Technical Description

Microcontroller

Microcontroller is a device which has a CPU, in addition to fixed amount of RAM, ROM, I/O Ports

and timer compared to microprocessor, which has only CPU and no RAM, no ROM, no I/O ports

and no Timers. In microcontroller all above devices are embedded together in a single chip. The

fixed amount of on chip ROM, RAM, and number of I/O Ports make them ideal for number of

applications in which cost and space are critical. Some microcontroller manufacturers are

integrating ADCs and other peripherals into the microcontroller.

There are four major microcontrollers: Freescale’s 6811, Intel’s 8051, Zilog’s Z8 and PIC

16X from Microchip Technology. Each of them has a unique instruction set and register set;

therefore, are not compatible with each other. Program runs for one will not run on others.

There are also 16 bit and 32 bit microcontrollers, made by various chip makers. Three criteria in

choosing microcontrollers are as follows:

1. meeting the computing needs, of the tasks at hand efficiently an cost effectively,

2. availability of software development tools such as compilers, assemblers and debuggers,

and

3. wide availability and reliable sources of the microcontroller.

In 1981, Intel Corporation introduced an 8 bit microcontroller called the 8051. This

microcontroller has following features:

1. 28 bytes of RAM,

2. 4Kbytes of on chip ROM.

3. Two Timers,

4. One Serial Port,

5. Six Interrupt Sources, and

6. Four Ports (each of 8 bits wide).

Microcontroller is considered as, “a system on chip”.

Microcontroller MCS-51 Architecture

Memory Organization

All 80C51 devices have separate address spaces for program and data memory, as shown

in Figures 1.1.1 and 1.1.2. The logical separation of program and data memory allows the data

memory to be accessed by 8-bit addresses, which can be quickly stored and manipulated by an 8-

bit CPU. Nevertheless, 16-bit data memory addresses can also be generated through the DPTR

register. Program memory (ROM, EPROM) can only be read, not written to. There can be up to

64k bytes of program memory. In the 89s51, the lowest 4k bytes of program are on-chip. In the

ROMless versions, all program memory is external. The read strobe for external program mem-

ory is the PSEN (program store enable).

Data Memory (RAM) occupies a separate address space from Program Memory. In the

80C51, the lowest 128 bytes of data memory are on-chip. Up to 64k bytes of external RAM can

be addressed in the external Data Memory space. In the ROM less version, the lowest 128 bytes

are on-chip. The CPU generates read and write signals, RD and WR, as needed during external

Data

Memory accesses. External Program Memory and external Data Memory may be combined if

desired by applying the RD and PSEN signals to the inputs of an AND gate and using the output

of the gate as the read strobe to the external Program/Data memory

Pin Configuration

Figure: Pin configuration of 8051 microcontroller

PIN DISCRIPTION:

VSS: Ground: 0 V reference.

VCC (40) Power Supply: This is the power supply voltage for normal, idle, and power-down

operation.

P0.0-P1.7(39–32) I/O Port 0: Port 0 is an open-drain, bidirectional I/O port with Schmitt trigger

inputs. Port 0 pins

that have 1s written to them float and can be used as high-impedance inputs. Port 0 is also

the multiplexed low-order address and data bus during accesses to external program and

data memory. In this application, it uses strong internal pull-ups when emitting 1s. Port 0

also outputs the code bytes during program verification and received code bytes during

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

P1.0–P1.7 ( 2–9) I/O Port 1: Port 1 is an 8-bit bidirectional I/O port with internal pull-ups and

Schmitt trigger inputs. Port 1 pins that have 1s written to them are pulled high by the internal

pull-ups and can be used as inputs. As inputs, port 1 pins that are externally pulled low will

source current because of the internal pull-ups. Port 1 also receives the low-order address byte

during program memory verification. Alternate functions for Port 1 include.

1 T2 (P1.0): Timer/Counter 2 external count input/clockout (see Programmable Clock-Out)

2 T2EX (P1.1): Timer/Counter 2 Reload/Capture/Direction control

P2.0–P2.7 (21–28) I/O Port 2: Port 2 is an 8-bit bidirectional I/O port with internal pull-ups and

Schmitt trigger inputs. Port 2 pins that have 1s written to them are pulled high by the internal

pull-ups and can be used as inputs. As inputs, port 2 pins that are externally being pulled low will

source current because of the internal pull-ups. Port 2 emits the high-order address byte during

fetches from external program memory and during accesses to external data memory that use 16-

bit addresses (MOVX @DPTR). In this application, it uses strong internal pull-ups when emit-

ting 1s. During accesses to external data memory that use 8-bit addresses (MOV @Ri), port 2

emits the contents of the P2 special function register. Some Port 2 pins receive the high order ad-

dress bits during EPROM programming and verification.

P3.0–P3.7 (10–17) I/O Port 3: Port 3 is an 8-bit bidirectional I/O port with internal pull-ups and

Schmitt trigger inputs. Port 3 pins that have 1s written to them are pulled high by the internal

pull-ups and can be used as inputs. As inputs, port 3 pins that are externally being pulled low will

source current because of the pull-ups. Port 3 also serves the special features of the 80C51 fam-

ily, as listed below:

10 I RxD (P3.0): Serial input port

11 O TxD (P3.1): Serial output port

12 I INT0 (P3.2): External interrupt

13 I INT1 (P3.3): External interrupt

14 I T0 (P3.4): Timer 0 external input

15 I T1 (P3.5): Timer 1 external input

16 O WR (P3.6): External data memory write strobe

17 O RD (P3.7): External data memory read strobe

RST (9 )I Reset: A high on this pin for two machine cycles while the oscillator is running, resets

the device. An internal diffused resistor to VSS permits a power-on reset using only an external

capacitor to VCC.

ALE/PROG (30) O Address Latch Enable/Program Pulse: Output pulse for latching the low

byte of the address during an access to external memory. In normal operation, ALE is emitted at

a constant rate of 1/6 the oscillator frequency, and can be used for external timing or clocking.

Note that one ALE pulse is skipped during each access to external data memory. This pin is also

the program pulse input (PROG) during EPROM programming. ALE can be disabled by setting

SFR auxiliary.0. With this bit set, ALE will be active only during a MOVX instruction.

PSEN (29) O Program Store Enable: The read strobe to external program memory. When the

device is executing code from the external program memory, PSEN is activated twice each ma-

chine cycle, except that two PSEN activations are skipped during each access to external data

memory. PSEN is not activated during fetches from internal program memory.

EA/VPP (31) I External Access Enable/Programming Supply Voltage: EA must be exter-

nally held low to enable the device to fetch code from external program memory locations

0000H to 0FFFH. If EA is held high, the device executes from internal program memory unless

the program counter contains an address greater than the on-chip ROM/OTP. This pin also

receives the 12.75 V programming supply voltage (VPP) during EPROM programming. If

security bit 1 is programmed, EA will be internally latched on Reset.

XTAL1 (19) I Crystal 1: Input to the inverting oscillator amplifier and input to the internal

clock generator circuits.

XTAL2 (18) O Crystal 2: Output from the inverting oscillator amplifier.

Power Supply

A transformer is a device made of two or more inductors, one of which is powered by

AC, inducing an AC voltage across the second inductor. If the second inductor is connected to

a load, power will be electromagnetically coupled from the first inductor’s power source to that

load. The powered inductor in a transformer is called the primary winding. The unpowered

inductor in a transformer is called the secondary winding. Total primary current in an unloaded

transformer is called the exciting current, and is comprised of magnetizing current plus any

additional current necessary to overcome core losses. It is never perfectly sinusoidal in a real

transformer, but may be made more so if the transformer is designed and operated so that

magnetic flux density is kept to a minimum. Core flux induces a voltage in any coil wrapped

around the core. The induces voltage(s) are ideally in- phase with the primary winding source

voltage and share the same waveshape.

Step down transformer is the first part of regulated power supply. To step down the mains

230V AC. We require step down transformer. Following are the main characteristic of electronic

transformer.

Power transformers are usually design to operate from source of low impedance at a single

frequency. It is required to construct with sufficient insulation of necessary dielectric strength.

Transformer ratings are expressed in volt-amp. The volt-amp of each secondary winding or

windings is added for the total secondary VA. To this are added the load losses.

Temperature rise of a transformer is decided on two well known factors i.e losses on

transformer and heat dissipating or cooling facility provided unit.

Rectifier:

Rectifier is a circuit which converts AC into pulsating DC. Semi-conducting diode is

used as rectifying element due to its property of conducting current in one direction only. There

are two types of rectifier,

1. Half wave rectifier

2. Full wave rectifier

In Half wave rectifier only half cycle of AC signal is rectified so its efficiency is very

poor. Therefore we you use full wave bridge type rectifier, in which four diodes are used. In each

cycle, two diodes conduct at a time and we get maximum efficiency at output.

Advantages of bridge rectifier:

The need of center tapped transformer is eliminated.

The O/P is twice that of center tap circuit for the same secondary voltage.

The PIV rating of diode is half of center tap circuit.

Disadvantages:

It requires four diodes.

As during each half cycle of AC input, two diode are conducting therefore voltage

drop in internal resistance of rectifying unit will be twice as compared to center

tap circuit.

Filter Circuit:

In electronic circuit there is requirement of pure DC supply. But rectifier produce

pulsating DC, if such DC signal is applied to electronic circuit it will produce a hum i.e it will

contain AC and DC The AC components are undesirable and must be kept away from the load.

To do so a filter circuit is used which filter out the AC components reaching the load. Obviously

a filter circuit is installed between rectifier and voltage regulator. In our project we use capacitor

filter because of its low cost, small size and little weight and good characteristic. Capacitors are

connected in parallel to the rectifier O/P because it passes AC, But dose not pass DC at All.

Three Terminal Voltage Regulator:

A voltage regulator is circuit that supplies constant voltage regardless of change in load

current. IC voltage regulators are versatile and relatively cheaper. The 78xx series consists of

three terminal positive voltage regulator. These ICs are designed as fixed voltage regulator and

with adequate heat sink, can deliver O/P current in excess of 1A. These devices do not require

external component. This IC also has internal thermal overload protection and internal short

circuit and current limiting protection. For our project we use 7805 voltage regulator IC.

IC 7805:

The 7805 is a VOLTAGE REGULATOR. It looks like a transistor but it is actually an integrated circuit with 3 legs. turn it into a nice, smooth 5 volts DC. You need to feed it at least 8 volts and no more than 30 volts to do this. It can handle around .5 to .75 amps, but itgets hot. Use a eatsink. run off of 5 volts. It can take a higher, crappy DC voltage and Use it to power circuits.

COM

LM7805

O/PI/P

VCC

3

21

D4

D3

D2

D1S1

S2

P1

P2

Cp

7805

RL

GND

230VAC

PINOUTS

Figure: Pinout of IC 7805

Specification of IC 7805:

Available O/P DC voltage : +5V

Line Ragulation: 0.03

Load Regulation: 0.5

Vin maximau: 35 V

Ripple Rejection: 66-80(db)

Circuit Diagram of Power Supply:

R

D

Figure: 5V power supply using voltage regulated IC 7805

Selection for Current Limiting Resistance for LED

As O/P of micro controller is equal to supply voltage I.e +5V DC

If we directly connected LED, very high current flowing through it because internal

resistance of LED is very small about 5 to 8 ohm so it is possibility to damage LED so we place

current limiting resistance R in series with diode the value of this resistance is calculated form

ohms law,

V=IR

Where, I=If safe forward current flowing through LED which normal intensity glow and this

value near about 8 to 10 mA.

5=R × 8 mA

R = 625 Ω

So we select standard value 680 Ω.

PCB Design

Introduction to Printed Circuit Board:

Printed circuit board pattern applied to one or both sides of an insulating base, depending

upon that, and it is called single sided PCB or double Sided PCB. Conductor materials available

are silver, brass, aluminum and copper, copper is the most widely used which is used here also.

The thickness of conducting material depends upon the current carrying capacity of the circuit.

The Printed Circuit Board usually serves three functions:

1. It provides mechanical support to the components mounted on it.

2. It provides necessary electrical interconnection.

3. It acts as heat sink i.e. it provides a conduction path leading to removeal of most of the

heat generated in the circuit.

Copper (Cu) Clad:

The base of laminate is either paper of glass fiber cloth. Cu foil, which is produced by the

method of electroplating, is placed on laminate and both are kept under hydraulic pressure for

proper adhesive pressure for proper adhesive. These Cu clad are easily available in the market.

Types of Laminates

National Electrical Manufacturers Association (NEMA) has various grades of laminates

that are obtained by different resins and filters.

Phenol

Phenol and Formaldehyde produce phenolic paper base laminate it has phenolic resins with

proper filter. This is Brown in color and opaque. Disadvantage is poor moisture resistance.

Epoxy Laminates

Epoxy paper this is also paper based but impregnated with epoxy resin, yellowish white

and translucent. Epoxy Glass base material has high mechanical strength and good electrical

properties usually green in color and semitransparent. There are a variety of laminates available.

We have selected Fiber Glass epoxy laminate.

PCB fabrication includes following steps:

1. Layout of the circuit

2. Artwork designing

3. Printing

4. Etching

5. Drilling

6. Mounting of components and soldering

7. Finishing

Layout

The layout of PCB has to incorporate all the information on the board before one can go

onto the all work preparation. Detailed circuit diagram, design concept and the philosophy

behind the equipment are very important for the layout.

Layout Scale

Depending on the accuracy required artwork should be produced at a 1:1 or 2:1 or even 4:1 scale.

The layout is best prepared on the same scale as the artwork to prevent the entire problem, which

might be caused by redrawing of layout to the artwork scale. The layout/artwork scale

commonly applied is 2:1 with a 1:1 scale, no demanding single sided boards can be designed but

sufficient care should be taken, particularly during the artwork preparation.

Procedure

The first rule is to replace each and every PCB layout as viewed from the component

side. This rule must be strictly followed to avoid confusion, which would otherwise be caused.

Among the components, the larger ones are placed first and the space in between is filled with

smaller ones. Components requiring input/output connecting come near the connector. All

components are placed in such a manner that de-soldering of other components is not necessary

if they have to be replaced.

Layout Sketch

The end product of the layout designing is the pencil sketched component and conductor

drawing which is caller ‘layout sketch’. It contains all information for the preparation of

network.

Basic Approaches

For ink drawing on white cardboard paper, good quality Indian ink and ink pen set are

minimum requirements. Drawing practice – drawing procedure is very at least by 0.1 – 0.2, and

solder pad locations.

And conductors can easily be displaced by 0.3 – 0.5mm.

Conductor Holes

A code can used for the conductor with a special width.

Minimum spacing should also be provided.

A) Holes B)Conductor Widths

Standard holesStandard width,

0.5mm

1.1 mm 1 mm

1.5 mm 2 mm

3.2 mm 4 mm

Screen Printing

The process of screen – printing is well known to the printing industry because of its

inherent capabilities of printing a wide range of inks on almost any kind of surface including

glass, metal, plastic fabrics, wooer, etc. Found their way into an extremely broad field of

applications.

Screen- printing offers the advantages of wide control on the ink deposition, thickness

though the selection of suitable mass density and composition, in the production of PCB’s. It is

successfully employed in printing of

Etch resists

Plate resists

Solder stop lacquers

Notation printing

In its basic form, the screen – printing process is very simple. A screen fabric with

uniform meshes and opening is stretched and fixed on a solid frame of metal or wood. The

circuit pattern area open, while the meshes in the rest of the area is closed.

In the actual printing step, ink is forced by the moving squeeze thorough the open meshes

onto the surface of the material to be printed. The ink deposition, in a magnified cross section,

shows the shape of a trapezoid.

Pattern Transfer onto The Screen

There are two different methods in use, and each method has its own advantages and

disadvantages.

With the direct method, the screen is prepared, by coating a photographic emulsion

directly onto the screen fabric and exposing it in the pattern area. The indirect method makes use

of a separate screen process film, supported on a backing sheet. The film on its backing sheet

that is there after pressed onto the screen fabric and sticks there. Finally, the backing sheet is

peeled off, opening all those screen meshes, which are not covered by the film pattern.

The direct method provides very durable screen stencils with a higher

dimensional accuracy but the finest details are not reproduced. The indirect method is more

suitable for smaller series and where the finest details to be reproduced. The indirect method is

faster but dimensionally less accurate and the screen stencils are less durable, more sensitive to

mechanical damages and interruption in printing.

Etching

In all subtractive PCB process, etching is one of the most important steps. The final

copper pattern is formed by selective removal of all the unwanted copper, which is not protected

by an etching unit.

Solutions, which are used in etching process, are known as enchants.

1. Ferric Chloride

2. Cupric Chloride

3. Chromic Acid

4. Alkaline Ammonia

Of these Ferric Chloride is widely used because it has short etching time and it can be stored for

a long time. Etching of PCBs as required in modern electronic equipment production, is usually

done in spray type etching machines.

Tank or bubble etching, in which the boards kept in tank, were lowered and fully

immersed into the agitated, has almost disappeared.

Component Mounting

Carefully mounting of components on PCB increases the reliability of assembly.

1. One leads must be cleaned before they are inserted in PCB holes. Asymmetric lead bend-

ing must be avoided, the ENT leads must fit into holes properly so that they can be sol-

dered.

2. When the space is to be saved then vertical mounting is preferred. The vertical lead must

have an insulating sleeve.

3. Where jumper wire crosses over conductors, they must be insulted.

4. For mounting of PCBs, TO5, DIP packages special jigs must be used of easy insertion.

5. For mounting transistors, each lead must have insulating sleeve.

All the flat radial components such as resistors, diodes, and inductors are mounted and soldered.

Then IC bases are soldered. The vertical components such as transistors, gang condenser and

FET are mounted and soldered.

Soldering

The next process after the component mounting is soldering, solder pint is achieved by heating

the solder and base metal about the melting point of the solders used.

The necessary heat depends upon:

1. The nature and type of joints

2. Melting temperature of solder

3. Flux

Soldering techniques are of so many types but we are using iron soldering.

Iron soldering

Soldering iron consists of an insulating handle connected through a metal shaft, of a bit

accurately makes contact with the component parts of the joint and solder and heats them up.

The electrical heating element is located in the hollow shank or handles to heat the bit.

Functions of Bit

It stores heat and convey it from the heat source to the work. It may be required to store

surplus solder from the joint. It may be required to store molten solder and flux to the work. It’s

surface must be lined or wetted, this encourages flow of solder into the joint. When the surface

of the work becomes ester by solder, a continuous film of liquid metal between the bit and work

provides a path of high thermal conductivity through which heat can flow into the work piece.

Solder bit are made up of copper, this metal has good wetting properly, heat capability ad

thermal conductivity. Tin-lead solder affects copper during soldering operation. Production of

copper bit can be made with thick iron coating followed by Ni/Tin plating. The life of the bit is

increased by a factor of 10 to 15. Solder irons are specified in terms of wattage. Depending on

heat input intended for working and types of work (Continuous or individual) the choice of the

solder iron can be made.

Procedure of Soldering

The points to be joined must be cleaned first and fluxed. The hard solder iron and solder

wire is applied to the work. The melted solder becomes bright and fluid. The iron must be

removed after sufficient time and joint is allowed to coal. At the end, finishing is done.