TDS 2013 – 2014 Department of Electronics and Communication, Sir MVIT Page 1 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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TDS 2013 – 2014
Department of Electronics and Communication, Sir MVIT Page 1
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:
Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output buffers can
sink/source four TTL inputs.
Port 3
Table 5.1 Port 3 pin details
Port 3 is an 8-bit bi-directional 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. 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.