Commit afe761a5 authored by Georges Khaznadar's avatar Georges Khaznadar

deleted generated files

parent 1a1d60b0
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<div class="section" id="introduction">
<h1>Introduction</h1>
<p>Science is the study of the physical world by systematic observations
and experiments. Proper science education is essential for cultivating a
society where reasoning and logical thinking prevails and not
superstition and irrational beliefs. Science education is also essential
for training enough technicians, engineers and scientists for the
economy of the modern world. It is widely accepted that personal
experience in the form of experiments and observations, either carried
out by students or performed as demonstrations by teachers, are
essential to the pedagogy of science. However, almost everywhere science
is mostly taught from the text books without giving importance to
experiments, partly due to lack of equipment. As a result, most of the
students fail to correlate their classroom experience to problems
encountered in daily life. To some extent this can be corrected by
learning science based on exploration and experimenting.</p>
<p>The advent of personal computers and their easy availability has opened
up a new path for making laboratory equipment. Addition of some hardware
to an ordinary computer can convert it in to a science laboratory.
Performing quick measurements with good accuracy enables one to study a
wide range of phenomena. Science experiments generally involve
measuring/controlling physical parameters like temperature, pressure,
velocity, acceleration, force, voltage, current etc. If the measured
physical property is changing rapidly, the measurements need to be
automated and a computer becomes a useful tool. For example,
understanding the variation of AC mains voltage with time requires
measuring it after every millisecond.</p>
<p>The ability to perform experiments with reasonable accuracy also opens
up the possibility of research oriented science education. Students can
compare the experimental data with mathematical models and examine the
fundamental laws governing various phenomena. Research scientists do the
same with highly sophisticated equipment. The expEYES ( expEriments for
Young Engineers &amp; Scientists) kit is designed to support a wide range of
experiments, from school to post graduate level. It also acts as a test
equipment for electronics engineers and hobbyists. The simple and open
architecture of expEYES allows the users to <em>develop new experiments,
without getting into the details of electronics or computer
programming</em>. This User’s manual describes <em>expEYES-17</em> along with
several experiments, there is also a Programmer’s manual available.</p>
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<div class="section" id="the-equipment">
<h1>The equipment</h1>
<p>ExpEYES-17 is interfaced and powered by the USB port of the computer,
and it is programmable in Python. It can function as a low frequency
oscilloscope, function generator, programmable voltage source, frequency
counter and data logger. For connecting external signals, it has two
spring loaded terminals blocks, one for output signals and another for
inputs, as shown in figure <a class="reference external" href="#fig:The-ExpEYES-toppanel">1.1↓</a>. The
software can monitor and control the voltages at these terminals. In
order to measure other parameters (like temperature, pressure etc.), we
need to convert them in to electrical signals by using appropriate
sensor elements. The accuracy of the voltage measurements is decided by
the stability of the 3.3V reference used, it is 50ppm per degree
celcius. The gain and offset errors are eliminated by initial
calibration, using a 16bit ADC. Even though our primary objective is to
do experiments, you are advised to read through the brief description of
the equipment given below. The device can be also used as a test
equipment for electrical and electronics engineering experiments.</p>
<p><em>IMPORTANT :</em></p>
<p><em>The external voltages connected to ExpEYES17 must be within the allowed
limits. Inputs A1 and A2 must be within ±16 volts range and Inputs IN1
and IN2 must be in 0 to 3.3V range. Exceeding these limits may result in
damage to the equipment. To measure higher voltages, scale them down
using resistive potential divider networks.</em></p>
<div class="figure" id="fig-e17">
<a class="reference internal image-reference" href="_images/eyes17-panel.jpg"><img alt="_images/eyes17-panel.jpg" src="_images/eyes17-panel.jpg" style="width: 500px;"/></a>
</div>
<p>Figure 1.1 The ExpEYES17 top panel showing the external connections.</p>
<div class="section" id="external-connections">
<h2>External connections</h2>
<p>The functions of the external connections briefly explained below. All
the black coulored terminals are at ground potential, all other voltages
are measured with respect to it.</p>
<div class="section" id="outputs">
<h3>Outputs:</h3>
<div class="section" id="constant-current-source-ccs">
<h4>Constant Current Source (CCS) :</h4>
<p>The constant current source can be switched ON and OFF under software
control. The nominal value is 1.1 mA but may vary from unit to unit, due
to component tolerances. To measure the exact value, connect an ammeter
from CCS to GND. Another method is to connect a known resistance (~1k)
and measure the voltage drop across it. The load resistor should be less
than 3k for this current source.</p>
</div>
<div class="section" id="programmable-voltage-pv1">
<h4>Programmable Voltage (PV1) :</h4>
<p>Can be set, from software, to any value in the -5V to +5V range. The
resolution is 12 bits, implies a minimum voltage step of around 2.5
millivolts.</p>
</div>
<div class="section" id="programmable-voltage-pv2">
<h4>Programmable Voltage (PV2) :</h4>
<p>Can be set, from software, to any value in the -3.3V to +3.3V range. The
resolution is 12 bits.</p>
</div>
<div class="section" id="square-wave-sq1">
<h4>Square Wave SQ1:</h4>
<p>Output swings from 0 to 5 volts and frequency can be varied 4Hz to
100kHz. All intermediate values of frequency are not possible. The duty
cycle of the output is programmable. Setting frequency to 0Hz will make
the output HIGH and setting it to  − 1 will make it LOW, in both cases
the wave generation is disabled. SQR1 output has a <img alt="100~\Omega" class="math" src="_images/math/36dfc0dd6f490d35fa65c29d9013ee762dc718f1.png"/> <strong>series
resistor</strong> inside so that it can drive LEDs directly.</p>
</div>
<div class="section" id="square-wave-sq2">
<h4>Square Wave SQ2:</h4>
<p>Output swings from 0 to 5 volts and frequency can be varied 4Hz to
100kHz. All intermediate values of frequency are not possible. The duty
cycle of the output is programmable. SQR2 is not available when WG is
active.</p>
</div>
<div class="section" id="digital-output-od1">
<h4>Digital Output (OD1) :</h4>
<p>The voltage at OD1 can be set to 0 or 5 volts, using software.</p>
</div>
<div class="section" id="sine-triangular-wave-wg">
<h4>Sine/Triangular Wave WG:</h4>
<p>Frequency can be varied from 5Hz to 5kHz. The peak value of the
amplitude can be set to 3 volts, 1.0 volt or 80 mV. Shape of the output
waveform is programmable. Using the GUI sine or triangular can be
selected. WG bar is inverted WG.</p>
</div>
</div>
<div class="section" id="inputs">
<h3>Inputs:</h3>
<div class="section" id="capacitance-meter-in1">
<h4>Capacitance meter IN1:</h4>
<p>Capacitance connected between IN1 and Ground can be measured. It works
better for lower capacitance values, upto 10 nanoFarads, results may not
be very accurate beyond that.</p>
</div>
<div class="section" id="frequency-counter-in2">
<h4>Frequency Counter IN2:</h4>
<p>Capable of measuring frequencies upto several MHz.</p>
</div>
<div class="section" id="resistive-sensor-input-sen">
<h4>Resistive Sensor Input (SEN):</h4>
<p>This is mainly meant for sensors like Light Dependent Resistor,
Thermistor, Photo-transistor etc. SEN is internally connected to 3.3
volts through a 5.1kΩ resistor.</p>
</div>
<div class="section" id="analog-inputs-a1-a2">
<h4><img alt="\pm16\ V" class="math" src="_images/math/bbc2ff13bad8d262b9cc56f16a664ff4871beaf1.png"/> Analog Inputs, A1 &amp; A2:</h4>
<p>Can measure voltage within the ±16 volts range. The input voltage range
can be selected from .5V to 16V fullscale. Voltage at these terminals
can be displayed as a function of time, giving the functionality of a
low frequency oscilloscope. The maximum sampling rate is 1 Msps
/channel. Both have an input impedance of 1MΩ .</p>
</div>
<div class="section" id="analog-input-a3">
<h4><img alt="\pm3.3\ V" class="math" src="_images/math/a8045cf7990709a0503df23e7cac7cf9fdfac062.png"/> Analog Input A3:</h4>
<p>Can measure voltage within the ±3.3 volts range. The input can be
amplified by connecting a resistor from Rg to Ground, gain
=1 + (Rg)/(10000). This enables displaying very small amplitude signals.
The input impedance of A3 is 10MΩ.</p>
</div>
<div class="section" id="microphone-input-mic">
<h4>Microphone input MIC:</h4>
<p>A condenser microphone can be connected to this terminal and the output
can be captured.</p>
</div>
</div>
<div class="section" id="i2c-sensor-interface">
<h3>I2C Sensor Interface:</h3>
<p>The four connections (+5V, Ground, SCL and SDA) of the 8 terminal berg
strip supports I2C sensors. The software is capable of recognizing a
large number of commercially available I2C sensors.</p>
</div>
<div class="section" id="power-supply">
<h3><img alt="\pm\ 6\ V/10\ mA" class="math" src="_images/math/2201dc802084bb28c4d086972d749820916bfaa6.png"/> Power supply:</h3>
<p>The VR+ and VR- are regulated power outputs. They can supply very little
current, but good enough to power an Op-Amp.</p>
</div>
</div>
<div class="section" id="accessory-set">
<h2>1.2.2 Accessory Set</h2>
<p>Some accessories are provided with expEYES.</p>
<ul class="simple">
<li>Pieces of wires, with pin and with crocodile clip.</li>
<li>Condenser microphone with leads.</li>
<li>Inductor Coil (2) : 44SWG wire on 1cm dia bobbin. Around 3000 Turns
(some may have more turns). These coils can be used for studying
inductance, electromagnetic induction etc.</li>
<li>Piezo Electric Discs (2) : Resonant frequency is around 3500 Hz. Can
be energized by WG output or SQR1. Discs are enclosed in a plastic
shell that forms a cavity, that enhances the amplitude of sound
produced.</li>
<li>DC Motor : Should be powered by a DC voltage less than 3 volts.</li>
<li>Permanent Magnets : (a) 10mm dia &amp; length (b) 5 mm dia &amp; 10 mm length
(c) Button size magnets(2)</li>
<li>5mm LEDS : RED, BLUE, GREEN, WHITE</li>
<li>Capacitors : 100pF, 0.1uF , 1 uF &amp; 22uF</li>
<li>Inductor : 10 mH / 20Ω,</li>
<li>Resistors : 560Ω, 1kΩ, 2.2kΩ , 10kΩ , 51kΩ and 100 kΩ</li>
<li>LDR</li>
<li>Two silicon diodes (1N4148) and one 3.3 volts zener diode</li>
<li>NPN Transistor( 2N2222)</li>
</ul>
</div>
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<div class="section" id="software-installation">
<h1>Software Installation</h1>
<p>ExpEYES can run on any computer having a Python Interpreter and required
modules. The USB interface is handled by a device driver program that
presents the USB port as a Serial port to the Python programs. The
communication the expEYES is done using a library written in Python.
Programs with GUI have been written for many experiments. Eyes17
software require the following packages</p>
<ul class="simple">
<li>python-serial</li>
<li>python-numpy</li>
<li>python-scipy</li>
<li>python-qt4</li>
<li>python-pyqtgraph</li>
</ul>
<div class="section" id="any-gnu-linux-distributions">
<h2>Any GNU/Linux distributions</h2>
<p>Download <strong>eyes17-x.x.x.zip</strong> (the latest version) from
<strong>http://expeyes.in</strong> and upzip it, and change to the newly created
folder. Issue the command</p>
<blockquote>
<div><p>$ sudo sh postinst # set user write permission</p>
<p>$ python main.py</p>
</div></blockquote>
<p>You will get error messages for any missing packages that are required
for expeyes. Install them one by one and try again. Python programs
required for several experiments are in the same directory, they are
called by ’main.py’.</p>
</div>
<div class="section" id="debian-or-ubuntu-gnu-linux-distributions">
<h2>Debian or Ubuntu GNU/Linux distributions</h2>
<p>Download <strong>eyes17-x.x.x.deb</strong> ( the latest version) from the software
section of <strong>http://expeyes.in</strong> and install it using the command;</p>
<blockquote>
<div>$ sudo gdebi eyes17-x.x.x.deb</div></blockquote>
<p>while connected to Internet</p>
<p>The package ’eyes17’ (later than version 3) does not depend on the
earlier versions of ExpEYES, like expeyes junior. During installation
gdebi will automatically dowload and install all the required packages.</p>
</div>
<div class="section" id="the-expeyes-live-cd-usb-pendrive">
<h2>The expEYES Live CD / USB pendrive</h2>
<p>The ISO image containing support for eyes17 can be downloaded from HERE.
Make a DVD or USB memory stick bootable using this ISO image (Download
rufus from <a class="reference external" href="https://rufus.akeo.ie">https://rufus.akeo.ie</a> to do this under MSWindows)</p>
<p>Switch off the PC and insert the liveCD/Pendrive and switch it on. Enter
the BIOS while booting, make the CDdrive/USB hard disk as the first boot
device. A desktop will appear and you can start expEYES-17 from the menu
<strong>Applications-&gt;Education</strong>-&gt;ExpEYES-17. You can also start it from a
Terminal using the command:</p>
<blockquote>
<div>$ python /usr/share/expeyes/eyes17/main.py</div></blockquote>
</div>
<div class="section" id="on-mswindows">
<h2>On MSWindows</h2>
<p>The first thing to do is to install the driver software for the USB to
serial converter IC MCP2200, available on Microchip website (also given
on expeyes website). After installing this the device will appear as a
COM port, that can be verified from the device manager of MSWindows.
After this there are two options.</p>
<p>A zip file containing all the necessary things for ExpEYES is available
on the website, named eyes17win.zip. Unzip this file and run main.py
from that. By using this method you will not able to write your own
Python code to access expeyes, for that you need to install the
following</p>
<ol class="arabic simple">
<li>Python-2.x version</li>
<li>python-serial</li>
<li>python-qt4</li>
<li>python-pyqtgraph,</li>
<li>python-numpy</li>
<li>python-scipy</li>
</ol>
<p>Download the eyes17-x.x.x.zip ( take latest version) from the website.
Unzipping the files will create a directory <strong>named eyes17</strong>, run
<strong>main.py</strong> from that.</p>
</div>
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<div class="section" id="the-main-gui-program">
<h1>The main GUI program</h1>
<p>Start Applications-&gt;Education-&gt;ExpEYES-17 from the menu. A four channel
oscilloscope screen with several extra features will open as shown in
figure <a class="reference internal" href="#the-scope17-screen"><span class="std std-ref">The scope17 screen showing two traces</span></a>. Various experiments can be
selected from the menu.</p>
<div class="figure" id="id1">
<span id="the-scope17-screen"/><img alt="_images/scope17.png" src="_images/scope17.png"/>
<p class="caption"><span class="caption-text">The scope17 screen showing two traces</span></p>
</div>
<p>The main window looks like a low frequency four channel oscilloscope,
with some extra features, on the right side panel. Applications for
various experiments can be selected from the pulldown menu. A brief
description of the oscilloscope program is given below.</p>
<ul class="simple">
<li>Any of the four inputs (A1, A2, A3 or MIC) can be enabled using the
corresponding checkbox. The input range can be selected by clicking
on the menubutton on the right side of the checkbox. Select the
desired input range from the popup menu.</li>
<li>There is another checkbox, to enable mathematical fitting of the data
using V = V0sin(2πft + θ) + C to show the amplitude and
frequency.</li>
<li>The horizontal scale (time base) can be changed by a slider, from .5
mS fullscale to 500 mS full scale.</li>
<li>The Checkbutton <strong>Freeze</strong>, allows to pause and resume the
oscilloscope operation.</li>
<li>The Trigger level can be set by a slider, and there is a menubutton
to select the trigger source.</li>
<li>To save the traces to a file, edit the filename and click on the
<strong>SaveTo</strong> button.</li>
<li>Clicking on <strong>FFT</strong> shows the frequency spectrum of all the eneabled
channels, appears on popup windows.</li>
</ul>
<p>In addition to the Oscilloscope, there are several measurement/control
options available on the GUI, they are explained below.</p>
<ul class="simple">
<li>If selected, the voltages at the inputs A1, A2 and A3 are sampled
every second and displayed.</li>
<li>The resistance connected between SEN and Ground is measured and
displayed every second.</li>
<li>Clicking <strong>Capacitance on IN1</strong>, measures the value of the capacitor
connected between IN1 and GND.</li>
<li>Clicking <strong>Frequency on IN2</strong>, measures the frequency of an external
digital (TTL standard) pulse connected to IN2</li>
<li>The shape of the waveform can be selected using the menubutton,
default shape is sine. It can be changed to triangular. When the
square wave option is selected, the output is shifted to SQ2. You
cannot have sine/triangular and SQ2 at the same time.</li>
<li>Frequency of the Waveform generator WG can be set using the slider or
the text entry window. The two input methods follow each other,
changing the slider will change the text field and entering data
using text field will set the slider to that value. The frequency
will be set to the nearest possible value and it will be displayed in
the message window at the bottom. The amplitude of WG output can be
set to 3 volts, 1 volt or 80 mV.</li>
<li>SQ1 can be set using the same method as explained above. The duty
cycle can be set between 1% to 99%, default is 50%.</li>
<li>The programmable volages PV1 and PV2 are also set in a similar
manner.</li>
<li>Checkbuttons are provided to control OD1 and CCS.</li>
</ul>
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<div class="section" id="getting-familiar-with-expeyes17">
<h1>Getting Familiar with ExpEYES17</h1>
<p>Before proceeding with the experiments, let us do some simple exercises
to become familiar with expEYES-17. Connect the device a USB port and
start the ExpEYES-17 program from the menu ’Applications-&gt;Education’.
Enable the ’Popup Help’ option and select the first few items from the
school menu.</p>
<p>The following chapters are organized according to the pulldown menus of
the eyes17 program, each chapter containing the experiments under the
corresponding menu; like School level, Eelectronics, Eelectrical etc. To
perform the expeiment, select it from the menu. Online help is available
for every experiment, making this manual almost redundant.</p>
<p>The screen shots given in this document are not from the GUI program,
because the black background images are difficult to print. The plots
are generated by separate code.</p>
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<div class="section" id="measuring-voltage">
<h1>Measuring Voltage</h1>
<p><strong>Objective</strong></p>
<p>Learn to measure voltage using expEYES and get some idea about the
concept of Electrical Ground. A dry-cell and two wires are required.</p>
<a class="reference internal image-reference" href="_images/measure-dc.svg"><img alt="_images/measure-dc.svg" src="_images/measure-dc.svg" width="300px"/></a>
<p><strong>Procedure</strong></p>
<ul class="simple">
<li>Observe the voltage at A1 displayed.</li>
<li>Repeat by reversing the cell connections.</li>
</ul>
<p><strong>Discussion</strong></p>
<p>Voltages measured value is +1.5 volts and it becomes -1.5 after
reversing the connections.</p>
<p>We are measuring the potential difference between two points. One of
them can be treated as at zero volts, or Ground potential. The voltage
measuring points of expEYES measure the voltage with respect to the
terminals marked GND. We have connected the negative terminal of the
cell to Ground. The positive terminal is at +1.5 volts with respect to
the negative terminal. <em>Will it show correct voltage if GND is not
connected ?</em></p>
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<div class="section" id="light-dependent-resistors">
<h1>Light dependent resistors</h1>
<p><strong>Objective</strong></p>
<p>Learn about LDR. Measure intensity of light and its variation with
distance from the source.</p>
<a class="reference internal image-reference" href="_images/ldr.svg"><img alt="_images/ldr.svg" src="_images/ldr.svg" width="300px"/></a>
<p><strong>Procedure</strong></p>
<ul class="simple">
<li>Measure the LDR’s resistance, for different light intensities.</li>
<li>Iluminate LDR using a fluorescent lamp, A1 should show ripples</li>
<li>Put A1 in AC mode and measure ripple frequency</li>
</ul>
<p><strong>Discussion</strong></p>
<p>The resistance vary from 1kΩ to around 100 kΩ depending on the intensity
of light falling on it. The voltage is proportional to the resistance.
The resistance decreases with intensity of light. If you use a point
source of light, the resistance should increase as the square of the
distance between the LDR and the light source.</p>
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<div class="section" id="voltage-of-a-lemon-cell">
<h1>Voltage of a lemon cell</h1>
<p><strong>Objective</strong></p>
<p>Make a voltage source by inserting Zinc and Copper plates into a lemon.
Explore the current driving capability and internal resistance.</p>
<a class="reference internal image-reference" href="_images/lemon-cell.svg"><img alt="_images/lemon-cell.svg" src="_images/lemon-cell.svg" width="300px"/></a>
<p><strong>Procedure</strong></p>
<ul class="simple">
<li>Click on A1 to measure voltage</li>
<li>Measure the voltage with and without the 1k resistor</li>
</ul>
<p><strong>Discussion</strong></p>
<p>Voltage across the Copper and Zinc terminals is nearly .9 volts.
Connecting the resistor reduces it to 0.33 volts. When connected,
current will start flowing through the resistor. But why is the voltage
going down ?</p>
<p>What is the internal resistance of the cell ?</p>
<p>Current is the flow of charges and it has to complete the path. That
means, current has to flow through the cell also. Depending on the
internal resistance of the cell, part of the voltage gets dropped inside
the cell itself. Does the same happen with a new dry-cell ?</p>
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<div class="section" id="a-simple-ac-generator">
<h1>A simple AC generator</h1>
<p><strong>Objective</strong></p>
<p>Measure the frequency and amplitude of the voltage induced across a
solenoid coil by a rotating magnet. Use the 10 mm x 10 mm magnet and the
3000T coils that comes with the kit.</p>
<a class="reference internal image-reference" href="_images/ac-generator.svg"><img alt="_images/ac-generator.svg" src="_images/ac-generator.svg" width="300px"/></a>
<a class="reference internal image-reference" href="_images/ac-gen-screen.png"><img alt="_images/ac-gen-screen.png" src="_images/ac-gen-screen.png" style="width: 300px;"/></a>
<p><strong>Procedure</strong></p>
<ul class="simple">
<li>Mount the magnet horizontally and power the DC motor from a 1.5 volts
cell</li>
<li>Enable A1 and A2, with analysis option</li>
<li>Set timebase to 100 mS full scale</li>
<li>Bring the coil near the magnet (not to touch it), watch the induced
voltage</li>
<li>Repeat the experiment using 2 coils.</li>
</ul>
<p><strong>Discussion</strong></p>
<p>The voltage output is shown in figure. The phase difference between the
two voltages depends on the angle between the axes of the two coils.</p>
<p>Bring a shorted coil near the magnet to observe the change in frequency.
The shorted coil is drawing energy from the generator and the speed get
reduced. The magnetic field in this generator is very weak. The
resistance of the coil is very high and trying to draw any current from
it will drop most of the voltage across the coil itself.</p>
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<div class="section" id="ac-transformer">
<h1>AC Transformer</h1>
<p><strong>Objective</strong></p>
<p>Demonstrate mutual induction using two coils, supplied with ExpEYES. One
coil, the primary, is connected between WG and Ground. The axes of the
coils are aligned and a ferrite core is inserted.begin_inset Separator
latexparend_inset</p>
<a class="reference internal image-reference" href="_images/transformer.svg"><img alt="_images/transformer.svg" src="_images/transformer.svg" width="300px"/></a>
<a class="reference internal image-reference" href="_images/transformer-screen.png"><img alt="_images/transformer-screen.png" src="_images/transformer-screen.png" style="width: 300px;"/></a>
<p><strong>Procedure</strong></p>
<ul class="simple">
<li>Make connections as shown in the figure</li>
<li>Enable A1 and A2</li>
<li>Set WG to 500 Hz</li>
<li>Bring the coils close and watch the voltage on A2.</li>
<li>Try inserting an ion core</li>
</ul>
<p><strong>Discussion</strong></p>
<p>The applied waveform and the induced waveform are shown in figure. A
changing magnetic filed is causing the induced voltage. In the previous
two experiments, the changing magnetic field was created by the movement
of permanent magnets. In the present case the changing magnetic field is
created by a time varying current.</p>
<p>Try doing this experiment using a squarewave. Connect a 1kΩ resistor
across secondary coil to reduce ringing.</p>
<p>The concept of Alternating Current is introduced by plotting the voltage
as a function of time. The behavior of circuits elements like capacitors
and inductors in AC and DC circuits are explored, by measuring
parameters like amplitude, frequency and phase. Converting electrical
signals into sound and back is demonstrated.</p>
<p>For each experiment, make connections as per the diagram given.</p>
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<div class="section" id="resistance-of-water-using-ac">
<h1>Resistance of water, using AC</h1>
<p><strong>Objective</strong></p>
<p>Measure the resistance of ionic solutions, using both DC and AC
voltages. We have used normal tap water. Try measuring the resistance
using a multimeter first.begin_inset Separator latexparend_inset</p>
<a class="reference internal image-reference" href="_images/res-water.svg"><img alt="_images/res-water.svg" src="_images/res-water.svg" width="300px"/></a>
<a class="reference internal image-reference" href="_images/water-conduct.png"><img alt="_images/water-conduct.png" src="_images/water-conduct.png" style="width: 300px;"/></a>
<p><strong>Procedure</strong></p>
<ul class="simple">
<li>R1 should be comparable to R, start with 10k.</li>
<li>Enable A1 and A2</li>
<li>Calculate the resistance as explained in section
<a class="reference external" href="#sec:Measure-resistance-by-comparison">2.4↑</a></li>
</ul>
<p><strong>Discussion</strong></p>
<p>Observed values are shown in the table. The DC and AC resistances seems
to be very different. With DC, the resistance of the liquid changes with
time, due to electrolysis and bubble formation. The resistance does not
depend much on the distance between the electrodes, the area of the
electrode is having some effect. The resistance depends on the ion
concentration and presence of impurities in the water used.</p>
<p>Try changing the distance between electrodes. Try adding some common
salt and repeat the measurements. Why is the behavior different for AC
and DC ? What are the charge carriers responsible for the flow of
electricity through solutions ? Is there any chemical reaction taking
place ?</p>
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<div class="section" id="generating-sound">
<h1>Generating sound</h1>
<p><strong>Objective</strong></p>
<p>Generate sound from electrical signals, using a Piezo-electric buzzer.
Digitize sound and measure its frequency. Use the Piezo buzzer or any
other source of sound like a tuning fork.</p>
<p><strong>Procedure</strong></p>
<a class="reference internal image-reference" href="_images/sound-generator.svg"><img alt="_images/sound-generator.svg" src="_images/sound-generator.svg" width="300px"/></a>
<ul class="simple">
<li>Enable A1, and its analysis</li>
<li>Set WG to 1000Hz, change it and listen to the sound.</li>
</ul>
<p><strong>Discussion</strong></p>
<p>When you change the frequency of the voltage that excites the Piezo,
both the frequency and the intesity of the sound changes. The intensity
is maximum near 3500 Hz, due to resonance. The resonant frequency of the
Piezo buzzer is decided by its size and mechanical properties.</p>
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<div class="section" id="digtizing-sound">
<h1>Digtizing sound</h1>
<p><strong>Objective</strong></p>
<p>Digitize sound signals from a microphone, and measure its frequency. Use
the Piezo buzzer or any other source of sound like a tuning fork.</p>
<p><strong>Procedure</strong></p>
<a class="reference internal image-reference" href="_images/sound-capture.svg"><img alt="_images/sound-capture.svg" src="_images/sound-capture.svg" width="300px"/></a>
<ul class="simple">
<li>Enable A1 and MIC , with analysis</li>
<li>Position the buzzer facing the microphone</li>
<li>Set WG to 1000Hz, change it and watch the MIC output</li>
<li>Use a whistle instead of the buzzer and find out the frequency of MIC
output.</li>
</ul>
<p><strong>Discussion</strong></p>
<p>The driving signal and the microphone output is shown in figure</p>
<p>Sound waves create pressure variations in the medium through which it
travel. The microphone generates a voltage proportional to the pressure.
The voltage variations are in tune with the pressure variations. You can
consider the microphone as a pressure sensor, but working only for time
varying pressures.</p>
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<div class="section" id="stroboscope">
<h1>Stroboscope</h1>
<p><strong>Objective</strong></p>
<p>Observation of a periodic phenomenon with a periodic flashed light.</p>
<p><strong>Procedure</strong></p>
<a class="reference internal image-reference" href="_images/stroboscope.svg"><img alt="_images/stroboscope.svg" src="_images/stroboscope.svg" width="300px"/></a>
<ul class="simple">
<li>The disk is rotated by powering the motor by a 1.5 V cell.</li>
<li>The disk is illuminated with light from the LED only, no other light
should be present.</li>
<li>Adjust the frequency of SQ1, the disk will appear stationary when it
is equal to the frequency of rotation of the disk.</li>
</ul>
<p><strong>Discussion</strong></p>
<p>When the frequency of the phenomenon under observation and the frequency
of the flashing light are matching, one can see a still image.</p>
<p>What happens when the frequency of the light is slightly increased, or slightly
decreased?</p>
<p>What happens when the frequency of the flasing light is twice the frequency
of the phenomenon? and when it is the half of its value?</p>
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<div class="section" id="measuring-resistance">
<h1>Measuring Resistance</h1>
<p><strong>Objective</strong></p>
<p>ExpEYES has a terminal marked <strong>SEN</strong>, that can be used for measuring
resistances in the range of <img alt="100~\Omega" class="math" src="_images/math/36dfc0dd6f490d35fa65c29d9013ee762dc718f1.png"/> to <img alt="100~k\Omega" class="math" src="_images/math/747baa849ddf46b5a4d2e10666b6ae1c7a95ee05.png"/>.
You can also study the series and parallel combination of resistors.</p>
<a class="reference internal image-reference" href="_images/res-measure.svg"><img alt="_images/res-measure.svg" src="_images/res-measure.svg" width="300px"/></a>
<p><strong>Procedure</strong></p>
<ul class="simple">
<li>Connect the resistor between SEN and any Ground terminal</li>
<li>Observe the value shown on the right side panel</li>