CHAPTER 1 INTRODUCTION
One of the main form of communication that has been in use since 19th century is Radio Wave communication. Radio Waves have found its place in each and every field whether it be medical, electronics or space. In general it exists in every system in one or the other form.
The use of Radio Waves had made life much simpler and safer. A heart patient can be monitored by a doctor remotely sitting in his chamber is because of the use of Radio Waves. Radio Waves have made communication through telephone, internet etc easier and cheaper.
Our project demonstrate one such example were Radio Wave is employed in a way which is helpful to us. This project is designed and developed for helping the passengers traveling in train and bus especially during night. The people who are not aware of the station on which one should get down will find this very helpful. Here the station name is displayed and announced simultaneously when the station is about to reach which can assist both literate and illiterate.
The RF technology is used in the project to communicate between the transmitter and receiver. Each transmitter has a unique binary code which is transmitted continuously to space in a particular range. This signal is captured by the receiver when it reaches in its range. So in the case of a train, the transmitter placed in the station is detected by the receiver in the train and the binary code is processed to give out the station name display and audio corresponding to the binary code in the receiver. A LCD unit is used for displaying the station name and a speaker is used for the announcement.
1.1. BLOCK DIAGRAM
The block diagram consists of the transmitter and receiver section. They can be represented as the following block diagrams.
1.1.1. Transmitter
Fig. 1.1 Block Diagram of Transmitter Module
The block diagram of the transmitter is given in fig. 1.1. The main parts in the transmitter are:
1. Power Supply
The power supply section is the section which provide +5V for the transmitter section to work. IC LM7805 is used for providing a constant power of +5V.
2. Encoder
This section contains the identity of the transmitter. An encoder can be a device used to change a signal (such as a bit stream) or data into a code. The code serves any of a number of purposes such as compressing information for transmission or storage, encrypting or adding
3. RF Transmitter
This section transmits the binary data to space in a particular range based on the antenna used. This signal is received by the receiver and it compares the binary code to find the corresponding station name from the database.
1.1.2. Receiver
Fig. 1.2 Block Diagram of Receiver Module 1. Power Supply
The power supply section is the section which provide +5V for the transmitter section to work. IC LM7805 is used for providing a constant power of +5V.
2. Decoder
A decoder is a device which does the reverse of the encoder, undoing the encoding so that the original information can be retrieved.
3. Microcontroller
Unlike microprocessors, microcontrollers are generally optimized for specific applications. As a result the peripherals can be simplified and reduced which cuts down the production cost.
4. RF Receiver
The RF signal transmitted by the transmitter is detected and received by this section of the receiver. This binary encoder data is sent to the decoder for decoding the original data.
5. LCD
This is the output unit in the receiver section. The station name is displayed on this display unit when the receiver comes in the range of the transmitter.
6. Voice Alert
This is another output unit in the receiver. This gives the voice alert of the station reached based on the RF transmitter signal received.
CHAPTER 2
PROJECT DESCRIPTION 2.1. INTRODUCTION
RF based station name intimation is based traditionally on RF signal. RF signal at the frequency range 434 MHz is employed for communication between transmitter unit and receiver unit in our project.
Each station is identified by a unique binary code, for example, 001 for Chennai and 100 for Nagerkoil. This binary code is transmitted by transmitter module continuously at a frequency range of 434 MHz within a distance of 400 foot outdoor and 200 foot indoor. This distance can be enhanced by using additional RF antenna.
When the receiver comes within the range of transmitter, it receives the data from the transmitter in the form of RF signal which is further decoded to collect the binary code and display the station name along with the voice play back.
2.2. TRANSMITTER MODULE
Transmitter section is the smallest section having few components which include:
1. RF transmitter TWS-434 A 2. Encoded HT-12 E
3. Voltage Regulator LM7805.
LM7805 assures a constant supply of +5 V for the transmitter module. This voltage of +5 V is used to drive transmitter and encoder.
2.2.1. Circuit Description
The third pin of TWS-434 A, RF transmitter and 18th pin of Encoder HT-12 E is connected to the output pin of Voltage Regulator LM7805 which drive the circuit with a constant voltage of 5V.
The first pin of TWS-434 A and all the address bus are connected to second pin of LM7805 which represent ground. The first pin of voltage regulator receives a voltage of 9V from a battery source.
The other connection include a connection between the Dout (7th pin) of HT-12 E and the data pin (2nd pin) of TWS-434 A.
2.2.2. Working Principle
The binary values unique to each station are assigned by the encoder HT-12 E. Each address/data input can be set to the logic state 0 or 1.
Grounding the pin is taken as 0 while 1 can be achieved by giving 5V or leaving the pins open (No connection). So in order to get a binary value of 0001 only one pin is pulled high i.e. 13th pin (D11) is pulled high while pins 10, 11 and 12 are grounded to represent logical zero.
On receipt of transmit enable i.e. TE-active (14th pin) is pulled low. The data which is here is the binary value is fed as input to the transmitter TWS-434 A from Dout (17th pin) along with header bits.
Received data from HT-12 E encoder is amplitude modulated and transmitted at a frequency range of 433.92 MHz.
2.3. RECEIVER MODULE
Receiver is the output section of the project. Receiver module includes the following components:
1. RF Receiver RWS-434 A
2. Microcontroller 89C51 which is regarded as the brain of the circuit. 3. LCD module for display the station name
4. Audio playback IC APR 9600
5. Power supply section which contains transformer, rectifier, filter, regulator which ensures a constant +5V.
Main function of the receiver unit is to detect the RF signal transmitted by the TWS-434A and give the response according to the received data from the receiver. Varies components of the receiver unit has its own function.RWS-434 receives the RF signal, AT 89C51 processes the input data and produces a corresponding response, LCD module considered as the output unit displays the processed data from the microprocessor, APR 9600 gives the output in the form of audio playback which is stored in the internal memory of the IC.
2.3.1. Circuit Description
A constant voltage of +5V is applied to the 4th and 5th pin of the receiver, 2nd pin of the LCD module, 40th pin of Microcontroller 89C51, 18th pin of the decoded IC HT-12D and various pins of APR 9600 as shown in figure below through voltage regulator LM7805. It derives its input voltage from bridge rectifier. The 8 bit data pins D0 - D7 are used to send information from port 2 of the microcontroller to the LCD. RS (register select) is one of the important registers inside the LCD. The RS pin is used for their selection as follows. If RS=0, the instruction code register is selected, allowing the user to send a command such as clear display, cursor at home, etc. if RS=1 the data register is selected, allowing the user to send data to be displayed on the LCD.R/W input pin of LCD allows the user to write information to the LCD or read information from it. R/W=1 when reading; R/W=0 when writing. E (enable) the enable pin is used by the LCD to latch information presented on its data pins. When data is supplied to data pins, a high to low pulse must be applied to this pin in order for the LCD to latch in the data present at the data pins. These 3 pins (RS, RW, and E) of LCD are connected to the 89C51 through port 0. The communication between AT 89C51 and audio IC APR 9600 is through address/data bus of port 0 of 89C51 and pin 1 and pin 2 namely M1 and M2 of APR 9600. Microcontroller receives data from decoder HT-12 D through port 1 which is an 8 bit bidirectional I/O port from the output data pins D8-D11 of HT-12 D.
The receiver RWS-434 is connected to decoder such that the received RF signal is fed as input to the data input pin Din (pin 14) of the decoder from 2nd pin of the receiver.
2.3.2. Working Principle
When the receiver unit comes in the range of transmitter unit which continuously transmit RF signal, the whole receiver unit gets activated. The receiver unit receives the RF signal at a frequency range of 434 MHz which actually is a digital data which includes the binary code assigned to the particular transmitter which denotes a station and a carrier signal. Digital output is taken from pin 2 of RWS-434 and received by decoder HT-12 D through data input pin (18th pin). The received serial input data are compared three times continuously with the local address. If no error or unmatched codes are found, the input codes are decoded and then transferred to the output pins. The VT (Valid Transmission) pin (12th pin) gives high to indicate a valid transmission.
The decoded signal is given as data input to AT 89C51 at port 1. On receipt of the binary code microcontroller which act as a database of station name, compares the received binary code with its stored binary code, on no error or unmatched code the station name corresponding to the binary code is displayed on the LCD screen along with a voice alert from APR 9600.
The whole cycle will be repeated when the receiver receives a new set of binary code transmitted by some other transmitter denoting a different station. The display will be active only for pre defined duration, after which the LCD return to its ideal state. The data to be displayed on the LCD screen is available at port 2 and control of the register of the LCD is through port 3.
CHAPTER 3
HARDWARE DESCRIPTION 3.1. RF TRANSMITTER
The function of a radio frequency (RF) transmitter is to modulate, up convert, and amplify signals for transmission into free space. An RF transmitter generally includes a modulator that modulates an input signal and a radio frequency power amplifier that is coupled to the modulator to amplify the modulated input signal. The radio frequency power amplifier is coupled to an antenna that transmits the amplified modulated input signal.
The RF transmitter used in our project is TWS-434A. This RF transmitter transmits data in the frequency range of 433.92 MHz with a range of approximately 400 foot (open area) outdoors. Indoors, the range is approximately 200 foot, and will go through most walls. TWS-434A has features which includes small in size, low power consumption i.e. 8mW and operate from 1.5 to 12 Volts-DC, excellent for applications requiring short-range RF signal. Data to be send is Amplitude modulation with the carrier RF signal.
3.1.1. Pin Description of Transmitter PIN 1: GROUND (-5V)
PIN2: INPUT PIN FOR DATA FROM ENCODER PIN3: SUPPLY (+5V)
PIN 4: PIN FOR EXTERNAL RF ANTENNA 3.2. RF RECEIVER
The RF receiver receives an RF signal, converts the RF signal to an IF signal, and then converts the IF signal to a base band signal, which it then provides to the base band processor. As is also known, RF transceivers typically include sensitive components susceptible to noise and interference with one another and with external sources. The RF receiver is coupled to the antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives an inbound RF signal via the antenna and amplifies it.
The RF receiver used is RWS-434. This RF receiver receives RF signal which is in the frequency of 434.92 MHz and has a sensitivity of 3uV. The RWS-434 receiver operates from 4.5 to 5.5 volts-DC, and has both linear and digital outputs and its tunable to match the frequency of the transmitter unit.
Fig. 3.2 RF Receiver 3.2.1. Pin Description of Receiver
PIN1: GROUND (-5V)
PIN2: OUTPUT PIN FOR DIGITAL DATA RECIEVED PIN 3: OUTPUT PIN FOR ANALOG DATA RECIEVED PIN4: SUPPLY (+5V)
PIN5: SUPPLY (+5V) PIN6: GROUND (-5V) PIN7: GROUND (-5V)
3.3. ENCODER
An encoder can be a device used to change a signal (such as a bit stream) or data into a code. The code serves any of a number of purposes such as compressing information for transmission or storage, encrypting or adding redundancies to the input code, or translating from one code to another. This is usually done by means of a programmed algorithm, especially if any part is digital, while most analog encoding is done with analog circuitry. Encoder used here is HT 12E. The HT12E encoder is a CMOS IC It is capable of encoding 8 bits of address (A0-A7) and 4-bits of data (AD8-AD11) information. Each address/data input can be set to one of the two logic states, 0 or 1. Grounding the pins is taken as a 0 while a high can be given by giving +5V or leaving the pins open (no connection). Upon reception of transmit enable (TE-active low), the programmed address/data are transmitted together with the header bits via an RF medium.
3.3.1. Pin Description of Encoder
Table. 3.1 Pin Description of Encoder
Pin Name I/O Internal Connection Description A0~A7 I CMOS IN Pull-high (HT12A)NMOS TRANSMISSI ON GATE PROTECTION DIODE (HT12E)
Input pins for address A0~A7 setting These pins can be externally set to VSS or left open AD8~A D11 I NMOS TRANSMISSI ON GATE PROTECTION DIODE (HT12E)
Input pins for address/data AD8~AD11 setting
These pins can be externally set to VSS or left open
D8~D11 I
CMOS IN Pull-High
Input pins for data D8~D11 setting and transmission en- able, active low
These pins should be externally set to VSS or left open
(see Note)
L/MB I CMOS IN Pull-high
Latch/Momentary transmission format selection pin: Latch: Floating or VDD Momentary: VSS
TE I
CMOS IN
Pull-high Transmission enable, active low (see Note)
OSC1 I OSCILLATOR
1
Oscillator input pin
OSC2 O OSCILLATOR
1
Oscillator output pin
X1 I OSCILLATOR
2
455kHz resonator oscillator input
X2 O OSCILLATOR
2
455kHz resonator oscillator output
VSS I Negative power supply, grounds
VDD I Positive power supply
3.4. DECODER
A decoder is a device which does the reverse of an encoder, undoing the encoding so that the original information can be retrieved. The same method used to encode is usually just reversed in order to decode. In digital electronics this would mean that a decoder is a multiple-input, multiple-output logic circuit that converts coded inputs into coded outputs. Enable inputs must be on for the decoder to function, otherwise its outputs assume a single "disabled" output code word.
Decoding is necessary in applications such as data multiplexing, 7 segment display and memory address decoding. The decoder used here is HT 12D. The HT12D is a decoder IC made especially to pair with the HT 12E encoder. It is a CMOS IC. The decoder is capable of decoding 8 bits of address (A0 - A7) and 4 bits of data (AD8 - AD11) information. For proper operation, a pair of encoder/decoder with the same number of addresses and data format should be chosen. The decoders receive serial addresses and data from programmed encoders that are transmitted by a carrier using an RF or an IR transmission medium. They compare the serial input data three times continuously with their local addresses. If no error or unmatched codes are found, the input data codes are decoded and then transferred to the output pins. The VT pin also goes high to indicate a valid transmission. The decoders are capable of decoding information that consists of N bits of address and 12_N bits of data. Of this series, the HT 12D is arranged to provide 8 address bits and 4 data bits.
Fig. 3.4 Decoder 3.4.1. Pin Description of Decoder
Table. 3.2 Pin Description of Decoder
Pin Name I/O Internal Connection Description A0~A7 (HT12D) NMOS Transmission Gate
Input pins for address A0~A7 setting These pins can be externally set to VSS or left open.
D8~D11 (HT12D)
O CMOS OUT Output data pins, power-on state is low.
DIN I CMOS IN Serial data input pin
VT O CMOS OUT Valid transmission, active high
OSC1 I Oscillator Oscillator input pin
OSC2 O Oscillator Oscillator output pin
VSS Negative power supply, ground
VDD Positive power supply
3.5. LCD MODULE
A liquid crystal display (LCD) is an electronically-modulated optical device shaped into a thin, flat panel made up of any number of color or monochrome pixels filled with liquid crystals and arrayed in front of a light source (backlight) or reflector. It is often utilized in battery-powered electronic devices because it uses very small amounts of electric power. LCD has material which combines the properties of both liquids and crystals. Rather than having a melting point, they have a temperature range within which the molecules are almost as mobile as they would be in a liquid, but are grouped together in an ordered form similar to a
LCD consists of two glass panels, with the liquid crystal materials sandwiched in between them. The inner surface of the glass plates is coated with transparent electrodes which define in between the electrodes and the crystal, which makes the liquid crystal molecules to maintain a defined orientation angle. When a potential is applied across the cell, charge carriers flowing through the liquid will disrupt the molecular alignment and produce turbulence. When the liquid is not activated, it is transparent. When the liquid is activated the molecular turbulence causes light to be scattered in all directions and the cell appears to be bright. Thus the required message is displayed.
When the LCD is in the off state, the two polarizers and the liquid crystal rotate the light rays, such that they come out of the LCD without any orientation, and hence the LCD appears transparent. When sufficient voltage is applied to the electrodes the liquid crystal molecules would be aligned in a specific direction. The light rays passing through the LCD would be rotated by the polarizer, which would result in activating/highlighting the desired characters. The power supply should be of +5v, with maximum allowable transients of 10mv.
To achieve a better/suitable contrast for the display the voltage (VL) at pin 3 should be adjusted properly. A module should not be removed from a live circuit. The ground terminal of the power supply must be isolated properly so that voltage is induced in it. The module should be isolated properly so that stray voltages are not induced, which could cause a flicking display. LCD is lightweight with only a few, millimeters thickness since the LCD consumes less power, they are compatible with low power electronic circuits, and can be powered for long durations. LCD does not generate light and so light is needed to read the display. By using backlighting, reading is possible in the dark. LCDs have long life and a wide operating temperature range. Before LCD is used for displaying proper initialization should be done.
LCDs with a small number of segments, such as those used in digital watches and pocket calculators, have individual electrical contacts for each segment. An external dedicated circuit supplies an electric charge to control each segment. This display structure is unwieldy for more than a few display elements. Small monochrome displays such as those found in personal organizers, or older laptop screens have a passive-matrix structure employing super-twisted nematic (STN) or double-layer STN (DSTN) technology—the latter of which addresses a color-shifting problem with the former—and color-STN (CSTN)—wherein color is added by using an internal filter.
Each row or column of the display has a single electrical circuit. The pixels are addressed one at a time by row and column addresses. This type of display is called passive-matrix addressed because the pixel must retain its state between refreshes without the benefit of a steady electrical charge. As the number of pixels (and correspondingly, columns and rows) increases, this type of display becomes less feasible. Very slow response times and poor contrast are typical of passive matrix addressed LCDs.
High-resolution color displays such as modern LCD computer monitors and televisions use an active matrix structure. A matrix of thin-film transistors (TFTs) is added to the polarizing and color filters. Each pixel has its own dedicated transistor, allowing each column line to access one pixel. When a row line is activated, all of the column lines are connected to a row of pixels and the correct voltage is driven onto all of the column lines. The row line is then deactivated and the next row line is activated. All of the row lines are activated in sequence during a refresh operation. Active-matrix addressed displays look "brighter" and "sharper" than passive-matrix addressed displays of the same size, and generally have
A general purpose alphanumeric LCD, with two lines of 16 characters. So the type of LCD used in this project is16 characters * 2 lines with 5*7 dots with cursor, built in controller, +5v power supply, 1/16 duty cycle.
3.5.1. LCD Layout
Fig. 3.5 LCD Layout 3.5.2. Pin Description of LCD Module
3.6. VOICE MODULE
APR9600 device to reproduce voice signals in their natural form. It eliminates the need for encoding and compression, which often introduce distortion. The APR9600 device offers true single-chip voice recording, non-volatile storage, and playback capability for 40 to 60 seconds. The device supports both random and sequential access of multiple messages. Sample rates are user-selectable, allowing designers to customize their design for unique quality and storage time needs. Integrated output amplifier, microphone amplifier, and AGC circuits greatly simplify system design. The device is ideal for use in portable voice recorders, toys, and many other consumer and industrial applications. APLUS integrated achieves these high levels of storage capability by using its proprietary analog/multilevel storage technology implemented in an advanced Flash non-volatile memory process, where each memory cell can store 256 voltage levels. This technology enables the APR9600 device to reproduce voice signals in their natural form. It eliminates the need for encoding and compression, which often introduce distortion.
3.6.1. Pin Diagram of APR 9600
Fig. 3.6 Pin Diagram of APR 9600
3.6.2. Pin Description of APR 9600
Table. 3.4 Pin Description of APR 9600
Pin Name Functions Pin Mane Functions
1 -M1 Select 1st section of sound or serial
15 SP- Speaker, negative end
2 -M2 Select 2nd section or fast forward control in serial mode (low active)
16 VCCA Analogue circuit power supply
3 -M3 Select 3 rd section of sound 17 MICIN Microphone input (electret type microphone)
4 -M4 Select 4th section of sound 18 MICREF Microphone reference input
5 -M5 Select 5th section of sound 19 AGC AGC control
6 -M6 Select 6th section of sound 20 ANA-IN Audio input (accept a signal of
100 mV p-to-p) 7 OSCR Resistor to set clock
frequency. See Table 3 for details
21 ANA-OUT Audio output from the microphone amplifier
8 -M7 Select 7th section of sound or IC
overflow indication
22 STROBE During recording and replaying, it produces a strobe signal
9 -M8 Select 8th section of sound or select mode (see Table 2)
23 CE Reset sound track counter to zero/ Stop or Start / Stop
10 -BUSY Busy (low active) 24 MSEL1 Mode selection 1 (see Table 2)
11 BE =1, beep when a key is pressed
=0, do not beep
25 MSEL2 Mode selection 2 (see Table 2)
13 VSSA Analogue circuit ground 27 -RE =0 to record, =1 to replay 14 SP+ Speaker, positive end 28 VCCD Digital circuit power
supply
3.7. POWER SUPPLY
The ac voltage, typically 220V, is connected to a transformer, which steps down that ac voltage down to the level of the desired dc output. A diode rectifier then provides a full-wave rectified voltage that is initially filtered by a simple capacitor filter to produce a dc voltage. This resulting dc voltage usually has some ripple or ac voltage variation.
A regulator circuit removes the ripples and also retains the same dc value even if the input dc voltage varies, or the load connected to the output dc voltage changes. This voltage regulation is usually obtained using one of the popular voltage regulator IC units.
3.7.1. Transformer
Transformers convert AC electricity from one voltage to another with little loss of power. Transformers work only with AC and this is one of the reasons why mains electricity is AC.
Step-up transformers increase voltage, step-down transformers reduce voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains voltage (230V in India) to a safer low voltage.
The input coil is called the primary and the output coil is called the secondary. There is no electrical connection between the two coils; instead they are linked by an alternating magnetic field created in the soft-iron core of the transformer. Transformers waste very little power so the power out is (almost) equal to the power in. Note that as voltage is stepped down current is stepped up.
The transformer will step down the power supply voltage 230V) to (0-6V) level. Then the secondary of the potential transformer will be connected to the bridge rectifier, which is constructed with the help of PN junction diodes. The advantages of using bridge rectifier are it will give peak voltage output as DC. 3.7.2. Rectifier
There are several ways of connecting diodes to make a rectifier to convert AC to DC. The bridge rectifier is the most important and it produces full-wave varying DC. A full-wave rectifier can also be made from just two diodes if a centre-tap transformer is used, but this method is rarely used now that diodes are cheaper. A single diode can be used as a rectifier but it only uses the positive (+)
3.7.2.1. Single Diode Rectifier
A single diode can be used as a rectifier but this produces half-wave varying DC which has gaps when the AC is negative. It is hard to smooth this sufficiently well to supply electronic circuits unless they require a very small current so the smoothing capacitor does not significantly discharge during the gaps
Fig. 3.8 Single Diode Rectifier
Fig. 3.9 Output waveform of Single Diode Rectifier 3.7.2.2. Bridge Rectifier
When four diodes are connected as shown in figure, the circuit is called as bridge rectifier. The input to the circuit is applied to the diagonally opposite corners of the network, and the output is taken from the remaining two corners. Let
us assume that the transformer is working properly and there is a positive potential, at point A and a negative potential at point B. the positive potential at point A will forward bias D3 and reverse bias D4.
The negative potential at point B will forward bias D1 and reverse D2. At this time D3 and D1 are forward biased and will allow current flow to pass through them; D4 and D2 are reverse biased and will block current flow.
One advantage of a bridge rectifier over a conventional full-wave rectifier is that with a given transformer the bridge rectifier produces a voltage output that is nearly twice that of the conventional full-wave circuit.
Assume that the same transformer is used in both circuits. The peak voltage developed between points X and y is 1000 volts in both circuits. In the conventional full-wave circuit, the peak voltage from the center tap to either X or Y is 500 volts. Since only one diode can conduct at any instant, the maximum voltage that can be rectified at any instant is 500 volts.
The maximum voltage that appears across the load resistor is nearly-but never exceeds-500 v0lts, as result of the small voltage drop across the diode. In the bridge rectifier shown in view B, the maximum voltage that can be rectified is the full secondary voltage, which is 1000 volts. Therefore, the peak output voltage across the load resistor is nearly 1000 volts. With both circuits using the same transformer, the bridge rectifier circuit produces a higher output voltage than the conventional full-wave rectifier circuit.
Fig. 3.10 Bridge Rectifier
3.7.3. Smoothing
Smoothing is performed by a large value electrolytic capacitor connected across the DC supply to act as a reservoir, supplying current to the output when the varying DC voltage from the rectifier is falling. The diagram shows the unsmoothed varying DC (dotted line) and the smoothed DC (solid line). The capacitor charges quickly near the peak of the varying DC, and then discharges as it supplies current to the output.
Note that smoothing significantly increases the average DC voltage to almost the peak value (1.4 × RMS value). For example 6V RMS AC is rectified to full wave DC of about 4.6V RMS (1.4V is lost in the bridge rectifier), with smoothing this increases to almost the peak value giving 1.4 × 4.6 = 6.4V smooth DC.
Fig. 3.12 Smoothing Capacitor and its Output Waveform
Smoothing is not perfect due to the capacitor voltage falls a little as it discharges, giving a small ripple voltage. For many circuits a ripple which is 10% of the supply voltage is satisfactory. A larger capacitor will give fewer ripples. The capacitor value must be doubled when smoothing half-wave DC.
3.7.4. Voltage Regulators
Voltage regulators comprise a class of widely used ICs. Regulator IC units contain the circuitry for reference source, comparator amplifier, control device, and overload protection all in a single IC. IC units provide regulation of either a fixed positive voltage, a fixed negative voltage, or an adjustably set voltage. The regulators can be selected for operation with load currents from hundreds of milli amperes to tens of amperes, corresponding to power ratings from milli watts to tens of watts.
A fixed three-terminal voltage regulator has an unregulated dc input voltage, Vi, applied to one input terminal, a regulated dc output voltage, Vo, from a second terminal, with the third terminal connected to ground.
The series 78 regulators provide fixed positive regulated voltages from 5 to 24 volts. Similarly, the series 79 regulators provide fixed negative regulated voltages from 5 to 24 volts.
3.7.4.1. IC Voltage Regulators
Voltage regulator ICs are available with fixed (typically 5, 12 and 15V) or variable output voltages. They are also rated by the maximum current they can pass. Negative voltage regulators are available, mainly for use in dual supplies. Most regulators include some automatic protection from excessive current ('overload protection') and overheating ('thermal protection').
Many of the fixed voltage regulator ICs has 3 leads and look like power transistors, such as the 7805 +5V 1Amp regulator. They include a hole for attaching a heat sink if necessary.
3.7.4.2. Zener Diode Regulator
For low current power supplies a simple voltage regulator can be made with a resistor and a zener diode connected in reverse as shown in the diagram. Zener diodes are rated by their breakdown voltage and maximum power (typically 400mW or 1.3W).
The resistor limits the current (like an LED resistor). The current through the resistor is constant, so when there are no output current all the current flows through the zener diode and its power rating must be large enough to withstand this.
Fig. 3.15 Circuit diagram of Power Supply
CHAPTER 4 MICROCONTROLLER
Basically, a microcontroller is a device which integrates a number of the components of a microprocessor system onto a single microchip. So a microcontroller combines onto the same microchip. The following components:
CPU Core
The microprocessor is the integration of a number of useful functions into a single IC package. Has the ability to execute a stored set of instructions to carry out user defined tasks; also has ability to access external memory chips to both read and write data from and to the memory.
Essentially, a microcontroller is obtained by integrating the key components of microprocessor, RAM, ROM, and Digital I/O onto the same chip die. Modern microcontrollers also contain a wealth of other modules such as Serial I/O, Timers, and Analogue to Digital Converters. There are a large number of specialized devices with additional modules for specific needs. E.g. CAN controllers.
4.1. ATMEL 89C51
In our project we are using microprocessor from Atmel namely AT89C51 is a low-power, high-performance CMOS 8-bit Microcomputer with 4K bytes of Flash programmable and erasable read only memory (PEROM). The device is manufactured using Atmel’s high-density nonvolatile memory technology and is compatible with the industry-standard MCS-51 instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a highly-flexible and cost-effective solution to many embedded control applications.
Fig. 4.1 Block Diagram of ATMEL 89C51
Fig. 4.2 Pin Configuration of AT89C51 4.1.3. Pin Description of AT89C51
VCC - Supply voltage. GND - Ground.
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. 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. When 1s are written to Port 2 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the internal pull-ups. Port 2 emits the high-order address byte during fetches from external program memory and during accesses to external data memory that uses 16-bit addresses (MOVX @ DPTR). In this application, it uses strong internal pull-ups when emitting 1s. During accesses to external data memory that uses 8-bit
Register. Port 2 also receives the high-order address bits and some control signals during Flash programming and verification.
PORT 3
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 pulled low will source current (IIL) because of the pull-ups. Port 3 also serves the functions of various special features of the AT89C51 as listed below: Port 3 also receives some control signals for Flash programming and verification.
Table. 4.1 Port 3 Pins
RST
Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.
ALE/PROG
Address Latch Enable output pulse for latching the low byte of the address during accesses to external memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in external execution mode. PSEN
Program Store Enable is the read strobe to external program memory. When the AT89C51 is executing code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory.
EA/VPP
External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to VCC for internal program executions. This pin also receives the 12-volt programming enable voltage (VPP) during Flash programming, for parts that require 12-volt VPP.
XTAL1
Input to the inverting oscillator amplifier and input to the internal clock operating circuit.
XTAL2
Output from the inverting oscillator amplifier. 4.2. OSCILLATOR CHARACTERISTICS
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can be configured for use as an on-chip oscillator, as shown in Figure 1. Either quartz crystal or ceramic resonator may be used. To drive the device from an external clock source, XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 2. There are no requirements on the duty cycle of the external clock signal, since the input to the internal clocking circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high and low time specifications must be observed.
4.2.1. Oscillator Connections
Fig. 4.3 Oscillator Connections 4.3. SPECIAL FUNCTION REGISTERS
A map of the on-chip memory area called the Special Function Register (SFR). Note that not all of the addresses are occupied, and unoccupied addresses may not be implemented on the chip. Read accesses to these addresses will in general return random data, and write accesses will have an indeterminate effect. User software should not write 1s to these unlisted locations, since they may be used in future products to invoke new features. In that case, the reset or inactive values of the new bits will always be 0.
4.3.1. SFRs (Special Function Registers)
timer control, interrupt, serial connection etc.). Even though there are 128 free memory locations intended for their storage, the basic core, shared by all types of 8051 controllers, has only 21 such registers. Rests of locations are intentionally left free in order to enable the producers to further improved models keeping at the same time compatibility with the previous versions. It also enables the use of programs written a long time ago for the microcontrollers which are out of production now.
4.3.2. Timer 2 Registers
Control and status bits are contained in registers T2CON and T2MOD for Timer 2. The register pair (RCAP2H, RCAP2L) is the Capture/Reload registers for Timer 2 in 16-bit capture mode or 16-bit auto-reload mode.
4.3.3. Interrupt Registers
The individual interrupt enable bits are in the IE register. Two priorities can be set for each of the six interrupt sources in the IP register.
4.4. DATA MEMORY
The Internal Data memory is divided into three blocks namely, The lower 128 Bytes of Internal RAM.
The Upper 128 Bytes of Internal RAM. Special Function Register.
Internal Data memory Addresses are always 1 byte wide, which implies an address space of only 256 bytes. However, the addressing modes for internal RAM can accommodate 384 bytes. Direct addresses higher than 7Fh access one memory space and indirect addresses higher than 7Fh access a different memory space.
The lowest 32 bytes are grouped into 4 banks of 8 registers. Program instructions call out these registers as R0 through R7. Two bits in the program status Word (PSW) select which register bank is in use. This architecture allows more efficient use of code space, since register instructions are shorter than instructions that use direct addressing.
The next 16-bytes above the register banks form a block of bit addressable memory space. The micro controller instruction set includes a wide selection of single - bit instructions and this instruction can directly address the 128 bytes in this area. These bit addresses are 00h through 7Fh
The Special Function Register includes Port latches, timers, peripheral controls etc., direct addressing can only access these register. In general, all
Atmel micro controllers have the same SFRs at the same addresses. However, upgrades to the AT89C51 have additional SFRs. Sixteen addresses in SFR space are both byte and bit Addressable. The bit Addressable SFRs are those whose address ends in 000B. The bit addresses in this area are 80h through FFh.
4.5. TIMERS
4.5.1. Timer 0 And 1
Timer 0 and Timer 1 in the AT89C52 operate the same way as Timer 0 and Timer 1 in the AT89C51.
4.5.2. Timer 2
Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event counter. The type of operation is selected by bit C/T2 in the SFR T2CON
down counting), and baud rate generator. The modes are selected by bits in T2CON, as shown in Table 3. Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer function, the TL2 register is incremented every machine cycle. Since a machine cycle consists of 12 oscillator periods, the count rate is 1/12 of the oscillator frequency. In the Counter function, the register is incremented in response to a 1-to-0 transition at its corresponding external input pin, T2. In this function, the external input is sampled during S5P2 of every machine cycle. When the samples show a high in one cycle and a low in the next cycle, the count is incremented. The new count value appears in the register during S3P1 of the cycle following the one in which the transition was detected. Since two machine cycles (24 oscillator periods) are required to recognize a 1-to-0 transition, the maximum count rate is 1/24 of the oscillator frequency. To ensure that a given level is sampled at least once before it changes, the level should be held for at least one full machine cycle.
CHAPTER 5
SOFTWARE DESCRIPITION 5.1. EMBEDDED LANGUAGE
Embedded software is in almost every electronic device designed today. There is software hidden away inside our watches, microwave, Music system, cellular phones etc .military uses embedded software to guide smart missiles and detect enemy aircraft; communication satellites, space probes and modern medicine could be nearly impossible without it. Embedded softwares are developed using a different version of c called embedded c which is a different version of c to suit the programming of microcontroller.
5.2. INTRODUCTION TO KEIL COMPILER
When the Keil µVision is used, the project development cycle is roughly the same as it is for any other software development project.
Create source file in C or assembly
Build application with the project manager Correct errors in source file
Test the linked application 5.3. µ VISION IDE
The µvision IDE combines project managements, a rich featured editor with interactive error correction, option setup make facility, and online help. Use
embedded application and provides a single focal point for your development efforts.
5.4. C51 COMPILER AND A51 MACRO ASSEMBLER
Source file created by µ vision IDE and passed to the C51 compiler macro assembler. The compiler and assembler process source files and create relocatable object files. The keil C51 compiler is a full ANSI implementation of the C programming language that supports all standard features of the C language.
5.5. LIB51 LIBRARY MANAGER
The LIB 51 lib manager allows you to create object library from the object file created by the compiler and assembler. Libraries are specially, ordered collection of object modules that may be used by the linker at a later time. When the linker processes a library, only those object modules in the library that are necessary to create the program are used.
5.6. BL 51 LINKER/LOCATOR
The BL 51 linker/locator creates an absolute ELF/DWARF files using the object module extracted from libraries and those created by the compilers and assembler. An absolute object file or module contains no relocatable code and data reside at a fixed memory location. The absolute ELF/DWARF file used:
To program ad flash ROM or other memory devices with µVision debugger for simulation and target debugging.
5.7. µVISION DEBUGGER
µVision symbolic source level debugger is ideally suited for fast, reliable program debugging. The debugger includes a high-speed simulator that can simulate an entire 8051 system including on-chip peripherals and external hardwares. The attributes of the chip used are automatically configured when device is selected from device database.
The µVision debugger provides several ways for testing programs on real target hardware.
Install the Mon51 target monitor on the target system and download the program using the Monitor51 interface built into the µVision Debugger.
Use the advanced GDI interface to attach, use the µVision Debugger
CHAPTER 6 CONCLUSION
The design and development of RF based station name intimation inside train compartment have been successfully designed, fabricated and tested. With the implementation of low cost and flexibility in design, this kit can reduce our tension in journey to unknown place. This project demonstrates how RF signal along with embedded system can make our life simpler without causing any ill effect or affecting other devices. There are plenty of such examples showing how embedded system makes our life simpler and tension free. Our project has plenty of rooms for expansion like the use of GPS system instead of RF signal, interfacing with pc for different forms of output, harness of solar energy as the unit consumes very low power etc. Its use is not limited to bus stand or railway station, with suitable modification the system can be used to serve other purposes like providing assistance to blind in their homes, providing security for valuable items etc.
APPENDIX
1. MICROCONTROLLER PROGRAM
1.1. Main Coding #include <REGX51.H> #include <intrins.H>
void wrt_lcd(unsigned char*); void lcd_init(void);
void cmd(unsigned int); bit station1,station2; void delay(unsigned int);
sbit v1=P2^2; sbit v2=P2^3; void main() { lcd_init(); P2=0xFF; //P2_0=0; cmd(0x01); cmd(0x80); wrt_lcd("RF Base station");
wrt_lcd(" Name Display "); delay(65000); delay(65000); delay(65000); //P2_0=1; while(!P2_0&&!P2_1); while(1) { if((P2_0==0)&&!station1) { P2_3=0; cmd(0x01); cmd(0x80); wrt_lcd("Nagerkoil"); delay(65000); delay(65000); delay(65000); delay(65000); delay(65000); delay(65000); cmd(0x01); cmd(0x80); wrt_lcd("RF Base station");
cmd(0xC0); wrt_lcd(" Name Display "); station1=1; station2=0; P2_3=1; } if((P2_1==0)&&!station2) { P2_2=0; cmd(0x01); cmd(0x80); wrt_lcd("Chennai"); delay(65000); delay(65000); delay(65000);delay(65000);delay(65000); cmd(0x01); cmd(0x80); wrt_lcd("RF Base station"); cmd(0xC0); wrt_lcd(" Name Display "); P2_2=1;
} // } } 1.2. LCD Coding #include<regx51.h> #include<intrins.h> //sbit busy=P2^7; sbit RS=P3^5; sbit RW=P3^6; sbit EN=P3^7;
void delay(unsigned int x) { unsigned int i; for(i=0;i<=x;i++) _nop_(); } //void check()
//{ // busy=1; // RS=0; // RW=1; // EN=0; // delay(3); // EN=1; // while(busy==1); //}
void cmd(unsigned char x) { P1=x; RS=0; RW=0; EN=1; delay(3); EN=0; delay(100); } void lcd_init() {
cmd(0x01); cmd(0x80); delay(100); }
void dat(unsigned char y) { P1=y; RS=1; RW=0; EN=1; delay(3); EN=0; delay(100); }
void wrt_lcd(unsigned char *p) { while(*p!='\0') { dat(*p); p++; } }
REFERENCES
1. Ajay V Deshmukh (2008), ‘Microcontrollers (Theory and Applications)’,
Tata McGraw Hill Publishing Limited.
2. Muhammad Ali Mazidi and Janice Mazidi F (2000), ‘051 microcontroller
and embedded system’, Pearson education.
3. Ray and Bhuruchandi (2000), ‘Advanced Microprocessor and Peripherals’,
Tata McGraw Hill Publishing Company Limited. 4. Websites:
www.atmel.com www.rentron.com
www.keil.com/ace/chip3611.htm www.wikipedia.com
