4 HARDWARE COMPONENTS.docx

7/27/2019 4 HARDWARE COMPONENTS.docx

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HARDWARE DESIGN

Introduction

In this chapter we are going to cover all parts of Automatic station indicator system for

railways in detailed manner and their functions in brief. Here we are more interested about the

Microcontroller since it is the heart of the project. So the complete architecture is explained and

also significance of the Microcontroller.

Hardware Tools:

1. Microcontroller AT89S52.2. RF receiver and transmitter3. RF encoder and decoder.4. LCD

MICRO CONTROLLER (AT89S51)

Introduction

A Micro controller consists of a powerful CPU tightly coupled with memory, various I/O

interfaces such as serial port, parallel port timer or counter, interrupt controller, data acquisition

interfaces-Analog to Digital converter, Digital to Analog converter, integrated on to a single

silicon chip.

If a system is developed with a microprocessor, the designer has to go for external

memory such as RAM, ROM, EPROM and peripherals. But controller is provided all these

facilities on a single chip. Development of a Micro controller reduces PCB size and cost of

design.


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One of the major differences between a Microprocessor and a Micro controller is that a

controller often deals with bits not bytes as in the real world application.

Intel has introduced a family of Micro controllers called the MCS-51.

Figure: micro controller

Features:

Compatible with MCS-51 Products

4K Bytes of In-System Programmable (ISP) Flash Memory

Endurance: 1000 Write/Erase Cycles

4.0V to 5.5V Operating Range

Fully Static Operation: 0 Hz to 33 MHz

Three-level Program Memory Lock

128 x 8-bit Internal RAM

32 Programmable I/O Lines

Two 16-bit Timer/Counters

Six Interrupt Sources

Full Duplex UART Serial Channel

Low-power Idle and Power-down Modes


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Description

The AT89S51 is a low-power, high-performance CMOS 8-bit microcontroller with 4K bytes of in-

system programmable Flash memory. The device is manufactured using Atmels high-density

nonvolatile memory technology and is compatible with the industry- standard 80C51 instruction set

and pinout. 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 in-system

programmable Flash on a monolithic chip, the Atmel AT89S51 is a powerful microcontroller which

provides a highly-flexible and cost-effective solution to many embedded control applications.

Block diagram:

Figure: Block diagram


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Pin diagram:

Figure: pin diagram of micro controller

Pin Description

VCC - Supply voltage.

GND - Ground.

Port 0:

Port 0 is an 8-bit open drain bidirectional 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

can also be configured to be the multiplexed low-order address/data bus during accesses to external


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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 bidirectional I/O port with internal pull-ups. The Port 1 output buffers can

sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal

pull-ups and can be used as inputs. 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:




source current (IIL) because of the internal pull-ups. Port 2 also receives the high-order address bits

and some control signals during Flash programming and verification.

Port 3:


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source current (IIL) because of the pull-ups. Port 3 receives some control signals for Flash

programming and verification. Port 3 also serves the functions of various special features of the

AT89S51, as shown in the following table.

RST:

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

device. This pin drives High for 98 oscillator periods after the Watchdog times out. The DISRTO bit

in SFR AUXR (address 8EH) can be used to disable this feature. In the default state of bit DISRTO,

the RESET HIGH out feature is enabled.

ALE/PROG:

Address Latch Enable (ALE) is an output pulse for latching the low byte of the address during

accesses to external memory. This pin is also the program pulse input (PROG) during Flash

programming. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency


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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 (PSEN) is the read strobe to external program memory. When the

AT89S51 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.

XTAL1:

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

XTAL2:

Output from the inverting oscillator amplifier.

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 Figs 6.2.3. Either a quartz

crystal or ceramic resonator may be used. To drive the device from an external clock source,


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XTAL2 should be left unconnected while XTAL1 is driven as shown in Figure 6.2.4.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.

Fig 6.2.3 Oscillator Connections Fig 6.2.4 External Clock Drive Configuration

REGULATED POWER SUPPLY

The power supplies are designed to convert high voltage AC mains electricity to a

suitable low voltage supply for electronics circuits and other devices. A RPS (Regulated Power

Supply) is the Power Supply with Rectification, Filtering and Regulation being done on the AC

mains to get a Regulated power supply for Microcontroller and for the other devices being

interfaced to it.

A power supply can by broken down into a series of blocks, each of which performs aparticular function. A d.c power supply which maintains the output voltage constant irrespective

of a.c mains fluctuations or load variations is known as Regulated D.C Power Supply

For example a 5V regulated power supply system as shown below:


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Transformer:

A transformer is an electrical device which is used to convert electrical power from one

Electrical circuit to another without change in frequency.

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 in output voltage, step-down transformers decrease in output

voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains

voltage 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. The two lines in the

middle of the circuit symbol represent the core. 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 ratio of the number of turns on each coil, called the turns ratio, determines the

ratio of the voltages. A step-down transformer has a large number of turns on its primary (input)


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coil which is connected to the high voltage mains supply, and a small number of turns on its

secondary (output) coil to give a low output voltage.

An Electrical Transformer

Turns ratio = Vp/ VS = Np/NS

Power Out= Power In

VS X IS=VP X IP

Vp = primary (input) voltage

Np = number of turns on primary coil

Ip = primary (input) current

RECTIFIER:

A circuit which is used to convert a.c to dc is known as RECTIFIER. The process ofconversion a.c to d.c is called rectification

TYPES OF RECTIFIERS:

Half wave Rectifier


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Full wave rectifier1. Centre tap full wave rectifier.

2. Bridge type full bridge rectifier.

Comparison of rectifier circuits:

Parameter

Type of Rectifier

Half wave Full wave Bridge

Number of diodes 1 2 4

PIV of diodes Vm 2Vm Vm

D.C output voltage Vm/z 2Vm/ 2Vm/

Vdc, at no-load 0.318Vm 0.636Vm 0.636Vm

Ripple factor 1.21 0.482 0.482

Ripple frequency f 2f 2f

Rectification efficiency 0.406 0.812 0.812

Transformer Utilization

Factor(TUF)0.287 0.693 0.812


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RMS voltage Vrms Vm/2 Vm/2 Vm/2

Full-wave Rectifier:

From the above comparison we came to know that full wave bridge rectifier as more

advantages than the other two rectifiers. So, in our project we are using full wave bridge rectifier

circuit.

Bridge Rectifier:

A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-

wave rectification. This is a widely used configuration, both with individual diodes wired as

shown and with single component bridges where the diode bridge is wired internally.

A bridge rectifier makes use of four diodes in a bridge arrangement as shown in fig (a) to

achieve full-wave rectification. This is a widely used configuration, both with individual diodes

wired as shown and with single component bridges where the diode bridge is wired internally.

Fig (A)

Operation:


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During positive half cycle of secondary, the diodes D2 and D3 are in forward biased while D1

and D4 are in reverse biased as shown in the fig(b). The current flow direction is shown in the fig

(b) with dotted arrows.

Fig (B)

During negative half cycle of secondary voltage, the diodes D1 and D4 are in forward

biased while D2 and D3 are in reverse biased as shown in the fig(c). The current flow direction is

shown in the fig (c) with dotted arrows.

Fig(C)

Filter:

A Filter is a device which removes the a.c component of rectifier output but allows the

d.c component to reach the load.


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Capacitor Filter:

We have seen that the ripple content in the rectified output of half wave rectifier is

121% or that of full-wave or bridge rectifier or bridge rectifier is 48% such high percentages of

ripples is not acceptable for most of the applications. Ripples can be removed by one of the

following methods of filtering.

(a) A capacitor, in parallel to the load, provides an easier by pass for the ripples voltage though

it due to low impedance. At ripple frequency and leave the D.C. to appear at the load.

(b) An inductor, in series with the load, prevents the passage of the ripple current (due to high

impedance at ripple frequency) while allowing the d.c (due to low resistance to d.c).

(c) Various combinations of capacitor and inductor, such as L-section filter section filter,

multiple section filter etc. which make use of both the properties mentioned in (a) and (b) above.

Two cases of capacitor filter, one applied on half wave rectifier and another with full wave

rectifier.

Filtering 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 capacitor charges quickly near the peak of the varying DC, and then

discharges as it supplies current to the output. Filtering significantly increases the average DC

voltage to almost the peak value (1.4 RMS value).

To calculate the value of capacitor(C),

C = *3*f*r*Rl

Where,

f = supply frequency,

r = ripple factor,

Rl = load resistance

Note: In our circuit we are using 1000F hence large value of capacitor is placed to

reduce ripples and to improve the DC component.

Regulator:


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Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable

output voltages. The maximum current they can pass also rates them. 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 regulators ICs have 3 leads and look like power transistors, such as the 7805

+5V 1A regulator shown on the right. The LM7805 is simple to use. You simply connect the

positive lead of your unregulated DC power supply (anything from 9VDC to 24VDC) to the

Input pin, connect the negative lead to the Common pin and then when you turn on the power,

you get a 5 volt supply from the output pin.

Fig 6.1.6 A Three Terminal Voltage Regulator

78XX:

The Bay Linear LM78XX is integrated linear positive regulator with three terminals. The

LM78XX offer several fixed output voltages making them useful in wide range of applications.

When used as a zener diode/resistor combination replacement, the LM78XX usually results in an

effective output impedance improvement of two orders of magnitude, lower quiescent current.

The LM78XX is available in the TO-252, TO-220 & TO-263packages,

Features:

Output Current of 1.5A

Output Voltage Tolerance of 5%

Internal thermal overload protection


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Internal Short-Circuit Limited

Output Voltage 5.0V, 6V, 8V, 9V, 10V, 12V, 15V, 18V, 24V.

Liquid Crystal Display

Introduction to LCD:

In recent years the LCD is finding widespread use replacing LED s (seven-segment LED or other

multi segment LED s). This is due to the following reasons:

1. The declining prices of LCD s.2. The ability to display numbers, characters and graphics. This is in

contract to LED s, which are limited to numbers and a few characters.

3. Incorporation of a refreshing controller into the LCD, there by relieving the CPU of thetask of refreshing the LCD. In the contrast, the LED must be refreshed by the CPU to

keep displaying the data.

4. Ease of programming for characters and graphics.

USES:

The LCD s used exclusively in watches, calculators and measuring instruments is the

simple seven-segment displays, having a limited amount of numeric data. The recent advances in

technology have resulted in better legibility, more information displaying capability and a wider


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temperature range. These have resulted in the LCD s being extensively used in

telecommunications and entertainment electronics. The LCD s has even started replacing the

cathode ray tubes (CRTs) used for the display of text and graphics, and also in small TV

applications.

S p e c i f i c a t i o n s

Number of Characters: 16 characters x 2 Lines Character Table: English-European (RS in Datasheet) Module dimension: 80.0mm x 36.0mm x 13.2mm(MAX) View area: 66.0 x 16.0 mm Active area: 56.2 x 11.5 mm Dot size: 0.56 x 0.66 mm Dot pitch: 0.60 x 0.70 mm Character size: 2.96 x 5.46 mm Character pitch: 3.55 x 5.94 mm LCD type: STN, Positive, Transflective, Yellow/Green Duty: 1/16 View direction: Wide viewing angle Backlight Type: yellow/green LED RoHS Compliant: lead free Operating Temperature: -20C to + 70C

LCD PIN DIAGRAM:
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LCD pin description

The LCD discussed in this section has 14 pins. The function of each pin is given in table.

TABLE 1: Pin description for LCD:

Pin symbol I/O Description

1 Vss -- Ground

2 Vcc -- +5V power supply

3 VEE -- Power supply to

control contrast

4 RS I RS=0 to select

command register

RS=1 to select

data register

5 R/W I R/W=0 for write

R/W=1 for read

6 E I/O Enable


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7 DB0 I/O The 8-bit data bus








TABLE 2: LCD Command Codes

Code

(hex)

Command to LCD Instruction

Register

1 Clear display screen

2 Return home

4 Decrement cursor

6 Increment cursor

5 Shift display right

7 Shift display left

8 Display off, cursor off


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A Display off, cursor on

C Display on, cursor off

E Display on, cursor on

F Display on, cursor blinking

10 Shift cursor position to left

14 Shift cursor position to right

18 Shift the entire display to the left

1C Shift the entire display to the right

80 Force cursor to beginning of 1st

line

C0 Force cursor to beginning of 2n

line

38 2 lines and 5x7 matrix

LCD INTERFACING

Sending commands and data to LCDs with a time delay:


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To send any command from table 2 to the LCD, make pin RS=0. For data, make RS=1.Then

place a high to low pulse on the E pin to enable the internal latch of the LCD.

plate is attached to a metal plate with adhesives.

Fig. 2 shows the oscillating system of a piezoelectric diaphragm. Applying D.C. voltage

between electrodes of a piezoelectric diaphragm causes mechanical distortion due to the

piezoelectric effect. For a misshaped piezoelectric element, the distortion of the piezoelectric

element expands in a radial direction. And the piezoelectric diaphragm bends toward the

direction shown in Fig.2 (a).


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The metal plate bonded to the piezoelectric element does not expand. Conversely, when

the piezoelectric element shrinks, the piezoelectric diaphragm bends in the direction shown in

Fig.2 (b). Thus, when AC voltage is applied across electrodes, the bending shown in Fig.2 (a)

and Fig.2 (b) is repeated as shown in Fig.2 (c), producing sound waves in the air.

DESIGN PROCEDURES:

In general, man's audible frequency range is about 20 Hz to 20kHz. Frequency ranges of

2kHz to 4kHz are most easily heard. For this reason, most piezoelectric sound components areused in this frequency range, and the resonant frequency (f0) is generally selected in the same

range too. As shown in Fig. 3, the resonant frequency depends on methods used to support the

piezoelectric diaphragm. If piezoelectric diaphragms are of the same shape, their values will

become smaller in the order of (a), (b) and (c).


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In general, the piezoelectric diaphragm is installed in a cavity to produce high sound

pressure. The resonant frequency (fcav) of the cavity in is obtained from Formula (1)

(Helmholtz's Formula). Since the piezoelectric diaphragm and cavity have proper resonant

frequencies, (f0) and (fcav) respectively, sound pressure in specific frequencies can be increased

and a specific bandwidth can be provided by controlling both positions.

RF transmitter section:

RF transmitters are electronic devices that create continuously varying electric current, encode

sine waves, and broadcast radio waves. RF transmitters use oscillators to create sine waves, the simplest

and smoothest form of continuously varying waves, which contain information such as audio and video.

Modulators encode these sign wives and antennas broadcast them as radio signals. There are several

ways to encode or modulate this information, including amplitude modulation (AM) and frequency

modulation (FM). Radio techniques limit localized interference and noise. With direct sequence spread

spectrum, signals are spread over a large band by multiplexing the signal with a code or signature that

modulates each bit. With frequency hopping spread spectrum, signals move through a narrow set of

channels in a sequential, cyclical, and predetermined pattern.

Selecting RF transmitters requires an understanding of modulation methods such as AM and

FM. On-off key (OOK), the simplest form of modulation, consists of turning the signal on or off.

Amplitude modulation (AM) causes the base band signal to vary the amplitude or height of the carrier


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wave to create the desired information content. Frequency modulation (FM) causes the instantaneous

frequency of a sine wave carrier to depart from the center frequency by an amount proportional to the

instantaneous value of the modulating signal. Amplitude shift key (ASK) transmits data by varying the

amplitude of the transmitted signal. Frequency shift key (FSK) is a digital modulation scheme using two

or more output frequencies. Phase shift key (PSK) is a digital modulation scheme in which the phase of

the transmitted signal is varied in accordance with the base band data signal.

Additional considerations when selecting RF transmitters include supply voltage, supply current,

RF connectors, special features, and packaging. Some RF transmitters include visual or audible alarms or

LED indicators that signal operating modes such as power on or reception. Other devices attach to

coaxial cables or include a connector or port to which an antenna can be attached. Typically, RFtransmitters that are rated for outdoor use feature a heavy-duty waterproof design. Devices with

internal calibration and a frequency range switch are also available.

RF transmitters are used in a variety of applications and industries. Often, devices that are used

with integrated circuits (ICs) incorporate surface mount technology (SMT), through hole technology

(THT), and flat pack. In the telecommunications industry, RF transmitters are designed to fit in a

metal rack that can be installed in a cabinet. RF transmitters are also used in radios and in electronic

article surveillance systems (EAS) found in retail stores. Inventory management systems use RF

transmitters as an alternative to barcodes.

RF transmitter ST-TX01-ASK:

General Description:

The ST-TX01-ASK is an ASK Hybrid transmitter module. The ST-TX01-ASK is

designed by the Saw Resonator, with an effective low cost, small size, and simple-to-use for

designing.


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Frequency Range: 315 / 433.92 MHZ. Supply Voltage: 3~12V. Output Power: 4~16dBm Circuit Shape: Saw

Applications

Wireless security systems Car Alarm systems Remote controls.

Sensor reporting Automation systems


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Fig 17: Pin Description of the Transmitter module


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Fig 18: Interfacing TX module to a Micro controller

RF ENCODER (HT12E):

Features

_ Operating voltage

_ 2.4V~5V for the HT12A

_ 2.4V~12V for the HT12E

_ Low power and high noise immunity CMOS technology

_ Low standby current: 0.1_A (typ.) at VDD=5V

_ HT12A with a 38kHz carrier for infrared transmission medium

_ Minimum transmission word

_ Four words for the HT12E

_ One word for the HT12A

_ Built-in oscillator needs only 5% resistor

_ Data code has positive polarity


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_ Minimal external components

_ HT12A/E: 18-pin DIP/20-pin SOP package

Applications

_ Burglar alarm system

_ Smoke and fire alarm system

_ Garage door controllers

_ Car door controllers

_ Car alarm system

_ Security system

_ Cordless telephones

_ Other remote control systems

General Description

The 212 encoders are a series of CMOS LSIs for remote control system applications. They are capable of

encoding information which consists of N address bits and 12_N data bits. Each address/data input can

be set to one of the two logic states. The programmed addresses/data are transmitted together with the

header bits via an RF or an infrared transmission medium upon receipt of a trigger signal. The capability

to select a TE trigger on the HT12E or a DATA trigger on the HT12A further enhances the application

flexibility of the 212 series of encoders. The HT12A additionally provides a 38kHz carrier for infrared

systems.


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Note: Address/Data represents pins that can be address or data according to the decoder requirement.

Fig 19: Block diagram of HT 12E Encoder

Pin Description:

Fig 20: Pin description of HT12E


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Note: D8~D11 are all data input and transmission enable pins of the HT12A.

TE is a transmission enable pin of the HT12E.

Absolute Maximum Ratings


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Supply Voltage (HT12A) .............._0.3V to 5.5V

Storage Temperature................._50_C to 125_C

Operating Temperature..............._20_C to 75_C

Supply Voltage (HT12E) ..............._0.3V to 13V

Input Voltage....................VSS_0.3 to VDD+0.3V


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Fig 21: Timing diagram of the HT12E and HT12A

Application Circuits:


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Fig 22: Application circuit of HT12E

Flow Chart:


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Fig 23: Flow chat for data transmission in HT12E

RF receiver section:

RF receivers are electronic devices that separate radio signals from one another and convert

specific signals into audio, video, or data formats. RF receivers use an antenna to receive transmitted

radio signals and a tuner to separate a specific signal from all of the other signals that the antenna

receives. Detectors or demodulators then extract information that was encoded before transmission.

There are several ways to decode or modulate this information, including amplitude modulation (AM)

and frequency modulation (FM). Radio techniques limit localized interference and noise. With direct

sequence spread spectrum, signals are spread over a large band by multiplexing the signal with a code

or signature that modulates each bit. With frequency hopping spread spectrum, signals move through a

narrow set of channels in a sequential, cyclical, and predetermined pattern.

Selecting RF receivers requires an understanding of modulation methods such as AM

and FM. On-off key (OOK), the simplest form of modulation, consists of turning the signal on or off.

Amplitude modulation (AM) causes the base band signal to vary the amplitude or height of the carrier

wave to create the desired information content. Frequency modulation (FM) causes the instantaneous

frequency of a sine wave carrier to depart from the center frequency by an amount proportional to the

instantaneous value of the modulating signal. Amplitude shift key (ASK) transmits data by varying the

amplitude of the transmitted signal. Frequency shift key (FSK) is a digital modulation scheme using two

or more output frequencies. Phase shift key (PSK) is a digital modulation scheme in which the phase of

the transmitted signal is varied in accordance with the base band data signal.

RF receivers vary in terms of performance specifications such as sensitivity, digital

sampling rate, measurement resolution, operating frequency, and communication interface. Sensitivity

is the minimum input signal required to produce a specified output signal having a specified signal-to-

noise (S/N) ratio. Digital sampling rate is the rate at which samples can be drawn from a digital signal in

kilo samples per second. Measurement resolution is the minimum digital resolution, while operating

frequency is the range of received signals. Communication interface is the method used to output data

to computers. Parallel interfaces include general-purpose interface bus (GPIB), which is also known as

IEEE 488 and HPIB Protocol. Serial interfaces include universal serial bus (USB), RS232, and RS485.


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Additional considerations when selecting RF receivers include supply voltage, supply

current, receiver inputs, RF connectors, special features, and packaging. Some RF receivers include visual

or audible alarms or LED indicators that signal operating modes such as power on or reception. Otherdevices attach to coaxial cables or include a connector or port to which an antenna can be attached.

Typically, RF receivers that are rated for outdoor use feature a heavy-duty waterproof design. Devices

with internal calibration and a frequency range switch are also available.

RF receiver ST-RX04-ASK:

Description:

The RX04 is a low power ASK receiver IC which is fully compatible with the

MitelKESRX01 IC and is suitable for use in a variety of low power radio applications including remote

keyless entry. The RX04 is based on a single-

Conversion, super-heterodyne receiver architecture and incorporates an entire phase-locked loop (PLL)

for precise local oscillator generation.

Applications:

Wireless security systems Sensor reporting automation system Remote Keyless entry

Features

Low power consumption. Easy for application. On-Chip VCO with integrated PLL using crystal oscillator reference.


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Integrated IF and data filters. Operation temperature range :1060 Operation voltage: 5 Volts.

Available frequency at : 315/434 MHz

Functional description:

Fig: RF receiver module.

Fig 24: RF receiver module.

RF DECODER (HT 12D):

Features

_ Operating voltage: 2.4V~12V

_ Low power and high noise immunity CMOS technology


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_ Low standby current

_ Capable of decoding 12 bits of information

_ Binary address setting

_ Received codes are checked 3 times

_ Address/Data number combination

_ HT12D: 8 address bits and 4 data bits

_ HT12F: 12 address bits only

_ Built-in oscillator needs only 5% resistor

_ Valid transmission indicator

_ Easy interface with an RF or an infrared transmission medium

_ Minimal external components

_ Pair with Holteks 212 series of encoders

_ 18-pin DIP, 20-pin SOP package

Applications

_ Burglar alarm system

_ Smoke and fire alarm system

_ Garage door controllers

_ Car door controllers

_ Car alarm system

_ Security system

_ Cordless telephones


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_ Other remote control systems

General Description

The 212 decoders are a series of CMOS LSIs for remote control system applications. They are

paired with Holteks 212 series of encoders (refer to the encoder/decoder cross reference table). 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 a programmed 212 series of

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 212 series of decoders are capable of decoding informations

that consist of N bits of address and 12_N bits of data. Of this series, the HT12D is arranged to provide 8

address bits and 4 data bits, and HT12F is used to decode 12 bits of address information.

Notes: Data type: L stands for latch type data output.

VT can be used as a momentary data output.


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Fig 25:

Block Diagram of HT 12D Decoder

Note: The address/data pins are available in various combinations (see the address/data table).

Pin Assignment:

Fig 26: Pin diagram of HT12D


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Absolute Maximum Ratings

Supply Voltage .........................................._0.3V to 13V

Storage Temperature ............................_50_C to 125_C

Input Voltage ................................VSS_0.3 to VDD+0.3V

Operating Temperature..........................._20_C to 75_C


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Functional Description

Operation

The 212 series of decoders provides various combinations of addresses and data pins in different

packages so as to pair with the 212 series of encoders. The decoders receive data that are transmitted

by an encoder and interpret the first N bits of code period as addresses and the last 12_N bits as data,

where N is the address code number. A signal on the DIN pin activates the oscillator, which in turn

decodes the incoming address and data. The decoders will then check the received address three times

continuously. If the received address codes all match the contents of the decoders local address, the

12_N bits of data are decoded to activate the output pins and the VT pin is set high to indicate a valid

transmission. This will last unless the address code is incorrect or no signal is received. The output of the

VT pin is high only when the transmission is valid. Otherwise it is always low.

Output type

Of the 212 series of decoders, the HT12F has no data output pin but its VT pin can be used as a

momentary data output. The HT12D, on the other hand, provides 4 latch type data pins whose data

remain unchanged until new data are received.


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Fig 27: Timing Diagram of Decoder HT12D


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Fig 28: Application circuit of HT12D

Flowchart

The oscillator is disabled in the standby state and activated when a logic _high_ signal applies to the DIN

pin. That is to say, the DIN should be kept low if there is no signal input.

Fig 29: Flow chart of HT12D for data transmission


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