Chapter-1

INTRODUCTION

1.1 INFRARED REMOTE CONTROL THEORY:

IR is electromagnetic (EM) radiation of wavelengths longer than visible light, but

shorter than RF spanning three orders of magnitude between 750 nm and 1 mm. IrDA, the

Infrared Data Association, champions IR in the electronics sector and most offerings

adhere to the organization's standards, aiding interoperability.

IR remote controls use IR LEDs to emit radiation that's focused by a plastic lens into a

narrow beam. Data is encoded by modulating the beam to provide immunity from other

IR sources such as fluorescent lights.

Thus, the Infrared refers to the energy radiations having frequency below visible

range. These radiations are invisible to human eye but may be perceived as heat signals.

Similarly, these radiations can be easily detected through readily available sensor

modules.

Figure 1.1: Electromagnetic spectrum

Infra-Red is interesting, because it is easily generated and doesn't suffer

electromagnetic interference, so it is nicely used to communication and control, but it is

not perfect, some other light emissions could contains infrared as well, and that can

interfere in this communication.

1

Highly Visible Ultra VioletInfra Red

The sun is an example, since it emits a wide spectrum or radiation. The adventure

of using lots of infra-red in TV/VCR remote controls and other applications, brought

infra-red diodes (emitter and receivers) at very low cost at the market.

This infrared light can mean something to the receiver, the "on or off" radiation

can transmit different meanings. Lot of things can generate infrared, anything that radiate

heat do it, including out body, lamps, stove, oven, friction your hands together, even the

hot water at the faucet. 

To allow a good communication using infra-red, and avoid those "fake" signals, it

is imperative to use a "key" that can tell the receiver what is the real data transmitted and

what is fake.  As an analogy, looking eye naked to the night sky you can see hundreds of

stars, but you can spot easily a far away airplane just by its flashing strobe light.  That

strobe light is the "key", the "coding" element that alerts us.

Similar to the airplane at the night sky, our TV room may have hundreds of tinny

IR sources, our body, and the lamps around, even the hot cup of tea.  A way to avoid all

those other sources, is generating a key, like the flashing airplane.

So, remote controls used to pulsate infrared in a certain frequency.  The IR

receiver module at the TV, VCR or stereo "tunes" to this certain frequency and ignores all

other IR received.  The best frequency for the job is between 30 and 60 kHz, the most

used is around 36 kHz.

So, remote controls use the 36 kHz (or around) to transmit information.  Infrared

light emitted by IR Diodes is pulsated at 36 thousand times per second, when transmitting

logic level "1" and silence for "0". To generate a 36 kHz pulsating infrared is quite easy,

more difficult is to receive and identify this frequency. 

This is why some companies produce infrared receives, that contains the filters,

decoding circuits and the output shaper, that delivers a square wave, meaning the

existence or not of the 36kHz incoming pulsating infrared.

It means that those 3 dollars small units, have an output pin that goes high (+5V)

when there is a pulsating 36kHz infrared in front of it, and zero volts when there is not

this radiation.

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A square wave of approximately 27uS (microseconds) injected at the base of a

transistor, can drive an infrared LED to transmit this pulsating light wave.  Upon its

presence, the commercial receiver will switch its output to high level (+5V).

If this frequency is turned on/off at the transmitter, the receiver indicates it

clearly. Those IR demodulators have inverted logic at its output, when a burst of IR is

sensed it drives its output to low level, meaning logic level = 1.

To avoid a Philips remote control to change channels in a Panasonic TV, they use

different codification at the infrared, even that all of them use basically the same

transmitted frequency, from 36 to 50 kHz. 

So, all of them use a different combination of bits or how to code the transmitted

data to avoid interference. Some standards were created.  In this project we will only

show one of them, the one used by Philips.

Philips adopted or created the RC5 standard that uses fixed bit length and fixed

quantity of bits. In this application RC5 pulse protocol used by Philips TV is decoded

using a microcontroller. In other words, this project develops the IR receiver for the

Philips RC5 protocol and the output has been shown on the hardware through relay

controlled devices corresponding to various channels switched with remote. Also, LEDs

glow corresponding to each output.

In this project we will make a TV receiver for Philips remote control. This remote

control is based on RC5 protocol. This receiver will be an embedded system which can be

used in television sets. The decoding of the RC5 pulse protocol has been done in

assembly level language although we can also use embedded C or Basscom for writing

the program for the microcontroller (We will be using Atmel’s AT89C51 8-bit

microcontroller). The project also involves the design and development of the Printed

Circuit Board (PCB). This provides the additional benefit that no or minimum wiring has

been done, and hence there are less chances of wear and tear. We have on our part tried to

solder the components as finely as possible.

The further chapters clearly explain the RC5 protocol and our efforts towards its

decoding.

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1.1 RC5 PROTOCOL:

The RC-5 code from Philips is possibly the most used protocol by hobbyists. The

protocol is well defined for different device types ensuring compatibility with your whole

entertainment system.

Features:

5 bit address and 6 bit command length (7 command bits for RC5X)

Bi-phase coding (aka Manchester coding)

Carrier frequency of 36kHz

Constant bit time of 1.778ms (64 cycles of 36 kHz)

Manufacturer Philips

Modulation:

The protocol uses bi-phase modulation (or so-called Manchester coding) of a 36

kHz IR carrier frequency. All bits are of equal length of 1.778ms in this protocol, with

half of the bit time filled with a burst of the 36 kHz carrier and the other half being idle.

A logical zero is represented by a burst in the first half of the bit time. A logical

one is represented by a burst in the second half of the bit time. The pulse/pause ratio of

the 36 kHz carrier frequency is 1/3 or 1/4 which reduces power consumption.

Figure 1.2: Modulation

Protocol:

4

889µs889µs 889µs889µs

The figure 3 below shows a typical pulse train of an RC-5 message. This example

transmits command $35 to address $05.

Figure 1.3

The first two pulses are the start pulses, and are both logical "1". Please note that

half a bit time is elapsed before the receiver will notice the real start of the message.

Extended RC-5 uses only one start bit. Bit S2 is transformed to command bit 6,

providing for a total of 7 command bits. The value of S2 must be inverted to get the

7th command bit though!

The 3rd bit is a toggle bit. This bit is inverted every time a key is released and

pressed again. This way the receiver can distinguish between a key that remains

down, or is pressed repeatedly. The next 5 bits represent the IR device address, which

is sent with MSB first.

The address is followed by a 6 bit command, again sent with MSB first.

A message consists of a total of 14 bits, which adds up to a total duration of 25 m sec.

Sometimes a message may appear to be shorter because the first half of the start bit S1

remains idle.

And if the last bit of the message is logic "0" the last half bit of the message is

idle too. As long as a key remains down the message will be repeated every 114ms.

The toggle bit will retain the same logical level during all of these repeated messages.

It is up to the receiver software to interpret this auto repeat feature.

Pre-defined Commands:

Philips has created a beautiful list of "standardized" commands. This ensures the

compatibility between devices from the same brand. A very nice feature, often to be

5

MSB MSBLSB LSB

Start bit (Always “1”)

S1

S2 Address Command

1 1 0 0 0 0 0 01 1 1 1 1 1

missed with other brands, is the fact that most devices are available twice in the table

allowing one to have 2 VCRs stacked on top of each other without having trouble

addressing only one of them with the remote control.

The addresses for various devices may be seen in the Table 1.1.

The TV and VCR commands corresponding to the RC5 command may be seen in

the Table 1.2.

RC-5 Address Device$00-0 TV1$01-1 TV2$02-2 Teletext$03-3 Video$04-4 LV1$05-5 VCR1$06-6 VCR2$07-7 Experimental$08-8 Sat1$09-9 Camera

$0A-10 Sat2$0B-11$0C-12 CDV$0D-13 Camcorder$0E-14$0F-15$10-16 Pre-amp$11-17 Tuner$12-18 Recorder1$13-19 Pre-amp$14-20 CD Player$15-21 Phono$16-22 SatA$17-23 Recorder2$18-24

$19-25$1A-26 CDR$1B-27$1C-28$1D-29 Lighting$1E-30 Lighting$1F-31 Phone

Table 1.1: The addresses for various devices

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RC-5 Command TV Command VCR Command

$00-0 0 0

$01-1 1 1

$02-2 2 2

$03-3 3 3

$04-4 4 4

$05-5 5 5

$06-6 6 6

$07-7 7 7

$08-8 8 8

$09-9 9 9

$0A-10 -/-- -/--

$0C-12 Standby Standby

$0D-13 Mute

$10-16 Volume+

$11-17 Volume-

$12-18 Brightness+

$13-19 Brightness-

$20-32 Program+ Program+

$21-33 Program- Program-

$32-50 Fastrewind

$34-52 Fastforward

$35-53 Play

$36-54 Stop

$37-55 Recording

Table 1.2: TV and VCR commands corresponding to the RC5 command

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Chapter-2

OVERVIEW OF MICROCONTROLLER (AT89C51)

2.1 MICROPROCESSOR AND MICROCONTROLLER BASICS

The past two decades have seen the introduction of a technology that has radically

changed the way in which we analyze and control the world around us. Born of parallel

development in computer architecture and integrated circuit fabrication, the

microprocessor, or “computer on a chip,” first become a commercial reality in 1971 with

the introduction of 4-bit 4004 by a small, unknown company by the name of Intel

Corporation. Other better established, semiconductor firms soon follow Intel’s pioneering

technology so that by the late 1970s one could choose from a half dozen or so

microprocessor types.

The microprocessor[1] has been with us for some 15-years now growing from an

awkward 4-bit chip to a robust 32-bit adult. Soon 64 and 128-bit wizards will appear to

crunch numbers, spreadsheets, and CAD CAM. The engineering community became

aware of, enamored with, the 8-bit microprocessor of the middle to late 1970’s.

The 1970s also saw the growth of the number of personal computer users from a

handful of hobbyists and “hackers” to millions of business, industrial, governmental,

defense, educational, and private users now enjoying the advantages of inexpensive

computing.

New technology makes possible, however, a better type of small computer-one

with not only the CPU on the chip, but RAM, ROM, Timer, UARTS, Ports, and other

common peripheral I/O functions also. The microprocessor has become the

microcontroller[4]. A by-product of microprocessor development was the microcontroller.

The same fabrication techniques and programming concepts that make possible the

general purpose microprocessor also yielded the microcontroller.

Microcontrollers are not as well known to the general public, or even the technical

community, as are the more glamorous microprocessor. The public is, however, very well

8

aware that “something” is responsible for all of the smart VCRs, clock radios washers,

and dryers, video games, telephones, microwaves, TVs, automobiles, toys, Vending

machines, copiers, elevators, irons, and a myriad of other articles that have suddenly

become intelligent and “programmable.” Companies are also aware that being

competitive in this age of microchip requires their products, or the machinery they use to

make those products, to have some “smarts.”

Some manufacturers, hoping to capitalize on our software investment, have

brought our families of microcontrollers that are software compatible with the older

microprocessor. Other, wishing to optimize the instruction set and architecture to improve

speed and reduce code size, produce totally new designs that had little in common with

their earlier microprocessors. Both of these trend continue.

Microprocessor:

A Microprocessor[4], as the term has come to be known is a general purpose

digital computer central processing unit (CPU). Although popularly known as a

“computer on a chip,” the microprocessor is in no sense a complete digital computer.

Figure 1 shows a block diagram of a microprocessor CPU, which contains

arithmetic and logic unit (ALU), a program counter (PC), a stack pointer (SP), some

working registers, a clock timing circuit and interrupt circuits. The microprocessor

contains no RAM, no ROM, and no I/O ports on the chip itself.

The key term in describing the design of microprocessor is “general purpose.” The

hardware design of a microprocessor CPU is arrange so that a small or very large system

can be configured around the CPU as the application demands. The internal CPU

architecture, as well as the resultant machine level code that operates that architecture, is

comprehensive but as flexible as possible.

Although the addition of external RAM, ROM, and I/O ports make these systems

bulkier and much more expensive, they have the advantage of versatility such that the

designer can decide on the amount of RAM, ROM, and I/O ports needed to fit the task at

hand

9

Figure 2.1: A Block Diagram of a Microprocessor

Microcontroller:

A microcontroller[5] has a CPU (a microprocessor) in addition to a fix amount of

RAM, ROM, I/O ports, and a timer all on a single chip. In other words, the processor,

RAM, ROM, I/O ports, and timer are all embedded together on one chip; therefore,

the designer cannot add any external memory, I/O, or timer to it.

Figure 2 shows the block diagram of a typical microcontroller which is a true

computer on a chip. The design incorporates all of the features found in a

microprocessor CPU: ALU, PC, SP, and registers. It also has added the others features

needed to make a complete computer: RAM, ROM, parallel I/O, serial I/O, counters,

and a clock circuit.

10

Accumulator

Working Register(s)

Interrupt Circuit

Clock Circuit

Program Counter Stack Pointer

Arithmetic and

logic unit

Figure 2.2: A block diagram of a Microcontroller

Like the microprocessor, a microcontroller is a general purpose device, but one

which is meant to fetch data, perform limited calculations on that data and control it

environment based on those calculations. The prime use of a microcontroller is to

control the operation of machine using a fixed program that is stored in ROM and that

does not change over the life time of the system.

2.2 CHARACTERISTICS FEATURES OF AT89C51

AT89C51 is an 8-bit microcontroller from Atmel Corporation.

Features

• Compatible with MCS-51™ Products

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Internal ROM

AccumulatorI/O Ports

Interrupt Circuits

Registers

Timer/Counter I/O Ports

Clock Circuit

ALU

Program Counter

Stack Pointer

Internal RAM

• 4K Bytes of In-System Reprogrammable Flash Memory

– Endurance: 1,000 Write/Erase Cycles

• Fully Static Operation: 0 Hz to 24 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

• Programmable Serial Channel

• Low-power Idle and Power-down Modes

2.3 BLOCK DIAGRAM OF AT89C51

The AT89C51[6] 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 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 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.

The AT89C51 provides the following standard features: 4K bytes of Flash, 128

bytes of RAM, 32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt

architecture, full duplex serial port, on-chip oscillator and clock circuitry. In addition, the

AT89C51 is designed with static logic for operation down to zero frequency and supports

two software selectable power saving modes. The Idle Mode stops the CPU while

allowing the RAM, timer/counters, serial port and interrupt system to continue

functioning. The Power-down Mode saves the RAM contents but freezes the oscillator

disabling all other chip functions until the next hardware reset.12

Figure 2.3: Block Diagram of AT89C512.4 PIN DESCRIPTION OF AT89C51:

13

PDIP: Plastic Dual Inline Package.

Figure 2.4: Pin diagram of AT89C51

Pin description:

In the AT89C51 there are a total of four ports for I/O operations.

Examining Figure 5, note that of the 40 pins, a total of 32 pins are set aside for the

four ports P0, P1, P2, and P3, where each port takes 8 pins. The rest of the pins are

designated as Vcc, GND, XTAL1, XTAL2, RST, EA, ALE/PEOG, and PSEN.

VCC:

Supply voltage.

GND:

14

GND

VCC

PO.O(AD 0)

PO.1(AD 1)

PO.3(AD 3)PO.4(AD 4)

PO.5(AD 5)

PO.6(AD 6)

PO.7(AD 7)

PO.2(AD 2)

EA/VPP

P2.7(AD 15)

P2.6(AD 14)

P2.5(AD 13)

P2.4(AD 12)

ALE/PROGPSEN

P2.3(AD 11)

P2.2(AD 10)

P2.1(AD 9)

P2.0(AD 8)

P1.0

P1.2

P1.3

P1.4P1.5

P1.6

P1.7

P1.1

RST

XTAL2

XTAL1

(RXD) P3.O

(TXD) P3.O

(INT0) P3.2 (INT1) P3.3

(T0) P3.4 (T1) P3.5

(WR) P3.6

(RD) P3.7

Ground.

I/O port pins and there functions:

The four ports P0, P1, P2, and P3 each use 8 pins, making them 8 bit ports.

All the ports upon RESET are configured as inputs, ready to be used as input

ports. When the first 0 is written to a port, it becomes an output. To reconfigure it

as an input, a 1 must be sent to the port.

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 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 pullups. Port 0 also receives the code

bytes during Flash programming, and outputs the code bytes during program

verification. External pullups are required during program verification.

Port 1:

Port 1 is an 8-bit bidirectional I/O port with internal pullups. 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 pullups 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 pullups. Port 1 also receives the low-order address bytes during Flash

programming and program verification.

Port 2:

Port 2 is an 8-bit bi-directional I/O port with internal pullups. 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 pullups 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 pullups. Port 2 emits the high-order address byte during fetches from

external program memory and during accesses to external data memory that use

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16-bit addresses (MOVX @ DPTR). In this application, it uses strong internal

pull-ups when emitting 1s. During accesses to external data memory that use 8-bit

addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function

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 pullups. 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 pullups and can be used as inputs. As inputs,

Port 3 pins that are externally being pulled low will source current (IIL) because

of the pullups. Port 3 also serves the functions of various special features of the

AT89C51 as listed below:

Table 2.1

Port 3 also receives some control signals for Flash programming and verification.

RST:

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

is running resets the device.

ALE/PROG:

16

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.

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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 6. Either a 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 7.

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.

Figure 2.5: Oscillator Connections Figure 2.6: External Clock Drive Configurations

Idle Mode:

In idle mode, the CPU puts itself to sleep while all the on-chip peripherals

remain active. The mode is invoked by software. The content of the on-chip RAM

and all the special functions registers remain unchanged during this mode.

The idle mode can be terminated by any enabled interrupt or by a

hardware reset. It should be noted that when idle is terminated by a hard ware

reset, the device normally resumes program execution, from where it left off, up to

two machine cycles before the internal reset algorithm takes control.

On-chip hardware inhibits access to internal RAM in this event, but access

to the port pins is not inhibited. To eliminate the possibility of an unexpected write

to a port pin when Idle is terminated by reset, the instruction following the one

that invokes Idle should not be one that writes to a port pin or to external memory.

18

Power-down Mode:

In the power-down mode, the oscillator is stopped, and the instruction that

invokes power-down is the last instruction executed. The on-chip RAM and

Special Function Registers retain their values until the power-down mode is

terminated. The only exit from power-down is a hardware reset. Reset redefines

the SFRs but does not change the on-chip RAM. The reset should not be activated

before VCC is restored to its normal operating level and must be held active long

enough to allow the oscillator to restart and stabilize.

Status of External Pins during Idle and Power-down Modes:

Table 2.2

Other Pin Configurations:

PQFP/TQFP:

PQFP: Plastic Gull Wing Quad Flatpack.

TQFP: Thin Plastic Gull Wing Quad Flatpack.

2.5 8051 ADDRESSING MODES:

An “addressing mode “refers to how you are addressing a given memory

location. The addressing modes are as follows.

With an example of each:

Immediate Addressing MOV A, #20h

Direct Addressing MOV A, 30h

Indirect Addressing MOV A,@R0

External Direct MOV A,@DPTR

Code Indirect MOV A,@+DPTR

19

Immediate Addressing:

Immediate addressing is so-named because the value to be stored in memory

immediately follows the operation code in memory. That is to say , the instruction

itself dictates what value will be stored in memory.

For example the instruction:

MOV A, #20h

This instruction uses immediate addressing because the Accumulator will

be loaded with the value that immediately follows, in this case 20 (hexadecimal).

Direct Addressing:

Direct addressing is so-named because the value to be stored in memory is

obtained by directly retrieving it from another memory location. For example:

MOV A, 30h

This instruction will read the date out of Internal RAM address30

(hexadecimal) and store it in the Accumulator. Direct addressing is generally fast

since, although the value to be loaded isn’t included in the instruction, it is quickly

accessible since it is stored in the 8051’s Internal RAM. It is also much more

flexible than Immediate Addressing since the value to be loaded is whatever is

found at the given address-which may be variable.

The obvious question that may arise is, “If direct addressing an address

from 80h through FFh refers to SFRs, how can I access the upper 128 bytes of

Internal RAM that are available on the 8052?” The answer is:

You can’t access them using direct addressing. As stated, if you directly refer to

an address of 80h through FFh you will be referring to an SFR. However, you may

access the 8052’s upper 128 bytes of RAM by using the next addressing mode,

“indirect addressing.”

Indirect Addressing:

Indirect addressing is a very powerful addressing mode which in many

cases provides an exceptional level of flexibility. Indirect addressing is also the

only way to access the extra 128 bytes of Internal RAM found on an 8052.

Indirect addressing appears as follows:

20

MOV A,@R0

This instructing causes the 8051 to analyze the value of the R0 register.

The 8051 will then load the accumulator with the value from Internal RAM which

is found at address indicated by R0. For example, let’s say R0 holds the value 40h

and Internal RAM address 40h holds the value 67h. When the above instruction is

executed the 8051 will check the value of R0. Since R0 holds 40h the 8051 will

get the value out of Internal RAM address 40h (which holds 67h) and store it in

the Accumulator. Thus, the Accumulator ends up holding 67h. Indirect never

refers to Internal RAM; it never refers to an SFR. Thus, in a prior example we

mentioned that SFr 99h can be used to write a value to the serial port. Thus one

may think that the following would be a valid solution to write the value’1’ to the

serial port:

MOV R0,#99h ; Load the address of the serial port

MOV @R0,#01h; Send 01 to the serial port—WRONG!!

This is not valid. Since indirect addressing always refers to Internal RAM

these two instructions would write the value 01h to Internal RAM address 99h on

an 8052. On an 8051 these two instructions would produce an undefined result

since the 8051 only has 128 btes of Internal RAM.

External Direct:

It is used to access external memory rather than internal memory. There

are only two commands that use External Direct addressing mode:

MOVXA,@DPTR

MOVX@DPTR,A

As you can see, both commands utilize DPTR. In these instructions, DPTR

must first be loaded with the address of external memory that you wish to read or

write. Once DPTR holds the correct external memory address, the first command

will move the contents of the external memory address into the Accumulator. The

second command will do the opposite: it will allow you to write the value of the

Accumulator to the external memory address pointed to by DPTR.

External Indirect:

21

This form of addressing is usually only used in relatively small projects

that have a very small amount of external RAM. An example of this addressing

mode is:

MOVX@R0,A

Once again, the value of R0 is first read and the value of the Accumulator

is written to that address in External RAM. Since the value of @R0 can only be

00h through FFh the project would effectively be limited to 256 bytes of External

RAM.

Chapter-3

22

TECHNICAL ASPECTS

3.1 FUNCTIONAL DESCRIPTION OF THE RECEIVER MODEL

The infra-red receiver is an essential element of a remote control unit based on

infra-red. The infrared receiver contains 8 relays that can be controlled by wireless. This

makes the unit very easy to operate and integrate with existing systems. Keys 1 to 8 on

the remote control operate the corresponding relay on the receiver board, i.e. Button 1

operates relay 1, button 2 operates relay 2, and etc.The block diagram of the Infrared

receiver developed in this is as shown in the fig 3.1. The various modules of the receiver

are as follows:

Figure 3.1: Block Diagram of IR receiver

3.1.1 IR Sensor Module:

This block represents the Infra-red sensor which receives the modulated infra-

red rays coming from the remote control transmitter and demodulates and converts

it into an electrical signal for further processing of the information being

transmitted. The IR sensor used for this project is TSOP1738 from VISHAY

Semiconductors.

3.1.2 RC5 Decoder Module:

23

IR Sensor Module

RC5 Decoder Module

Address checking module

Command checking module

Control module

Toggle check

module

Output control module

Schmitt Trigger

Relay Driver

Output Module

IR rays

This block comprises of the microcontroller used for decoding the received

infra-red signal. The microcontroller used for the purpose of the application is

AT89C51. The decoder module may be further divided into sub-blocks- Toggle

check module, Address checking module, Command checking module and the

Control module.

The Toggle checking module checks whether a key has been pressed on the

remote or not. The Address checking module and Command checking module

check for the valid addresses and command statements i.e. they collect the

decoded data into a 5-bit address and a 6-bit command format. The control

module ensures correct functionality among all the components.

3.1.3 Output control module:

The output control module is responsible for proper presentation of the output.

It comprises of the Schmitt trigger and Relay driver. For Schmitt trigger IC

74HC14 when the input is higher than a certain chosen threshold, the output is

high; when the input is below another (lower) chosen threshold, the output is low;

when the input is between the two, the output retains its value. The trigger is so

named because the output retains its value until the input changes sufficiently to

trigger a change. This dual threshold action is called hysteresis, and implies that

the Schmitt trigger has some memory.

The benefit of a Schmitt trigger over a circuit with only a single input

threshold is greater stability (noise immunity). With only one input threshold, a

noisy input signal near that threshold could cause the output to switch rapidly back

and forth from noise alone. A noisy Schmitt Trigger input signal near one

threshold can cause only one switch in output value, after which it would have to

move beyond the other threshold in order to cause another switch. A ULN2803 is

an Integrated Circuit (IC) chip with a High Voltage/High Current Darlington

Transistor Array which is ideally suited for interfacing between low-level logic

circuitry and multiple peripheral power loads. This relay driver IC is used to

switch different relays.

3.1.4 Output module:

24

This module represents the output of the receiver. In case of an actual

television it would represent the change of channel. However, in this project the

output has been shown with the help of LEDs. The lighting up of an LED

corresponds to the selection of that particular channel. Further, the output of relays

may be used to light a bulb or drive a motor and do similar other tasks.

In other words, Relay contact can control any equipment in momentary

mode (On till key pressed) or Latch Mode (Toggle on each key press). Each relay

has indicator LED showing current status. This represents the output of the

receiver.

25

26

3.2 OPERATION/WORKING:

The RC5 code set was developed by Phillips and allows 2048 commands to be

transmitted divided into 32 addressable groups of 64 commands each. The

transmitted code consists of a 14 bit data word of the following structure.

2 run-in bits to adjust the AGC level in the receiver IC

1 check bit

5 system address bits

6 command bits.

The basic timing is derived from a 36KHZ oscillator. The code is transmitted in

bi-phase format. In this system, logic 1 is transmitted as a half bit time without signal,

followed by a half bit time with signal. Logic 0 has exactly the opposite structure. Each

half bit consists of 32 shorter pulses. Each transmitted bit has a length of 1.778 m sec; the

shorter pulses have a pulse width of 6.9444 u sec on time and 20.8332 u sec off time. A

complete data word has a length of 24.889 m sec, and is always transmitted completely. If

the key is held pressed the code is repeated in intervals of 64 bit times (i.e. 113.778 m

sec). The RC5 code thus, makes use of a fixed bit length and fixed quantity of bits. Each

bit is sliced in two halves.  The left and right half has opposed levels.  If the bit to be

transmitted is one (1), its left side is zero while its right side is one.   If the bit to be

transmitted is zero (0), its left side is one while the right side is zero. This can be seen in

the Figure 3

|---+ || | || | || +---|<----->1.7778msLogic 0| +---|| | || | ||---+ |<----->1.7778msLogic 1

Figure 3.3(a): Logic representation

27

Figure 3.3(b): (This is the right logic, reversed from what you can see at the IR

receiver output.)

It means that the second half of the bit is actually the same meaning of the bit to

be transmitted, as you can see at the shaded blue right side of the bit as on, means bit

transmitted = 1.To measure the correct logic level directly from the Receiver Output, one

should measure at the first half of the bit. The correct interpretation is that it changes level

exactly at the middle of bit time.  At the IR Receiver output a bit Zero changes level from

Low to up, while a bit one changes level from Up to Low.

There are a minimum quantity of incoming 27µs pulses to the demodulator

understand it is at the right frequency and then drop its output.  The quantity of pulses

used at the Philips remotes are 32 pulses per each half of the bit, 64 pulses per bit.   So, a

bit "0" to be transmitted it means 32 square pulses of 27µs each, then 32 x 27µs of

silence.  The bit "1" is the opposite, 32 x 27µs of silence followed by 32 square pulses

of 27µs. To decode the received waveform at the demodulator output observe the

direction of the changing at the middle of the bit, if going down, means bit 0, going up,

means bit 1. It is relatively easier to sample the middle of the first half of the bit, so it

directly gives the bit state.

Figure 3.4: The 14 bits of the RC-5 system above.

28

OFF OFF OFFON ON ON

Bit time

105ms

Address Command

FLIP OFF OFF OFF OFF OFF OFF OFF OFF OFFOFF OFF

CHK

ON ON

The first two bits, #1 and #2, are called ACG calibration. They are "ON" level, and

serve to calibrate the IR Receivers Auto Gain Control.

In the Philips remotes, the bit #3 is the CHECK bit, every time a key is pressed at

the remote, even pressing repeatedly the same key, this bit flips state.  This is an

interesting feature.  Suppose number "1" is pressed at the remote (trying to select channel

15 at TV) and holding it for 2 seconds, and then the Infrared signal is blocked with the

hand.  The TV would receive two trains of pulses, generated by hand breaking a long

train in two.  Other systems would understand transmission of two keys "1" selecting

channel "11", but this do not happens in the Philips system.   This bit flips state every

time a key is pressed, so blocking the signal with hand doesn't change this bit, so the TV

will understand that still the same key pressed.  To select channel "11" key "1" needs to

be pressed really twice.

The next 5 bits, #4 to #8, are used for SYSTEM ADDRESS, or to identify which

kind of device should execute the COMMAND bits.  For example, TV set uses

ADDRESS ZERO.  Bit #8 is the Less Significant Bit.

The next 6 bits, #9 to #14, are used for COMMAND information to the device

selected at the ADDRESS bits.   Bit #14 is the LESS SIGNIFICANT BIT, and it is last

transmitted.

The project uses Atmel micro-controller AT89C51 to receive the infrared signal

from the Philips remote. It is interesting to note that the Infrared Receiver inverts the bit

signal, low level means bit ON. During inactivity (no Infrared present) the output of the

Infrared receiver is UP (bit zero).

The output of the infrared sensor module may be connected to any port pin of the

microcontroller or interrupt pin of the microcontroller, and keep polling it or prepare the

interrupt routine to trigger your reading after the first low level sensed.

When a key is pressed at the remote, it transmits the train of pulses, and

microcontroller receives bit #1 first.  It will be sensed right after the middle of the bit

when it changes from high to low level to means bit "1".  This is the first time that the

microcontroller will "see" the incoming IR signal.

Upon sensing the first low level, indicating the presence of a bit the

microcontroller needs to be programmed so as to wait for 3.024 ms so as to detect the flip

bit. To read the address and command bits which happen to be the next 11 bits of the

received signal shift them left into a register and store the old and new commands. In this

29

application the microcontroller has been programmed in assembly language. However,

the microcontroller may even be programmed using embedded C and Basscom which

reduces the size of the code so that it can be well accommodated in the limited on-chip

memory of the microcontroller.

The address is decoded to determine the equipment type. The address for Philips

remote should correspond to ‘00’. However, that is a code 10 at the universal

programmable remote, because of the detection circuit waiting for a falling edge. There

are addresses associated with other devices as shown in the table.

Address Equipment0 Television2 Tele text5 Vedeo recorder7 Experimantal

16 Preamplifier17 Receiver/tuner18 Tape/cassette recorder19 experimental

Table 3.1: Addresses used by various devices

The infrared receiver unit contains 8 relays that can be controlled by wireless. This

makes the unit very easy to operate and integrate with existing systems. Keys 1 to 8 on

the remote control operate the corresponding relay on the receiver printed circuit board,

i.e. button 1 operates relay 1, button 2 operates relay 2, etc. Relay contact can control any

equipment in momentary mode (On till key pressed) or Latch Mode (Toggle on each key

press). Each relay has indicator LED showing current status.

The entire working of the infrared remote control receiver printed circuit board

designed and developed for decoding RC5 pulse protocol used in Philips television may

be summarized as stated below:

At the receiver end the IR receiver module (TSOP1738 of VISHAY

Semiconductors make is used for this purpose in this application) extracts the data

signal from the modulated carrier. The RC5 protocol of Philips IR remote control for

television makes use of Manchester coding for transmission of the data. The Manchester

coding is also referred to as bi-phase coding. The receiver chip (Atmel microcontroller

AT89C51 in this case) decodes this signal and sets the corresponding output high. This

30

active HIGH output is used to operate a relay via ULN2803 which is an octal transistor

array.

3.3 ALGORITHM FOR THE RECEIVER PROGRAM:

STEP 1: START

STEP 2: Declare and Initialize temporary variables/memory spaces

STEP 3: Define Input port and read IR input at port P3.3

STEP 4: Define P1 as output port

STEP 5: Reset all relays i.e. turn all output switches off initially

STEP 6: CHECK if Infrared signal is received i.e. check if key is pressed on the

remote

STEP 7: Generate time delay to sample the toggle bit

STEP 8: Read the toggle/Flip bit and store it in variable FLIP

STEP 9: Set count=5 to sample 5 address bit next

STEP 10: Generate time delay

STEP 11: Read IR signal in C

STEP 12: Rotate left through C and store the result in accumulator

STEP 13: Decrement count

STEP 14: IF count! =200 repeat steps 10 to 14 else go to step 15

STEP 15: Store the address in ADDR

STEP 16: Clear Accumulator

STEP 17: Set count=6 to sample 6 command bits next

STEP 18: Generate time delay

STEP 19: Read Infrared signal in C

STEP 20: Rotate Accumulator left through carry

STEP 21: Decrement count

STEP 22: IF count!=0 repeat steps 18 to 22 else go to step 23

STEP 23: Save the old command in TEMP

STEP 24: Save the new command in CMD

STEP 25: Check for valid address i.e. if address! =0 go to start

STEP 26: Check for valid command i.e. if TEMP=CMD go to start

STEP 27: Check if key is pressed i.e. if no then go to start

STEP 28: Compare command, IF it is 01 then set or reset switch 1 accordingly

31

STEP 29: IF command is 02, then set or reset switch 2 accordingly

STEP 30: IF CMD is 03, then set or reset switch 3 accordingly

STEP 31: IF CMD is 04, then set or reset switch 4 accordingly

STEP 32: IF CMD is 05, then set or reset switch 5 accordingly

STEP 33: IF CMD is 06, then set or reset switch 6 accordingly

STEP 34: IF CMD is 07, then set or reset switch 7 accordingly

STEP 35: IF CMD is 08, then set or reset switch 8 accordingly

STEP 36: Check command for all switches, IF true reset all switches

STEP 37: STOP

3.4 FLOWCHART FOR THE RECEIVER PROGRAM

32

IS P3.3=0

Define variables

Generate delay

Move P3.3 to C

Copy C to Flip

Clear ACC.

Clear C

X

START

33

Move 5 to count

X

Copy A to ADDR

Generate delay

Clear A

Count= count - 1

RLC A

Is count= 0

Y

34

Generate delay

Move 6 to count

Y

Read P3.3 to C

RLC A

YES

Count= count - 1

Store old command in TEMP

Store new command in CMD

Is count =

0

Z

35

Z

NO

Set A = TEMP

Move ADDR to A

Is A=0

START

YES

Is A= CMDD

Invalid comman

d

START

P

Clear A

Set C=FLIP

RLC A

36

P

Set TEMP=A

Clear A

Set C=TOG

RLC A

Is A! =TEMP

NO START

TOG=FLIP

YES

Is A= CMDD

STARTSet SW1 high/low

Q

37

Q

Is A= CMDD

STARTSet SW2 high/low

Is A= CMDD

STARTSet SW3 high/low

Is A= CMDD

STARTSet SW4 high/low

Is A= CMDD

STARTSet SW5 high/low

Is A= CMDD

STARTSet SW6 high/low

R

Figure 3.5: Flowchart

38

R

Is A= CMDD

STARTSet SW7 high/low

Is A= CMDD

STARTSet SW8 high/low

STOP

Chapter-4

DESIGN AND DEVELOPMENT

4.1 INTRODUCTION:

The designing of the project forms the major portion of the project. In the

designing of the project we had to pass through many macro phases. The designing part

broadly consists of writing the program, burning the program in the microcontroller and

the fabrication of the chip. The program is given in the appendix.

4.2 FABRICATION OF THE CARD:

The hardware projects often require the use of strip boards or other pre-fabricated

boards for the implementation of the circuit. However, solder less breadboards are the

fastest and most flexible way to design and experiment. The printed circuit boards

provide for efficient and effective solution to the complexities encountered while using

other boards for circuit realization.

The following steps were used for developing the printed circuit board for this

application:

1) Designing the artwork: The first thing to do is to make the schematic of the circuit

to be realized. This is also known as the artwork. The schematic may be drawn

using PCB CAD layout programs. The Orcad 9.1 suite may be used for drawing

the schematic but it is expensive. The freely available and easy to use software

ExpressPCB was used for designing the schematic.

The ExpressPCB online help is written with beginners in mind, the internet

ordering option is convenient, and its regular updated features was the motivation

behind using this software though it has limited component library. The layout of

the circuit as drawn using ExpressPCB is as shown in Figure 1.

39

Figure 4.1: PCB layout

2) Print out the layout on transparency film. The printer must be of Laser type that

uses toner as the printing method.

3) Cut a blank copper plate to the same dimensions as the artwork. The plate is

polished properly so that the toner is transferred effectively onto it.

4) Now, the paper with the artwork is placed face down onto the copper plate and put

tape over it and place again A4 size paper over the transparency film.

5) Put the pcb into lamination machine around 240 c temp for transfer of toner image from transparency film into pcb.

6) The copper plate with design stuck onto it is now immersed in soap solution for

almost 20 minutes to loosen the paper.

7) Carefully remove the paper. Be sure not to remove any of the black ink traces

because these are what stop the acid in the etching process. A kind of rubbing

40

motion was used to remove the paper. Keep the paper wet all the time so that it

separates easily from the copper board.

8) Etch the board using a solution of Ammonium Per sulphate. Proper instructions

for the dilution level should be followed. A normal ceramic or glass bowl can be

used as a tank for carrying out the etching.

9) Slowly swirl or rock the bowl around. The liquid must be always moving over the

copper board to get it to etch properly.

10) Remove the board from the etchant and wash any residue from the board.

11) Scrub the black ink off the PCB.

12) Drill out the holes.

13) Mount the components at their respective positions and solder them properly.

Following the above mentioned steps the Printed circuit board for this application was

developed.

41

Chapter-5

COMPONENT DETAILS

5.1 INTRODUCTION:

In the designing of the project the detail knowledge of the components is very important

for the successful working of the project. In the chapter we desire to give the details of the

macro level components used in the project. The macro level components used are IR Sensor

Module (TSOP 1738), Crystal Oscillator, Voltage Regulator, Relays, Schmitt Inverter and LEDs.

5.2 COMPONENTS USED:

5.2.1 IR Sensor Module:

The most common device used for detecting light energy is a photodiode. A

photodiode is similar in many ways to a standard diode, with the exception of its

packaging. A photodiode is packaged in such a way as to allow light to strike the PN

junction.

Figure 5.1 Photodiode

In infrared applications, it is it is common practice to apply a reverse bias to the device.

There will be a reverse current that will vary with the light level. Like all diodes, there is

an intrinsic capacitance that varies with the reverse bias voltage. This capacitance is an

important factor in speed.

42

The TSOP 17 series are miniaturized receivers for infrared remote control systems. PIN

diode and preamplifiers are assembled on lead frame. The epoxy package is designed as

IR filter.

The demodulated output signal can directly be decoded by microprocessor. TSOP 17 is

the standard IR remote control receiver series, supporting all major transmission codes.

Features

Photo detector and preamplifier in one package.

Internal filter for PCM frequency.

Improved shielding against electric field disturbance.

TTL and CMOS compatibility.

Output active low.

Low power consumption.

High immunity against ambient light.

5.2.2 Crystal Oscillator:

Crystal oscillators are oscillators where the primary frequency determining

element is a quartz crystal. Because of the inherent characteristics of the quartz crystal the

crystal oscillator may be held to extreme accuracy of frequency stability. Temperature

compensation may be applied to crystal oscillators to improve thermal stability of the

crystal oscillator.

Crystal oscillators are usually, fixed frequency oscillators where stability and

accuracy are the primary considerations. For example it is almost impossible to design a

stable and accurate LC oscillator for the upper HF and higher frequencies without

resorting to some sort of crystal control. Hence, the reason for using crystal oscillators.

A crystal oscillator is basically a tuned oscillator. It uses a piezoelectric crystal as

a resonant tank circuit. The crystal (usually quartz) provides a high degree of frequency

stability. Therefore, the crystal oscillators are used whenever great stability is required.

Examples are communication transmitters, digital clocks, etc.43

Operation

A crystal is a solid in which the constituent atoms, molecules, or ions are packed

in a regularly ordered, repeating pattern extending in all three spatial dimensions.

Almost any object made of an elastic material could be used like a crystal, with

appropriate transducers, since all objects have natural resonant frequencies of vibration.

The resonant frequency depends on size, shape, elasticity, and the speed of sound in the

material.

High-frequency crystals are typically cut in the shape of a simple, rectangular

plate. Low-frequency crystals, such as those used in digital watches, are typically cut in

the shape of a tuning fork.

When a crystal of quartz is properly cut and mounted, it can be made to distort in

an electric field by applying a voltage to an electrode near or on the crystal. This property

is known as piezoelectricity. When the field is removed, the quartz will generate an

electric field as it returns to its previous shape, and this can generate a voltage. The result

is that a quartz crystal behaves like a circuit composed of an inductor, capacitor and

resistor, with a precise resonant frequency.

Quartz has the further advantage that its elastic constants and its size change in

such a way that the frequency dependence on temperature can be very low. The specific

characteristics will depend on the mode of vibration and the angle at which the quartz is

cut (relative to its crystallographic axes).[5] Therefore, the resonant frequency of the plate,

which depends on its size, will not change much, either. This means that a quartz clock,

filter or oscillator will remain accurate. For critical applications the quartz oscillator is

mounted in a temperature-controlled container, called a crystal oven, and can also be

mounted on shock absorbers to prevent perturbation by external mechanical vibrations.

Quartz timing crystals are manufactured for frequencies from a few tens of

kilohertz to tens of megahertz. More than two billion (2×109) crystals are manufactured

annually. Most are small devices for consumer devices such as wristwatches, clocks,

radios, computers, and cell phones. Quartz crystals are also found inside test and

measurement equipment, such as counters, signal generators, and oscilloscopes.

44

5.2.3 Voltage Regulator:

A voltage regulator[7] is a circuit that supplies a constant voltage regardless of

changes in load currents. It should be capable of providing substantial output current.

Voltage regulators are very robust. These can withstand over-current draw due to

short circuits and also over-heating. In both cases, the regulator will cut off before any

damage occurs. The only way to destroy a regulator is to apply reverse voltage to its

input. Reverse polarity destroys the regulator almost instantly.

Voltage regulators are classified as:

1. Series regulator (Linear regulator)

2. Shunt regulator (switching regulator)

Series regulator

Series regulator use a power transistor connected in series between the

unregulated DC input and load. Output voltage is controlled by continuous voltage

drop taking place across series pass transistor.

These are known as linear regulators as transistor works in active or linear

region.

Figure 5.2 Series regulator

Shunt regulator

Switching regulator operates the power transistors as a high frequency on/off

switch, so that power transistor does not conduct current continuously. Here desired

current is delivered in periodic pulses.

45

Figure 5.3 Shunt regulator

IC Voltage Regulator

IC voltage regulators are versatile and relatively inexpensive and are available

with features such as programmable output, current/voltage boosting, internal short circuit

current limiting, thermal shutdown and floating operation for high voltage applications.

With the advent of microelectronics, it is possible to incorporate complete voltage

regulator circuits on a single monolithic silicon chip. This gives low cost, high reliability,

reduction in size and excellent performance. Examples of monolithic regulators are

78XX/79XX series and 723 general purpose regulators.

IC voltage regulators are of following types:

Fixed output voltage regulator

Adjustable output voltage regulator

Switching regulator

Special regulator

Three Terminal IC Voltage Regulators

46

Figure 5.4IC Voltage regulator

Fixed voltage series (78XX/79XX) regulator

78XX series are three terminal, positive fixed voltage regulators. There are seven

output voltage options available such as 5, 6, 8,12,15,18 and 24V. In 78XX, the last two

numbers (XX) indicate the output voltage.

These regulators are available in two types of packages.

Metal package (TO- 3type)

Plastic package (TO- 220 types)

Characteristics:

1. VO: The regulated output voltage is fixed at value specified by manufacturer.

2. Vin >= Vo +2

3. Io (max): The load current may vary from zero to rated maximum output current.

IC is always provided with heat sink; otherwise it may not provide rated

maximum output current.

4. Thermal Shutdown: IC has temperature sensor (built in) which turns off the IC

when it becomes too hot.

The IC regulators not only keep the output voltage constant but also reduce the

amount of ripple voltage.

47

5.2.4 Relays:

A relay is an electrical switch that opens and closes under the control of another

electrical circuit. In the original form, the switch is operated by an electromagnet to open

or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a

relay is able to control an output circuit of higher power than the input circuit, it can be

considered to be, in a broad sense, a form of an electrical amplifier.

Relays allow one circuit to switch a second circuit which can be completely

separate from the first. For example a low voltage battery circuit can use a relay to switch

a 230V AC mains circuit. There is no electrical connection inside the relay between the

two circuits; the link is magnetic and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V

relay, but it can be as much as 100mA for relays designed to operate from lower voltages.

Most ICs (chips) cannot provide this current and a transistor is usually used to amplify the

small IC current to the larger value required for the relay coil. The maximum output

current for the popular 555 timer IC is 200mA so these devices can supply relay coils

directly without amplification.

Circuit Symbol for Relay

Figure 5.5 Circuit symbol for relay

The relay's switch connections are usually labeled COM, NC and NO:

COM = Common, always connect to this; it is the moving part of the switch.

NC = Normally Closed, COM is connected to this when the relay coil is off.

NO = Normally Open, COM is connected to this when the relay coil is on.

Connect to COM and NO if you want the switched circuit to be on when the

relay coil is on.

Connect to COM and NC if you want the switched circuit to be on when the

relay coil is off.

48

A simple electromagnetic relay, such as the one taken from a car in the figure, is

an adaptation of an electromagnet. It consists of a coil of wire surrounding a soft iron

core, an iron yoke, which provides a low reluctance path for magnetic flux, a moveable

iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is

hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in

place by a spring so that when the relay is de-energized there is an air gap in the magnetic

circuit. In this condition, one of the two sets of contacts in the relay pictured is closed,

and the other set is open. Other relays may have more or fewer sets of contacts depending

on their function. The relay in the picture also has a wire connecting the armature to the

yoke. This ensures continuity of the circuit between the moving contacts on the armature,

and the circuit track on the Printed Circuit Board (PCB) via the yoke, which is soldered to

the PCB.

When an electric current is passed through the coil, the resulting magnetic field

attracts the armature and the consequent movement of the movable contact or contacts

either makes or breaks a connection with a fixed contact. If the set of contacts was closed

when the relay was de-energized, then the movement opens the contacts and breaks the

connection, and vice versa if the contacts were open. When the current to the coil is

switched off, the armature is returned by a force, approximately half as strong as the

magnetic force, to its relaxed position. Usually this force is provided by a spring, but

gravity is also used commonly in industrial motor starters. Most relays are manufactured

to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage

or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to

dissipate the energy from the collapsing magnetic field at deactivation, which would

otherwise generate a voltage spike dangerous to circuit components. Some automotive

relays already include that diode inside the relay case. Alternatively a contact protection

network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil

is designed to be energized with AC, a small copper ring can be crimped to the end of the

solenoid. This "shading ring" creates a small out-of-phase current, which increases the

minimum pull on the armature during the AC cycle. By analogy with the functions of the

original electromagnetic device, a solid-state relay is made with a thyristor or other solid-

state switching device. To achieve electrical isolation an optocoupler can be used which is

a light-emitting diode (LED) coupled with a photo transistor.

49

5.2.5 Schmitt Inverter:

A Schmitt trigger is a comparator circuit that incorporates positive feedback.

When the input is higher than a certain chosen threshold, the output is high; when

the input is below another (lower) chosen threshold, the output is low; when the input is

between the two, the output retains its value. The trigger is so named because the output

retains its value until the input changes sufficiently to trigger a change. This dual

threshold action is called hysteresis, and implies that the Schmitt trigger has some

memory.

The benefit of a Schmitt trigger over a circuit with only a single input threshold is

greater stability (noise immunity). With only one input threshold, a noisy input signal

near that threshold could cause the output to switch rapidly back and forth from noise

alone. A noisy Schmitt Trigger input signal near one threshold can cause only one switch

in output value, after which it would have to move beyond the other threshold in order to

cause another switch.

The Schmitt trigger was invented by US scientist Otto H. Schmitt in 1934 while

he was still a graduate student, later described in his doctoral dissertation (1937) as a

"thermionic trigger". It was a direct result of Schmitt's study of nerve propagation in squid

nerves.

The symbol for Schmitt triggers in circuit diagrams is a triangle with a hysteresis

symbol. The symbol depicts a typical hysteresis curve.

 

50

Standard Schmitt trigger Inverting Schmitt trigger

Figure 5.6 Standard and Inverting Schmitt Trigger

When the Schmitt trigger is inverting (i.e., when very negative inputs lead to

positive outputs and vice versa), the hysteresis symbol is top–bottom mirrored.

Schmitt triggers are typically built around comparators, connected to have positive

feedback instead of the usual negative feedback. For this circuit the switching occurs near

ground, with the amount of hysteresis controlled by the resistances of R1 and R2:

Figure 5.7 Circuit diagram of Schmitt Trigger

The comparator gives out the highest voltage it can, +VS, when the non-inverting

(+) input is at a higher voltage than the inverting (-) input, and then switches to the lowest

output voltage it can, −VS, when the positive input drops below the negative input. For

very negative inputs, the output will be low, and for very positive inputs, the output will

be high, and so this is an implementation of a "non-inverting" Schmitt trigger.

For instance, if the Schmitt trigger is currently in the high state, the output will be

at the positive power supply rail (+VS). V+ is then a voltage divider between Vin and +VS.

The comparator will switch when V+=0 (ground). Current conservation shows that this

requires

Vin/R1 = −VS/R2,

51

And so Vin must drop below −(R1/R2)VS to get the output to switch. Once the

comparator output has switched to −VS, the threshold becomes +(R1/R2)VS to switch back

to high.

Figure 5.8 Output of Schmitt trigger

So this circuit creates a switching band centred around zero, with trigger levels ±

(R1/R2)VS. The input voltage must rise above the top of the band, and then below the

bottom of the band, for the output to switch on and then back off. If R1 is zero or R2 is

infinity (i.e., an open circuit), the band collapses to zero width, and it behaves as a

standard comparator. The output characteristic is shown in the picture on the right. The

value of the threshold T is given by (R1/R2)VS and the maximum value of the output M is

the power supply rail.

HEX SCHMITT INVERTER (M74HC14)

Each circuit functions as an inverter, but because of the Schmitt action, it has

different input threshold levels for positive-going (VT+) and negative-going (VT–)

signals.

These circuits are temperature compensated and can be triggered from the slowest

of input ramps and still give clean, jitter-free output signals.

The M74HC14 is an high speed CMOS HEX Schmitt inverter fabricated with

silicon gate C2mos technology. All inputs have 20% Vcc hysteresis level. This, together

with its Schmitt trigger function, allows it to be used on line receivers with slow rise/fall

input signals.

All inputs are equipped with protection circuits against static discharge and

transient excess voltage.52

Figure 5.9 Input and Output Equivalent Circuit

Features

High speed ( tpd=12ns at Vcc = 6V)

Low power dissipation.

High noise immunity.

Symmetrical output impedance.

Balanced propagation delays.

Wide operating voltage range (Vcc= 2V to 6V).

5.2.6 Light Emitting Diodes (LEDs):

Light emitting diodes are small but powerful devices in terms of their diverse

applications. LED lights assume greater significance in the context of need for electrical

energy conservation and pollution control world over. These are used as indicators in

various equipments for lighting and decorations at homes, and in flashlights, signboards

and car lights.

53

LED lights differ from traditional light sources in the way these produce light. In

incandescent bulbs, a tungsten filament is heated by electric current until it glows or emits

light.

In fluorescent lamps, an electric arc excites mercury atoms, which emit UV

radiation. After striking the phosphor coating on the inner side of glass tubes, the UV

radiation is converted into visible light and emitted.

On the other hand, LEDs are diodes made from semiconductor materials. This is

why these are referred to as solid state devices. They rely on indium-gallium nitride to

convert electricity into photons when current flows through it.

An LED is basically a small area source, often with extra optics added to the chip

that shapes its radiation pattern. The specific wavelength or color emitted by the LED

depends on the materials used to make the diode. It depends on the composition and

condition of the semiconducting material used, and can be infrared, visible or near-

ultraviolet.

How does an LED WORK?

Light generates inside the semiconductor chip when current flows across the

junction of different material compositions. An LED consists of two elements of

processed semiconductor material called p-type and n-type semiconductors. These two

elements form a p-n junction when placed in contact with each other. The material

composition of the p- and n-type semiconductors determines the color of light generated.

LED structure

To achieve a high radiance and high quantum efficiency, the LED structure must

provide a means of confining the charge carriers and the stimulated optical emission to

the active region of the p-n junction where radiative recombination takes place. Carrier

confinement is used to achieve a high level of radiative recombination in the active region

of the device, which yields high quantum efficiency. Optical confinement is of

importance for preventing absorption of the emitted radiation by the material surrounding

the p-n junction.

To achieve carrier and optical confinement, LED configurations such as

homojunctions and single and double hetrojunctions have been widely investigated. The

most widely used structure is double hetrostructure device because of the two different

alloy layers on each side of the active region.

54

By means of this sandwich structure of differently composed alloy layers, both the

carriers and the optical field are confined in the central active layer. The band gap

differences of adjacent layers confine the charge carriers, while the difference in the

indices of refraction of adjoining layers confine the optical field to the central active

layer. This dual confinement leads to both high efficiency and high radiance.

Materials used for production

LEDs are usually built on an n-type substrate, with an electrode attached to the p-

type layer deposited on its surface.

Most materials used for LED production have very high refractive indices. This

means most of the light reflects back into the material at the material/air interface.

Therefore light extraction is an important aspect of LED design and production.

Why use LED for lighting

1. Lifetime: As a solid state light source, LEDs have a very long lifetime and are

generally very robust due to no mechanical or moving parts. Good quality LEDs

can last up to 50,000hrs- more than five years of continuous use.

2. Low maintenance: The long lifetime of LEDs reduces the need to replace failed

lamps, and this can lead to significant financial and environmental savings.

3. Efficiency: As a semiconductor device, LEDs are highly efficient. Current device

technology is allowing their performance to be pushed to limits that exceed that of

standard lighting. The directional nature of light produced by LEDs allows the

design of luminaries with higher overall efficiency.

4. Low power consumption: this leads to large energy savings.

5. Brightness: Light outputs of LEDs are constantly being increased, and there are

several products that have higher lumen output than traditional lighting.

6. Heat: Almost 80% of the energy consumed by LEDs is converted into light and

only some of it’s dissipated as heat.

7. Small form factor: LEDs are very small. Typically, high brightness LED chips

measure 0.3*0.3mm2.

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8. Instantaneous switch on: LEDs switch on rapidly, even when cold, and this is a

particular advantage for certain applications such as vehicle brake lights.

9. Color: LEDs are available in a broad range of brilliant, saturated colors. White

devices are also available.

Also LED lights are shock resistance, and a solid package of the LEDs can be

designed to focus their light.

Chapter-6

RESULT

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6.1 CONCLUSION:

The project is done as the final assignment of the under graduate program. This

project has given as an opportunity to sharpen our edges in the technical field. The

working of this project had passed through various ups and downs. Many a times it

became very difficult to progress but the constant support of the mentor made it possible

to complete the project to the requirement.

This project makes the communication possible with the use of infrared rays. We

have developed Philips TV receiver. The transmitter part is contained inside the remote

which is used and the receiver part is placed in the switch board.

While designing the project we have faced many problems especially while

programming the microcontroller. But the biggest hurdle was of tuning the IR transmitter

and the receiver, and the coding part. The range up to which receiver can receive the IR

rays is experimentally found to be 33 feet.

Another problem is that of the relays. In order to operate high power points we

need heavy relays which can alternately damage the microcontroller. So we have used

small relays in order to operate the simple switches.

At the epitome we would like to state that although the project is not flawless, but

undoubtedly we achieved to make the concept of the project clear. From the project one

can come to know how the RC pulse protocol based remote works. As per our knowledge

and hard work we succeeded in achieving the aim of the project.

APPENDIX-A

PROGRAM CODE FOR RECEIVER:

VAR1 equ r7

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TEMP equ 10H

COUNT equ 11H

ADDR equ 12H

CMD equ 13H

FLIP bit 00H

TOG bit 01H

IR equ p3.2

SW1 equ p2.7

SW2 equ p2.6

SW3 equ p2.5

SW4 equ p2.4

SW5 equ p2.z

SW6 equ p2.2

SW7 equ p2.1

SW8 equ p2.0

Swport equ p2

org 00H

mov swport,#0FFH

mov sp,#50H

clr TOG

main:

jb IR,$

mov c,IR

mov p0.o,c

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,#$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

58

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#100

djnz VAR1,$

mov c,IR

mov p0.7,c

mov FLIP,c

clr A

mov COUNT,#5

fadd:

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#140

djnz VAR1,$

mov c,IR

rlc a

djnz COUNT,fadd

mov ADDR,A

clr a

mov COUNT,#6

fcmd:

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#255

djnz VAR1,$

mov VAR1,#140

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djnz VAR1,$

mov c,IR

rlc a

djnz COUNT,fcmd

mov TEMP,CMD

mov CMD,a

mov a,ADDR

cjne a,CMD,valid

nvalid:

ljmp main

valid:

clr a

mov c,FLIP

rlc a

mov TEMP,a

clr a

mov c,TOG

rlc a

cjne a,TEMP,valid1

sjmp nvalid

valid1:

mov c,FLIP

mov TOG,c

mov a,CMD

clr c

cjne a,#1,skip1

jb sw1,isset1

setb sw1

ljmp main

isset:

clr sw1

ljmp main

skip1:

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cjne a,#2,skip2

jb sw2,isset2

setb sw2

ljmp main

isset2:

clr sw2

ljmp main

skip2:

cjne a,#3,skip3

jb sw3,isset3

setb sw3

ljmp main

isset3:

clr sw3

ljmp main

skip3:

cjne a,#4,skip4

jb sw4,isset4

setb sw4

ljmp main

isset4:

clr sw4

ljmp main

skip4:

cjne a,#5,skip5

jb sw5,isset5

setb sw5

ljmp main

isset5:

clr sw5

ljmp main

skip5:

cjne a,#6,skip6

61

jb sw6,isset6

setb sw6

ljmp main

isset6:

clr sw6

ljmp main

skip6:

cjne a,#7,skip7

jb sw7,isset7

setb sw7

ljmp main

isset7:

clr sw7

ljmp main

skip7:

cjne a,#8,skip8

jb sw8,isset8

setb sw8

ljmp main

isset8:

clr sw8

ljmp main

skip8:

cjne a,#0cH,exit

mov swport,#00H

ljmp main

exit:

ljmp main

END

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APPENDIX-B

DATA SHEET AT89C51

63

64

65

66

67

68

69

70

71

APPENDIX-C

TSOP-1738

72

73

74

75

76

77

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REFERENCES

[1] Muhammad Ali Mazidi, Janice Gillispie Mazidi, Rolin D. McKinlay, “The 8051

Microcontroller and Embedded Systems Using Assembly and C”, Prentice Hall, Edition

2008

[2] R. L. Boylestad, L. Nashelsky, “Electronics Devices and Circuit Theory”, Prentice

Hall, Edition 2005

[3] G. E. Keser, “Optical Fiber Communication” McGraw Hill, Edition 2007

[4] Kenneth j. Ayala, “The 8051 Microcontroller Architecture, Programming and

Applications”, West Publishing Company, Edition 2000

[5] Marcus O. Durham, “Systems Designs and the 8051”, Techno press, second edition

[6] Sunil S. Rao, “Switchgear protection and power systems”, Khanna publishers, 11 th

edition

[7] D. R. Choudhary, “Linear Integrated Circuits”, New Age International Publishers, 2nd

edition

[8] Wikipedia.org

[9] The Electronics Club, http://www.kpsec.freeuk.com/

[10] Electronics for You

[11] Data sheets

[12] A primer on remote control technology, Innotech Systems Inc.

[13] Gunter Zeisel, Philippe Thomas, Peter Tomaszewski SGS-THOMSON MicroeIectronics Munichl Germany, Grenoblel France, “AN INTERACTIVE MENU-DRIVEN REMOTE CONTROL UNIT FOR TV-RECEIVERS AND VC-RECORDERS”, IEEE Transactions on Consumer Electronici, Vol. 34, No. 3

[14] C. S. Choy, member IEEE, “AN INFRA-RED REMOTE CONTROL SYSTEM DESIGNED FOR UNIVERSAL CONTROL”

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