3) I/O PORTS

There are a total of 32 I/O pins available on this chip. The amazing part about these ports is

that they can be programmed to be either input or output ports, even "on the fly" during

operation! Each pin can source 20 mA (max) so it can directly drive an LED. They can also

sink a maximum of 25 mA current.

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Some pins for these I/O ports are multiplexed with an alternate function for the peripheral

features on the device. In general, when a peripheral is enabled, that pin may not be used as a

general purpose I/O pin. The alternate function of each pin is not discussed here, as port

accessing circuit takes care of that.

This 89C51 IC has four I/O ports and is discussed in detail:

P0.0 TO P0.7

PORT0 is an 8-bit [pins 32 to 39] open drain bi-directional I/O port. As an output port, each

pin can sink eight TTL inputs and configured to be multiplexed low order address/data bus then

has internal pull ups. External pull ups are required during program verification.

P1.0 TO P1.7

PORT1 is an 8-bit wide [pins 1 to 8], bi-directional port with internal pull ups. P1.0 and P1.1

can be configured to be the timer/counter 2 external count input and the timer/counter 2 trigger

input respectively.

P2.0 TO P2.7

PORT2 is an 8-bit wide [pins 21 to 28], bi-directional port with internal pull ups. The PORT2

output buffers can sink/source four TTL inputs. It receives the high-order address bits and some

control signals during Flash programming and verification.

P3.0 TO P3.7

PORT3 is an 8-bit wide [pins 10 to 17], bi-directional port with internal pull ups. The Port3

output buffers can sink/source four TTL inputs. It also receives some control signals for Flash

programming and verification.

4) PSEN

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Program Store Enable [Pin 29] is the read strobe to external program memory.

5) ALE

Address Latch Enable [Pin 30] is an output pulse for latching the low byte of the address during

accesses to external memory.

6) EA

External Access Enable [Pin 31] must be strapped to GND in order to enable the device to fetch

code from external program memory locations starting at 0000H upto FFFFH.

7) RST

Reset input [Pin 9] must be made high for two machine cycles to resets the device’s oscillator.

The potential difference is created using 10MFD/63V electrolytic capacitor and 20KOhm

resistor with a reset switch.

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5.2 RF MODULE

The circuit of this project utilises the RF module (Tx/Rx) for making a wireless remote, which

could be used to drive an output from a distant place. RF module, as the name suggests, uses

radio frequency to send signals. These signals are transmitted at a particular frequency and a

baud rate. A receiver can receive these signals only if it is configured for that frequency.

A four channel encoder/decoder pair has also been used in this system. The input signals, at

the transmitter side, are taken through four switches while the outputs are monitored on a set

of four LEDs corresponding to each input switch.

The circuit can be used for designing Remote Appliance Control system. The outputs from the

receiver can drive corresponding relays connected to any household appliance.

This radio frequency (RF) transmission project employs Amplitude Shift Keying (ASK) with

transmitter/receiver (Tx/Rx) pair operating at 434 MHz. The transmitter module takes serial

input and transmits these signals through RF. The transmitted signals are received by the

receiver module placed away from the source of transmission.

The system allows one way communication between two nodes, namely, transmission and

reception. The RF module has been used in conjunction with a set of four channel

encoder/decoder ICs. Here HT12E & HT12D have been used as encoder and decoder

respectively. The encoder converts the parallel inputs (from the remote switches) into serial set

of signals. These signals are serially transferred through RF to the reception point. The decoder

is used after the RF receiver to decode the serial format and retrieve the original signals as

outputs. These outputs can be observed on corresponding LEDs.

http://www.engineersgarage.com/content/rf-module

http://www.engineersgarage.com/content/led

http://www.engineersgarage.com/content/relay

http://www.engineersgarage.com/content/rf-module

http://www.engineersgarage.com/content/ht12e

http://www.engineersgarage.com/content/ht12d

http://www.engineersgarage.com/content/led

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Fig 5.3 Transmission of data from transmitter to receiver using RF module

Encoder IC (HT12E) receives parallel data in the form of address bits and control bits. The

control signals from remote switches along with 8 address bits constitute a set of 12 parallel

signals. The encoder HT12E encodes these parallel signals into serial bits. Transmission is

enabled by providing ground to pin14 which is active low. The control signals are given at pins

10-13 of HT12E. The serial data is fed to the RF transmitter through pin17 of HT12E.

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Fig 5.4 RF Transmitter

Transmitter, upon receiving serial data from encoder IC (HT12E), transmits it wirelessly to the

RF receiver. The receiver, upon receiving these signals, sends them to the decoder IC (HT12D)

through pin2. The serial data is received at the data pin (DIN, pin14) of HT12D. The decoder

then retrieves the original parallel format from the received serial data.

Fig 5.5 RF Receiver

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When no signal is received at data pin of HT12D, it remains in standby mode and consumes

very less current (less than 1µA) for a voltage of 5V. When signal is received by receiver, it is

given to DIN pin (pin14) of HT12D. On reception of signal, oscillator of HT12D gets activated.

IC HT12D then decodes the serial data and checks the address bits three times. If these bits

match with the local address pins (pins 1-8) of HT12D, then it puts the data bits on its data pins

(pins 10-13) and makes the VT pin high. An LED is connected to VT pin (pin17) of the decoder.

This LED works as an indicator to indicate a valid transmission. The corresponding output is

thus generated at the data pins of decoder IC.

A signal is sent by lowering any or all the pins 10-13 of HT12E and corresponding signal is

received at receiver’s end (at HT12D). Address bits are configured by using the by using the

first 8 pins of both encoder and decoder ICs. To send a particular signal, address bits must be

same at encoder and decoder ICs. By configuring the address bits properly, a single RF

transmitter can also be used to control different RF receivers of same frequency.

To summarize, on each transmission, 12 bits of data is transmitted consisting of 8 address bits

and 4 data bits. The signal is received at receiver’s end which is then fed into decoder IC. If

address bits get matched, decoder converts it into parallel data and the corresponding data bits

get lowered which could be then used to drive the LEDs. The outputs from this system can

either be used in negative logic or NOT gates (like 74LS04) can be incorporated at data pins.

http://www.engineersgarage.com/content/ic-74ls04

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5.3 HALL EFFECT SENSOR

5.3.1 HALL EFFECT

The Hall Effect is the production of a voltage difference (the Hall voltage) across an electrical

conductor, transverse to an electric current in the conductor and a magnetic field perpendicular

to the current. It was discovered by Edwin Hall in 1879.

The Hall coefficient is defined as the ratio of the induced electric field to the product of the

current density and the applied magnetic field. It is a characteristic of the material from which

the conductor is made, since its value depends on the type, number, and properties of the charge

carriers that constitute the current.

5.3.2 THEORY

The Hall Effect is due to the nature of the current in a conductor. Current consists of the

movement of many small charge carriers, typically electrons, holes, ions or all three. When a

magnetic field is present that is not parallel to the direction of motion of moving charges, these

charges experience a force, called the Lorentz force. When such a magnetic field is absent, the

charges follow approximately straight, 'line of sight' paths between collisions with impurities,

phonons, etc. However, when a magnetic field with a perpendicular component is applied, their

paths between collisions are curved so that moving charges accumulate on one face of the

material.

This leaves equal and opposite charges exposed on the other face, where there is a scarcity of

mobile charges. The result is an asymmetric distribution of charge density across the Hall

element that is perpendicular to both the 'line of sight' path and the applied magnetic field. The

separation of charge establishes an electric field that opposes the migration of further charge,

so a steady electrical potential is established for as long as the charge is flowing.

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In the classical view, there are only electrons moving in the same average direction both in the

case of electron or hole conductivity. This cannot explain the opposite sign of the Hall Effect

observed. The difference is that electrons in the upper bound of the valence band have opposite

group velocity and wave vector direction when moving, which can be effectively treated as if

positively charged particles (holes) moved in the opposite direction to that of the electrons.

For simple metal where there is only one type of charge carrier (electrons) the Hall Voltage VH

is given by

𝑉𝐻 = −𝐼𝐵

𝑛𝑡𝑒

where I is the current across the plate length, B is the magnetic field, t is the thickness of the

plate, e is the elementary charge, and n is the charge carrier density of the carrier electrons.

The Hall Effect coefficient is defined as

𝑅𝐻 = 𝐸𝑦

𝑗𝑥𝐵

where j is the current density of the carrier electrons and Ey is the induced electric field. In SI

unit, this becomes

𝑅𝐻 = 𝐸𝑦

𝑗𝑥𝐵=

𝑉𝐻𝑡

𝐼𝐵= −

1

𝑛𝑒

As a result, the Hall Effect is very useful as a means to measure either the carrier density or the

magnetic field.

When a current-carrying semiconductor is kept in a magnetic field, the charge carriers of the

semiconductor experience a force in a direction perpendicular to both the magnetic field and

the current. At equilibrium, a voltage appears at the semiconductor edges.

The simple formula for the Hall coefficient given above becomes more complex in

semiconductors where the carriers are generally both electrons and holes which may be present

in different concentrations and have different mobilities. For moderate magnetic fields the Hall

coefficient is

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𝑅𝐻 = 𝑝𝜇ℎ

2 − 𝑛𝜇𝑒2

𝑒(𝑝𝜇ℎ + 𝑛𝜇𝑒)2

Here n is the electron concentration, p the hole concentration, µe the electron mobility, µh the

hole mobility and e the absolute value of electronic charge. For larger applied fields the simpler

expression analogous to that for a single carrier type holds.

Fig 5.6 Hall Effect in Semiconductors

5.3.3 HALL EFFECT SENSOR HISTORY

The invention of the Hall phenomenon took place in the year 1879 in the Johns Hopkins

University in Baltimore. An American scientist named Edwin Herbert Hall, while working for

his doctoral degree, he discovered that, if current is flowing through an electrical conductor,

and this conductor is placed perpendicular to a magnetic field, then a voltage is developed on

this conductor on a right angle to the currents' path. This effect is called the "Hall effect", and

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the voltage developed is called "Hall voltage". The Hall voltage is measured in micro-volts.

This invention was firstly used for making sensor to measure the DC current, or the intensity

of static magnetic fields in laboratories, as the amplifiers to measure this voltage were big and

expensive. The Hall Effect sensors was widely used after the silicon semiconductors became

popular, and an implementation of a sensor along with an amplifier in a closed package was

possible.

5.3.4 INSIDE THE HALL EFFECT SENSOR SWITCH

The simplest Hall sensor, has inside the Hall element and a differential amplifier. This amplifier

must have some special characteristics. The Hall element may produce Hall voltages down to

20 microvolts. Therefore, the amplifier must have very low noise, high input impedance and

high gain in order to detect and amplify this micro voltage. The output of the amplifier is

usually driven through a Schmitt trigger and the sensor acts as a switch sensitive to magnetism.

The Hall voltage (VH) is proportional to the current across the Hall element (I) and the density

of the magnetic flux (B). To make the Hall voltage proportional to the density of the magnetic

flux, the current must be kept constant. Therefore, usually Hall sensors have also a built in

current regulator. The chip integrates also temperature compensation. A typical Hall sensor

diagram is shown in Figure 5.7.

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Fig 5.7 Inside the Hall Effect Sensor Switch

5.3.5 ADVANTAGES

It can be operated as a switch.

It can be operated up to 100 kHz.

Cost is less than other mechanical switches.

It does not suffer from contact bounce because a sequence of contacts are used

rather than a single contact.

It will not be affected by environmental contaminants. Therefore it can be used

under severe conditions.

It can be used as position, displacement and proximity sensors.

5.3.6 APPLICATIONS

The Hall Effect has been applied to numerous applications. Using hall sensors, contactless

current flow meters have been made. The current flow within a wire generates a magnetic field

around it. The hall sensor is wrapped onto the cable and measures the magnetism. The intensity

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of the field is proportional to the current flow, while the Hall voltage is proportional to the

intensity of the field. The great advantage is that the cable does not even need to be stripped.

Also, it can be used to measure the intensity of magnetic fields for measuring applications.

Furthermore, the Hall sensors can distinguish the polarity of the magnetic field.

Hall sensors are also used extensively in the car industry. The solid construction and the lack

of moving parts makes the hall sensor ideal to work in harsh environments and under heavy

vibrations. The Hall sensors are used to find the position of the crankshaft, just like it used to

be done with the distributor. The electronic fuel ignition systems needs to know when the

crankshaft is in this very position, so that they calculate and ignite the spark plugs accordingly.

Another application is found on the anti-block system of the cars. The sensor will sense if the

magnetic field from the wheel is stopped and it will send a pulse to the controller to release

part of the pressure on the break piston. Also it is used for measuring a vehicle's (usually

bicycle) speed. A permanent magnet is attached to the perimeter of the wheel. Opposite this

position, on the fork, the Hall sensor is positioned. It will sense a pulse every time the magnet

passes in front of the sensor, once per wheel revolution. The controller will calculate the speed

of the vehicle by knowing the wheel diameter.

The Hall sensors are also used for synchronization in brushless motors. Their capability to

switch on and off many times a second, makes them possible to be used for high speed BLDCs.

The Hall sensor are used to distinguish which pole of the rotor permanent magnet is in which

position, and turn on or off the appropriate coils accordingly. They are also used to measure

the speed of these motors.

Many applications in automation uses also Hall sensors. Pneumatic systems use them to find

if a cylinder is extended or retracted. The piston of the cylinder carries a permanent magnet. A

Hall sensor is positioned outside the cylinder. When the magnet is in front of the Hall sensor,

it transmits a signal to the controller.

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5.4 THE H – BRIGGE DRIVER

5.4.1 H – BRIDGE DRIVER WORKING PRINCIPLE

Generally, even the simplest robot requires a motor to rotate a wheel or performs particular

action. Since motors require more current then the microcontroller pin can typically generate,

you need some type of a switch (Transistors, MOSFET, Relay etc.,) which can accept a small

current, amplify it and generate a larger current, which further drives a motor. This entire

process is done by what is known as a motor driver.

Fig 5.8 Amplification of current generated by microcontroller pin for running a motor

Motor driver is basically a current amplifier which takes a low-current signal from the

microcontroller and gives out a proportionally higher current signal which can control and drive

a motor. In most cases, a transistor can act as a switch and perform this task which drives the

motor in a single direction.

Turning a motor ON and OFF requires only one switch to control a single motor in a single

direction. What if you want your motor to reverse its direction? The simple answer is to reverse

its polarity. This can be achieved by using four switches that are arranged in an intelligent

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manner such that the circuit not only drives the motor, but also controls its direction. Out of

many, one of the most common and clever design is an H – Bridge circuit where transistors are

arranged in a shape that resembles the English alphabet "H".

Fig 5.9 An H – Bridge Circuit

As we can see in the Figure 5.9, the circuit has four switches A, B, C and D. Turning these

switches ON and OFF can drive a motor in different ways.

1. Turning on Switches A and D makes the motor rotate clockwise.

2. Turning on Switches B and C makes the motor rotate anti-clockwise.

3. Turning on Switches A and B will stop the motor (Brakes).

4. Turning off all the switches gives the motor a free wheel drive.

5. Lastly turning on A & C at the same time or B & D at the same time shorts your entire

circuit.

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5.4.2 L293D IC OVERVIEW

L293D IC generally comes as a standard 16-pin DIP (dual-in line package) as shown in Figure

5.10. This motor driver IC can simultaneously control two small motors in either direction;

forward and reverse with just 4 microcontroller pins (if we do not use enable pins). Some of

the features (and drawbacks) of this IC are:

1. Output current capability is limited to 600mA per channel with peak output current

limited to 1.2A (non-repetitive). This means we cannot drive bigger motors with this

IC. However, most small motors used in hobby robotics should work. If we are unsure

whether the IC can handle a particular motor, connect the IC to its circuit and run the

motor with your finger on the IC. If it gets really hot, then beware... Also note the words

"non-repetitive"; if the current output repeatedly reaches 1.2A, it might destroy the

drive transistors.

2. Supply voltage can be as large as 36 Volts. This means we do not have to worry much

about voltage regulation.

3. L293D has an enable facility which helps you enable the IC output pins. If an enable

pin is set to logic high, then state of the inputs match the state of the outputs. If we pull

this low, then the outputs will be turned off regardless of the input states

4. The datasheet also mentions an "over temperature protection" built into the IC. This

means an internal sensor senses its internal temperature and stops driving the motors if

the temperature crosses a set point

5. Another major feature of L293D is its internal clamp diodes. This flyback diode helps

protect the driver IC from voltage spikes that occur when the motor coil is turned on

and off (mostly when turned off)

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6. The logical low in the IC is set to 1.5V. This means the pin is set high only if the voltage

across the pin crosses 1.5V which makes it suitable for use in high frequency

applications like switching applications (upto 5KHz)

7. Lastly, this integrated circuit not only drives DC motors, but can also be used to drive

relay solenoids, stepper motors etc.

Fig 5.10 Pin Diagram of L293D

5.4.3 L293D CONNECTIONS

The circuit shown in Figure 5.11 is the most basic implementation of L293D IC. There are 16

pins sticking out of this IC and we have to understand the functionality of each pin before

implementing this in a circuit

1. Pin1 and Pin9 are "Enable" pins. They should be connected to +12V for the drivers to

function. If they pulled low (GND), then the outputs will be turned off regardless of the

input states, stopping the motors.

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2. Pin4, Pin5, Pin12 and Pin13 are ground pins which should ideally be connected to

microcontroller's ground.

3. Pin2, Pin7, Pin10 and Pin15 are logic input pins. These are control pins which should

be connected to microcontroller pins. Pin2 and Pin7 control the first motor (left); Pin10

and Pin15 control the second motor (right).

4. Pin3, Pin6, Pin11, and Pin14 are output pins. Tie Pin3 and Pin6 to the first motor, Pin11

and Pin14 to second motor

5. Pin16 powers the IC and it should be connected to regulated +12Volts.

6. Pin8 powers the two motors and should be connected to positive lead of a secondary

battery. As per the datasheet, supply voltage can be as high as 36 Volts.

Fig 5.11 L293D Connections

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5.4.4 TRUTH TABLE

Table 5.2 shows the truth table representing the functionality of L293D motor driver.

Pin 1 Pin 2 Pin 7 Function

High High Low Turn Anti-clockwise (Reverse)

High Low High Turn clockwise (Forward)

High High High Stop

High Low Low Stop

Low X X Stop

High ~ +12V, Low ~0V, X = either high or low (don't care)

Table 5.2 Truth Table of L293D Motor Driver

In the truth table shown in Table 5.2 we can observe that if Pin1 (E1) is low then the motor

stops, irrespective of the states on Pin2 and Pin7. Hence it is essential to hold E1 high for the

driver to function, or simply connect enable pins to positive 12 volts.

With Pin1 high, if Pin2 is set high and Pin7 is pulled low, then current flows from Pin2 to Pin7

driving the motor in anti-clockwise direction. If the states of Pin2 and Pin7 are flipped, then

current flows from Pin7 to Pin2 driving the motor in clockwise direction.

The above concept holds true for other side of the IC too. Connect your motor to Pin11 and

Pin14; Pin10 and Pin15 are input pins, and Pin9 (E2) enables the driver.

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5.5 THE POWER SUPPLY

The LM317 is a popular adjustable linear voltage regulator. It was invented by Robert C.

Dobkin and Robert J. Widlar in 1970 while they worked at National Semiconductor. The

LM317 Voltage Regulator is a 3-terminal adjustable voltage regulator which can supply an

output voltage adjustable from 1.2V to 37V. It can supply more than 1.5A of load current to a

load.

5.5.1 LM317 PINOUT

The LM317 Voltage Regulator has 3 pins. Figure 5.12 shows the pinout.

Fig 5.12 LM317 Pinout

Looking from the front of the voltage regulator, the first pin (on the left) is the Adjustable Pin,

the middle is Vout, and the last pin (on the right) is VIN.

VIN – VIN is the pin which receives the incoming voltage which is to be regulated down to a

specified voltage. For example, the input voltage pin can be fed 12V, which the regulator will

regulate down to 10V. The input pin receives the incoming, unregulated voltage.

Adjustable – The Adjustable pin (Adj) is the pin which allows for adjustable voltage output.

To adjust output, we swap out resistor R2 value for a different resistance. This creates

adjustable voltages.

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VOUT – VOUT is the pin which outputs the regulated voltage. For example, the LM317 may

receive 12V as the input and output a constant 10V as output.

5.5.2 LM317 SCHEMATIC

To modify the voltage to the level we want as output, we change the value of the resistor

connected to the Adj pin of the voltage regulator.

Fig 5.13 Schematic of LM317 voltage regulator

As shown in Figure 5.13 we connect two resistors to the voltage regulator. These resistors

determine the voltage that the voltage regulator adjusts to and outputs.

The voltage that the adjustable regulator outputs is determined by the equation:

𝑉𝑂𝑈𝑇 = 1.25 (1 + 𝑅2

𝑅1) 𝑣𝑜𝑙𝑡𝑠

Therefore, you can see based on this formula, that the more the value of resistor R2 increases,

the greater the voltage output.

In our setup now, these are the values we're going to use. We're going to put 12 volts into the

voltage regulator and regulate it down to 5V. Based on the formula above, in order for the

LM317 to output 5 volts, the value of R2 must be 720Ω. We can this above circuit up and then

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use a multimeter to check the output voltage by placing it across the 1μF capacitor or across

the resistors. We find that it is very close to 5 volts. Now if swap out the R2 resistor and place

a 1.5KΩ resistor in its place we find the voltage output to be 10V.

This is the advantage of adjustable voltage regulators. You can adjust it to any voltage within

the range that the voltage regulator supports.

Note that the capacitors C1 and C2 are used to clean up the power line. C1 is optional and it's

used to clean up transient response. C2 is needed if the device is far from any filter capacitors.

This capacitors helps smooth out the power supply line in case of abrupt current spikes.

5.5.3 LM317 CIRCUIT

Figure 5.14 shows how LM317 regulator would look when connected to a circuit so that it

supplies a constant DC voltage output.

Fig 5.14 LM317 Circuit

In this circuit, we add a DC voltage supply to the VIN pin of the regulator. This is the pin

which, again, receives incoming voltage which the chip will then regulate down. The voltage

which enters this pin must be larger than the voltage it is feeding out. Remember, voltage

regulators are just devices that regulate voltage down to a certain level. They do not and cannot

create voltage on their own. Therefore, in order to a get a voltage, VOUT, VIN must be greater

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than VOUT. In this circuit, we want a regulated 5VDC as output. Therefore, VIN must be

greater than 5 volts. Generally, with regulators, unless they are low drop out regulators, you

want the input voltage to be about 2 volts higher. So therefore, since we want 5 volts as output,

we will feed into this regulator 7 volts.

Now that we've dealt with the input pin, we must now deal with the adjustable pin (Adj). This

is the pin which allows us to adjust the voltage to the level we want. Since we want 5 volts to

be output, we must calculate which value of R2 will yield an output of 5 volts. Using the

formula for the output voltage, VOUT= 1.25V (1 + R2/R1).

Being that R1=240Ω, our equation is now 5V= 1.25V (1 + R2/240Ω), so R2=720Ω. So with

R2 being a value of 720Ω, the LM317 will output 5V if fed an input voltage greater than 5

volts.

The last pin of the LM317 is the output pin. This is where the regulated voltage (in this case, 5

volts) will come out. To feed a circuit the regulated 5 volts, we just connect it to the output pin.

5.6 PROXIMITY SENSOR

A proximity sensor is a sensor able to detect the presence of nearby objects without any

physical contact. Since there is no contact between the sensors and sensed object and lack of

mechanical parts, these sensors have long functional life and high reliability. The different

types of proximity sensors are Inductive Proximity sensors, Capacitive Proximity sensors,

Ultrasonic proximity sensors, photoelectric sensors, Hall-effect sensors, etc.

5.6.1 WORKING PRINCIPLE

A proximity sensor often emits an electromagnetic field or a beam of electromagnetic radiation

(infrared, for instance), and looks for changes in the field or return signal. The object being

sensed is often referred to as the proximity sensor's target. Different proximity sensor targets

demand different sensors. For example Inductive Proximity sensors have an oscillator as input

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to change the loss resistance by the proximity of an electrically conductive medium. These

sensors are preferred for metal targets. Capacitive Proximity sensors convert the electrostatic

capacitance variation flanked by the detecting electrode and the ground electrode. This occurs

by approaching the nearby object with a variation in an oscillation frequency. To detect the

nearby object, the oscillation frequency is transformed into a direct current voltage which is

compared with a predetermined threshold value. These sensors are preferred for plastic targets.

The maximum distance that this sensor can detect is defined "nominal range". Some sensors

have adjustments of the nominal range or means to report a graduated detection distance.

Proximity sensors can have a high reliability and long functional life because of the absence of

mechanical parts and lack of physical contact between sensor and the sensed object.

5.6.2 ADVANTAGES OF PROXIMITY SENSORS

No physical contact required with the target to be detected, therefore, no moving parts,

so no friction and wear out.

Fast switching characteristics

Unlimited number of switching cycles since there is no mechanical contact

Can work in harsh conditions

Any type of target material can be detected.

5.6.3 APPLICATIONS OF PROXIMITY SENSORS

Parking sensors, systems mounted on car bumpers that sense distance to nearby cars for

parking

Ground proximity warning system for aviation safety

Vibration measurements of rotating shafts in machinery

Top dead centre (TDC)/camshaft sensor in reciprocating engines.

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Sheet break sensing in paper machine.

Anti-aircraft warfare

Roller coasters

Conveyor systems

Beverage and food can making lines

Mobile devices

Touch screens that come in close proximity to the face

Attenuating radio power in close proximity to the body, in order to reduce

radiation exposure

5.7 DC MOTOR

In our project, we have used two 12V geared DC motors as shown in figure 5.15 for running

the wheelchair. We have used 2 motors one for left and one for right so that turning might be

made easy. Right motor at rest and left motor in forward motion moves the wheelchair right.

Left motor at rest and right motor in forward motion moves the wheelchair left. For moving

forward, both the motors move in forward motion at same speed. For moving backward, both

the motors move in reverse motion at same speed.

Fig 5.15 12 V DC Motor

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CHAPTER 6

SOFTWARE

6.1 EMBEDDED C

6.1.1 OVERVIEW

Embedded C is a set of language extensions for the C Programming language by the C

Standards committee to address commonality issues that exist between C extensions for

different embedded systems. Historically, embedded C programming requires nonstandard

extensions to the C language in order to support exotic features such as fixed-point arithmetic,

multiple distinct memory banks and I/O operations.

In 2008, the C Standards Committee extended the C language to address these issues by

providing a common standard for all implementations to adhere to. It includes a number of

features not available in normal C, such as, fixed- point arithmetic, named address spaces, and

basic I/O hardware addressing.

Embedded C use most of the syntax and semantics of standard C, e.g. main () function, variable

definition, data type declaration, conditional statements (if, switch, case), loops (while, for),

functions, arrays and strings, structures and union, bit operations, macros, unions, etc.

In short, Embedded C deals with Microcontrollers, I/O Ports (RAM, ROM).whereas C deals

with only memory, operating systems. C is a desktop programming language used for

embedding a piece of software code into the hardware for its functioning.

6.1.2 COMPONENTS OF AN EMBEDDED C PROGRAM

Embedded C use most of the syntax and semantics of standard C, e.g. main () function, variable

definition, data type declaration, conditional statements (if, switch, case), loops (while, for),

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functions, arrays and strings, structures and union, bit operations, macros, etc. In addition, there

are some specifics to embedded C which are mentioned below:

1. Low Level Codes

Embedded programming requires access to underlying hardware, i.e., timers, memory, ports,

etc. In addition, it is often needed to handle interrupts, manage job queues, etc. As C offers

pointers and bit manipulation features, they are extensively used for direct hardware access.

2. In-line Assembly Code

For a particular embedded device, there may be instructions for which no equivalent C code is

available. In such cases, inline assembly code, i.e., assembly code embedded within C

programs is used; the syntax depends upon the compiler. Writing inline assembly code is much

easier than writing full-fledged assembly code.

3. Features like Heap, recursion

Embedded devices have no or limited heap area (where dynamic memory allocation takes

place). Hence, embedded programs do not use standard C functions like malloc. Structures like

linked lists/trees are implemented using static allocation only.

Similarly, recursion is not supported by most embedded devices because of its inefficiency in

terms of space and execution time. Such other costly features of standard C which consume

space and execution time are either not available or not recommended

4. I/O Registers

Microcontrollers typically have I/O, ADCs, serial interfaces and other peripherals in-built into

the chips. These are accessed as I/O Registers, i.e., to perform any operation on these

peripherals, bits in these registers are read / written.

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Special function registers (SFRs) are accessed as shown below:

SFR portb=0x0B;

It is used to declare portB at location 0x0B.

Some embedded processors have separate I/O space for such registers. Since there are no such

concepts in C, compilers provide special mechanisms to access them.

Unsigned char portB @portB 0x08;

In this example, ‘@portB<address>’ declares portB at location 0x8B by the variable portB.

Such extensions are not a part of standard C, syntax and semantics differ in various embedded

C compilers.

5. Memory Pointers

Some CPU architectures allow us to access I/O registers as memory addresses. This allows

treating them just like any other memory pointers.

6. Bit Access

Embedded controllers frequently need bit operations as individual bits of I/O registers

correspond to the output pin of an I/O port. Standard C has quite powerful tools to do bitwise

operations. However, care must be taken while using them in structures because C standard

doesn’t define the bit field allocation order and C compilers may allocate bit fields either from

left to right or from right to left.

7. Use of Variable data type

In C, data types can be simply declared, and compiler takes care of the storage allocation as

well as that of code generation. But, data type’s usage should be carefully done to generate

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optimized code. For most 8-bit C compilers, ‘char’ is 8-bits, ‘short’ and ‘int’ are 16-bits, ‘long’

is 32-bits.

Some embedded processors favour use of 69unsigned type. Use of ‘long’ and floating variable

should be avoided unless it is very necessary. Using long data types increase code size and

execution time. Use of floating point variables is not advised due to intrinsic imprecise nature

of floating point operations, alongside speed and code penalty.

8. Use of Const and Volatile

Volatile is quite useful for embedded programming. It means that the value can change without

the program touching it. Consequently, the compiler cannot make any assumptions about its

value. The optimizer must reload the variable every time it is used instead of holding a copy in

a register.

Const is useful where something is not going to change, for e.g., function declarations, etc.

6.1.3 ADVANTAGES OF USING EMBEDDED C

1. Direct access to low level hardware API’s

2. You can find a C compiler for the vast majority of these devices. This is not true for any

high level language.

3. C (the runtime and your generated executable) is “small”. You don’t have to load a bunch

of stuff into the system to get the code running.

4. The hardware API/drivers will likely be written in C or C++.

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6.2 KEIL C CROSS COMPILER

Keil Software provides the software development tools for the 8051 family of microcontrollers.

With these tools embedded applications for the multitude of 8051 derivatives is generated. Keil

provides following tools for 8051 development

1. C51 Optimizing C Cross Compiler.

2. A51 Macro Assembler.

3. 8051 Utilities (linker, object file converter, library manager).

4. Source-level Debugger/Simulator.

5. µVision for Windows Integrated Development Environment.

The Keil 8051 tool kit includes three main tools, assembler, compiler and linker.

An assembler is used to assemble 8051 assembly program.

A compiler is used to compile C source code into an object file.

A linker is used to create an absolute object module suitable for your in-circuit emulator.

8051 project development cycle: These are the steps to develop 8051 project using Keil

1. Create source files in C or assembly.

2. Compile or assemble source files.

3. Correct errors in source files.

4. Link object files from compiler and assembler.

5. Test linked application.

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6.2.1 CONFIGURING THE SIMULATOR

1 .Open Keil µVision 4.

2. Create a new project.

Fig 6.1 Step 2 of Keil Configuration

3. Select the required microcontroller and click ok.


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4. Creating new file


5. Type the code and save it as filename.c


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6. Go to Project – Manage – Select components, environments and books and add the C file to

source group.


7. Save the project


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8. Compile (Translate) the C file


9. Build target files


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10. Rebuild Target Files


11. Go to Project and select Options for Target “Target 1”..


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12 Make sure that the oscillator crystal frequency is 11.0592 MHz.


13. Go to output tab under Options for Target “Target 1” and select “Create HEX File”.


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6.3 WILLAR PROGRAMMER

We are using WILLAR Programmer to burn the hex files generated by Keil µVision to the

ATMEL AT89S52 microcontroller. The steps to do the same are shown below,

1. Open WILLAR Programmer

2. Select the target device as AT89S52

Fig 6.13 Step 2 of Willar Programmer Configuration

3. Load the hex file generated by Keil µVision.

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4. Click Auto to blank check, program, verify and protect the hex code into AT89S52.


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CHAPTER 7

ADVANTAGES AND DISADVANTAGES OF TDS

7.1 ADVANTAGES

Simple to implement, low cost and easy to operate.

Unobtrusive.

Offers better privacy to users.

7.2 DISADVANTAGES

User should avoid inserting ferromagnetic objects in their mouth.

Magnetic tracer should be removed if user is undergoing MRI scan.

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CHAPTER 8

CHALLENGES FACED

We have faced a number of challenges in this project and also learned a number of new terms

and microcontroller terminology.

Hall sensor output not enough to drive microcontroller.

Back emf produced by motors (took a long time for rectification, had burned 2 IC’s

and one ATMEL AT89S52 microcontroller PCB)

Exact positioning of sensors

Turning the vehicle left and right

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CHAPTER 9

CONCLUSION

This project “Tongue Drive Assistive Technology for paralysed persons” is mainly intended to

design a wheelchair which can be controlled by movement of tongue, which is very useful for

handicapped and paralysed persons. This system consists of Hall Effect sensors and a

Wheelchair interfaced to microcontrollers. This device could revolutionize the field of assistive

technologies by helping individuals with severe disabilities such as those with severe high level

spinal cord injuries return to rich, active, independent and productive lives. Also this Hall

Effect sensor can be used to control different devices basing on the movement of the tongue.

For example, home appliances like fan, TV can be controlled by paralysed person on his own.

Thus this model helps severely paralysed person in reducing his/her dependency on others.

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CHAPTER 10

REFERENCES

BOOKS

The 8051 Microcontroller and Embedded System using assembly and C by Muhammad

Ali Mazzidi (Author), Janice Gillespie Mazzidi (Author) and Rollin D Mckinlay

(Author); Pearson

Hall Effect Sensors : Theory and Applications by Edward Ramsden (Author); Elsevier

The 8051 Microcontroller by Kenneth Ayala (Author); Thomson Delmar Learning, 3rd

Edition, 2005

WEBSITES

Datasheets, http://www.DatasheetCatalog.com

Keil C Evaluator edition, http://www.keil.com

Assistive Technology Devices, http://www.wheelchairnet.org

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APPENDIXES

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APPENDIX A

SOURCE CODE

TRANSMITTER SOURCE CODE

#include<reg51.h>

#define SW P1

void main()

unsigned char input;

SW=0xff;

SW=SW&0x0f;

input=0x00;

while(1)

input=SW;

if (input==0x0f)

P0=0x05;

else if(input==0x0E)

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P0=0x02;

else if(input==0x0D)

P0=0x08;

else if(input==0x0B)

P0=0x04;

else if(input==0x07)

P0=0x06;

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RECEIVER SOURCE CODE

#include<reg51.h>

#define MOVE_FORWARD 0x0A

#define TURN_RIGHT 0x02

#define TURN_LEFT 0x08

#define STOP 0x00

#define REVERSE 0x05

#define MOTOR P1

#define INPUT_PORT P2

sbit r = P2^4;

void main()

unsigned char input;

INPUT_PORT = 0xff;

input = 0x00;

while(1)

input = INPUT_PORT;

input = input & 0x0f;

if(input == 0x08)

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MOTOR = REVERSE;

else if(input == 0x05)

MOTOR = STOP;

if(r == 0)

if(input == 0x02)

MOTOR = MOVE_FORWARD;


MOTOR = TURN_RIGHT;


MOTOR = TURN_LEFT;

TDS 2013 – 2014


else if(r == 1 && input != 0x08)

MOTOR = STOP;

TDS 2013 – 2014


APPENDIX B

DATA SHEETS

TDS 2013 – 2014


wireless control of powered wheelchair using tongue report,tongue drive system report,tds...

Engineering

puff system

puff wheelchair

humming recognition

speech recognition software

sir mvit page

department of electronics

hall effect sensor

initial hard sip