2 channel rf switch

5/26/2018 2 Channel RF switch

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Project ReportWireless

remote control

switch


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Circuit diagram


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Component list


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Component placement


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Pcb layout


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Program

#include

void delay(int time) //This function produces a delay in msec.

{

int i,j;

for(i=0;i


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{

P0=0x00;

delay(50);

P0=0xff;

delay(50);

}

}

Component description

Resistor

A Typical Resistor


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Resistors are "Passive Devices",that is they contain no source of power or

amplification but only attenuate or reduce the voltage or current signal passing

through them. This attenuation results in electrical energy being lost in the form of

heat as the resistor resists the flow of electrons through it.

Then a potential difference is required between the two terminals of a resistor for

current to flow. This potential difference balances out the energy lost. When used

in DC circuits the potential difference, also known as a resistors voltage drop, is

measured across the terminals as the circuit current flows through the resistor.

Most resistors are linear devices that produce a voltage drop across themselves

when an electrical current flows through them because they obey Ohm's Law, and

different values of resistance produces different values of current or voltage. This

can be very useful in Electronic circuits by controlling or reducing either the

current flow or voltage produced across them.

There are many thousands of different Types of Resistorsand are produced in a

variety of forms because their particular characteristics and accuracy suit certain

areas of application, such as High Stability, High Voltage, High Current etc, or are

used as general purpose resistors where their characteristics are less of a problem.

Some of the common characteristics associated with the humble resistor

are; Temperature Coefficient, Voltage Coefficient, Noise, Frequency Response,Poweras well as Temperature Rating, Physical Sizeand Reliability.

In all Electrical and Electronic circuit diagrams and schematics, the most

commonly used symbol for a fixed value resistor is that of a "zig-zag" type line

with the value of its resistance given in Ohms, . Resistors have fixed resistance

values from less than one ohm, ( 10M) in value. Fixed resistors have only one single value of resistance, for

example 100'sbut variable resistors (potentiometers) can provide an infinite

number of resistance values between zero and their maximum value.

Standard Resistor Symbols


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The symbol used in schematic and electrical drawings for a Resistor can either be a

"zig-zag" type line or a rectangular box.

All modern fixed value resistors can be classified into four broad groups;

Carbon Composition Resistor - Made of carbon dust or graphite paste, low wattagevalues

Film or Cermet Resistor - Made from conductive metal oxide paste, very lowwattage values

Wire-wound Resistor - Metallic bodies for heatsink mounting, very high wattageratings

Semiconductor Resistor - High frequency/precision surface mount thin filmtechnology

There are a large variety of fixed and variable resistor types with different

construction styles available for each group, with each one having its own

particular characteristics, advantages and disadvantages compared to the others. To

include all types would make this section very large so I shall limit it to the most

commonly used, and readily available general purpose types of resistors.

Resistor Colour Code

We saw in the previous tutorial that there are many different types

of Resistorsavailable and that they can be used in both electrical and electronic

circuits to control the flow of current or voltage in many different ways. But in

order to do this the actual resistor needs to have some form of "resistive" or

"resistance" value. Resistors are available in a range of different resistance values

from fractions of an Ohm ( ) to millions of Ohms.

Obviously, it would be impractical to have available resistors of every possiblevalue for example, 1,2,3,4etc, because literally hundreds of thousands, if

not millions of different resistors would need to exist to cover all the possible

values. Instead, resistors are manufactured in what are called "preferred values"

with their resistance value printed onto their body in coloured ink.


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4 Coloured Bands

The resistance value, tolerance, and wattage rating are generally printed onto the

body of the resistor as numbers or letters when the resistors body is big enough to

read the print, such as large power resistors. But when the resistor is small such as

a 1/4W carbon or film type, these specifications must be shown in some other

manner as the print would be too small to read.

So to overcome this, small resistors use coloured painted bands to indicate both

their resistive value and their tolerance with the physical size of the resistor

indicating its wattage rating. These coloured painted bands produce a system of

identification generally known as a Resistors Colour Code.

An international and universally accepted resistor colour coding scheme was

developed many years ago as a simple and quick way of identifying a resistors

ohmic value no matter what its size or condition. It consists of a set of individual

coloured rings or bands in spectral order representing each digit of the resistors

value.

A resistors colour code markings are always read one band at a time starting from

the left to the right, with the larger width tolerance band oriented to the right side

indicating its tolerance. By matching the colour of the first band with its associated

number in the digit column of the colour chart below the first digit is identified and

this represents the first digit of the resistance value. Again, by matching the colour

of the second band with its associated number in the digit column of the colour

chart we get the second digit of the resistance value and so on as illustrated below:


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The Standard Resistor Colour Code Chart.


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The Resistor Colour Code Table.

Colour Digit Multiplier Tolerance

Black 0 1

Brown 1 10 1%

Red 2 100 2%

Orange 3 1,000

Yellow 4 10,000

Green 5 100,000 0.5%

Blue 6 1,000,000 0.25%

Violet 7 10,000,000 0.1%

Grey 8

White 9

Gold 0.1 5%

Silver 0.01 10%

None 20%

Calculating Resistor Values

The Resistor Colour Codesystem is all well and good but we need to understand

how to apply it in order to get the correct value of the resistor. The "left-hand" or

the most significant coloured band is the band which is nearest to a connecting lead

with the colour coded bands being read from left-to-right as follows;

Digit, Digit, Multiplier = Colour, Colour x 10colour

in Ohm's ('s)

For example, a resistor has the following coloured markings;

Yellow Violet Red = 4 7 2 = 4 7 x 102= 4700 or4k7.


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The fourth and fifth bands are used to determine the percentage tolerance of the

resistor. Resistor tolerance is a measure of the resistors variation from the specified

resistive value and is a consequence of the manufacturing process and is expressed

as a percentage of its "nominal" or preferred value.

Typical resistor tolerances for film resistors range from 1% to 10% while carbon

resistors have tolerances up to 20%. Resistors with tolerances lower than 2% are

called precision resistors with the or lower tolerance resistors being more

expensive. Most five band resistors are precision resistors with tolerances of either

1% or 2% while most of the four band resistors have tolerances of 5%, 10% and

20%. The colour code used to denote the tolerance rating of a resistor is given as;

Brown = 1%, Red = 2%, Gold = 5%, Silver = 10 %

If resistor has no fourth tolerance band then the default tolerance would be at 20%.

Capacitor

Just like the Resistor, the Capacitor, sometimes referred to as a Condenser, is a simple passive

device. The capacitor is a component which has the ability or "capacity" to store energy in the

form of an electrical charge producing a potential difference (Static Voltage) across its plates,much like a small rechargable battery. In its basic form, a capacitor consists of two or more

parallel conductive (metal) plates which are not connected or touching each other, but are

electrically separated either by air or by some form of insulating material such as paper, mica,

ceramic or plastic and which is commonly called the capacitors Dielectric.

A Typical Capacitor

The conductive metal plates of a capacitor can be either square, circular or rectangular, or they

can be of a cylindrical or spherical shape with the general shape, size and construction of a

parallel plate capacitor depending on its application and voltage rating.


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When used in a direct current or DC circuit, a capacitor charges up to its supply voltage but

blocks the flow of current through it because the dielectric of a capacitor is non-conductive and

basically an insulator. However, when a capacitoris connected to an alternating current or ACcircuit, the flow of the current appears to pass straight through the capacitor with little or no

resistance.

If a DC voltage is applied to the capacitors conductive plates, a current is unable to flow through

the capacitor itself due to the dielectric insulation and an electrical charge builds up on the

capacitors plates with electrons producing a positive charge on one and an equal and opposite

negative charge on the other plate.

This flow of electrons to the plates is known as the capacitors Charging Currentwhich

continues to flow until the voltage across both plates (and hence the capacitor) is equal to the

applied voltage Vc. At this point the capacitor is said to be "fully charged" with electrons. The

strength or rate of this charging current is at its maximum value when the plates are fully

discharged (initial condition) and slowly reduces in value to zero as the plates charge up to a

potential difference across the capacitors plates equal to the applied supply voltage and this is

illustrated below.

Capacitor Construction

The parallel plate capacitor is the simplest form of capacitor. It can be constructed

using two metal or metallised foil plates at a distance parallel to each other, with its

capacitance value in Farads, being fixed by the surface area of the conductive

plates and the distance of separation between them. Altering any two of these


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values alters the the value of its capacitance and this forms the basis of operation of

the variable capacitors.

Also, because capacitors store the energy of the electrons in the form of an

electrical charge on the plates the larger the plates and/or smaller their separationthe greater will be the charge that the capacitor holds for any given voltage across

its plates. In other words, larger plates, smaller distance, more capacitance.

By applying a voltage to a capacitor and measuring the charge on the plates, the

ratio of the charge Q to the voltage V will give the capacitance value of the

capacitor and is therefore given as: C = Q/V this equation can also be re-arranged

to give the more familiar formula for the quantity of charge on the plates as: Q = C

x V

Although we have said that the charge is stored on the plates of a capacitor, it is

more correct to say that the energy within the charge is stored in an "electrostatic

field" between the two plates. When an electric current flows into the capacitor,

charging it up, the electrostatic field becomes more stronger as it stores more

energy. Likewise, as the current flows out of the capacitor, discharging it, the

potential difference between the two plates decreases and the electrostatic field

decreases as the energy moves out of the plates.

The property of a capacitor to store charge on its plates in the form of an

electrostatic field is called the Capacitanceof the capacitor. Not only that, but

capacitance is also the property of a capacitor which resists the change of voltage

across it.

The Capacitance of a Capacitor

The unit of capacitance is the Farad(abbreviated to F) named after the British

physicist Michael Faraday and is defined as a capacitor has the capacitance of OneFaradwhen a charge of One Coulombis stored on the plates by a voltage of One

volt. Capacitance, C is always positive and has no negative units. However, the

Farad is a very large unit of measurement to use on its own so sub-multiples of the

Farad are generally used such as micro-farads, nano-farads and pico-farads, for

example.


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Units of Capacitance

Microfarad (F) 1F = 1/1,000,000 = 0.000001 = 10-6F Nanofarad (nF) 1nF = 1/1,000,000,000 = 0.000000001 = 10-9F Picofarad (pF) 1pF = 1/1,000,000,000,000 = 0.000000000001 = 10

-12

F

The capacitance of a parallel plate capacitor is proportional to the area, A of the

plates and inversely proportional to their distance or separation, d (i.e. the

dielectric thickness) giving us a value for capacitance of C = k( A/d ) where in a

vacuum the value of the constant k is 8.84 x 10-12F/m or 1/4..9 x 109, which is the

permittivity of free space. Generally, the conductive plates of a capacitor are

separated by air or some kind of insulating material or gel rather than the vacuum

of free space.

Types of Capacitor

Ceramic Capacitors

Ceramic Capacitorsor Disc Capacitorsas they are generally called, are made by

coating two sides of a small porcelain or ceramic disc with silver and are then

stacked together to make a capacitor. For very low capacitance values a single

ceramic disc of about 3-6mm is used. Ceramic capacitors have a high dielectric

constant (High-K) and are available so that relatively high capacitances can be

obtained in a small physical size.


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Ceramic Capacitor

They exhibit large non-linear changes in capacitance against temperature and as a

result are used as de-coupling or by-pass capacitors as they are also non-polarized

devices. Ceramic capacitors have values ranging from a few picofarads to one or

two microfarads but their voltage ratings are generally quite low.

Ceramic types of capacitors generally have a 3-digit code printed onto their bodyto identify their capacitance value in pico-farads. Generally the first two digits

indicate the capacitors value and the third digit indicates the number of zero's to be

added. For example, a ceramic disc capacitor with the markings 103 would

indicate 10 and 3 zero's in pico-farads which is equivalent to 10,000 pF or10nF.

Likewise, the digits 104 would indicate 10 and 4 zero's in pico-farads which is

equivalent to 100,000 pFor 100nF and so on. Then on the image of a ceramic

capacitor above the numbers 154 indicate 15 and 4 zero's in pico-farads which is

equivalent to 150,000 pF or 150nF. Letter codes are sometimes used to indicate

their tolerance value such as: J = 5%, K = 10% or M = 20% etc.

Electrolytic Capacitors

Electrolytic Capacitorsare generally used when very large capacitance values are

required. Here instead of using a very thin metallic film layer for one of the

electrodes, a semi-liquid electrolyte solution in the form of a jelly or paste is used

which serves as the second electrode (usually the cathode). The dielectric is a verythin layer of oxide which is grown electro-chemically in production with the

thickness of the film being less than ten microns. This insulating layer is so thin

that it is possible to make capacitors with a large value of capacitance for a small

physical size as the distance between the plates, d is very small.


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Electrolytic Capacitor

The majority of electrolytic types of capacitors are Polarised, that is the DC

voltage applied to the capacitor terminals must be of the correct polarity, i.e.

positive to the positive terminal and negative to the negative terminal as an

incorrect polarisation will break down the insulating oxide layer and permanent

damage may result. All polarised electrolytic capacitors have their polarity clearly

marked with a negative sign to indicate the negative terminal and this polarity mustbe followed.

Electrolytic Capacitorsare generally used in DC power supply circuits due to

their large capacitances and small size to help reduce the ripple voltage or for

coupling and decoupling applications. One main disadvantage of electrolytic

capacitors is their relatively low voltage rating and due to the polarisation of

electrolytic capacitors, it follows then that they must not be used on AC supplies.

Electrolytic's generally come in two basic forms; Aluminum Electrolytic

Capacitorsand Tantalum Electrolytic Capacitors.

Electrolytic Capacitor


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Aluminium Electrolytic Capacitors

There are basically two types of Aluminium Electrolytic Capacitor, the plain foil

type and the etched foil type. The thickness of the aluminium oxide film and high

breakdown voltage give these capacitors very high capacitance values for theirsize. The foil plates of the capacitor are anodized with a DC current. This

anodizing process sets up the polarity of the plate material and determines which

side of the plate is positive and which side is negative.

The etched foil type differs from the plain foil type in that the aluminium oxide on

the anode and cathode foils has been chemically etched to increase its surface area

and permittivity. This gives a smaller sized capacitor than a plain foil type of

equivalent value but has the disadvantage of not being able to withstand high DC

currents compared to the plain type. Also their tolerance range is quite large at up

to 20%. Typical values of capacitance for an aluminium electrolytic capacitor

range from 1uF up to 47,000uF.

Etched foil electrolytic's are best used in coupling, DC blocking and by-pass

circuits while plain foil types are better suited as smoothing capacitors in power

supplies. But aluminium electrolytic's are "polarised" devices so reversing the

applied voltage on the leads will cause the insulating layer within the capacitor to

become destroyed along with the capacitor. However, the electrolyte used withinthe capacitor helps heal a damaged plate if the damage is small.

Since the electrolyte has the properties to self-heal a damaged plate, it also has the

ability to re-anodize the foil plate. As the anodizing process can be reversed, the

electrolyte has the ability to remove the oxide coating from the foil as would

happen if the capacitor was connected with a reverse polarity. Since the electrolyte

has the ability to conduct electricity, if the aluminum oxide layer was removed or

destroyed, the capacitor would allow current to pass from one plate to the other

destroying the capacitor, "so be aware".

Capacitor Characteristics

There are a bewildering array of capacitor characteristics and specifications

associated with the humble capacitor and reading the information printed onto the


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body of a capacitor can sometimes be difficult especially when colours or numeric

codes are used. Each family or type of capacitor uses its own unique identification

system with some systems being easy to understand, and others that use misleading

letters, colours or symbols. The best way to figure out what a capacitor label means

is to first figure out what type of family the capacitor belongs to whether it isceramic, film, plastic or electrolytic.

Even though two capacitors may have exactly the same capacitance value, they

may have different voltage ratings. If a smaller rated voltage capacitor is

substituted in place of a higher rated voltage capacitor, the increased voltage may

damage the smaller capacitor. Also we remember from the last tutorial that with a

polarised electrolytic capacitor, the positive lead must go to the positive connection

and the negative lead to the negative connection otherwise it may again becomedamaged. So it is always better to substitute an old or damaged capacitor with the

same type as the specified one. An example of capacitor markings is given below.

Capacitor Characteristics

The capacitor, as with any other electronic component, comes defined by a series

of characteristics. These Capacitor Characteristicscan always be found in the

datasheets that the capacitor manufacturer provides to us so here are just a few of

the more important ones.

1. Nominal Capacitance, (C)

The nominal value of the Capacitance, C of a capacitor is measured in pico-

Farads (pF), nano-Farads (nF) or micro-Farads (F) and is marked onto the body

of the capacitor as numbers, letters or coloured bands. The capacitance of a


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capacitor can change value with the circuit frequency (Hz) y with the ambient

temperature. Smaller ceramic capacitors can have a nominal value as low as one

pico-Farad, ( 1pF ) while larger electrolytic's can have a nominal capacitance value

of up to one Farad, ( 1F ). All capacitors have a tolerance rating that can range

from -20% to as high as +80% for aluminium electrolytic's affecting its actual orreal value. The choice of capacitance is determined by the circuit configuration but

the value read on the side of a capacitor may not necessarily be its actual value.

2. Working Voltage, (WV)

The Working Voltageis the maximum continuous voltage either DC or AC that

can be applied to the capacitor without failure during its working life. Generally,

the working voltage printed onto the side of a capacitors body refers to its DC

working voltage, ( WV-DC ). DC and AC voltage values are usually not the same

for a capacitor as the AC voltage value refers to the r.m.s. value and NOT the

maximum or peak value which is 1.414 times greater. Also, the specified DC

working voltage is valid within a certain temperature range, normally - 30C to +

70C.

Any DC voltage in excess of its working voltage or an excessive AC ripple current

may cause failure. It follows therefore, that a capacitor will have a longer working

life if operated in a cool environment and within its rated voltage. Commonworking DC voltages are 10V, 16V, 25V, 35V, 50V, 63V, 100V, 160V, 250V,

400V and 1000V and are printed onto the body of the capacitor.

3. Tolerance, (%)

As with resistors, capacitors also have a Tolerancerating expressed as a plus-or-

minus value either in picofarad's (pF) for low value capacitors generally less than

100pF or as a percentage (%) for higher value capacitors generally higher than

100pF. The tolerance value is the extent to which the actual capacitance is allowed

to vary from its nominal value and can range anywhere from -20% to +80%. Thus

a 100F capacitor with a 20% tolerance could legitimately vary from 80F to

120F and still remain within tolerance.


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Capacitors are rated according to how near to their actual values they are compared

to the rated nominal capacitance with coloured bands or letters used to indicated

their actual tolerance. The most common tolerance variation for capacitors is 5% or

10% but some plastic capacitors are rated as low as 1%.

4. Leakage Current

The dielectric used inside the capacitor to separate the conductive plates is not a

perfect insulator resulting in a very small current flowing or "leaking" through the

dielectric due to the influence of the powerful electric fields built up by the charge

on the plates when applied to a constant supply voltage. This small DC current

flow in the region of nano-amps (nA) is called the capacitors Leakage Current.

Leakage current is a result of electrons physically making their way through the

dielectric medium, around its edges or across its leads and which will over timefully discharging the capacitor if the supply voltage is removed.

When the leakage is very low such as in film or foil type capacitors it is generally

referred to as "insulation resistance" ( Rp) and can be expressed as a

high value resistance in parallel with the capacitor as shown. When

the leakage current is high as in electrolytic's it is referred to as a

"leakage current" as electrons flow directly through the electrolyte.

Capacitor leakage current is an important parameter in amplifier

coupling circuits or in power supply circuits, with the best choices

for coupling and/or storage applications being Teflon and the other

plastic capacitor types (polypropylene, polystyrene, etc) because the lower the

dielectric constant, the higher the insulation resistance.

Electrolytic-type capacitors (tantalum and aluminum) on the other hand may have

very high capacitances, but they also have very high leakage currents (typically of

the order of about 5-20 A per F) due to their poor isolation resistance, and aretherefore not suited for storage or coupling applications. Also, the flow of leakage

current for aluminium electrolytic's increases with temperature.

5. Working Temperature, (T)


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Changes in temperature around the capacitor affect the value of the capacitance

because of changes in the dielectric properties. If the air or surrounding

temperature becomes to hot or to cold the capacitance value of the capacitor may

change so much as to affect the correct operation of the circuit. The normal

working range for most capacitors is -30C to +125C with nominal voltage ratingsgiven for a Working Temperatureof no more than +70C especially for the

plastic capacitor types.

Generally for electrolytic capacitors and especially aluminium electrolytic

capacitor, at high temperatures (over +85C the liquids within the electrolyte can

be lost to evaporation, and the body of the capacitor (especially the small sizes)

may become deformed due to the internal pressure and leak outright. Also,

electrolytic capacitors can not be used at low temperatures, below about -10C, asthe electrolyte jelly freezes.

6. Temperature Coefficient, (TC)

The Temperature Coefficientof a capacitor is the maximum change in its

capacitance over a specified temperature range. The temperature coefficient of a

capacitor is generally expressed linearly as parts per million per degree centigrade

(PPM/C), or as a percent change over a particular range of temperatures. Some

capacitors are non linear (Class 2 capacitors) and increase their value as thetemperature rises giving them a temperature coefficient that is expressed as a

positive "P".

Some capacitors decrease their value as the temperature rises giving them a

temperature coefficient that is expressed as a negative "N". For example "P100" is

+100 ppm/C or "N200", which is -200 ppm/C etc. However, some capacitors do

not change their value and remain constant over a certain temperature range, such

capacitors have a zero temperature coefficient or "NPO". These types of capacitors

such as Mica or Polyester are generally referred to as Class 1 capacitors.

Most capacitors, especially electrolytic's lose their capacitance when they get hot

but temperature compensating capacitors are available in the range of at least

P1000 through to N5000 (+1000 ppm/C through to -5000 ppm/C). It is also

possible to connect a capacitor with a positive temperature coefficient in series or


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parallel with a capacitor having a negative temperature coefficient the net result

being that the two opposite effects will cancel each other out over a certain range

of temperatures. Another useful application of temperature coefficient capacitors is

to use them to cancel out the effect of temperature on other components within a

circuit, such as inductors or resistors etc.

7. Polarization

Capacitor Polarizationgenerally refers to the electrolytic type capacitors but

mainly the Aluminium Electrolytic's, with regards to their electrical connection.

The majority of electrolytic capacitors are polarized types, that is the voltage

connected to the capacitor terminals must have the correct polarity,

i.e. positive to positive and negative to negative.

Incorrect polarization can cause the oxide layer inside

the capacitor to break down resulting in very large

currents flowing through the device resulting in

destruction as we have mentioned earlier.

The majority of electrolytic capacitors have their

negative, -ve terminal clearly marked with either a

black stripe, band, arrows or chevrons down one side oftheir body as shown, to prevent any incorrect connection to the DC supply.

Some larger electrolytic's have their metal can or body connected to the negative

terminal but high voltage types have their metal can insulated with the electrodes

being brought out to separate spade or screw terminals for safety.

Also, when using aluminium electrolytic's in power supply smoothing circuits care

should be taken to prevent the sum of the peak DC voltage and AC ripple voltage

from becoming a "reverse voltage".

The Farad

We now know that the ability of a capacitor to store a charge gives it its

capacitance value C, which has the unit of the Farad, F. But the farad is an


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extremely large unit on its own making it impractical to use, so submultiple's or

fractions of the standard Farad unit are used instead. To get an idea of how big a

Farad really is, the surface area of the plates required producing a capacitor with a

value of one Farad with a reasonable plate separation of just 1mm operating in a

vacuum and rearranging the equation for capacitance above would be:

A = Cd 8.85pF/m = (1 x 0.001) 8.85x10-12= 112,994,350 m2

or 113 million m2which would be equivalent to a plate of more than 10 kilometres

x 10 kilometres square.

Capacitors which have a value of one Farad or more tend to have a solid dielectric

and as "One Farad" is such a large unit to use, prefixes are used instead in

electronic formulas with capacitor values given in micro-Farads (F), nano-Farads(nF) and the pico-Farads (pF). For example:

Sub-units of the Farad

Convert the following capacitance values from a) 22nFto uF, b) 0.2uFto nF,c) 550pFto uF.

a) 22nF = 0.022Uf

b) 0.2uF = 200nF


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c) 550pF = 0.00055uF

Capacitor Letter Codes Table

Picofarad

(pF)

Nanofarad

(nF)

Microfarad

(uF)Code

Picofarad

(pF)

Nanofarad

(nF)

Microfarad

(uF)Code

10 0.01 0.00001 100 4700 4.7 0.0047 472

15 0.015 0.000015 150 5000 5.0 0.005 502

22 0.022 0.000022 220 5600 5.6 0.0056 562

33 0.033 0.000033 330 6800 6.8 0.0068 682

47 0.047 0.000047 470 10000 10 0.01 103

100 0.1 0.0001 101 15000 15 0.015 153

120 0.12 0.00012 121 22000 22 0.022 223

130 0.13 0.00013 131 33000 33 0.033 333

150 0.15 0.00015 151 47000 47 0.047 473

180 0.18 0.00018 181 68000 68 0.068 683

220 0.22 0.00022 221 100000 100 0.1 104

330 0.33 0.00033 331 150000 150 0.15 154

470 0.47 0.00047 471 200000 200 0.2 254

560 0.56 0.00056 561 220000 220 0.22 224

680 0.68 0.00068 681 330000 330 0.33 334

750 0.75 0.00075 751 470000 470 0.47 474

820 0.82 0.00082 821 680000 680 0.68 684

1000 1.0 0.001 102 1000000 1000 1.0 105

1500 1.5 0.0015 152 1500000 1500 1.5 155

2000 2.0 0.002 202 2000000 2000 2.0 205

2200 2.2 0.0022 222 2200000 2200 2.2 225

3300 3.3 0.0033 332 3300000 3300 3.3 335

Crystal oscillator


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A crystal oscillator is an electronic oscillator circuit that uses the mechanical resonance of a

vibrating crystal of piezoelectric material to create an electrical signal with a very precise

frequency. This frequency is commonly used to keep track of time (as in quartz wristwatches), toprovide a stable clock signal for digital integrated circuits, and to stabilize frequencies for radio

transmitters and receivers. The most common type of piezoelectric resonator used is the quartz

crystal, so oscillator circuits incorporating them became known as crystal oscillators,[1] but other

piezoelectric materials including polycrystalline ceramics are used in similar circuits.

Quartz crystals are manufactured for frequencies from a few tens of kilohertz to tens of

megahertz. More than two billion crystals are manufactured annually. Most are used for

consumer devices such as wristwatches, clocks, radios, computers, and cellphones. Quartz

crystals are also found inside test and measurement equipment, such as counters, signal

generators, and oscilloscopes.

Ic base


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Using an IC base saves the IC from burning due to overheat if IC is soldered directly. Also, changing an IC

becomes very easy if the IC gets damaged due to some reason and once the IC- base is soldered, the IC

can be easily taken out and fitted back n number of times. Before soldering the IC-Base it should be

checked that all the pins have successfully pierced the holes of the PCB and appeared on back side

because sometimes the some pins are not able to pierce and get damaged in the process. The IC-Base

should be carefully installed upright according to circuit, but if it gets soldered oppositely by mistake

then there is no need to de-solder the IC-Base, rather the IC should be fitted in the base keeping in mind

the orientation of the circuit.

Diode

A diode is a semiconductor device which allows current to flow through it in only one direction.

Although a transistor is also a semiconductor device, it does not operate the way a diode does. A

diode is specifically made to allow current to flow through it in only one direction.

Some ways in which the diode can be used are listed here.

A diode can be used as a rectifier that converts AC (Alternating Current) to DC (Direct Current)

for a power supply device..

What is a Diode and how to work?

A diode is the simplest sort of semiconductor device. Broadly speaking, a semiconductor is a

material with a varying ability to conduct electrical current. Most semiconductors are made of apoor conductor that has had impurities (atoms of another material) added to it. The process of

adding impurities is called doping.

In the case of LEDs, the conductor material is typically aluminum-gallium-arsenide (AlGaAs). In

pure aluminum-gallium-arsenide, all of the atoms bond perfectly to their neighbors, leaving nofree electrons (negatively-charged particles) to conduct electric current. In doped material,

additional atoms change the balance, either adding free electrons or creating holes where

electrons can go. Either of these additions make the material more conductive.

A semiconductor with extra electrons is called N-type material, since it has extra negatively-charged particles. In N-type material, free electrons move from a negatively-charged area to a

positively charged area.


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A semiconductor with extra holes is called P-type material, since it effectively has extra

positively-charged particles. Electrons can jump from hole to hole, moving from a negatively-

charged area to a positively-charged area. As a result, the holes themselves appear to move froma positively-charged area to a negatively-charged area.

A diode comprises a section of N-type material bonded to a section of P-type material, with

electrodes on each end. This arrangement conducts electricity in only one direction. When novoltage is applied to the diode, electrons from the N-type material fill holes from the P-typematerial along the junction between the layers, forming a depletion zone. In a depletion zone, the

semiconductor material is returned to its original insulating state -- all of the holes are filled, so

there are no free electrons or empty spaces for electrons, and charge can't flow.

At the junction, free electrons from the N-type material fill holes from the P-type material. This

creates an insulating layer in the middle of the diode called the depletion zone.

To get rid of the depletion zone, you have to get electrons moving from the N-type area to the P-

type area and holes moving in the reverse direction. To do this, you connect the N-type side ofthe diode to the negative end of a circuit and the P-type side to the positive end. The free

electrons in the N-type material are repelled by the negative electrode and drawn to the positive

electrode. The holes in the P-type material move the other way. When the voltage differencebetween the electrodes is high enough, the electrons in the depletion zone are boosted out of their

holes and begin moving freely again. The depletion zone disappears, and charge moves across

the diode.


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When the negative end of the circuit is hooked up to the N-type layer and the positive end ishooked up to P-type layer, electrons and holes start moving and the depletion zone disappears.

If you try to run current the other way, with the P-type side connected to the negative end of the

circuit and the N-type side connected to the positive end, current will not flow. The negativeelectrons in the N-type material are attracted to the positive electrode. The positive holes in the

P-type material are attracted to the negative electrode. No current flows across the junction

because the holes and the electrons are each moving in the wrong direction. The depletion zoneincreases. (See How Semiconductors Work for more information on the entire process.)

When the positive end of the circuit is hooked up to the N-type layer and the negative end ishooked up to the P-type layer, free electrons collect on one end of the diode and holes collect on

the other. The depletion zone gets bigger.

The interaction between electrons and holes in this setup has an interesting side effect -- it

generates light! In the next section, we'll find out exactly why this is.


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leds :

LED working principle

What is LED?Light emitting diodes, commonly called LEDs, are real unsung heroes in the electronics world.

They do dozens of different jobs and are found in all kinds of devices. Among other things, theyform the numbers on digital clocks, transmit information from remote controls, light up watches

and tell you when your appliances are turned on. Collected together, they can form images on a

jumbo television screen or illuminate a traffic light.

Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike

ordinary incandescent bulbs, they don't have a filament that will burn out, and they don't get

especially hot. They are illuminated solely by the movement of electrons in a semiconductormaterial, and they last just as long as a standard transistor.

In this article, we'll examine the simple principles behind these ubiquitous blinkers, illuminating

some cool principles of electricity and light in the process.

How Can a Diode Produce Light?Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass. These particles, called photons, are

the most basic units of light.

Photons are released as a result of moving electrons. In an atom, electrons move in orbitalsaround the nucleus. Electrons in different orbitals have different amounts of energy. Generally

speaking, electrons with greater energy move in orbitals farther away from the nucleus.

For an electron to jump from a lower orbital to a higher orbital, something has to boost its energy

level. Conversely, an electron releases energy when it drops from a higher orbital to a lower one.

This energy is released in the form of a photon. A greater energy drop releases a higher-energyphoton, which is characterized by a higher frequency. (Check out How Light Works for a full

explanation.)As we saw in the last section, free electrons moving across a diode can fall into empty holes

from the P-type layer. This involves a drop from the conduction band to a lower orbital, so the

electrons release energy in the form of photons. This happens in any diode, but you can only see

the photons when the diode is composed of certain material. The atoms in a standard silicondiode, for example, are arranged in such a way that the electron drops a relatively short distance.


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As a result, the photon's frequency is so low that it is invisible to the human eye -- it is in the

infrared portion of the light spectrum. This isn't necessarily a bad thing, of course: Infrared LEDs

are ideal for remote controls, among other things.

Visible light-emitting diodes (VLEDs), such as the ones that light up numbers in a digital clock,

are made of materials characterized by a wider gap between the conduction band and the lowerorbitals. The size of the gap determines the frequency of the photon -- in other words, it

determines the color of the light.

While all diodes release light, most don't do it very effectively. In an ordinary diode, thesemiconductor material itself ends up absorbing a lot of the light energy. LEDs are speciallyconstructed to release a large number of photons outward. Additionally, they are housed in a

plastic bulb that concentrates the light in a particular direction. As you can see in the diagram,

most of the light from the diode bounces off the sides of the bulb, traveling on through the

rounded end.

LEDs have several advantages over conventional incandescent lamps. For one thing, they don't

have a filament that will burn out, so they last much longer. Additionally, their small plastic bulbmakes them a lot more durable. They also fit more easily into modern electronic circuits.

But the main advantage is efficiency. In conventional incandescent bulbs, the light-production

process involves generating a lot of heat (the filament must be warmed). This is completely

wasted energy, unless you're using the lamp as a heater, because a huge portion of the availableelectricity isn't going toward producing visible light. LEDs generate very little heat, relatively

speaking. A much higher percentage of the electrical power is going directly to generating light,

which cuts down on the electricity demands considerably.Up until recently, LEDs were too expensive to use for most lighting applications because they're

built around advanced semiconductor material. The price of semiconductor devices has

plummeted over the past decade, however, making LEDs a more cost-effective lighting option


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for a wide range of situations. While they may be more expensive than incandescent lights up

front, their lower cost in the long run can make them a better buy. In the future, they will play an

even bigger role in the world of technology.

Sip resistor

SIP means 'single in-line package', so it is a pack of several resistors, often with one end

common. The connections are a series of pins like one side of a DIP (dual in-line package) as

often seen in integrated circuits. The resistors may be used for a variety of purposes, like bus

terminators, resistor ladder networks, pull-ups or pull-downs, but usually in microcontroller

boards.

Voltage Regulator

A LM7805 Voltage Regulator is a voltage regulator that outputs +5 volts.

An easy way to remember the voltage output by a LM78XX series of voltage regulators is the

last two digits of the number. A LM7805 ends with "05"; thus, it outputs 5 volts. The "78" part is

just the convention that the chip makers use to denote the series of regulators that output positive

voltage. The other series of regulators, the LM79XX, is the series that outputs negative voltage.

So:


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LM78XX: Voltage regulators that output positive voltage, "XX"=voltage output.

LM79XX: Voltage regulators that output negative voltage, "XX"=voltage output

The LM7805, like most other regulators, is a three-pin IC.

Pin 1 (Input Pin): The Input pin is the pin that accepts the incoming DC voltage, which the

voltage regulator will eventually regulate down to 5 volts.

Pin 2 (Ground): Ground pin establishes the ground for the regulator.

Pin 3 (Output Pin): The Output pin is the regulated 5 volts DC.

Be advised, though, that though this voltage regulator can accept an input voltage of 36 volts, it

is recommended to limit the voltage to 2-3 volts higher than the output regulated voltage. For a5-volt regulator, no more than 8 volts should be applied as the input voltage. The difference

between the input and output voltage appears as heat. The greater the difference between the

input and output voltage, the more heat is generated. If too much heat is generated, through high

input voltage, the regulator can overheat. If the regulator does not have a heat sink to dissipate

this heat, it can be destroyed and malfunction. So the two options are, design your circuit so that

the input voltage going into the regulator is limited to 2-3 volts above the output regulated

voltage or place a heat sink in your circuit to dissipate the created heat.

Key Features

Output current up to 1.5 A Output voltages of 5; 6; 8; 8.5; 9; 12; 15; 18; 24 V Thermal overload protection Short circuit protection Output transition SOA protection 2 % output voltage tolerance (A version)


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Guaranteed in extended temperature range (A version)Microcontroller:

It was electricity in the beginning....The people were happy because they did not know that it

was all around them and could be utilized. That was good. Then Faraday came and a stone hasstarted to roll slowly...

The first machines using a new sort of energy appeared soon. A long time has passed since then

and just when the people finally got used to them and stopped paying attention to what a newgeneration of specialists were doing, someone came to an idea that electrons could be a very

convenient toy being closed in a glass pipe. It was just a good idea at first, but there was no

return. Electonics was born and the stone kept on rolling down the hill faster and faster...

A new science - new specialists. Blue coats were replaced with white ones and people who knew

something about electronics appeared on the stage. While the rest of humanity were passively

watching in disbelief what was going on, the plotters split in two groups - software-orientedand hardware-oriented. Somewhat younger than their teachers, very enthusiastic and full of

ideas, both of them kept on working but separate ways. While the first group was developingconstantly and gradually, the hardware-oriented people, driven by success, threw caution to the

wind and invented transistors.

Up till that moment, the things could be more or less kept under control, but a broad publicity

was not aware of what was going on, which soon led to a fatal mistake! Being naive in belief thatcheap tricks could slow down technology development and development of the world and

retrieve the good all days, mass market opened its doors for the products of Electronics Industry,

thus closing a magic circle. A rapid drop in prices made these components available for a great

variety of people. The stone was falling freely...

The first integrated circuits and processors appeared soon, which caused computers and otherproducts of electronics to drop down in price even more. They could be bought everywhere.

Another circle was closed! Ordinary people got hold of computers and computer era has begun...

While this drama was going on, hobbyists and professionals, also split in two groups and

protected by anonymity, were working hard on their projects. Then, someone suddenly put aquestion: Why should not we make a universal component? A cheap, universal integrated circuit

that could be programmed and used in any field of electronics, device or wherever needed?

Technology has been developed enough as well as the market. Why not? So it happened, body

and spirit were united and the first integrated circuit was designed and called theMICROCONTROLLER.

1.1 what are microcontrollers and what are they used for?Like all good things, this powerful component is basically very simple. It is made by mixing

tested and high- quality "ingredients" (components) as per following receipt:


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1. The simplest computer processor is used as the "brain" of the future system.2. Depending on the taste of the manufacturer, a bit of memory, a few A/D converters, time

input/output lines etc. are added

3. All that is placed in some of the standard packages.4. A simple software able to control it all and which everyone can easily learn about has bee

developed.

On the basis of these rules, numerous types of microcontrollers were designed and they quickly

became man's invisible companion. Their incredible simplicity and flexibility conquered us along time ago and if you try to invent something about them, you should know that you are

probably late, someone before you has either done it or at least has tried to do it.

The following things have had a crucial influence on development and success of the

microcontrollers:

Powerful and carefully chosen electronics embedded in the microcontrollers canindependetly or via input/output devices (switches, push buttons, sensors, LCD displays,relays etc.), control various processes and devices such as industrial automation, electric

current, temperature, engine performance etc.

Very low prices enable them to be embedded in such devices in which, until recent timeit was not worthwhile to embed anything. Thanks to that, the world is overwhelmed today

with cheap automatic devices and various smart appliences.

Prior knowledge is hardly needed for programming. It is sufficient to have a PC (softwarein use is not demanding at all and is easy to learn) and a simple device (called theprogrammer) used for loading raedy-to-use programs into the microcontroller.

So, if you are infected with a virus called electronics, there is nothing left for you to do but to

learn how to use and control its power.

HOW DOES THE MICROCONTROLLER OPERATE?

Even though there is a large number of different types of microcontrollers and even more

programs created for their use only, all of them have many things in common. Thus, if you learn

to handle one of them you will be able to handle them all. A typical scenario on the basis of

which it all functions is as follows:

1. Power supply is turned off and everything is stillthe program is loaded into themicrocontroller, nothing indicates what is about to come

2. Power supply is turned on and everything starts to happen at high speed! The control logiunit keeps everything under control. It disables all other circuits except quartz crystal tooperate. While the preparations are in progress, the first milliseconds go by.

3. Power supply voltage reaches its maximum and oscillator frequency becomes stable. SFRare being filled with bits reflecting the state of all circuits within the microcontroller. All

pins are configured as inputs. The overall electronis starts operation in rhythm with pulse

sequence. From now on the time is measured in micro and nanoseconds.

4. Program Counter is set to zero. Instruction from that address is sent to instruction decodewhich recognizes it, after which it is executed with immediate effect.


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5. The value of the Program Counter is incremented by 1 and the whole process isrepeated...several million times per second.

1.2 WHAT IS IN THE MICROCONTROLLER?

As you can see, all the operations within the microcontroller are performed at high speed andquite simply, but the microcontroller itself would not be so useful if there are not special circuits

which make it complete. In continuation, we are going to call your attention to them.

I. Read Only Memory (ROM)Read Only Memory (ROM) is a type of memory used to permanently save the program beingexecuted. The size of the program that can be written depends on the size of this memory. ROMcan be built in the microcontroller or added as an external chip, which depends on the type of the

microcontroller. Both options have some disadvantages. If ROM is added as an external chip, the

microcontroller is cheaper and the program can be considerably longer. At the same time, anumber of available pins is reduced as the microcontroller uses its own input/output ports for

connection to the chip. The internal ROM is usually smaller and more expensive, but leaves

more pins available for connecting to peripheral environment. The size of ROM ranges from

512B to 64KB.

II.

Random Access Memory (RAM)Random Access Memory (RAM) is a type of memory used for temporary storing data and

intermediate results created and used during the operation of the microcontrollers. The content of

this memory is cleared once the power supply is off. For example, if the program performes an

addition, it is necessary to have a register standing for what in everyday life is called the sum .For that purpose, one of the registers in RAM is called the "sum" and used for storing results of

addition. The size of RAM goes up to a few KBs.


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III. Electrically Erasable Programmable ROM (EEPROM)The EEPROM is a special type of memory not contained in all microcontrollers. Its contents may

be changed during program execution (similar to RAM ), but remains permanently saved evenafter the loss of power (similar to ROM). It is often used to store values, created and used during

operation (such as calibration values, codes, values to count up to etc.), which must be saved

after turning the power supply off. A disadvantage of this memory is that the process ofprogramming is relatively slow. It is measured in milliseconds(ms).

IV. Special Function Registers (SFR)Special function registers are part of RAM memory. Their purpose is predefined by the

manufacturer and cannot be changed therefore. Since their bits are physically connected toparticular circuits within the microcontroller, such as A/D converter, serial communication

module etc., any change of their state directly affects the operation of the microcontroller or

some of the circuits. For example, writing zero or one to the SFR controlling an input/output port

causes the appropriate port pin to be configured as input or output. In other words, each bit of

this register controls the function of one single pin.

V. Program CounterProgram Counter is an engine running the program and points to the memory address containingthe next instruction to execute. After each instruction execution, the value of the counter is

incremented by 1. For this reason, the program executes only one instruction at a time just as it iswritten. Howeverthe value of the program counter can be changed at any moment, which

causes a jump to a new memory location. This is how subroutines and branch instructions are


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executed. After jumping, the counter resumes even and monotonous automatic counting +1, +1,

+1

VI. Central Processor Unit (CPU)As its name suggests, this is a unit which monitors and controls all processes within the

microcontroller and the user cannot affect its work. It consists of several smaller subunits, ofwhich the most important are:

I nstruction decoderis a part of the electronics which recognizes program instructionsand runs other circuits on the basis of that. The abilities of this circuit are expressed in the"instruction set" which is different for each microcontroller family.

Ari thmetical L ogical Un it (ALU)performs all mathematical and logical operations upondata.

Accumulatoris an SFR closely related to the operation of ALU. It is a kind of workingdesk used for storing all data upon which some operations should be executed (addition,shift etc.). It also stores the results ready for use in further processing. One of the SFRs,

called the Status Register, is closely related to the accumulator, showing at any giventime the "status" of a number stored in the accumulator (the number is greater or less thanzero etc.).

A bitis just a word invented to confuse novices at electronics. Joking aside, this word in practice

indicates whether the voltage is present on a conductor or not. If it is present, the approprite pin

is set to logic one (1), i.e. the bits value is 1. Otherwise, if the voltage is 0 V, the appropriate pin

is cleared (0), i.e. the bits value is 0. It is more complicated in theory where a bit is referred to asa binary digit, but even in this case, its value can be either 0 or 1.

Input/output ports (I/O Ports)

In order to make the microcontroller useful, it is necessary to connect it to peripheral devices.Each microcontroller has one or more registers (called a port) connected to the microcontroller

pins.


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Why do we call them input/output ports? Because it is possible to change a pin function

according to the user's needs. These registers are the only registers in the microcontroller the

state of which can be checked by voltmeter!Oscillator

Even pulses generated by the oscillator enable harmonic and synchronous operation of allcircuits within the microcontroller. It is usually configured as to use quartz-crystal or ceramics

resonator for frequency stabilization. It can also operate without elements for frequency

stabilization (like RC oscillator). It is important to say that program instructions are not executedat the rate imposed by the oscillator itself, but several times slower. It happens because each

instruction is executed in several steps. For some microcontrollers, the same number of cycles is


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needed to execute any instruction, while it's different for other microcontrollers. Accordingly, if

the system uses quartz crystal with a frequency of 20MHz, the execution time of an instruction is

not expected 50nS, but 200, 400 or even 800 nS, depending on the type of the microcontroller!

Timers/Counters

Most programs use these miniature electronic "stopwatches" in their operation. These arecommonly 8- or 16-bit SFRs the contents of which is automatically incremented by each coming

pulse. Once the register is completely loaded, an interrupt is generated!

If these registers use an internal quartz oscillator as a clock source, then it is possible to measurethe time between two events (if the register value is T1 at the moment measurement has started,

and T2 at the moment it has finished, then the elapsed time is equal to the result of subtraction

T2-T1 ). If the registers use pulses coming from external source, then such a timer is turned into

a counter.

This is only a simple explanation of the operation itself. Its somehow more complicated inpractice.

A registeror a memory cell is an electronic circuit which can memorize the state of one byte.Besides 8 bits available to the user, each register has also a number of addressing bits. It is

important to remember that:

All registers of ROM as well as those of RAM referred to as general-purpose registers aremutually equal and nameless. During programming, each of them can be assigned a

name, which makes the whole operation much easier.

All SFRs are assigned names which are different for different types of themicrocontrollers and each of them has a special function as their name suggests.


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Watchdog timer

The Watchdog Timer is a timer connected to a completely separate RC oscillator within the

microcontroller.

If the watchdog timer is enabled, every time it counts up to the program end, the microcontroller

reset occurs and program execution starts from the first instruction. The point is to prevent thisfrom happening by using a special command. The whole idea is based on the fact that every

program is executed in several longer or shorter loops.

If instructions resetting the watchdog timer are set at the appropriate program locations, besidescommands being regularly executed, then the operation of the watchdog timer will not affect the

program execution.

If for any reason (usually electrical noise in industry), the program counter "gets stuck" at some

memory location from which there is no return, the watchdog will not be cleared, so the

registers value being constantly incremented will reach the maximum et voila! Reset occurs!

Power Supply CircuitThere are two things worth attention concerning the microcontroller power supply circuit:

Brown outis a potentially dangerous state which occurs at the moment the microcontroller is

being turned off or when power supply voltage drops to the lowest level due to electric noise. As

the microcontroller consists of several circuits which have different operating voltage levels, this

can cause its out of control performance. In order to prevent it, the microcontroller usually has acircuit for brown out reset built-in. This circuit immediately resets the whole electronics when

the voltage level drops below the lower limit.

Reset pinis usually referred to as Master Clear Reset (MCLR) and serves for external reset ofthe microcontroller by applying logic zero (0) or one (1) depending on the type of the

microcontroller. In case the brown out is not built in the microcontroller, a simple external circuit

for brown out reset can be connected to this pin.

Serial communication


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Parallel connections between the microcontroller and peripherals established over I/O ports are

the ideal solution for shorter distances up to several meters. However, in other cases, when it isnecessary to establish communication between two devices on longer distances it is obviously

not possible to use parallel connections. Then, serial communication is the best solution.

Today, most microcontrollers have several different systems for serial communication built in as

a standard equipment. Which of them will be used depends on many factors of which the most

important are:

How many devices the microcontroller has to exchange data with? How fast the data exchange has to be? What is the distance between devices? Is it necessary to send and receive data simultaneously?

One of the most important things concerning serial communication is the Protocol which should

be strictly observed. It is a set of rules which must be applied in order that devices can correctly

interpret data they mutually exchange. Fortunately, the microcontrollers automatically take care

of this, so the work of the programmer/user is reduced to a simple write (data to be sent) and read(received data).

A byteconsists of 8 bits grouped together. If a bit is a digit then it is logical that bytes arenumbers. All mathematical operations can be performed upon them, just like upon common

decimal numbers, which is carried out in the ALU. It is important to remember that byte digits

are not of equal significance. The largest value has the leftmost bit called the most significant bit

(MSB). The rightmost bit has the least value and is therefore called the least significant bit(LSB). Since 8 digits (zeros and ones) of one byte can be combined in 256 different ways, the

largest decimal number which can be represented by one byte is 255 (one combination represents

zero).ProgramUnlike other integrated circuits which only need to be connected to other components and turn

the power supply on, the microcontrollers need to be programmed first. This is a so called "bitter

pill" and the main reason why hardware-oriented electronics engineers stay away frommicrocontrollers. It is a trap causing huge losses because the process of programming the

microcontroller is basically very simple.


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In order to write a program for the microcontroller, several "low-level" programming languages

can be used such as Assembly, C and Basic (and their versions as well). Writing program

procedure consists of simple writing instructions in the order in which they should be executed.There are also many programs running in Windows environment used to facilitate the work

providing additional visual tools.

This book describes the use of Assembly because it is the simplest language with the fastest

execution allowing entire control on what is going on in the circuit.

Interrupt- electronics is usually more faster than physical processes it should keep under

control. This is why the microcontroller spends most of its time waiting for something to happen

or execute. In other words, when some event takes place, the microcontroller does something. In

order to prevent the microcontroller from spending most of its time endlessly checking for logicstate on input pins and registers, an interrupt is generated. It is the signal which informs the

central processor that something attention worthy has happened. As its name suggests, itinterrupts regular program execution. It can be generated by different sources so when it occurs,

the microcontroller immediately stops operation and checks for the cause. If it is needed to

perform some operations, a current state of the program counter is pushed onto the Stack and theappropriate program is executed. It's the so called interrupt routine.

Stackis a part of RAM used for storing the current state of the program counter (address) when

an interrupt occurs. In this way, after a subroutine or an interrupt execution, the microcontrollerknows from where to continue regular program execution. This address is cleared after returning

to the program because there is no need to save it any longer, and one location of the stack isautomatically availale for further use. In addition, the stack can consist of several levels. This

enables subroutines nesting, i.e. calling one subroutine from another.

ARCHITECTURE OF 8051 MICROCONTROLLER

2.1 WHAT IS 8051 STANDARD?

Microcontroller manufacturers have been competing for a long time for attracting choosy

customers and every couple of days a new chip with a higher operating frequency, more memoryand upgraded A/D converters appeared on the market.

However, most of them had the same or at least very similar architecture known in the world of

microcontrollers as 8051 compatible. What is all this about?

The whole story has its beginnings in the far 80s when Intel launched the first series of

microcontrollers called the MCS 051. Even though these microcontrollers had quite modest


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features in comparison to the new ones, they conquered the world very soon and became a

standard for what nowadays is called the microcontroller.

The main reason for their great success and popularity is a skillfully chosen configuration which

satisfies different needs of a large number of users allowing at the same time constant expansions

(refers to the new types of microcontrollers). Besides, the software has been developed in greatextend in the meantime, and it simply was not profitable to change anything in the

microcontrollers basic core. This is the reason for having a great number of various

microcontrollers which basically are solely upgraded versions of the 8051 family. What makesthis microcontroller so special and universal so that almost all manufacturers all over the world

manufacture it today under different name?

As seen in figure above, the 8051 microcontroller has nothing impressive in appearance:

4 Kb of ROM is not much at all. 128b of RAM (including SFRs) satisfies the user's basic needs. 4 ports having in total of 32 input/output lines are in most cases sufficient to make all

necessary connections to peripheral environment.

The whole configuration is obviously thought of as to satisfy the needs of most programmers

working on development of automation devices. One of its advantages is that nothing is missingand nothing is too much. In other words, it is created exactly in accordance to the average userstaste and needs. Another advantages are RAM organization, the operation of Central Processor

Unit (CPU) and ports which completely use all recourses and enable further upgrade.

2.2 PINOUT DISCRIPTION

Pins 1-8:Port 1 Each of these pins can be configured as an input or an output.


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Pin 9: RS A logic one on this pin disables the microcontroller and clears the contents of most

registers. In other words, the positive voltage on this pin resets the microcontroller. By applying

logic zero to this pin, the program starts execution from the beginning.

Pins10-17:Port 3 Similar to port 1, each of these pins can serve as general input or output.

Besides, all of them have alternative functions:

Pin 10:RXD Serial asynchronous communication input or Serial synchronous communicationoutput.

Pin 11:TXD Serial asynchronous communication output or Serial synchronous communication

clock output.

Pin 12:INT0 Interrupt 0 input.

Pin 13:INT1 Interrupt 1 input.

Pin 14:T0 Counter 0 clock input.

Pin 15:T1 Counter 1 clock input.

Pin 16:WR Write to external (additional) RAM.

Pin 17:RD Read from external RAM.

Pin 18, 19:X2, X1 Internal oscillator input and output. A quartz crystal which specifies

operating frequency is usually connected to these pins. Instead of it, miniature ceramics

resonators can also be used for frequency stability. Later versions of microcontrollers operate ata frequency of 0 Hz up to over 50 Hz.

Pin 20:GND Ground.

Pin 21-28:Port 2 If there is no intention to use external memory then these port pins are

configured as general inputs/outputs. In case external memory is used, the higher address byte,i.e. addresses A8-A15 will appear on this port. Even though memory with capacity of 64Kb is

not used, which means that not all eight port bits are used for its addressing, the rest of them are

not available as inputs/outputs.

Pin 29:PSEN If external ROM is used for storing program then a logic zero (0) appears on it

every time the microcontroller reads a byte from memory.Pin 30:ALE Prior to reading from external memory, the microcontroller puts the lower address

byte (A0-A7) on P0 and activates the ALE output. After receiving signal from the ALE pin, theexternal register (usually 74HCT373 or 74HCT375 add-on chip) memorizes the state of P0 and

uses it as a memory chip address. Immediately after that, the ALU pin is returned its previous

logic state and P0 is now used as a Data Bus. As seen, port data multiplexing is performed by

means of only one additional (and cheap) integrated circuit. In other words, this port is used forboth data and address transmission.

Pin 31:EA By applying logic zero to this pin, P2 and P3 are used for data and address

transmission with no regard to whether there is internal memory or not. It means that even there

is a program written to the microcontroller, it will not be executed. Instead, the program written

to external ROM will be executed. By applying logic one to the EA pin, the microcontroller willuse both memories, first internal then external (if exists).

Pin 32-39:Port 0 Similar to P2, if external memory is not used, these pins can be used as

general inputs/outputs. Otherwise, P0 is configured as address output (A0-A7) when the ALE pinis driven high (1) or as data output (Data Bus) when the ALE pin is driven low (0).

Pin 40:VCC +5V power supply.


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2.3 INPUT/OUTPUT PORTS (I/O PORTS)

All 8051 microcontrollers have 4 I/O ports each comprising 8 bits which can be configured as

inputs or outputs. Accordingly, in total of 32 input/output pins enabling the microcontroller to be

connected to peripheral devices are available for use.

Pin configuration, i.e. whether it is to be configured as an input (1) or an output (0), depends onits logic state. In order to configure a microcontroller pin as an input, it is necessary to apply

logic zero (0) to appropriate I/O port bit. In this case, voltage level on appropriate pin will be 0.

Similarly, in order to configure a microcontroller pin as an input, it is necessary to apply a logic

one (1) to appropriate port. In this case, voltage level on appropriate pin will be 5V (as is thecase with any TTL input). This may seem confusing but don't loose your patience. It all becomes

clear after studying simple electronic circuits connected to an I/O pin.

Input/Output (I/O) pinFigure above illustrates a simplified schematic of all circuits within the microcontroler connected

to one of its pins. It refers to all the pins except those of the P0 port which do not have pull-up

resistors built-in.


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Output pinA logic zero (0) is applied to a bit of the P register. The output FE transistor is turned on, thus

connecting the appropriate pin to ground.

Input pin

A logic one (1) is applied to a bit of the P register. The output FE transistor is turned off and theappropriate pin remains connected to the power supply voltage over a pull-up resistor of high

resistance.

Logic state (voltage) of any pin can be changed or read at any moment. A logic zero (0) and logic one (1) are not

equal. A logic one (0) represents a short circuit to ground. Such a pin acts as an output.

A logic one (1) is loosely connected to the power supply voltage over a resistor of high resistance. Since this

voltage can be easily reduced by an external signal, such a pin acts as an input.

Port 0

The P0 port is characterized by two functions. If external memory is used then the lower address

byte (addresses A0-A7) is applied on it. Otherwise, all bits of this port are configured as

inputs/outputs.

The other function is expressed when it is configured as an output. Unlike other ports consisting

of pins with built-in pull-up resistor connected by its end to 5 Vpower supply, pins of this porthave this resistor left out. This apparently small difference has its consequences:


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If any pin of this port is configured as an input then it acts as if it floats. Such an input hasunlimited input resistance and indetermined potential.

When the pin is configured as an output, it acts as an open drain. By applying logic 0 to a portbit, the appropriate pin will be connected to ground (0V). By applying logic 1, the external

output will keep on floating. In order to apply logic 1 (5V) on this output pin, it is necessary to

built in an external pull-up resistor.

Only in case P0 is used for addressing external memory, the microcontroller will provide internalpower supply source in order to supply its pins with logic one. There is no need to add external

pull-up resistors.

Port 1

P1 is a true I/O port, because it doesn't have any alternative functions as is the case with P0, but

can be cofigured as general I/O only. It has a pull-up resistor built-in and is completely

compatible with TTL circuits.

Port 2

P2 acts similarly to P0 when external memory is used. Pins of this port occupy addresses

intended for external memory chip. This time it is about the higher address byte with addresses

A8-A15. When no memory is added, this port can be used as a general input/output port showingfeatures similar to P1.


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Port 3

All port pins can be used as general I/O, but they also have an alternative function. In order to

use these alternative functions, a logic one (1) must be applied to appropriate bit of the P3

register. In tems of hardware, this port is similar to P0, with the difference that its pins have apull-up resistor built-in.

Pin's Current limitations

When configured as outputs (logic zero (0)), single port pins can receive a current of 10mA. If

all 8 bits of a port are active, a total current must be limited to 15mA (port P0: 26mA). If all

ports (32 bits) are active, total maximum current must be limited to 71mA. When these pins areconfigured as inputs (logic 1), built-in pull-up resistors provide very weak current, but strong

enough to activate up to 4 TTL inputs of LS series.

As seen from description of some ports, even though all of them have more or less similar architecture, it is

necessary to pay attention to which of them is to be used for what and how.

For example, if they shall be used as outputs with high voltage level (5V), then P0 should be avoided because its

pins do not have pull-up resistors, thus giving low logic level only. When using other ports, one should have in mind

that pull-up resistors have a relatively high resistance, so that their pins can give a current of several hundreds

microamperes only.

2.4 MEMORY ORGANIZATION

The 8051 has two types of memory and these are Program Memory and Data Memory. Program

Memory (ROM) is used to permanently save the program being executed, while Data Memory(RAM) is used for temporarily storing data and intermediate results created and used during the

operation of the microcontroller. Depending on the model in use (we are still talking about the

8051 microcontroller family in general) at most a few Kb of ROM and 128 or 256 bytes of RAMis used. However

All 8051 microcontrollers have a 16-bit addressing bus and are capable of addressing 64 kb

memory. It is neither a mistake nor a big ambition of engineers who were working on basic core

development. It is a matter of smart memory organization which makes these microcontrollers a

real programmers goody.

Program Memory

The first models of the 8051 microcontroller family did not have internal program memory. Itwas added as an external separate chip. These models are recognizable by their label beginning

with 803 (for example 8031 or 8032). All later models have a few Kbyte ROM embedded. Even

though such an amount of memory is sufficient for writing most of the programs, there aresituations when it is necessary to use additional memory as well. A typical example are so called

lookup tables. They are used in cases when equations describing some processes are too

complicated or when there is no time for solving them. In suchcases all necessary estimates and


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approximates are executed in advance and the final results are put in the tables (similar to

logarithmic tables).

How does the microcontroller handle external memory depends on the EA pin logic state:

EA=0In this case, the microcontroller completely ignores internal program memory and

executes only the program stored in external memory.

EA=1In this case, the microcontroller executes first the program from built-in ROM, then theprogram stored in external memory.

In both cases, P0 and P2 are not available for use since being used for data and address

transmission. Besides, the ALE and PSEN pins are also used.

Data Memory

As already mentioned, Data Memory is used for temporarily storing data and intermediate results

created and used during the operation of the microcontroller. Besides, RAM memory built in the8051 family includes many registers such as hardware counters and timers, input/output ports,

serial data buffers etc. The previous models had 256 RAM locations, while for the later models

this number was incremented by additional 128 registers. However, the first 256 memorylocations (addresses 0-FFh) are the heart of memory common to all the models belonging to the


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8051 family. Locations available to the user occupy memory space with addresses 0-7Fh, i.e.

first 128 registers. This part of RAM is divided in several blocks.

The first block consists of 4 banks each including 8 registers denoted by R0-R7. Prior to

accessing any of these registers, it is necessary to select the bank containing it. The next memory

block (address 20h-2Fh) is bit- addressable, which means that each bit has its own address (0-7Fh). Since there are 16 such registers, this block contains in total of 128 bits with separate

addresses (address of bit 0 of the 20h byte is 0, while address of bit 7 of the 2Fh byte is 7Fh).

The third group of registers occupy addresses 2Fh-7Fh, i.e. 80 locations, and does not have anyspecial functions or features.

Additional RAM

In order to satisfy the programmers constant hunger for Data Memory, the manufacturers

decided to embed an additional memory block of 128 locations into the latest versions of the

8051 microcontrollers. However, its not as simple as it seems to be The problem is thatelectronics performing addressing has 1 byte (8 bits) on disposal and is capable of reaching only

the first 256 locations, therefore. In order to keep already existing 8-bit architecture andcompatibility with other existing models a small trick was done.

What does it mean? It means that additional memory block shares the same addresses withlocations intended for the SFRs (80h- FFh). In order to differentiate between these twophysically separated memory spaces, different ways of addressing are used. The SFRs memory

locations are accessed by direct addressing, while additional RAM memory locations are

accessed by indirect addressing.


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Memory expansion

In case memory (RAM or ROM) built in the microcontroller is not sufficient, it is possible to add

two external memory chips with capacity of 64Kb each. P2 and P3 I/O ports are used for their

addressing and data transmission.


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From the users point of view, everything works quite simply when properly connected because

most operations are performed by the microcontroller itself. The 8051 microcontroller has two

pins for data read RD#(P3.7) and PSEN#. The first one is used for reading data from externaldata memory (RAM), while the other is used for reading data from external program memory

(ROM). Both pins are active low. A typical example of memory expansion by adding RAM and

ROM chips (Hardward architecture), is shown in figure above.

Even though additional memory is rarely used with the latest versions of the microcontrollers,we will describe in short what happens when memory chips are connected according to the

previous schematic. The whole process described below is performed automatically.

When the program during execution encounters an instruction which resides in externalmemory (ROM), the microcontroller will activate its control output ALE and set the first

8 bits of address (A0-A7) on P0. IC circuit 74HCT573 passes the first 8 bits to memoryaddress pins.

A signal on the ALE pin latches the IC circuit 74HCT573 and immediately afterwards 8higher bits of address (A8-A15) appear on the port. In this way, a desired location ofadditional program memory is addressed. It is left over to read its content.


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Port P0 pins are configured as inputs, the PSEN pin is activated and the microcontrollerreads from memory chip.

Similar occurs when it is necessary to read location from external RAM. Addressing isperformed in the same way, while read and write are performed via signals appearing on the

control outputs RD (is short for read) or WR (is short for write).

Learning section

Soldering

Soldering is a process in which two or more metal items are joined together by melting andflowing a filler metal into the joint, the filler metal having a relatively low melting point. Soft

soldering is characterized by the melting point of the filler metal, which is below 400 C

(800 F). The filler metal used in the process is called solder.

Soldering is distinguished from brazing by use of a lower melting-temperature filler metal; it is

distinguished from welding by the base metals not being melted during the joining process. In asoldering process, heat is applied to th

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