Posted by Jayesh Yewale
Posted on 10:07:00 PM
with 1 comment
Battery Tester Project Using LM3914 IC
This objective of this project is to design and build a battery tester that is able to test various types of dry cell and rechargable battery with a voltage of less than 2V. Configured as a bar graph battery level indicator, the LM3914 IC from National Semiconductor senses the voltage levels of the battery under test and drives the 10 LEDs to ON or OFF based on the voltage that is detected. The current driving the LEDs is regulated by using the external resistor R1 and hence limiting resistors are not required.
The schematic shows the simple connections where the reference voltage at pin 8 of U1 can be adjusted by adjusting the variable resistor VR1. The voltage at pin 8 will set the maximum scale of the LED. In testing dry cellbattery of 1.5V, set the voltage at pin 8 to 2.0V. Each of the LED will thus represent 200mV when lighted up.
If testing of rechargable battery such as NiCd or NiMH is required, set the reference voltage to a lower value such as 1.5Vas the typical voltage of a rechargable battery is approximately 1.2V.
When testing the battery, take note of the polarity of the probe to the terminals of the battery. T1 is to be placed on the positive terminal and T2 the negative terminal of the battery.
Posted by Jayesh Yewale
Posted on 7:13:00 PM
with No comments
GSM(Global System for Mobile Communications) is a Digital Wireless Technologyused for cell phone in the world that is, it is a cellular technology used for transmitting mobile voice and data services. It was developed by the European companies.
It uses SIM card so u can easily switch your SIM card between phones
International roaming is easier on a GSM network
In GSM every user requires a separate frequency channel for communication
GSM accounts for 80% of total mobile phone technologies market
The Frequency Band(range) in GSMThe frequency of the carrier is very important, because it determines the Size, power, efficiency of your mobile phones.
It supports FDMA & TDMA as Multiple Access Techniques
Posted by Jayesh Yewale
Posted on 7:02:00 PM
with No comments
Microwave is a kind of electromagnetic wave. In a broad sense, the microwave frequency range is from 300 MHz to 300 GHz. But In microwave communication, the frequency range is generally from 3 GHz to 30 GHz.
Concept of Digital Microwave Communication
Digital microwave communication is a way of transmitting digital information in atmosphere through microwave or radio frequency (RF).
Microwave communication refers to the communication that use microwave as carrier.
Digital microwave communication refers to the microwave communication that adopts the digital modulation.
The baseband signal is modulated to intermediate frequency (IF) first . Then the intermediate frequency is converted into the microwave frequency.
The baseband signal can also be modulated directly to microwave frequency, but only phase shift keying (PSK) modulation method is applicable.
Posted by Jayesh Yewale
Posted on 1:51:00 PM
with 1 comment
Cascode amplifier is a two stage circuit
consisting of a transconductance amplifier followed by a buffer
amplifier. The word “cascode” was originated from the phrase “cascade to
cathode”. This circuit have a lot of advantages over the single stage
amplifier like, better input output isolation, better gain, improved
bandwidth, higher input impedance, higher output impedance, better
stability, higher slew rate etc. The reason behind the increase in
bandwidth is the reduction of Miller effect. Cascode amplifier
is generally constructed using FET ( field effect transistor) or BJT (
bipolar junction transistor). One stage will be usually wired in common
source/common emitter mode and the other stage will be wired in common
base/ common emitter mode.
Miller effect.
Miller effect is actually the
multiplication of the drain to source stray capacitance by the voltage
gain. The drain to source stray capacitance always reduces the bandwidth
and when it gets multiplied by the voltage gain the situation is made
further worse. Mulitiplication of stray capacitance increases the
effective input capacitance and as we know, for an amplifier, the
increase in input capacitance increases the lower cut of frequency and
that means reduced bandwidth. Miller effect can be reduced by adding a
current buffer stage at the output of the amplifier or by adding a
voltage buffer stage before the input.
FET Cascode amplifier.
FET cascode amplifier
The circuit diagram of a typical Cascode
amplifier using FET is shown above. The input stage of the circuit is
an FET common source amplifier and the input voltage (Vin) is applied to
its gate. The output stage is an FET common gate amplifier which is
driven by the input stage. Rd is the drain resistance of the output
stage. Output voltage (Vout) is taken from the drain terminal of Q2.
Since the gate of Q2 is grounded, FET Q2′s source voltage and the FET
Q1′s drain voltage are held almost constant. That means the upper FET Q2
offers a low input resistance to the lower FET Q1. This reduces the
gain of lower FET Q1 and as a result the Miller effect also gets reduced
which results in increased bandwidth. The reduction in gain of the
lower FET Q1 does not affect the overall gain because the upper FET Q2
compensates it. The upper FET Q2 is not affected by the Miller effect
because the charging and discharging of the drain to source stray
capacitance is carried out through the drain resistor and the load and
the frequency response if affected only for high frequencies (well over
the audio range).
In Cascode configuration, the output is
well isolated from the input. Q1 has almost constant voltage at the
drain and source terminals while Q2 has almost constant voltage at its
source and gate terminals and practically there is nothing to feed back
from the output to input. The only points with importance in terms of
voltage are the input and output terminals and they are well isolated by
a central connection of constant voltage.
Practical Cascode amplifier circuit.
Practical cascode amplifier circuit
A practical Cascode amplifier circuit based on FET is shown above.
Resistors R4 and R5 form a voltage divider biasing network for the FET
Q2. R3 is the drain resistor for Q2 and it limits the drain current. R2
is the source resistor of Q1 and C1 is its by-pass capacitor. R1 ensures
zero voltage at the gate of Q1 during zero signal condition
Posted by Jayesh Yewale
Posted on 12:09:00 PM
with No comments
Google (Nasdaq: GOOG) has revealed its long-rumored plans to create augmented reality (AR) eyeglasses.
Google's Project Glass
Augmented reality
is a live, direct or indirect view of a physical environment that's
augmented by computer-generated input such as sound, video, graphics or GPS data.
Work on the AR glasses is proceeding as Project Glass, which is part
of the Google X Lab, a facility run by Google said to be somewhere in
California's Bay Area where about 100 leading-edge projects are
reportedly being undertaken.
The scientists behind Project Glass are Babak Parviz, Steve Lee and
Sebastian Thrun. They asked for viewer feedback on a video they posted
on YouTube.
Through the Looking Glass
The video is shot from the point of view of someone wearing a pair of
AR glasses. The wearer can apparently take a phone call while wearing
the glasses, listening and speaking with the caller, whose avatar or
photo pops up on one lens of the glasses.
The wearer can also transmit what he or she sees during the
conversation. For example, looking out of the window triggers data about
the weather that's shown on the lens.
Looking at objects while walking pulls up information on the lens.
For example, when the wearer passes a subway station, a notice that
service had been suspended is called up a Google Map showing a walking
route.
A Siri-like voice application puts up information in response to
questions. For example, when the user walked into a bookstore and asked
where the music section was, a map indicating that section came up on
the lens.
The user can also instruct the glasses to take a photo.
Project Glass seems to incorporate features from Google Maps,
Android's voice response system, Google's geolocation service and other
features.
"We plan to share a lot more details as we continue to work on this
project," Google spokesperson Katelin Todhunter-Gerberg told
TechNewsWorld. However, "our only on-the-record statement is in the
Google+ post."
Who's Making the Glasses
Babak Parviz, from the Project Glass Team, is an associate professor of electrical engineering at the University of Washington
who has been working on bionic contact lenses that could wirelessly
stream information across their surface, much like the AR glasses.
He led a team that created a prototype contact lens that contained a
single pixel of information as a proof of concept. The lens has an
antenna to draw power from an external source. An integrated circuit in
the lens stores this energy and transfers it to a transparent sapphire
chip containing one blue LED.
Another member of the Project Glass team, Sebastian Thrun, is a Google Fellow and a part-time research professor of computer science at Stanford University.
He was formerly the director of the Stanford Artificial Intelligence
Laboratory and led the development of the Google self-driving car.
My AR Glasses Cup Runneth Over
"The question is whether [AR glasses] will initially be more helpful or more annoying," Rob Enderle, principal analyst at the Enderle Group, told TechNewsWorld.
"Let's say you are driving, and just before the guy in front of you
hits his brakes a note pops up warning you of traffic ahead so you don't
actually see his brake lights in time," he said. "In that instance, the
glasses will become a huge liability."
However, if the glasses work, Enderle will use them. "They would
alert me to things I want to know and likely otherwise would miss," he
explained. "And they'd be very handy in navigation, particularly while
walking or on a bike."
Google will have to work out some knots in its idea first in order to have the glasses accepted by the general public.
"Putting something over someone's eyes to create a new human/machine
interface is fascinating, but given how much we use our eyes, it doesn't
come without risk," Enderle pointed out.
"This is like the 3D TV thing all over again," Maribel Lopez, principal analyst at Lopez Research, told TechNewsWorld. "Nobody wants to buy 3D TV because nobody wants to wear the dorky glasses."
Further, it's not likely that people whose vision doesn't require
correcting would want to wear AR glasses, Lopez pointed out. "It's got
to be something that's integrated into your normal routine, like cycling
glasses for when you're going to ride your bike, and not a stretch."
