Soldering:
Soldering is a process in which two or more metal items are joined together by melting and flowing 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 (752 °F).[1]
The filler metal used in the process is called solder.
Soldering is distinguished from brazing by use of a lower melting-temperature filler metal. The filler metals are typically alloys that have liquidus temperatures below 350°C. It is distinguished fromwelding by the base metals not being melted during the joining process which may or may not include the addition of a filler metal.[2] In a soldering process, heat is applied to the parts to be joined, causing the solder to melt and be drawn into the joint by capillary action and to bond to the materials to be joined by wetting action. After the metal cools, the resulting joints are not as strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses. There is evidence that it was employed up to 5000 years ago in Mesopotamia.[3]
Deaoldring:
n electronics, desoldering is the removal of solder and components from a circuit for troubleshooting, for repair purposes, component replacement, and to salvage components. Electronic components are often mounted on a circuit board, and it is usually desirable to avoid damaging the circuit board, surrounding components, and the component being removed.
Soldering is distinguished from brazing by use of a lower melting-temperature filler metal. The filler metals are typically alloys that have liquidus temperatures below 350°C. It is distinguished fromwelding by the base metals not being melted during the joining process which may or may not include the addition of a filler metal.[2] In a soldering process, heat is applied to the parts to be joined, causing the solder to melt and be drawn into the joint by capillary action and to bond to the materials to be joined by wetting action. After the metal cools, the resulting joints are not as strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses. There is evidence that it was employed up to 5000 years ago in Mesopotamia.[3]
Deaoldring:
n electronics, desoldering is the removal of solder and components from a circuit for troubleshooting, for repair purposes, component replacement, and to salvage components. Electronic components are often mounted on a circuit board, and it is usually desirable to avoid damaging the circuit board, surrounding components, and the component being removed.
A digital multimeter is one the most versatile and useful instruments in your auto shop. It is important to own a good model and understand how to use it properly. A digital multimeter is actually three devices in one. It is a voltmeter that measure electrical potential across a device in volts.It is an ammeter that measures the amount of electric current through a device. This is measured in amps. Finally, a digital multimeter is an ohmmeter that measures electrical resistance of a device. Electrical resistance is measured in ohms.
Today, modern digital multimeters are designed to be rugged and easy to operate. A good multimeter will have a rugged plastic case and large, easy to use selector knobs. The top part contains the digital read out screen. This is something you should thoroughly check out before you purchase one. Make sure the screen is large enough to read it and make sure you see the readout in sunlight. Chances are you will be using this instrument outside in direct sunlight.
Below the digital readout is a large knob called the function switch. The function switch allows you to change the modes the digital multimeter operates in. For example, you can easily change from voltmeter to ammeter to ohmmeter with the turn of the dial. Again make sure the function switch is large and easy to operate. Most function switches have approximately eight positions. Most have three V markings that measure voltage. They measure AC, DC and low voltage currents in the millivolt range. Next there will be two positions marked with A~ and A=. The A~ measures AC current in amps and the A= measures DC current in amps. The upside down horseshoe Ω measures resistance in ohms.
In order to measure voltage, first turn on the digital multimeter and let it go through its startup procedure. Generally the digital readout lights up and the unit goes through its self diagnostic checkout. Once that is completed you are ready to measure volts. Now turn the function switch to V= to measure DC volts. Now you will need to connect the red and black leads to the digital multimeter. Connect the red lead to the red input terminal labeled VΩ and connect the black lead to the terminal labeled COM for common terminal. Now you can measure volts by putting the red lead on the terminal with the higher potential and the black lead on the lower one.
To measure amps, the leads must be connected in a different fashion. First set the function switch to A= position. Connect the black lead to the COM terminal. Now you must connect the red lead to the terminal labeled 300mA. Now you are ready to connect the meter in series the device being measured by opening up the circuit and inserting the meter between the open points. The results will be in milliamps because you are using the 300mA terminal.
The third feature of a digital multimeter is its ability to measure to Ohms. Ohms is a measurement of resistance in an electrical circuit. First disconnect all wiring and power sources from the device being measured. Now turn the function switch to the Ω position and connect your leads. The red lead is connected to the terminal labeled VΩ and the black terminal connects to the COM terminal. The display will indicate OL. This is normal and means there is an overload. Now connect the leads across the device to measure the Ohms.
These are the basic functions of a digital multimeter. Remember to shut off your multimeter before storing it back in the your toolbox. You do not want a drained battery the next time you will need it. There are several good brands on the market today. Fluke digital multimeters are probably the most popular and you won't go wrong with one.
A bipolar (junction) transistor (BJT) is a three-terminal electronic device constructed of
doped semiconductor material and may be used in amplifying or switching applications.
Bipolar transistors are so named because their operation involves both electrons and
holes. Charge flow in a BJT is due to bidirectional diffusion of charge carriers across
a junction between two regions of different charge concentrations.
This mode of operation
is contrasted with unipolar transistors, such as field-effect transistors, in which only one
carrier type is involved in charge flow due to drift. By design, most of the BJT collector
current is due to the flow of charges injected from a high-concentration emitter into the
base where they are minority carriers that diffuse toward the collector, and so BJTs are
classified as minority-carrier devices.
An NPN transistor can be considered as twodiodes with a shared anode. In typical operation
, the base-emitter junction is forward biased and the base–collector junction is reverse
biased. In an NPN transistor, for example, when a positive voltage is applied to the
base–emitter junction, the equilibrium between thermally generatedcarriers and the repelling
electric field of thedepletion region becomes unbalanced, allowing thermally excited electrons
to inject into the base region. These electrons wander (or "diffuse") through the base from
the region of high concentration near the emitter towards the region of low concentration near
the collector. The electrons in the base are called minority carriersbecause the base is
doped p-type which would make holes the majority carrier in the base.
To minimize the percentage of carriers that recombine before reaching the collector–base
junction, the transistor's base region must be thin enough that carriers can diffuse across
it in much less time than the semiconductor's minority carrier lifetime. In particular, the
thickness of the base must be much less than the diffusion length of the electrons. The
collector–base junction is reverse-biased, and so little electron injection occurs from the
collector to the base, but electrons that diffuse through the base towards the collector are
swept into the collector by the electric field in the depletion region of the collector–base
junction. The thin shared base and asymmetric collector–emitter doping is what differentiates
a bipolar transistor from two separate and oppositely biased diodes connected in series.
A Zener diode is a type of diode that permits current not only in the forward direction like
a normal diode, but also in the reverse direction if the voltage is larger than the breakdown
a normal diode, but also in the reverse direction if the voltage is larger than the breakdown
voltage known as "Zener kneevoltage" or "Zener voltage". The device was named after
Clarence Zener, who discovered this electrical property.
A conventional solid-state diode will not allow significant current if it is reverse-biased
below its reverse breakdown voltage. When the reverse bias breakdown voltage is exceeded
, a conventional diode is subject to high current due to avalanche breakdown. Unless this
current is limited by circuitry, the diode will be permanently damaged due to overheating.
In case of large forward bias (current in the direction of the arrow), the diode exhibits a
voltage drop due to its junction built-in voltage and internal resistance. The amount of the
voltage drop depends on the semiconductor material and the doping concentrations.
A Zener diode exhibits almost the same properties, except the device is specially
designed so as to have a greatly reduced breakdown voltage, the so-called Zener voltage.
By contrast with the conventionaldevice, a reverse-biased Zener diode will exhibit a
controlled breakdown and allow the current to keep the voltage across the Zener diode
close to the Zener voltage. For example, a diode with a Zener breakdown voltage of 3.2 V
will exhibit a voltage drop of very nearly 3.2 V across a wide range of reversecurrents.
The Zener diode is therefore ideal for applications such as the generation of a reference
voltageor as a voltage stabilizer for low-current applications.
The Zener diode is mainly made of heavely dooped with impurities.
Another mechanism that produces a similar effect is the avalanche effect as in the
avalanche diode. Thetwo types of diode are in fact constructed the same way and
both effects are present in diodes of this type. In silicon diodes up to about 5.6 volts
, the Zener effect is the predominant effect and shows a marked negative temperature
coefficient. Above 5.6 volts, the avalanche effect becomes predominant andexhibits
a positive temperature coefficient[1]. In a 5.6 V diode, the two effects occur together
and their temperature coefficients neatly cancel each other out, thus the 5.6 V diode
is the component of choicein temperature-critical applications. Modern manufacturing
techniques have produced devices with voltageslower than 5.6 V with negligible
temperature coefficients, but as higher voltage devices are encountered,the temperature
coefficient rises dramatically. A 75 V diode
has 10 times the coefficient of a 12 V diode.
The V-I characteristics of Zener Diode will be like:
All such diodes, regardless of breakdown voltage, are usually marketed under the umbrella term of
"Zener diode".
Logic Gate:-"Logic gate is an electronic circuit which operates on one or more input signals to perform a particular logical function and produce the perfect output"
Logic gates process signals which represent true or false. Normally the positive supply voltage +Vs represent true and 0V represents false.
Some important logic gates are: - AND gate, OR gate, NOT gate, NAND gate, NOR gate, EX-OR gate, EX-NOR gate..
Based on properties Logic gates are further classified into two types:
1. Basic Logic gates.
2. Universal Logic gates.
1. Basic Gates:-the basic gates are:-
i) AND Gate.
ii) NOT Gate.
iii) OR Gate.
iv) Exclusive OR Gate. &
v) Exclusive NOR Gate.
AND Gate:-If anyone of the two inputs is false then the output 'y'i s also false (equal to zero)
if both inputs are true then the output 'y' is also true (1)..
There fore by the above condition the logic expression for AND gate is given by
"Y=A.B"
OR Gate:-In OR gate the output Y is true when any one of the input is true or both the inputs are true.
There fore the expression for OR gate is given by
"Y=A+B"
NOT gate (inverter):-The output Y is true when the input A is NOT true, the output is the inverse of the input: Y = inversion of A.A NOT gate have one input. A NOT gate is also called an inverter.
EX-OR (Exclusive-OR) gate:- The output Y is true if either input A is true OR input B is true, but not when both of them are true: Y= (A . B|) OR (A|.B) i.e. = A Ex-OR B.
This is like an OR gate but excluding both inputs being true.
The output is true if inputs A and B are DIFFERENT.
EX-OR gates can only have 2 inputs.
EX-NOR (Exclusive-NOR) gate:- This is an EX-OR gate with the output inverted, as shown by the 'o' on the output.
The output Y is true if inputs A and B are the SAME (either both are true or both false):
Y = (A .B) + (NOT A. NOT B) EX-NOR gate has 2 inputs.
2.Universal Logic gates: - These are the gates by which all other basic gates can be realized...
The two universal gates are 1.NAND Gate. 2. NOR Gate.
NAND gate (NAND = NOT+AND):- This is an AND gate with the output inverted, as shown by the 'o' on the output.
The output is true if input A & input B are NOT both true: Y= complement (A .B)
A NAND gate can have two or more inputs, its output is true if NOT all inputs are true..
NOR gate (NOR = NOT +OR):-This is an OR gate with the output inverted, as shown by the 'o' on the output.
The output Y is true if inputs A OR B are true: Y = Complement (A + B)
A NOR gate can have two or more inputs, its output is true if no inputs are true.
The output Y is true if inputs A OR B are true: Y = Complement (A + B)
A NOR gate can have two or more inputs, its output is true if no inputs are true.
BCD code
The BCD code is represented using binary digits consisting of four bits.
8421 code is a type of BCD and is composed of four bits representing the
decimal digits 0-9.8421 indicates the binary weight of 4bits.(i.e) two to the
power 3, two to the power 2, two to the power 1 and two to the power 0.
the BCD code for the decimal digits 0-15 are
given below:
Using 4 bits 16 binary numbers 0000 to 1111 can be represented but in BCD
code only 10 of these are used.The remaining 6 code combinations are not used
in bcd code.
Gray code
Gray code is an unweighted code which means that there is no specific
weighted assigned to the bit position.Gray code exhibt only one single bit
change from one code to next code.This propperty is used in the encoders.
