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A PROJECT REPORT ON
TEMPERATURE CONTROL OF INFANT INCUBATOR
Project report submitted in partial fulfillment of the requirement for the
Award of the Degree of
BACHELOR OF TECHNOLOGY
IN
BIOMEDICAL ENGINEERING
By
N NIHARIKA 09241A1112P APARNA S SRUTHI 09241A1124
Under the guidance of
Mrs. S.BHARGAVI
Assistant Professor
DEPARTMENT OF BIOMEDICAL ENGINEERING
GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING &
TECHNOLOGY
BACHUPALLY, HYDERABAD 500090
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2009-2013
GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING & TECHNOLOGY
Hyderabad, Andhra Pradesh.
DEPARTMENT OF BIOMEDICAL ENGINEERING
C E R T I F I C A T E
This is to certify that the project report entitled TEMPERATURE CONTROL OF INFANT
INCUBATOR that is being submitted by N NIHARIKA and P APARNA S SRUTHI in partial
fulfillment for the award of the Degree of Bachelor of Technology in BIOMEDICAL ENGINEERING
to the Jawaharlal Nehru Technological University as a record of bonafide work carried out by them undermy supervision. The results embodied in this project report have not been submitted to any other
University or Institute for the award of any graduation degree.
Prof. T. PADMA Mrs. S. BHARGAVI
HOD, BME Assistant Professor, Internal guide
GRIET, Hyderabad GRIET, Hyderabad
External Examiner
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ABSTRACT
Temperature plays an important part in our environment. Changes in temperature can
affect the behavior of human beings, plants and even materials such as semiconductors. This
project is to control the temperature of a given environment such as baby incubator.
Incubators provide warmth and prevent heat loss to significantly improve survival
rates. The use of air-heated incubators has been the standard method of providing a stable,
individualized thermal environment for the newborn infant at risk.
A microcontroller is used to control the temperature in a baby incubator Where the
temperature had to be kept constant at 36.90C as in mothers womb. The system will function as
stated in the programming code of Aurduino in order to keep the temperature stable. A simpletemperature controller which has least complex circuitry has to be designed so that it saves space
and be more reliable for an incubator. Present design which uses microprocessor as main
controller in digital signal processing combined with complex combinational logic circuit are
redundant and needs to be improved in the sense of functionality. Hence, replacement of
microcontroller with an Aurduino microcontroller is prudent action due to its efficiency and
reliability especially in an incubator Where the life of an infant relies on.
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CONTENTSCHAPTER 1 ................................................................... Error! Bookmark not defined.
1.1 INFANT THERMOREGULATION ................. Error! Bookmark not defined.
CHAPTER 2 ................................................................... Error! Bookmark not defined.
2.1 OVERVIEW .......................................................... Error! Bookmark not defined.
2.2 PROBLEM STATEMENT .................................... Error! Bookmark not defined.
2.3 NEEDS FOR INCUBATION ................................ Error! Bookmark not defined.
2.4 OBJECTIVE ..........................................................Error! Bookmark not defined.
2.5 STEPS INVOLVED .............................................. Error! Bookmark not defined.
CHAPTER 3 ................................................................... Error! Bookmark not defined.
3.1 ACRYLIC SHEET ................................................ Error! Bookmark not defined.3.1.1 Expansion and Contraction .............................. Error! Bookmark not defined.
3.1.2 Flexibility ........................................................ Error! Bookmark not defined.
3.1.3 Chemical Resistance ........................................ Error! Bookmark not defined.
3.1.4 Electrical Properties ........................................ Error! Bookmark not defined.
3.1.5 Light Transmission .......................................... Error! Bookmark not defined.
3.1.6 UV Light Resistance ....................................... Error! Bookmark not defined.
3.1.7 Optical Clarity .................................................Error! Bookmark not defined.
3.1.8 Weather Resistance ......................................... Error! Bookmark not defined.
3.1.9 Safety .............................................................. Error! Bookmark not defined.
3.1.10 Light Weight ................................................. Error! Bookmark not defined.
3.2 COMPARTMENT DESCRIPTION ......................... Error! Bookmark not defined.
3.2.1 Compartment A ...............................................Error! Bookmark not defined.
3.2.1.1 Heating unit .................................................. Error! Bookmark not defined.
3.2.1.2 Cooling unit.................................................. Error! Bookmark not defined.
3.2.2 Compartment B ............................................... Error! Bookmark not defined.
CHAPTER 4 ................................................................... Error! Bookmark not defined.
4.1 SENSING THE TEMPERATURE......................... Error! Bookmark not defined.
4.1.1 Thermistor ....................................................... Error! Bookmark not defined.
4.2 READING THE TEMPERATURE ....................... Error! Bookmark not defined.
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4.3 TEMPERATURE CONTROL ............................... Error! Bookmark not defined.
4.3.1 Relay ............................................................... Error! Bookmark not defined.
4.3.1.1 Basic design and operation ........................... Error! Bookmark not defined.
4.3.2 Power supply +12 Volts ................................. Error! Bookmark not defined.
4.3.2.1 Center tapped transformer ............................ Error! Bookmark not defined.
4.3.2.2 Volts center tapped ....................................... Error! Bookmark not defined.
4.3.2.3 Linear regulator ............................................ Error! Bookmark not defined.
4.3.2.4 Step transformer ........................................... Error! Bookmark not defined.
4.3.2.5 Step-down transformer consideration ............ Error! Bookmark not defined.
4.3.3 Aurduino Uno kit ............................................ Error! Bookmark not defined.
CHAPTER 5 ................................................................... Error! Bookmark not defined.
5.1 PROGRAM FOR TEMPERATURE READING AND CONTROLError! Bookmark not
defined.
5.2 FLOW CHART ..................................................... Error! Bookmark not defined.
CONCLUSION ............................................................... Error! Bookmark not defined.
RESULT ......................................................................... Error! Bookmark not defined.
FUTURE SCOPE............................................................ Error! Bookmark not defined.
REFERENCES: .............................................................. Error! Bookmark not defined.
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LIST OF FIGURES
Figure 3.1 Incubation chamber ........................................ Error! Bookmark not defined.
Figure 3.2 Acrylic sheet .................................................. Error! Bookmark not defined.
Figure 3.3 Chamber showing two compartments. ............ Error! Bookmark not defined.
Figure 3.4 Compartment A .............................................. Error! Bookmark not defined.
Figure 3.5 Compartment B .............................................. Error! Bookmark not defined.
Figure 4.1Thermistors ..................................................... Error! Bookmark not defined.
Figure 4.2 Resistance characteristics with temperature. ... Error! Bookmark not defined.
Figure4.3 Circuit for temperature sensing. ....................... Error! Bookmark not defined.
Figure 4.4 Circuit for Temperature Control. .................... Error! Bookmark not defined.
Figure 4.5 DC power Supply +12 volts circuit ................ Error! Bookmark not defined.
Figure 4.6 PCB for DC power Supply +12 volts .............. Error! Bookmark not defined.
Figure 4.6 Step down Transformer .................................. Error! Bookmark not defined.
Figure 4.7 Aurduino Uno ................................................ Error! Bookmark not defined.
Figure 5.1 Flowchart for temperature sensing and control Error! Bookmark not defined.
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CHAPTER 1
INTRODUCTION
Of the four million babies worldwide who die in the first month of life, one million die on
their first day. Preterm birth is attributed, either directly or indirectly, to at least 25 percent ofneonatal deaths, and low birth weight (LBW) newborns are at the greatest risk. About half of the
worldwide total, or 1.8 million babies each year, die for lack of a consistent heat until they have
the body fat and metabolic rate to stay warm. The current recommended method of providing
infant temperature regulation in resource constrained settings is Kangaroo Mother Care (KMC),
the practice of placing newborns directly onto the mother's chest. KMC has demonstrated
benefits in terms of improved weight gain for preterm infants, earlier hospital discharge and
higher breast feeding rates. At the same time, KMC also has important limitations:
If the mother either dies in childbirth (as one of the 529,000 maternal deaths annuallyworldwide), or is too ill after delivery, mother is unable to provide KMC.
The majority of mothers have other obligations that prevent them from being able toprovide continuous KMC, such as other children and/or a job to which they must attend.
If no one else is able to provide KMC, a baby sent home for this care may receive it
inconsistently at best and therefore suffer the complications of hypothermia, including
respiratory distress, acidosis, hypoglycemia and even death.
Skin to skin contact is considered a culturally inappropriate violation of privacy in someareas that rely on KMC.
As a consequence, at risk newborns in developing countries need a warm, clean
environment in which to grow stronger. Incubators can help provide millions of at risk infants
with shorter hospitals stays and can enable infants who might otherwise have faced a lifetime of
severe disability to experience active lives.
1.1INFANT THERMOREGULATION
Thermoregulation is a critical physiological function that is closely associated with the
neonates survival. Extremely low birth weight infants have inefficient thermoregulation due to
immaturity and care giver procedures such as umbilical line insertions, intubations, and chest x-
rays can lead to heat loss as well. As a result, infants may exhibit cold body temperatures after
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birth and during their first 12 hours of life. Thermoregulation plays a unique and crucial role in
the nurturing and development of neonates. It helps neonatal care practitioners to provide a
balanced environment through the management of temperature.
As a result of a high body surface area to body weight ratio, decreased brown fat stores, non
keratinized skin, and decreased glycogen supply, infants with extremely low birth weight
(ELBW) are particularly susceptible to heat loss immediately after birth. Hypothermia may result
in hypoglycimea, apnea, and metabolic acidosis.
Heat loss can occur in infants with extremely low birth weight in following ways:
a) Conduction: The transfer of energy from the molecules of a body to the molecules of asolid object in contact with the body, resulting in heat loss.
b) Convection: The similar loss of thermal energy to an adjacent gas.c) Evaporation: Evaporative heat loss is the total heat transfer by energy carrying water
molecules from the skin and respiratory tract to the drier environment.
d) Radiation: Radiant loss is the net rate of heat loss from the body to environmentalsurfaces not in contact with the body.
Extremely preterm infants are especially prone to these losses secondary to the poor barrier
provided by their thin, poorly keratinized skin. Normal body temperature is maintained by
balancing heat loss and heat gain in a changing environment. Less than 1C separates a baby
from cold stress and warm stress which divert energy away from growth and towards the
struggle of regulating body temperature.
The importance of maintaining the temperature of the newborn baby has been known for
centuries. Thermal stress has been associated with an increase in morbidity and mortality,
making early detection an important part of monitoring in sick infants.
Temperature control is paramount to survival and is typically achieved with use of radiant
warmers or double walled incubators. Hypothermia (< 35C) has been associated with poor
outcome, including chronic oxygen dependency. Immediately after birth, the infant should be
dried and placed on a radiant warmer.
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CHAPTER 2
DESIGN APPROACH
2.1 OVERVIEW
This project is to design a temperature controller to be used to control the temperature of
a small environment such as a baby incubator. A baby incubator is an infant stimulating system
used for intensive care of the newborn, premature or sick baby. It provides a safe and clean
environment, which has fresh air, clean and sterile ambient conditions for the babies. Usually the
controller used in the baby incubator is a Microprocessor.
2.2 PROBLEM STATEMENT
Premature or tiny babies are unable to keep themselves sufficiently warm. They are alsovery weak and prone to infections. An incubator is a special type of a coat which provides an
ideal environment for the baby. It tries to stimulate the conditions as inside the mothers womb.
2.3 NEEDS FOR INCUBATION
Temperature regulation is one of the most important factors affecting survival innewborn
infants. Infants typically lose heat to their environment in four different ways: through
conduction, convection, radiation, and evaporation. Premature infants, as compared to term
infants, are at an even greater disadvantage in temperature maintenance, because of the larger
skin surface area to body mass ratio, decreased subcutaneous fat, and low supplies of brown fat.
Furthermore, the normal surge in metabolic rate that occurs after birth is reduced in preterm
infants, resulting in limited heat production. Preterm infants birth rates are especially high in
developing countries. A combination of poor facilities, poor after birth care and a lack of
knowledge have propelled preterm birth to be one of the leading causes of infant mortality in
developing countries.
Incubators provide warmth and prevent heat loss to significantly improve survival rates.
The use of air-heated incubators has been the standard method of providing a stable,
individualized thermal environment for the newborn infant at risk. One of the very first
incubators invented by Stephane Tarnier in the late 19th century, reportedly reduced mortality
among infants with birth weights between 1200 and 2000 g from 66% to 38%. The availability
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of incubators and radiant warmers in industrialized countries has made neonatal hypothermia
uncommon, except in infants transported over long distances.
2.4 OBJECTIVE
The main objective of this project is to design a baby incubator with temperature control
using Aurduino Microcontroller, while monitoring the incubator temperature.
2.5 STEPS INVOLVED
Search for information related to required environment, for example the size of the babyincubator, function of the incubator and any information related to this project.
Search for the material and equipment required for this project.
Build an incubator that is suitable and functions almost the same as available incubator.This may require some research at the hospital.
Design the Aurduino Microcontroller programming code according to the specification oftemperature control in C language.
Design the temperature control circuit using Aurduino software. Program the microcontroller according to the specifications of the temperature control
system. Construct the circuit and build the model of incubator that is suitable for this
environment.
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CHAPTER 3
CONSTRUCTION
The chamber of the infant incubator is transparent. The chamber has two compartments a
larger and smaller compartment. The smaller compartment (compartment A) consist of thetemperature controlling unit and the larger compartment (compartment B) consist of the mattress
where the infant is kept. The chamber is constructed in such a way that the baby is kept away
from the temperature controlling part so the baby is assured to be safe. The entire chamber is
constructed using Acrylic sheets. Acrylic is chosen because it is more advantageous over Glass
and Plastic.
Figure 3.1 Incubation chamber
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3.1 ACRYLIC SHEETCast acrylic sheet is a material with unique physical properties and performance
characteristics. It weighs half as much as the finest optical glass, yet is equal to it inclarity and is
up to 17 times more impact resistant. Cast acrylic sheet is made in over 250 colors, in
thicknesses from .030" to 4.25'' and can transmit ultraviolet light or filter it out as required.
Figure 3.2 Acrylic sheet
Aircraft manufacturers use Cast Acrylic sheet in jets and helicopters. Because of its light and
energy transmission properties architects find Cast acrylic sheet ideal for skylights, sun screens,
fascia panels and dome structures.
3.1.1Expansion and Contraction
Cast acrylic sheet responds to temperature changes by expanding or contracting at a far
greater rate than glass.
3.1.2 Flexibility
Cast acrylic sheet is much more flexible than glass or many other building materials.
3.1.3 Chemical Resistance
Cast acrylic sheet has excellent resistance to attack by many chemicals. It is affected, in
varying degrees, by benzene, toluene, carbon tetrachloride, ethyl and methyl alcohol, lacquer
thinners, ethers, ketones and esters.
3.1.4 Electrical Properties
Cast acrylic sheet is an excellent insulator. Its surface resistivity is higher than that of
most plastics.
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3.1.5 Light Transmission
Colorless Cast acrylic sheet has a light transmittance of 92%. It is clearer than window
glass and will not turn yellow. Cast acrylic sheet is also available in a large variety of transparent
and translucent colors.
3.1.6 UV Light Resistance
Clear acrylic sheet resists ultraviolet light degradation. Each acrylic sheet has a ten-year-
limited warranty against yellowing and loss of light transmission.
3.1.7 Optical Clarity
Acrylic sheets have excellent light transmission. Clearer than glass. Will not yellow after
prolonged sun exposure.
3.1.8 Weather Resistance
Despite heat, cold, sunlight, and humidity acrylic sheet maintains its original appearanceand color.
3.1.9 Safety
Shatter-resistant, earthquake safe and burglar-resistant.
3.1.10 Light Weight
Even with its strength and durability, acrylic sheet is only half the weight of glass. The
two compartments compartment A and compartment B are separated from each other. A
detailed description of the two compartments are given below.
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3.2 COMPARTMENT DESCRIPTION
Figure 3.3 Chamber showing two compartments.
3.2.1 Compartment A
The compartment A consists of the temperature controlling unit which holds a heating
and cooling system.
The compartment A is again divided in to two sections:
a) The heating unit.
b) The cooling unit.
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Figure 3.4 Compartment A
3.2.1.1 Heating unit
It consists of a 100 watts bulb which is controlled by an Aurduino Microcontroller. The
bulb is given 120 volts using a step down transformer so that the baby is assured safe. A fan
which is continuously working is placed infront of the bulb with an opening to the compartment
B in such a way that the warm air is forced towards the compartment B.
3.2.1.2 Cooling unit
It consists of an Aluminum vessel filled with ice. This unit is aimed to cool the system
when the temperature goes beyond 37oC. A reliable opening is made between the ice box and
the compartment B to help cooling of compartment B. Even the fan in the Heating unit also helps
in cooling.The heating unit and the cooling unit work in such a way that the temperature in the
compartment B is maintained at a constant temperature.
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3.2.2 Compartment B
It consists of a mattress where the Infant is kept. It is provided with proper ventilation.
The chamber is provided with doors one on the top and other infront, so that the chamber can be
opened and closed according to the convenience over the take care (The person who cares the
infant).
Figure 3.5 Compartment B
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CHAPTER 4
TEMPERATURE SENSING AND CONTROL
The temperature in the chamber need to sensed and read before controlling it. A sensor is
placed in the compartment B where the baby is kept and the sensed temperature is given to the
Aurduino Uno Microcontroller.
4.1 SENSING THE TEMPERATURE
The temperature is sensed using a Thermistor.
4.1.1 Thermistor
Thermistors are inexpensive, easily obtainable temperature sensors. They are easy to use
and adaptable. They respond quickly. Circuits with thermistors can have reasonable out voltages
not the millivolt outputs thermocouples have. Because of these qualities, thermistors are widely
used for simple temperature measurements. They are not used for high temperatures, but in the
temperature ranges where they work they are widely used.
Figure 4.1Thermistors
Thermistors are temperature sensitive resistors. All resistors vary with temperature, but
thermistors are constructed of semiconductor material with a resistivity that is especially
sensitive to temperature. However, unlike most other resistive devices, the resistance of a
thermistor decreases with increasing temperature. That's due to the properties of the
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semiconductor material that the thermistor is made from. For some, that may be counterintuitive,
but it is correct. Here is a graph of resistance as a function of temperature for a typical
thermistor. Notice how the resistance drops from 100 kW, to a very small value in a range
around room temperature. Not only is the resistance change in the opposite direction from what
you expect, but the magnitude of the percentage resistance change is substantial.
Figure 4.2 Resistance characteristics with temperature.
4.2 READING THE TEMPERATURE
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The temperature sensed by the Thermistor is given to Aurduino Uno which is connected
to a laptop/Computer. A program is written and uploaded to the Aurduino which makes the
temperature to be displayed on the monitor in volts i.e.3.1 volts equal to 31oC, 3.2 volts equal to
32oC and so on. The programming part is discussed in the coming unit.
The connections given to Aurduino Uno is shown in figure 4.3 below
Figure 4.3 Circuit for temperature sensing
4.3 TEMPERATURE CONTROL
Aurduino Uno is the controller used here. The program is written to control the bulb.
when the temperature in the chamber falls down below 37 o
C the bulb glows and whenever the
temperature in the chamber goes beyond 37 o
C the bulb automatically switch off. An icebox
placed in the compartment A helps in cooling the chamber if the temperature goes beyond the
required temperature.
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The circuit is given below:
Figure 4.4 Circuit for Temperature Control.
The Relay here acts as a switch and 12 V DC supply is given to the Relay. The Step
down transformer here transforms the 230 V power supply to 120 V.
4.3.1 Relay
A relay is an electrically operated switch. Many relays use an electromagnet to operate a
switching mechanism mechanically, but other operating principles are also used. Relays are used
where it is necessary to control a circuit by a low power signal (with complete electrical isolation
between control and controlled circuits), or where several circuits must be controlled by one
signal. The first relays were used in long distance telegraph circuits, repeating the signal coming
in from one circuit and re-transmitting it to another. Relays were used extensively in telephone
exchanges and early computers to perform logical operations.
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A type of relay that can handle the high power required to directly control an electric
motor or other loads is called a contactor. Solid-state relays control power circuits with no
moving parts, instead using a semiconductor device to perform switching. Relays with calibrated
operating characteristics and sometimes multiple operating coils are used to protect electrical
circuits from overload or faults in modern electric power systems these functions are performed
by digital instruments still called "protective relays".
4.3.1.1 Basic design and operation
A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core,
an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature,
and one or more sets of contacts (there are two in the relay pictured). The armature is hinged to
the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a
spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this
condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open.
Other relays may have more or fewer sets of contacts depending on their function. The relay in
the picture also has a wire connecting the armature to the yoke. This ensures continuity of the
circuit between the moving contacts on the armature, and the circuit track on the printed circuit
board (PCB) via the yoke, which is soldered to the PCB.
When an electric current is passed through the coil it generates a magnetic field that
activates the armature and the consequent movement of the movable contacts either makes or
breaks (depending upon construction) a connection with a fixed contact. If the set of contacts
was closed when the relay was de-energized, then the movement opens the contacts and breaks
the connection, and vice versa if the contacts were open. When the current to the coil is switched
off, the armature is returned by a force, approximately half as strong as the magnetic force, to its
relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in
industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage
application this reduces noise in a high voltage or current application it reduces arcing.
When the coil is energized with direct current, a diode is often placed across the coil to
dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise
generate a voltage spike dangerous to semiconductor circuit components. Some automotive
relays include a diode inside the relay case. Alternatively, a contact protection network
consisting of a capacitor and resistor in series (snubber circuit) may absorb the surge. If the coil
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is designed to be energized with alternating current (AC), a small copper "shading ring" can be
crimped to the end of the solenoid, creating a small out-of-phase current which increases the
minimum pull on the armature during the AC cycle.
A solid-state relay uses a thyristor or other solid-state switching device, activated by the
control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-
emitting diode (LED) coupled with a photo transistor) can be used to isolate control and
controlled circuits.
4.3.2 Power supply +12 Volts
Figure 4.5 DC power Supply +12 volts circuit
For the operation of relays 12V DC supply is required to excite them. So there is a need
of 12V DC power supply. This can get from the circuit shown in Fig 4.5. The main components
of this circuit are, a 230 to (18-0-18) step down transformer, bridge rectifier, capacitors and
voltage regulator (LM7812 ).
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Figure 4.6 PCB for DC power Supply +12 volts
4.3.2.1 Center tapped transformer
In electronics, a center tap is a contact made to a point halfway along a winding of a
transformer or inductor, or along the element of a resistor or a potentiometer. Taps are
sometimes used on inductors for the coupling of signals, and may not necessarily be at the half
way point, but rather, closer to one end. A common application of this is in the Hartley oscillator.
Inductors with taps also permit the transformation of the amplitude of alternating current (AC)
voltages for the purpose of power conversion, in which case, they are referred to as
autotransformers, since there is only one winding. An example of an autotransformer is an
automobile ignition coil. Potentiometer tapping provides one or more connections along the
device's element, along with the usual connections at each of the two ends of the element, and
the slider connection. Potentiometer taps allow for circuit functions that would otherwise not be
available with the usual construction of just the two end connections and one slider connection.
In a rectifier, a center tapped transformer and two diodes can form a full-wave rectifier that
allows both half cycles of the AC waveform to contribute to the direct current, making it
smoother than a half wave rectifier. This form of circuit saves on rectifier diodes compared to a
diode bridge, but has poorer utilization of the transformer windings. Center-tapped two diode
rectifiers were a common feature of power supplies in vacuum tube equipment. Modern
semiconductor diodes are low cost and compact so usually a four-diode bridge is used (up to a
few hundred watts total output) which produces the same quality of DC as the center tapped
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configuration with a more compact and cheaper power transformer. Center tapped configurations
may still be used in high current applications, such as large automotive battery chargers, where
the extra transformer cost is offset by less costly rectifiers. Center tapped transformers are also
used for dual voltage power supplies. When a center tapped transformer is combined with a four
diode type bridge rectifier, it is possible to produce a positive and a negative voltage with
respect to a ground at the tap. Dual voltage supplies are important for all sorts of electronics
equipment. In early vacuum tube audio amplifiers, center tapped transformers were sometimes
used as the phase inverter to drive the two output tubes of a push pull stage. This technique was
carried over into transistor designs also, part of the reason for which was that capacitors were
large, expensive and unreliable. However, capacitors have become vastly smaller, cheaper and
more reliable, whereas transformers are still relatively expensive. Furthermore, as designers
acquired more experience with transistors, they stopped trying to treat them like tubes. Coupling
a class A intermediate amplification stage to a class AB power stage using a transformer doesn't
make sense anymore even in small systems powered from a single-voltage supply. Modern
higher end equipment is based on dual supply designs which eliminates coupling. It is possible
for an amplifier, from the input all the way to the loudspeaker, to be DC coupled without any
capacitance or inductance. In vacuum tube amplifiers, center tapped transformers are used to
couple a push pull output stage to the speaker. This use is still relevant today because tubes and
tube amplifiers continue to be produced for niche markets. In analog telecommunications
systems center tapped transformers can be used to provide a DC path around an AC coupled
amplifier for signaling purposes. The center tapped rectifiers are preferred to the full bridge
rectifier when the output DC current is high and the output voltage is low. Phantom power can be
supplied to a condenser microphone using center tap transformers. One method, called "direct
center tap" uses two center tap transformers, one at the microphone body and one at the
microphone preamp. Filtered DC voltage is connected to the microphone preamp center tap, and
the microphone body center tap is grounded through the cable shield. The second method uses
the same center tap transformer topology at the microphone body, but at the microphone preamp,
a matched pair of resistors spanning the signal lines in series creates an "artificial center tap".
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4.3.2.2 Volts center tapped
Volts center tapped (VCT) describes the voltage output of a center tapped transformer.
For example, A 24 VCT transformer will measure 24 VAC across the outer two taps (winding as
a whole), and 12 VAC from each outer tap to the center-tap (half winding). These two 12 VAC
supplies are 180 degrees out of phase with each other, thus making it easy to derive positive and
negative 12 volt DC power supplies from them.
4.3.2.3 Linear regulator
In electronics, a linear regulator is a system used to maintain a steady voltage. The
resistance of the regulator varies in accordance with the load resulting in a constant output
voltage. The regulating device is made to act like a variable resistor, continuously adjusting a
voltage divider network to maintain a constant output voltage, and continually dissipating the
difference between the input and regulated voltages as waste heat. By contrast, a switching
regulator uses an active device that switches on and off to maintain an average value of output.
Because the regulated voltage of a linear regulator must always be lower than input voltage,
efficiency is limited and the input voltage must be high enough to always allow the active device
to drop some voltage.
Linear regulators may place the regulating device between the source and the regulated
load (a series regulator), or may place the regulating device in parallel with the load (shuntregulator). Simple linear regulators may only contain a Zener diode and a series resistor more
complicated regulators include separate stages of voltage reference, error amplifier and power
pass element. Because a linear voltage regulator is a common element of many devices,
integrated circuit regulators are very common linear regulators may also be made up of
assemblies of discrete solid state or vacuum tube components.
The transistor (or other device) is used as one half of a potential divider to establish the
regulated output voltage. The output voltage is compared to a reference voltage to produce a
control signal to the transistor which will drive its gate or base. With negative feedback and good
choice of compensation, the output voltage is kept reasonably constant. Linear regulators are
often inefficient: since the transistor is acting like a resistor, it will waste electrical energy by
converting it to heat. In fact, the power loss due to heating in the transistor is the current times
the voltage dropped across the transistor. The same function can often be performed much more
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efficiently by a switched mode power supply, but a linear regulator may be preferred for light
loads or where the desired output voltage approaches the source voltage. In these cases, the
linear regulator may dissipate less power than a switcher. The linear regulator also has the
advantage of not requiring magnetic devices (inductors or transformers) which can be relatively
expensive or bulky, being often of simpler design, and being quieter.
Linear regulators exist in two basic forms:
(i) Series regulators.
(ii) Shunt regulators.
Series regulators are the more common form. The series regulator works by providing a
path from the supply voltage to the load through a variable resistance (the main transistor is in
the "top half" of the voltage divider). The power dissipated by the regulating device is equal to
the power supply output current times the voltage drop in the regulating device.
The shunt regulator works by providing a path from the supply voltage to ground through
a variable resistance (the main transistor is in the "bottom half" of the voltage divider). The
current through the shunt regulator is diverted away from the load and flows uselessly to ground,
making this form even less efficient than the series regulator. It is, however, simpler, sometimes
consisting of just a voltage-reference diode, and is used in very low-powered circuits where the
wasted current is too small to be of concern. This form is very common for voltage referencecircuit.
All linear regulators require an input voltage at least some minimum amount higher than
the desired output voltage. That minimum amount is called the dropout voltage. A common
regulator such as the 7805 has an output voltage of 5V, but it can only maintain this if the input
voltage remains above about 7V, before the output voltage begins sagging below the rated
output. Its dropout voltage is therefore 7V - 5V = 2V. When the supply voltage is less than about
2V above the desired output voltage, as is the case in low voltage microprocessor powersupplies, so called low dropout regulators (LDOs) must be used.
When the output regulated voltage must be higher than the available input voltage, no
linear regulator will work, (not even a Low dropout regulator). In this situation, a switching
regulator of the "boost" type must be used.
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4.3.2.4 Step transformer
Step down transformer is one whose secondary voltage is less than its primary voltage. It
is designed to reduce the voltage from the primary winding to the secondary winding. This kind
of transformer steps down the voltage applied to it.
As a step down unit, the transformer converts high-voltage, low-current power into low-
voltage, high-current power. The larger-gauge wire used in the secondary winding is necessary
due to the increase in current. The primary winding, which doesnt have to conduct as much
current, may be made of smaller gauge wire.
4.3.2.5 Step-down transformer consideration
Figure 4.6 Step down Transformer
It is possible to operate either of these transformer types backwards (powering the
secondary winding with an AC source and letting the primary winding power a load) to performthe opposite function a step up can function as a step down and vice versa. One convention used
in the electric power industry is the use of H designations for the higher voltage winding (the
primary winding in a step down unit, the secondary winding in a step-up) and X designations
for the lower voltage winding.
One of the most important considerations to increase transformer efficiency and reduce
heat is choosing the metal type of the windings. Copper windings are much more efficient than
aluminum and many other winding metal choices, but it also costs more. Transformers with
copper windings cost more to purchase initially, but save on electrical cost over time as the
efficiency more than makes up for the initial cost.
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4.3.3 Aurduino Uno kit
Aurduino is an open source electronics prototyping platform based on flexible, easy to
use hardware and software. It's intended for artists, designers, hobbyists, and anyone interested in
creating interactive objects or environments.
Aurduino can sense the environment by receiving input from a variety of sensors and can
affect its surroundings by controlling lights, motors, and other actuators. The microcontroller on
the board is programmed using the Aurduino programming language (based on Wiring) and the
Aurduino development environment (based on Processing). Aurduino projects can be stand alone
or they can communicate with software running on a computer (e.g. Flash, Processing and Max
MSP).
Aurduino boards can be purchased pre assembled or do it oneself kits. Hardware design
information is available for those who would like to assemble an Aurduino by hand. There are
sixteen official Aurduino that have been commercially produced to date.
The Aurduino Uno is a microcontroller board based on the AT mega328 (datasheet). It
has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a
16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button.
It contains everything needed to support the microcontroller simply connect it to a computer with
a USB cable or power it with a AC to DC adapter or battery to get started.
The Uno differs from all preceding boards in that it does not use the FTDI USB to serial
driver chip. Instead, it features the Atmega16U2 (Atmega8U2 up to version R2) programmed as
a USB-to-serial converter. Revision 2 of the Uno board has a resistor pulling the 8U2 HWB line
to ground, making it easier to put into DFU mode. Revision 3 of the board has the following new
features:
1.0 pin out: added SDA and SCL pins that are near to the AREF pin and two other newpins placed near to the RESET pin, the IOREF that allow the shields to adapt to the
voltage provided from the board. In future, shields will be compatible both with the board
that uses the AVR, which operate with 5V and with the Aurduino Uno that operate with
3.3V. The second one is a not connected pin that is reserved for future purposes.
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Stronger RESET circuit. At mega 16U2 replace the 8U2.
The Aurduino Uno can be powered via the USB connection or with an external power
supply. The power source is selected automatically. External (non-USB) power can come
either from an AC-to-DC adapter (wall-wart) or battery. The adapter can be connected by
plugging a 2.1mm center-positive plug into the board's power jack. Leads from a battery can
be inserted in the Ground and Vinpin headers of the POWER connector.
Figure 4.7 Aurduino Uno
Power
The board can operate on an external supply of 6 to 20 volts. If supplied with less than 7V,
however, the 5V pin may supply less than five volts and the board may be unstable. If using
more than 12V, the voltage regulator may overheat and damage the board. The recommended
range is 7 to 12 volts. The power pins are as follows:
VIN:The input voltage to the Aurduino board when it's using an external power source(as opposed to 5 volts from the USB connection or other regulated power source). You
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can supply voltage through this pin, or, if supplying voltage via the power jack, access it
through this pin.
5V: This pin outputs a regulated 5V from the regulator on the board. The board can besupplied with power either from the DC power jack (7 - 12V), the USB connector (5V),
or the VIN pin of the board (7-12V). Supplying voltage via the 5V or 3.3V pins bypasses
the regulator, and can damage your board. We don't advise it.
3V3:A 3.3 volt supply generated by the on-board regulator. Maximum current draw is50mA.
GND.Ground pins.Memory
The ATmega328 has 32 KB (with 0.5 KB used for the boot loader). It also has 2 KB of
SRAM and 1 KB of EEPROM (which can be read and written with the EEPROM library).
Input and Output
Each of the 14 digital pins on the Uno can be used as an input or output, using pinMode, digital Write, and digital Read functions. They operate at 5 volts. Each pin can provide orreceive a maximum of 40mA and has an internal pull up resistor (disconnected by default) of 20-
50 K ohms. In addition, some pins have specialized functions:
Serial: 0 (RX) and 1 (TX). Used to receive (RX) and transmit (TX) TTL serial data.These pins are connected to the corresponding pins of the ATmega8U2 USB-to-TTL
Serial chip.
External Interrupts: 2 and 3.These pins can be configured to trigger an interrupt on alow value, a rising or falling edge, or a change in value. See the attach Interrupt
() function for details.
PWM: 3, 5, 6, 9, 10, and 11.Provide 8-bit PWM output with the analog Write function. SPI: 10(SS), 11(MOSI), 12(MISO) and 13(SCK).These pins support SPI
communication using the SPI library.
LED: 13. There is a built in LED connected to digital pin 13. When the pin is HIGHvalue, the LED is on, when the pin is LOW, it's off.
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The Uno has 6 analog inputs, labeled A0 through A5, each of which provide 10 bits of
resolution (i.e. 1024 different values). By default they measure from ground to 5 volts, though is
it possible to change the upper end of their range using the AREF pin and the analog Reference
function. Additionally, some pins have specialized functionality:
TWI: A4 or SDA pin and A5 or SCL pin.Support TWI communication using the Wirelibrary.
There are a couple of other pins on the board:
AREF.Reference voltage for the analog inputs. Used with analog Reference. Reset. Bring this line LOW to reset the microcontroller. Typically used to add a reset
button to shields which block the one on the board.
The Aurduino Uno has a number of facilities for communicating with a computer,
another Aurduino, or other microcontrollers. The ATmega328 provides UART TTL (5V) serial
communication, which is available on digital pins 0 (RX) and 1 (TX). An ATmega16U2 on the
board channels this serial communication over USB and appears as a virtual com port to
software on the computer. The '16U2 firmware uses the standard USB COM drivers, and no
external driver is needed. However on Windows, a .inf file is required. The Aurduino software
includes a serial monitor which allows simple textual data to be sent to and from the Aurduino
board. The RX and TX LEDs on the board will flash when data is being transmitted via the USB
to serial chip and USB connection to the computer (but not for serial communication on pins 0
and 1).
A Software Serial library allows for serial communication on any of the Uno's digital
pins. The ATmega328 also supports I2C (TWI) and SPI communication. The Arduino software
includes a Wire library to simplify use of the I2C bus.
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CHAPTER 5
PROGRAMMING FOR AURDUINO
The Aurduino Uno is a cross platform application written in Java, and is derived from the
Uno for the Processing programming language and the Wiring project. It is designed to introduceprogramming to artists and other newcomers unfamiliar with software development. It includes a
code editor with features such as syntax high lighting, brace matching, and automatic
indentation, and is also capable of compiling and uploading programs to the board with a single
click. There is typically no need to edit make files or run programs on a command line interface.
Although building on command line is possible if required with some third-party tools.
The Aurduino Uno comes with a C/C++ library called "Wiring" (from the project of the same
name), which makes many common input/output operations much easier. Aurduino programs arewritten in C/C++, although users only need define two functions to make a run able program:
setup( ) a function run once at the start of a program that can initialize settings loop( ) a function called repeatedly until the board powers offIt is a feature of most Aurduino boards that they have an LED and load resistor connected
between pin 13 and ground, a convenient feature for many simple tests. The above code would
not be seen by a standard C++ compiler as a valid program, so when the user clicks the "Upload
to I/O board" button in the Uno, a copy of the code is written to a temporary file with an extra
include header at the top and a very simple main ( ) function at the bottom, to make it a valid
C++ program.
The Aurduino Uno uses the GNU tool chain and AVR Lib to compile programs, and uses
avrdude to upload programs to the board. As the Aurduino platform uses Atmel microcontrollers
Atmels development environment, AVR Studio or the newer Atmel Studio, may also be used to
develop software for the Aurduino.
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5.1 PROGRAM FOR TEMPERATURE READING AND CONTROL
The program for the Temperature control using Aurduino is given as follows:
void setup( )
{
Serial.begin(9600);
pinMode(A1,INPUT);
pinMode(7,OUTPUT);
}
void loop( )
{
float x=analogRead(A1);
float v=x*5;
float v1=v/1023;
if(v1>3.7)
digitalWrite(7,HIGH);
else if(v1
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5.2 FLOW CHART
Figure 5.1 Flowchart for temperature sensing and control
start
Initialize input and output pins
A1=Input&&D7=Output
Read input atA1 =V1
If v1>3.7
D9=High D9=Low
YES
Stop
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RESULT
When the temperature in the chamber crosses the set temperature value the bulb is turned
off automatically and when the temperature falls below the set temperature value the bulb glows.
The temperature in the chamber is observed to be at a constant value.
Given below shows the state of the heating element (bulb) according to the readings
noted during the first 20 minutes of the experiment.
Output State of bulb
V1=2.08 ON
V1=2.09 ON
V1=3.12 ON
V1=3.23 ON
V1=3.34 ON
V1=3.45 ON
V1=3.50 ON
V1=3.53 ON
V1=3.54 ON
V1=3.64 ON
V1=3.68 ON
V1=3.71 OFF
V1=3.70 OFF
V1=3.68 ON
V1=3.71 OFF
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FUTURE SCOPE
We can incorporate the idea of Peltier effect to control the temperature of the chamber. They can
be used either for heating or for cooling (refrigeration), although in practice the main application
is cooling. It can also be used as a temperature controller that either heats or cools. But Peltier
elements are costly and shows poor power efficiency. Many researchers and companies are
trying to develop Peltier coolers that are both cheap and efficient. If such type of Peltier elements
are developed we can also introduce it in Infant incubators.
For Infants affected with Jaundice bile lights can be introduced in to the chamber. Apnea
monitoring can also be introduced for infants affected with Respiratory disorders.
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REFERENCES
[1] http://arduino.cc/en/Main/arduinoBoardUno
[2] http://www.me.umn.edu/courses/me2011/arduino/arduinoGuide.pdf
3 http://www.control.aau.dk/~jdn/edu/doc/arduino/litt/ArduinoTutorials.pdf
4 http://www.nunoalves.com/classes/spring_2012_cpe355/cpe355-02-a.pdf
5 http://www.fairchildsemi.com/ds/PN/PN2222A.pdf
[6] http://www.ia.omron.com/products/category/relays/general-purpose- relays/index.html
7 http://www.datasheetcatalog.com/datasheets_pdf/7/8/1/2/7812.shtml
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Appendix-B
2N2222
This device[9]
is for use as a medium power amplifier and switch requiring collector currents up
to 500mA.
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Typical Performance Characteristics:
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Appendix-C
Relay 12V dc[10]
, 7A
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