Monday, September 3, 2012

Using circuit magic to calculate circuit resistances

Circuit simplifications using star-to-
delta, parallel and series
transformations, seems pretty
powerful. It allows one to obtain
resistances a circuit that has a planar,
mesh structure (the "window pane"
structure). The term planar is used to
describe circuits that can be drawn in
a plane without the need for wires to
cross one another. Circuit Magic can
help you to obtain both planar and
non-planar circuits resistances.
Sample circuit. Resistors resistances
are different values (not simple, Try to
simplify it using star-to-delta, parallel
and series transformationsü).


Step 2. Solve circuit using Node
Voltage method
Step 2. Calculate circuit resistance
using Ohms Law

Saturday, September 1, 2012

Kennelly's Star-Delta Transformation

Kennelly's Star-Delta
Transformation



Kennelly's Delta - Star
Transformation


Using Circuit Magic to calculate Norton Thévenin's & Norton's equivalents

Sample circuit shown below

Step 1 Remove branch connecting
node 1 and node 2.



Step 2: Solve circuit using Node
Voltage method.
Result shown below.
V1=-10
V2=0
V3=-5
V4=-5
V5=0



Step 3.: Resistance calculation. Remove
All DC Voltage sources and branches
with current sources. And connect
node 1 and node 2 using the branch
with current source (current =1 A). (as
shown below)



Step 4: Solve circuit using node voltage
method.
V1=-7,2727
V2=4,5455
V3=-3,6364
V4=-0,90909
V5=0


Step 5. Calculate resistance using
Ohms law.



ohms


Thévenin's equivalent



Tuesday, August 28, 2012

Ohm’s law

Ohm's law is the main basic electrical
law and defines the resistance of a
device to the flow of electrons.


There are three different notations of
Ohm’s law


Unknown Current


Unknown Voltage


Unknown Resistance


(Most people can remember a picture
easier than a mathematical formula.
By knowing any two values you can
figure out the third. Simply put your
finger over the portion of the symbol
you are trying to figure out and you
have your formula).





Monday, August 27, 2012

Resistors in Series & Resistors in Parallel

Series Connection
A series circuit is one with all the loads
in a row. Like links in a chain. There is
only one path for the electricity to
flow.


Parallel Connection
A parallel circuit is one that has two or
more paths for the electricity to flow.
In other words, the loads are parallel
to each other.


Sunday, August 26, 2012

Compilers vs Interpreters – Anoverview of the differences

It is a general notion that people try to
classify programming languages as
either “compiled” language or
“interpreted” language. Even
experienced programmers tend to get
confused here! But the fact is,
programming languages are
neither “compiled” nor
“interpreted” types
. They can be
both at the same time. Compiling or
interpreting -both are 2 different ways
of implementing the same program
written using a programming
language. A program written in C
language can either be compiled or
can be interpreted. Same is the case
with Java or any other programming
languages. The only requirement is,
we need a C or Java compiler to
compile a C/Java program and
similarly we need an C/Java
Interpreter to interpret a program
written in C/Java. So the difference is
not with programming languages, it is
with the way programs written in
different languages are implemented.


Any one serious about programming
should understand the working of
compilers,interpreters and the
differences between them.So here I
am trying to outline generic
differences between compiling and
interpreting (compilers vs interpreters).


Though I said programs written in any
programming language can be either
compiled or interpreted, it is not the
case always. Theoretically what I wrote
above is right – any program can be
compiled/interpreted. But a
programming language is usually
developed with an orientation to one
particular form of execution – for
example- C language was designed to
be compiled where as Java was
designed to be interpreted. But there
are interpreters available for C
programs too which will be helpful as
debugging aids. But in most cases a C
program is compiled for execution
and not interpreted. Before going
through differences, keep in mind the
following technical terms.


Compile time– The time taken to
compile a program.


Run time– The time taken for
executing a program.


Source code- The program in its user
written form of the language. Source
code is given as input to the compiler.


Object code- is actually the machine
code which is obtained by converting
source code. The computer can read
and execute machine code directly.
An object code is also known as
binary code/machine code.



So the primary difference between a
compiler and interpreter is in the way
a program is executed. A compiler
reduces the source code to machine
code and then save it as an object
code before creating an executable
file for the same. When executed, the
compiled program is executed directly
using the machine code (object code).
Where as an interpreter does not
convert the source code to an object
code before execution. An interpreter
executes the source code line by line
and conversion to native code is
performed line by line while
execution is going on (at runtime). In
such a scenario, the run time
required for an interpreted program
will be high compared to a compiled
program. Even though the run time
required for interpreted program are
high, the execution using an
interpreter has its own advantages.
For example -interpreted programs
can modify themselves at runtime by
adding/changing functions. A
compiled program has to be
recompiled fully even for the small
modifications we make to a small
section of the program; where as an
in the case of an interpreter there is
no such problem (only the modified
section needs to be recompiled)



Let us summarize the advantages of
both implementation methods–
compiling and interpreting


Advantages of using compiler:-


  • Since compiler converts the
    program to native code of the
    target machine (object code), faster
    performance can be expected.

  • There is a scope for code
    optimisation.

Advantages of using interpreter:-


  • Process of execution can be done
    in a single stage. There is no need
    of a compilation stage.

  • Alteration of codes possible during
    runtime.

  • Really useful for debugging the
    codes (because source code
    execution can be analyzed in an
    IDE).

  • Facilitates interactive code
    development.

Norton & Thevenin theorem

Thé venin's Theorem

Any voltage network which may be
viewed from two terminals can be
replaced by a voltage-source
equivalent circuit comprising a single
voltage source E and a single series
resistance R.. The voltage V is the
open-circuit voltage between the two
terminals and the resistance Z is the
resistance of the network viewed from
the terminals with all voltage sources
removed from circuit.


Sample




All circuits are equivalent. Resistors
R1,R2, R3 and voltage source are
transformed into Required Eq,


see parallel,
series simplifications.


To determine Eequ we shall break off
branch connecting node 1 and node
2




Norton's Theorem


Any current network which may be
viewed from two terminals can be
replaced by a current-source
equivalent circuit comprising a single
current source I and a single shunt
conductance G. The current I is the
short-circuit current between the two
terminals and the conductance G is
the conductance of the network
viewed from the terminals with all
branches containing current sources
are broken off.




Thursday, August 23, 2012

Rainbow Versatile Disk –Future Storage device

The whole world always moves towards
the small size and high capacity
storage devices. But instead of
inventing a new storage device for our
future needs, there is a new
technique to store enormous amount
of data in nowhere else, but in a paper.
You can store an awesome amount of data about 250GB of data in just a sheet of A4 paper. This new technology is the ‘Rainbow ‘. Rainbow technology is the upcoming storage technology and it is currently in its developmental stage. So, how it is
done? Read below to find it out more..

Rainbow Versatile Disk


What’s behind it?
This technology uses geometric
shapes to store data instead of the
usual digital format of 0′s and 1′s. The
geometric shapes used to store data
also included Textures and Diagrams.
Development
Mr. Sainul Abideen, a Computer
Applications student of MES college of
Engineering – Kerala, India has
designed this Rainbow technology.
His design combines various
techniques to create an unique one.
Storing the data as geometric shapes,
we can compress data in 450 sheets
of plain text into a 1 inch square. Also.
the bits and bytes of a 45 second
audio clip can also be compressed on
to a A4 sheet. Based on the sampling
frequency, depth of bit and
compression of audio, the size of the
45 second audio clip can vary from
few kilo bytes to few mega bytes of
data.
The highly advantageous thing with
the Rainbow Technology is that, the
same principle can be extended up to
256 GB of data by using specific
materials and devices.
Rainbow Versatile Disc (RVD)
Data from 90GB to 450GB can be
stored in an RVD, which is 131 times
the capacity of a normal CD. RVD
supports the data in any format like
movie files, MP3 files, picture files,
data files, etc. Special drives need to
be developed in order to support
RVDs. A method called “Vertical
Lining” is applied in RVD.
How it’s done?
In Rainbow technology, the data in
any format termed ‘rainbow format'
has been designed in such a way that
it can be printed out in the form of
images. The data is converted to
rainbow format on the basis of
Rainbow Algorithm. Trigonometric
forms like circle or square, certain
color combinations and certain other
forms are being used. Each
trigonometric form, color
combination represents a complete
pattern.
Most modern technologies like image
processing, pattern matching, etc. are
used for the purpose. The data which
gets converted into an image form is
then printed on paper or any other
thing. This is how the data storage is
made possible. When the steps are
reversed, the rainbow picture is
converted into data.

This is how it’s done!


Although environmental light
differences and color shading is a
problem, it can be overcome up to a certain extent by using efficient
mapping function. Each rainbow
format contains a header, body,
footer, parity, Rainbow boundary
mapper, etc. Header contains the
measurement of the rainbow picture, the algorithm that is being used, etc. It
also contains an efficiently-designed
error checking system.
Pros
CDs are made using Poly
Carbonate which costs about Rs.
400 to Rs. 450 per kilogram and 16
Grams of Poly Carbonate is needed
to make a CD. But the RVD which
offers 131 times storage capacity
than the CD can be made from
paper.
It is highly portable and bio-
disposable.
Cons
Since it is made of paper, it can be
easily destroyed.
A scanner can reliably distinguish
256 unique colors and the scanner
which can distinguish 1,440,000
colors is costly.
Final Words…
Technologies like these will drag us
more towards it. In future, we will see RVD’s replacing DVD’s and Blu Ray Disks as the major storage device. To do that, it has to overcome it’s shortcomings. Let’s hope this environment friendly technology comes into our everyday computing life.

Dear Readers! Let us know your
thoughts about Rainbow Versatile
Disks through the comments!

Direct currents devices

Electrical Symbols

Electronic component are classed into
either being Passive devices or Active
devices. A Passive Device is one that
contributes no power gain to a circuit
or system. Examples are Resistors,
Light Bulb, Electrical Heaters. Active
Devices are components that are
capable of generating voltages or
currents. Examples are Batteries and
other Electrical Curent & Voltage
Sources.


By using schematics symbols we can
represent real-life devices.

Resistance -This is a resistance,
measured in units ohms ohms, . Most
often it will be a resistor.


This is a source of emf
(electromotive force) or voltage
source, with a voltage of , measured
in units of volts, V. The most common
source you will see will be a battery.
However, batteries are really not
resistance-free. We can model this
case by putting a 'resistor' in the
circuit which has the same resistance
as the batterys would have.


This is a current source, with a
current of , measured in units of
amperes , A. Current source is ideal
model of electrical power source. The
internal current source resistance is
infinity. We can model real life battery
by putting a 'resistor' in parallel with
curent source.

Voltage, Current & Resistance

In electronics we are dealing with
voltage, current and resistance in
circuits.
Voltage
Voltage is the electrical force, that
causes current to flow in a circuit. It is
measured in VOLTS .
Electrical Current
Current is the movement of electrical
charge - the flow of electrons other
charged particles through the
electronic circuit. The direction of a
current is opposite to electrons flow
direction. Current is measured in
AMPERES (AMPS, A ).
Resistance
Resistance causes an opposition to
the flow of electricity in a circuit. It is
used to control the amount of voltage
and/or amperage in a circuit. It is
measured in OHMS.
There is a relation between Voltage, Current & Resistance i.e VR=I

Sunday, August 19, 2012

Superposition theorem

In a network with multiple voltage
sources, the current in any branch is
the sum of the currents which would
flow in that branch due to each
voltage source acting alone with all
other voltage sources replaced by
their internal impedances.
The goal of folowing text is to check
superposition theorem.


Step 1. Construct following circuit
using Circuit Magic then run Node
Voltage Analysis. (popular circuits
analysis technique). You can
alsocalculate currents using other
techniques.


Electrical scheme
Inital variables
R2=10Ohms; R1 =10Ohms;
R3 =10Ohms;
E1 =3V; E3 =4V;
Solution
V1 ·G11=I11
G11=1/R1 +1/R2+1/R3=0,3
I11 =-E1/R1 -E3 /R3 =-0,7
0,3V 1 =-0,7
V1 =-2,3333
V2 =0
I1 =(V1 -V2 +E1)/R1 =0,0666667
I2=(V1-V2)/R2 =-0,233333
I3=(V1-V2+E3 )/R3=0,166667
These values are used to check
currents determined from
superposition theorem
Step 2. Remove a voltage source
from the third branch then run
Node Voltage Analysis.


Electrical scheme
Inital variables
R2=10Ohms; R1 =10Ohms;
R3 =10Ohms;
E1=3V;
Solution
V1 ·G11=I11
G11=1/R1 +1/R2 +1/R3=0,3
I11 =-E1 /R1 =-0,3
0,3V 1 =-0,3
V1 =-1
V2 =0
I1(1) =(V1 -V2 +E1)/R1 =0,2
I2(1) =(V1 -V2 )/R2 =-0,1
I3(1) =(V1 -V2 )/R3 =-0,1
These values are used to
determine current from
superposition theorem.
Step 3. Remove a voltage source
from the first branch then run
Node Voltage Analysis.


Electrical scheme
Inital variables
R2=10Ohms; R1 =10Ohms;
R3 =10Ohms;
E3=4V;
Solution
V1 ·G11=I11
G11=1/R1 +1/R2 +1/R3=0,3
I11 =-E3 /R3 =-0,4
0,3V1 =-0,4
V1 =-1,3333
V2 =0
I1(2) =(V1 -V2 )/R1 =-0,133333
I2(2) =(V1 -V2 )/R2 =-0,133333
I3(2) =(V1 -V2 +E3)/R3 =0,266667
Superposition theorem checking
I1 =I1(1) +I1(2) =0,2-0,133333=0,0666666
I2 =I2(1) +I2(2) =-0,1-0,133333=-0,233333
I3 =I3(1) +I3(2) ==-0,1+0,266667=0,166667

Kirchhoff's Current and Voltage Laws & circuit analysis sample

Kirchhoff's Current Law (KCL)
KCL states that the algebraic sum of
the currents in all the branches which
converge in a common node is equal
to zero
SIin = SIout
Kirchhoff's Voltage Law
Kirchhoff's Voltage Law states that the
algebraic sum of the voltages between
successive nodes in a closed path in
the network is equal to zero.
SE = SIR
Solution using Kirchhoff’s Voltage and
current laws
Steps to solve circuit by Kirchhoff’s
Laws.
1. Construct circuit with circuit magic
schematics editor.

Circuit sample from circuit magic


2. Construct loops. (See “creating
loop” section in user guide) Number
of loops (and number of Kirhhoff’s
Voltage laws equations) can be
determined using following formula.
Loop can not include branches with
current sources. Due current sources
resistance equal infinity.
Loop Number = Branch Number –
(Nodes Number –1) – Current sources
Number
3. Select Analyze->Solve by Kirhhoff’s
laws menu item
4. In dialog box press OK button. if no
warning shown.
5. Read solution.
Solution example from circuit magic.
Writing Kirchhoff current law for 3-1
nodes
(Note number of Kirchhoff current
laws equations equal Nodes Number
–1)
(Node 1)J1+I3+I4+I7=0
(Node 2)-J1 +I2 -I4=0
Wrining Kirchoff voltage law for 5-1-
(3-1) loops
(Loop1) I3·R3 -I7 ·R5 =-E2
(Loop2) I2 ·R2 -I7 ·R5 +I4 ·R4 =E1 -E2
Linear equations
I3+I4 +I7 =-2
I2 -I4 =2
10I3 -10I7 =-10
11I2 +10I4 -10I7 =-7
Equations solution
I1 =2
I2 =0,692
I3 =-0,846
I4 =-1,308
I7 =0,154

Tuesday, July 31, 2012

Humidity Sensor: Types of Humidity Sensors & Working Principle

Humidity is the presence of water in
air. The amount of water vapor in air
can affect human comfort as well as
many manufacturing processes in
industries. The presence of water
vapor also influences various physical,
chemical, and biological processes
Humidity measurement in industries
is critical because it may affect the
business cost of the product and the
health and safety of the personnel.
Hence, humidity sensing is very
important, especially in the control
systems for industrial processes and
human comfort.
Controlling or monitoring humidity is
of paramount importance in many
industrial & domestic applications. In
semiconductor industry, humidity or
moisture levels needs to be properly
controlled & monitored during wafer
processing. In medical applications,
humidity control is required for
respiratory equipments, sterilizers,
incubators, pharmaceutical
processing, and biological products.
Humidity control is also necessary in
chemical gas purification, dryers,
ovens, film desiccation, paper and
textile production, and food
processing. In agriculture,
measurement of humidity is
important for plantation protection
(dew prevention), soil moisture
monitoring, etc. For domestic
applications, humidity control is
required for living environment in
buildings, cooking control for
microwave ovens, etc. In all such
applications and many others,
humidity sensors are employed to
provide an indication of the moisture
levels in the environment.
RELEVANT MOISTURE TERMS
To mention moisture levels, variety of
terminologies are used. The study of
water vapour concentration in air as a
function of temperature and pressure
falls under the area of psychometrics.
Psychometrics deals with the
thermodynamic properties of moist
gases while the term “humidity’ simply
refers to the presence of water vapour
in air or other carrier gas.
Humidity measurement determines
the amount of water vapor present in
a gas that can be a mixture, such as
air, or a pure gas, such as nitrogen or
argon.
CHARACTERISTICS
Sensor characterisation is done based
on the n-point(usually 9)
characterisation of the sensor.
Characterisation is performed at a
specific temperature (25°C) and
excitation.
In 9 point characterisation method,
humidity levels are swept the through
the RH values and measuring the
corresponding dc output voltage for
the individual sensor: Values are taken
at humidity levels of 0%, 25%, 53.2%,
75.3%, 93.8%, 75.3%, 53.2%, 25% and
0%. Based on the characterisation
results, Best Fit Straight Line (BFSL) is
plotted and sensor characteristics are
specified in the datasheets.
  • Acuracy
    Accuracy is specified based on the
    specific calibration curves for any
    individual sensor. It is specified using
    the linear Best Fit Straight Line (BFSL)
    and the non-linear 2 nd order curve.
    As an example let us consider a
    sensor with an accuracy of ±2% RH
    (BFSL). If the sensor has an output
    voltage of 0.689 V at 0%RH, an
    average slope(BFSL) of 0.036 V/%RH
    and offset of 0.662, then its BFSL
    accuracy error is given by (0.689 -
    0.662)/0.036 = 0.75% RH. As sensors
    accuracy is ±2% RH (BFSL), i.e. 0.072V,
    the sensor should always output
    0.662 ±0.072 V or a value in the range
    of 0.59 V to 0.734 V.
  • Hysteresis
    Hysteresis is the difference between
    the two voltages to %RH conversions
    (using average BFSL slope) at each of
    the four duplicated points in the nine
    point characterization. Hysteresis is
    recorded in absolute %RH terms.
    The value taken is the largest %RH
    figure for an individual sensor over
    each of the four characterization
    points.
  • Interchangeability
    Interchangeability defines the range of
    voltages for any population of sensors
    at this RH point.
    As an example let us consider a
    sensor from a particular company
    with an interchangeabilty of ±5% at
    0% RH. With an average slope (BFSL)
    of 0.036 V/%RH and offset of 0.662 V,
    ±5% RH is equal to ±0.18 V. This
    means that the output voltage for this
    device is 0.662 V ±0.18 V, or a range of
    0.482V to 0.842 V. When exposed to
    an RH of 0%, the output of the entire
    population of sensors will fall within
    this range.
  • Linearity
    Linearity indicates the voltage
    deviation from the BFSL value and the
    measured output voltage value,
    converted to RH.
  • Reliability
    Sensors are subjected to accelerated
    stress tests. If the tests causes the
    sensor to drift and report RH outside
    prescribed specifications, the sensor
    is considered a failed sensor. Based
    on such tests, reliability figures like
    MTTF(Mean-time-to-failure) and FIT
    (Number of Failures per billion
    operating hours) are specified.
  • Repeatability
    Repeatability is the maximum
    variation between sensor outputs for
    repeated sweeps of humidity levels
    across the sensors’ measurement
    range under identical conditions.
    For example, if the point value is
    0.013 V using the 31 mV/RH slope this
    is 0.42% RH.
  • Response Time
    Response Time is measured in “slow
    moving air” (less than 5 m/s).
    Typically, maximum time required for
    the output voltage of the sensor to
    rise to 63% of its final value or to fall
    to 37% of its final value when exposed
    to a step rise or fall in humidity is
    specified as response time
  • Temperature Compensation
    Voltage output for an individual
    sensor at a given excitation and RH is
    affected by temperature. In many
    sensors, the temperature is measured
    and the effect of temperature of
    humidity measurement is reduced
    and this is referred to as temperature
    compensation.
  • StabilityOutput voltage stability is the output
    voltage drift in time at the specified RH
    level converted to a %RH value.
    This figure is also generated through
    accelerated stress tests and is typically
    taken as the change in mean output
    voltage from a large batch of sensors
    in specific environmental conditions.

SELECTING A HUMIDITY SENSOR
As there no real physical standard for
relative humidity calibration, humidity
instruments are not specified
properly. And it makes it really difficult
for a user to compare the sensors
from different manufacturers. This
makes it mandatory for a user to go
deeper into the specifications and
attempt to verify the claims of the
instrument manufacturer. Various
sensor characteristics, viz., accuracy,
linearity, hysteresis, calibration errors,
long term stability of sensor and
electronics, needs to be examined
using the support documentation
from the OEM.
Source: Engineersgarage

Monday, July 30, 2012

Hydrogen Race Car Takes On Fossil- Fueled Rivals


For the first time a hydrogen race car
entered the annual Formula Student
competition held in the UK. Built by
the Forze hydrogen racing team of the
Dutch Delft University of Technology,
the Forze V race car is equipped with
a hydrogen fuel cell which powers two
electric motors.
The Formula Student (FS) challenge
invites teams from universities across
the world to build a car and race
them against each other at the
Silverstone race circuit. FS started in
1998 and aims to inspire young
engineers to go through the full cycle
of building a single-seat racing car,
including business plan, design,
presentation and -of course- building
and competing.
In 2008 Class 1A was introduced, a
special category apart from Class 1,
dedicated to low carbon emission
cars.
However, the Forze V team decided to
race their car- which only exhaust is
pure water- against its Class 1 gas-
guzzling brethren. They came in 29th
of 103 contestants.
Alistair Wardrope, a judge of the FS
races said that the Forze V ‘beat many
gasoline powered race cars on a level
playing field. Internal combustion
engines have been developed for over
a hundred years. The significance of
the achievement lies in Delft Forzes’
skill in adopting a new technology to
compete against a well developed
technology.’
The car weighs 280kg (617lbs) and is
powered by a 18kW hydrogen fuel
cell. Its top speed is 120km/h
(75mph) and accelerates from 0 to
96km/h (0-60mph) in less than 5
seconds. On a full tank of 600 grams
of gaseous hydrogen the car can race
for an hour. Its only exhaust product:
three liters of water (0.8 gal).
The Delft Force V team hopes their car
will convince people that fuel cells are
the long term solution for sustainable
mobility.
Source: Formulazero.tudelft.nlW

Sunday, July 29, 2012

Operational princle of SCR


SCR working principle
The SCR is a four-layer, three-junction
and a three-terminal device and is
shown in fig.a. The end P-region is the
anode, the end N-region is the
cathode and the inner P-region is the
gate. The anode to cathode is
connected in series with the load
circuit. Essentially the device is a
switch. Ideally it remains off (voltage
blocking state), or appears to have an
infinite impedance until both the
anode and gate terminals have
suitable positive voltages with respect
to the cathode terminal. The thyristor
then switches on and current flows
and continues to conduct without
further gate signals. Ideally the
thyristor has zero impedance in
conduction state. For switching off or
reverting to the blocking state, there
must be no gate signal and the anode
current must be reduced to zero.
Current can flow only in one direction.
In absence of external bias voltages,
the majority carrier in each layer
diffuses until there is a built-in voltage
that retards further diffusion. Some
majority carriers have enough energy
to cross the barrier caused by the
retarding electric field at each
junction. These carriers then become
minority carriers and can recombine
with majority carriers. Minority carriers
in each layer can be accelerated
across each junction by the fixed field,
but because of absence of external
circuit in this case the sum of majority
and minority carrier currents must be
zero.
A voltage bias, as shown in figure, and
an external circuit to carry current
allow internal currents which include
the following terms:

The current Ix is due to
  • Majority carriers (holes) crossing
    junction J1
  • Minority carriers crossing junction
    J1
  • Holes injected at junction J2
    diffusing through the N-region and
    crossing junction J1 and
Minority carriers from junction J2
diffusing through the N-region and
crossing junction J1 .
Similarly I2 is due to six terms and I3
is due to four terms.
The two simple analogues to explain
the basic action for the thyristor are
those of the diode and the two
transistor models.
1. Diode Model. The thyristor is
similar to three diodes in series as
there are three P-N junctions.
Without gate bias, there is always
at least one reverse biased junction
to prevent conduction irrespective
of the polarity of an applied voltage
between anode and cathode. If the
anode is made positive and the
gate is also biased positively with
respect to cathode, the P-layer at
the gate is flooded by the electrons
from the cathode and loses its
identity as a P-layer. Accordingly
the thyristor becomes equivalent
to a conducting diode.

Scr working
2. Two Transistor Model.
Imagine the SCR cut along the
dotted line, as shown in fig. a.
Then we can have two devices, as
shown in fig.b. These two devices
can be recognized as two
transistors. The upper left one is P-
N-P transistor and the lower right
N-P-N type. Further it can be
recognized that the base of the P-
N-P transistor is joined to the
collector of the N-P-N transistor
while the collector of P-N-P is
joined to the base of N-P-N
transistor, as illustrated in fig. c.
The gate terminal is brought out
from the base of the N-P-N
material. This construction has
been conceived merely to explain
the working of SCR, otherwise in
physical shape the SCR has four
solid layers of P-N-P-N type only.
Now we can see that the two
transistors are connected in such a
manner that the collector of Q1 is
connected to the base of Q2 i.e. the
output collector current of Qt
becomes the base current for Q2 . In
the similar way the collector of Q2 is
joined to the base of Q1 which shows
that the output collector current of Q2
is fed to Q1 as input base current.
These are back to back connections of
transistors in such a way that the
output of one goes into as input of
other transistor and vice-versa. This
gives net gain of loop circuit as β1x
β2 where β1 and β2 are current gains
of two transistors respectively.
When the gate current is zero or the
gate terminal is open, the only current
in circulation is the leakage current,
which is very small in case of silicon
device specially and the total current
is a little higher than sum of individual
leakage currents. Under these
conditions P-N-P-N device is said to
be in its forward blocking or high
impedance ‘off state. As soon as a
small amount of gate current is given
to the base of transistor Q2 by
applying forward bias to its base-
emitter junction, it generates the
collector current as β2 times the base
current. This collector current of Q2 is
fed as input base current to Q : which
is further multiplied by β1 times as ICl
which forms input base current of Q2
and undergoes further amplification.
In this way both transistors feedback
each other and the collector current
of each goes on multiplying. This
process is very quick and soon both
the transistors drive each other to
saturation. Now the device is said to
be in.on-state. The current through
the on-state SCR is controlled by
external impedance only.
Souce: circuitstoday

Friday, July 27, 2012

12V BATTERY LEVEL INDICATOR CIRCUIT

This battery level indicator offers (5)
LEDs that light up progressively as the
voltage increases:
  • Red: Power Connected (0%)
  • Yellow: Greater than 10.5V (25%)
  • Green 1: Greater than 11.5V (50%)
  • Green 2: Greater than 12.5V (75%)
Green 3: Greater than 13.5V (100%)
Of course, you may select your own
colors if desired.
12 Volts Battery Level Indicator
Circuit Schematic


Operation of the battery level
indicator

D1 is the voltage reference zener. Tied
to this is a string of divider resistors
(R2-6) that set the various fixed
voltage levels. R7 & 8 form a voltage
divider to that reduces the battery
voltage by a factor of 3. U1 is an
LM339 quad comparator that
compares the various voltages from
the two dividers. The comparator
sections have open collector outputs
that simply function as switches to
operate the LEDs. D7 protects against
reverse battery connection.
The LEDs are biased to operate at
about 4mA which is quite bright if
modern LEDs are used. This current
can be adjusted simply by varying the
series resistors (R9 through R13). The
overall current drain as shown is
about 25mA which tends to be
wasteful for continuous operation. For
energy conservation, connect to
battery via a pushbutton (Push to
Test).
Printed Circuit Board
I did a www.expresspcb.com SMT
layout using 0805 size components,
1N753 zener and SOIC-14 IC. D7 is in
a SOT-23 package. These components
are about as small as I like to work
with. The layout has not yet been
carefully checked or built. Note that
surprises abound when constructing
prototypes.
The circuit board measures only 0.5” x
1.5”.
download the PCB layout
More recently, I located an
inexpensive SOT-23 zener with a 2%
voltage tolerance—this has not yet
been incorporated.
I have had good results with 0805 size
LEDs purchased from China on eBay.
They are both inexpensive and
BRIGHT!

The 12v battery level indicator unit in
the photo has no reverse polarity
diode and R2 is the calibration
potentiometer.
Source: Elektro symetrics

Tuesday, July 24, 2012

LM358 DATASHEET


The LM358 series consists of two
independent, high gain, internally
frequency compensated operational
amplifiers which were designed
specifically to operate from a single
power supply over a wide range of
voltages. Operation from split power
supplies is also possible and the low
power supply current drain is
independent of the magnitude of the
power supply voltage.
The LM358 and LM2904 are available
in a chip sized package (8-Bump
micro SMD) using National’s micro
SMD package technology.
LM358 pin diagram

LM358 Features
  • Available in 8-Bump micro SMD chip
    sized package, (See AN-1112)
  • Internally frequency compensated
    for unity gain
  • Large dc voltage gain: 100 dB
  • Wide bandwidth (unity gain): 1 MHz
    (temperature compensated)
  • Wide power supply range:
  • Single supply: 3V to 32V
  • or dual supplies: ±1.5V to ±16V
  • Very low supply current drain (500
    μA)—essentially independent of
    supply voltage
  • Low input offset voltage: 2 mV
  • Input common-mode voltage range
    includes ground
  • Differential input voltage range equal
    to the power supply voltage
Large output voltage swing

Monday, July 23, 2012

HIGH TEMPERATURE INDICATOR CIRCUIT

In some areas there is a need of
temperature detectors which help
them to detect temperature and
indicate them whether the
temperature is low or not.
Below shown circuit is the simple high
temperature indicator circuit. It will
not show the current temperature
but if it exceeds some threshold
temperature it will detect and indicate.
You can use this circuit anywhere you
needed.

The components needed for the
circuit are:
3 Resistors
1 Temperature dependent resistor
5v battery
Two 1n4007 diodes
One Op-Amp
One LED
And the circuit working is actually very
simple, the Op-amp is connected as
Non-inverting comparator. And a
bridge circuit is made with the
resistors and a Temperature
Dependent Resistor. From above
circuit R1, R2 and R3 are normal
resistors but RT is Temperature
Dependent Resistor.
The bridge resistance and RT are
selected in such a way that as long as
temperature is less than threshold
value, the bridge is unbalanced by
making Voltage at B more than
voltage at A . Hence Vo = -Vsat and
LED is reverse biased and remains
OFF. When temperature becomes
more than threshold then Voltage at B
becomes less that Voltage at A hence
it drives Vo = +Vsat. Due to this, LED
glows and gives high temperature
indication.

iPhone 5 Dock Smaller

A smaller dock connector means
the iPhone 5 will be incompatible
with accessories made for Apple
products going back nearly 10 years.


Apple is preparing to ditch the thirty-pin
connector it has used since the early
days of its iPod media player. The
iPhone 5 will instead ship with a
smaller dock connector containing 19
pins. The design change, long
rumored for the new iPhone, means
that the iPhone 5 will be incompatible
with the bulk of existing iPhone
accessories.
Why the change ? According to
sources cited by Reuters, the dock
switcheroo is meant "to make room
for the earphone moving to the
bottom." Souce: InformationWeek