INTRODUCTION
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. 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 & 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 develop new experiments, without
getting into the details of electronics or computer programming
ExpEYES
ExpEYES is from the PHOENIX project of Inter-University Accelerator Centre, New
Delhi. It is a hardware & software framework for developing science experiments,
demonstrations and projects without getting in to the details of electronics or
computer programming. It converts your PC into a science laboratory. PHOENIX
(Physics with Home-made Equipment and Innovative Experiments) project was
started, in 2005 as a part of IUAC's outreach program, with the objectives of
developing affordable laboratory equipment and training teachers. Design of
ExpEYES combines the real-time measurement capability of micro-controllers
with the ease and flexibility of Python programming language for data analysis
and visualization. It also functions as a test equipment for electronics hobbyists
and engineering students. Software for all products from PHOENIX are distributed
under GNU General Public License and the hardware designs are under CERN
OHL.
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
Simple Harmonic Motion
In mechanics and physics, simple harmonic motion is a special type of periodic
motion or oscillation where the restoring force is directly proportional to
the displacement and acts in the direction opposite to that of displacement.
Simple harmonic motion can serve as a mathematical model for a variety of
motions, such as the oscillation of a spring. In addition, other phenomena can be
approximated by simple harmonic motion, including the motion of a simple
pendulum as well as molecular vibration. Simple harmonic motion is typified by
the motion of a mass on a spring when it is subject to the linear elastic restoring
force given by Hooke's law. The motion is sinusoidal in time and demonstrates a
single resonant frequency. For simple harmonic motion to be an accurate model
for a pendulum, the net force on the object at the end of the pendulum must be
proportional to the displacement. This is a good approximation when the angle of
the swing is small.
Simple harmonic motion, or SHM, is a type of oscillating motion. It is used to
model many situations in real life where a mass oscillates about an equilibrium
point. Examples of such situations include:
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A mass on a spring.
A pendulum.
The microscopic vibrations of molecules.
This project deals with the Automation of systems performing simple harmonic
motion with the help of an IR sensor module. The data is collected using the
ExpEYES and is then processed further. By this method it saves us a lot of time
and also this method will provide us accurate results. The Non linearity of simple
harmonic motion can be studied and verified through this method
IR Sensor
An infrared sensor is an electronic device, that emits in order to sense some
aspects of the surroundings. An IR sensor can measure the heat of an object as
well as detects the motion. These types of sensors measure only infrared
radiation, rather than emitting it that is called a passive IR sensor. Usually, in the
infrared spectrum, all the objects radiate some form of thermal radiation. These
types of radiations are invisible to our eyes, that can be detected by an infrared
sensor. The emitter is simply an IR LED (Light Emitting Diode) and the detector is
simply an IR photodiode that is sensitive to IR light of the same wavelength as
that emitted by the IR LED. When IR light falls on the photodiode, the resistances
and the output voltages will change in proportion to the magnitude of the IR light
received.
ExpEYES
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. 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 Celsius.
The gain and oset 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
Schematic Representation Of ExpEYES-17
External connections
The functions of the external connections briefly explained below. All the black
colored terminals are at ground potential, all other voltages are measured with
respect to it. Outputs: Constant Current Source (CCS) : 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.
Programmable Voltage (PV1) :
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.
Programmable Voltage (PV2) :
Can be set, from software, to any value in the -3.3V to +3.3V range. The resolution
is 12 bits.
Square Wave SQ1:
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 100Ω series resistor inside so that it can drive LEDs directly.
Square Wave SQ2:
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.
Digital Output (OD1) :
The voltage at OD1 can be set to 0 or 5 volts, using software.
Sine/Triangular Wave WG:
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.
Inputs:
Capacitance meter IN1:
Capacitance connected between IN1 and Ground can be measured. It works
better for lower capacitance values, up to 10 nanoFarads, results may not be very
accurate beyond that.
Frequency Counter IN2:
Capable of measuring frequencies upto several MHz.
Resistive Sensor Input (SEN):
This is mainly meant for sensors like Light Dependent Resistor, Thermostat,
Phototransistor etc. SEN is internally connected to 3.3 volts through a 5.1kΩ
resistor
Analog Inputs, A1 & A2:
Can measure voltage within the ±16 volts range. The input voltage range can be
selected from .5V to 16V full-scale. 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
Analog Input A3:
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.
Microphone input MIC:
A condenser microphone can be connected to this terminal and the output can
be captured.
I2C Sensor Interface:
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.
±6V /10mA Power supply:
The VR+ and VR- are regulated power outputs. They can supply very little current,
but good enough to power an Op-Amp.
IR SENSOR
An infrared sensor is an electronic instrument that is used to sense
certain characteristics of its surroundings. It does this by either emitting or
detecting infrared radiation. Infrared sensors are also capable of measuring the
heat being emitted by an object and detecting motion.
Infrared technology is found not just in industry, but also in
every-day life. Televisions, for example, use an infrared detector to interpret the
signals sent from a remote control. Passive Infrared sensors are used for motion
detection systems, and LDR sensors are used for outdoor lighting systems. The
key benefits of infrared sensors include their low power requirements, their
simple circuitry and their portable features.
Infrared Radiation Theory
Infrared waves are not visible to the human eye. In the
electromagnetic spectrum, infrared radiation can be found between the visible
and microwave regions. The infrared waves typically have wavelengths between
0.75 and 1000µm.
The infrared spectrum can be split into near IR, mid IR and far IR. The
wavelength region from 0.75 to 3µm is known as the near infrared region. The
region between 3 and 6µm is known as the mid-infrared region, and infrared
radiation which has a wavelength greater higher than 6µm is known as far
infrared.
The Foundations of Infrared Science
The theory of infrared spectroscopy had been around since F.W.
Herschel discovered infrared light in 1800. Herschel conducted an experiment
using a prism to refract light from the sun and was able to detect the presence of
infrared radiation beyond the red part of the visible spectrum using a
thermometer to measure an increase in temperature.
The Types of Infrared Sensors
Infrared sensors can be passive or active. Passive infrared sensors are
basically Infrared detectors. Passive infrared sensors do not use any infrared
source and detects energy emitted by obstacles in the field of view. They are of
two types: quantum and thermal. Thermal infrared sensors use infrared energy as
the source of heat and are independent of wavelength. Thermocouples,
piezoelectric detectors and bolometer are the common types of thermal infrared
detectors.
Quantum type infrared detectors offer higher detection performance and are
faster than thermal type infrared detectors. The photosensitivity of quantum type
detectors is wavelength dependent. Quantum type detectors are further
classified into two types: intrinsic and extrinsic types. Intrinsic type quantum
detectors are photoconductive cells and photovoltaic cells.
Active infrared sensors consist of two elements: infrared source and infrared
detector. Infrared sources include an LED or infrared laser diode. Infrared
detectors include photodiodes or phototransistors. The energy emitted by the
infrared source is reflected by an object and falls on the infrared detector.
The Working Principle of Infrared Sensors
The physics behind infrared sensors is governed by three laws:
1. Planck’s radiation law: Every object at a temperature T not equal to 0 K
emits radiation
2. Stephan Boltzmann Law: The total energy emitted at all wavelengths by a
black body is related to the absolute temperature
3. Wien's Displacement Law: Objects of different temperature emit spectra
that peak at different wavelengths
All objects which have a temperature greater than absolute zero (0 Kelvin) posses
thermal energy and are sources of infrared radiation as a result.
Sources of infrared radiation include blackbody radiators, tungsten
lamps and silicon carbide. Infrared sensors typically use infrared lasers and LEDs
with specific infrared wavelengths as sources.
A transmission medium is required for infrared transmission, which
can be comprised of either a vacuum, the atmosphere or an optical fiber. Optical
components such as optical lenses made from quartz, CaF2, Ge and Si,
polyethylene Fresnel lenses and Al or Au mirrors are used to converge or focus
the infrared radiation. In order to limit spectral response, band-pass filters can be
used.
Next, infrared detectors are used to detect the radiation which has been
focused. The output from the detector is usually very small and hence preamplifiers coupled with circuitry are required to further process the received
signals.
Working of an IR Sensor
The principle of an IR sensor working as an Object Detection Sensor can be
explained using the following figure. An IR sensor consists of an IR LED and an IR
Photodiode; together they are called as Photo – Coupler or Opto – Coupler.
When the IR transmitter emits radiation, it reaches the object and some of the
radiation reflects back to the IR receiver. Based on the intensity of the reception by
the IR receiver, the output of the sensor is defined.
Obstacle Sensing Circuit or IR Sensor Circuit
A typical IR sensing circuit is shown below.
It consists of an IR LED, a photodiode, a potentiometer, an IC Operational
amplifier and an LED.
IR LED emits infrared light. The Photodiode detects the infrared
light. An IC Op – Amp is used as a voltage comparator. The potentiometer is used
to calibrate the output of the sensor according to the requirement.
When the light emitted by the IR LED is incident on the photodiode
after hitting an object, the resistance of the photodiode falls down from a huge
value. One of the input of the op – amp is at threshold value set by the
potentiometer. The other input to the op-amp is from the photodiode’s series
resistor. When the incident radiation is more on the photodiode, the voltage drop
across the series resistor will be high. In the IC, both the threshold voltage and the
voltage across the series resistor are compared. If the voltage across the resistor
series to photodiode is greater than that of the threshold voltage, the output of
the IC Op – Amp is high. As the output of the IC is connected to an LED, it lightens
up. The threshold voltage can be adjusted by adjusting the potentiometer
depending on the environmental conditions.
The positioning of the IR LED and the IR Receiver is an important
factor. When the IR LED is held directly in front of the IR receiver, this setup is
called Direct Incidence. In this case, almost the entire radiation from the IR LED
will fall on the IR receiver. Hence there is a line of sight communication between
the infrared transmitter and the receiver. If an object falls in this line, it obstructs
the radiation from reaching the receiver either by reflecting the radiation or
absorbing the radiation.
IR SENSOR MODULE
Different Types of IR Sensors and Their Applications
IR sensors are classified into different types depending on the applications. Some of
the typical applications of different types of sensors are
The speed sensor is used for synchronizing the speed of multiple motors.
The temperature sensor is used for industrial temperature control. PIR sensor is used
for automatic door opening system and Ultrasonic sensor are used for distance
measurement.
Radiation Thermometers
IR sensors are used in radiation thermometers to measure the temperature depend
upon the temperature and the material of the object and these thermometers have
some of the following features
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Measurement without direct contact with the object
Faster response
Easy pattern measurements
Flame Monitors
These types of devices are used for detecting the light emitted from the flames and
to monitor how the flames are burning. The Light emitted from flames extend from
UV to IR region types. PbS, PbSe, Two-color detector, pyro electric detector are some
of the commonly employed detector used in flame monitors.
Moisture Analyzers
Moisture analyzers use wavelengths which are absorbed by the moisture in the IR
region. Objects are irradiated with light having these wavelengths(1.1 µm, 1.4 µm,
1.9 µm, and 2.7µm) and also with reference wavelengths. The Lights reflected from
the objects depend upon the moisture content and is detected by analyzer to
measure moisture (ratio of reflected light at these wavelengths to the reflected light
at reference wavelength). In GaAs PIN photodiodes, Pbs photoconductive detectors
are employed in moisture analyzer circuits.
Gas Analyzers
IR sensors are used in gas analyzers which use absorption characteristics of gases in
the IR region. Two types of methods are used to measure the density of gas such as
dispersive and non dispersive.
Dispersive: An Emitted light is spectroscopically divided and their absorption
characteristics are used to analyze the gas ingredients and the sample quantity.
Non dispersive: It is most commonly used method and it uses absorption
characteristics without dividing the emitted light. Non dispersive types use discrete
optical band pass filters, similar to sunglasses that are used for eye protection to
filter out unwanted UV radiation.
This type of configuration is commonly referred to as non dispersive
infrared (NDIR) technology. This type of analyzer is used for carbonated drinks,
whereas non dispersive analyzer is used in most of the commercial IR instruments,
for an automobile exhaust gas fuel leakages.
IR Imaging Devices
IR image device is one of the major applications of IR waves, primarily by virtue of its
property that is not visible. It is used for thermal imagers, night vision devices, etc.
For examples Water, rocks, soil, vegetation, an atmosphere, and
human tissue all features emit IR radiation. The Thermal infrared detectors measure
these radiations in IR range and map the spatial temperature distributions of the
object/area on an image. Thermal imagers usually composed of a Sb (indium
antimonite), Gd Hg (mercury-doped germanium), Hg Cd Te (mercury-cadmiumtelluride) sensors.