DESIGN AND DEVELOPMENT OF

MICROCONTROLLER BASED

TEMPERATURE AND HUMIDITY CONTROLLER

FOR INFANT INCUBATOR

BY

NADA ELSHEIKH BABIKIR MOHAMMED

INDEX NO. 064085

Supervisor

Dr. Abdulrahmman Karrar

REPORT SUBMITTED TO

University of Khartoum

In partial fulfillment of the requirement for the degree of

B.Sc. (HONS) Electrical and Electronic Engineering

(CONTROL ENGINEERING)

Faculty of Engineering

Department of Electrical and Electronic Engineering

July 2011

ii

ACKNOWLEDGEMENT

Depth of gratitude and gratefulness is owed to those who have contributed to this work.

Their effort will definitely prepare us for our professional life and improve our capacity to

contribute to the profession; we assure them at least we will try our best.

Among those we thank Dr. Abdulrahman Karrar for his continuous support during our

course of study and through this graduation study project.

I wish to express my gratitude to Dr. Shareif F. Babikir, for his constant support and

encouragement.

We also thank Omer and U`staz Khalid and for `assistance in developing the Model.

I would like also to thank my friend, Rayan M. Elmubarak, for helping me formatting this

thesis.

I would like also to thank my partner in this project, Wafa Husam, for her kind sharing of

time and knowledge.

My family always deserve my sincere thanks whole heartedly. I thank them beyond

comprehension.

iii

ABSTRACT

Infant Incubator is of great interest for some newborns, especially if they are weak, low-

birth-weight, sick, preterm, some parameters are to be monitored and their accuracy remains an

important matter. Temperature and humidity remain the most important. This work is focused on

the control problem of these parameters.

This system can automatically control the infant’s temperature at optimum level using

PID concept and to maintain high relative humidity so as to minimize the thermal loss

iv

المستخلص

حاظت اىخذيج هي راث أهيت مبيشة باىسبت ىبعط األطفاه حذيثي اىىالدة، خاصت إرا ماج حاىخه اىصحيت ظعيفت، او

اك فإ ه, ارا ما هاك ظيق ف اىخفس اوف ف حاىت اخفاض اىىص عذ والدحه، او ارا ما شيط او حج والدحه بنشا

.بعط اىششوط اىخي يخعي سصذها ودقخها ألها سأىت هت

ىزىل فإ هزا اىظا ينه اىخحن حيقائيا ف دسجت حشاسة ,دسجت اىحشاسة واىشطىبت اىششوط اىحيطيت اىهت

.اىحشاسيواىحفاظ عي سطىبت سبيت عاىيت ورىل ىخقييو اىفقذ PIDاىشظيع في اىسخىي األثو باسخخذا فهى اه

v

TABLE OF CONTENTS

Contents 1 INTRODUCTION .............................................................................................................. 1

1.1 Overview...................................................................................................................... 1

1.2 Problem Statement and Motivation ............................................................................. 1

1.3 Project Objectives ........................................................................................................ 2

1.4 Report Layout .............................................................................................................. 2

2 Theory and Literature Review ............................................................................................ 3

2.1 Introduction.................................................................................................................. 3

2.2 Premature Infant .......................................................................................................... 4

2.3 Thermal Protection in New Born ................................................................................. 4

2.4 Cold Stress or Hypothermia ........................................................................................ 6

2.4.1 Management of Cold Stress .................................................................................. 7

2.5 Hyperthermia ............................................................................................................... 9

2.5.1 Management of Hyperthermia .............................................................................. 9

2.6 Measurement of Body Temperature .......................................................................... 10

2.7 Devices for Thermal Protection in Preterm Infants ................................................... 10

2.8 History of Infant Incubators....................................................................................... 10

2.8.1 Early years .......................................................................................................... 11

2.8.2 Increasing technology ......................................................................................... 12

2.8.3 Changing priorities ............................................................................................. 13

2.9 Functions of a neonatal incubator .............................................................................. 15

2.10 Types of Incubators ................................................................................................. 15

2.10.1 Manually controlled incubators ........................................................................ 15

2.10.2 Servo-Controlled incubators ............................................................................. 15

2.10.3 3. Transport Incubators ..................................................................................... 16

2.11 PID Control .............................................................................................................. 16

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2.11.1 PID Terms ......................................................................................................... 16

2.11.2 High and Low Cutback ..................................................................................... 17

3 Materials and Tools .......................................................................................................... 18

3.1 Introduction................................................................................................................ 18

3.2 Hardware Components .............................................................................................. 18

3.2.1 LM35 Temperature Sensor ................................................................................. 18

3.2.2 Humidity Sensor ................................................................................................. 19

3.2.3 PIC16F877A Microcontroller ............................................................................. 20

3.2.4 BT 136 or TRIAC ............................................................................................... 21

3.2.5 MOC 3011 or Optotriac ...................................................................................... 22

3.2.6 12-Volt Unipolar Stepper Motor ........................................................................ 22

3.2.7 220V Fan ............................................................................................................ 23

3.2.8 ULN2003A ......................................................................................................... 23

3.2.9 Buzzer: ................................................................................................................ 23

3.2.10 Power Supply .................................................................................................... 24

3.2.11 Other Small Components .................................................................................. 24

3.3 Software Tools ........................................................................................................... 25

4 Design and Implementation .............................................................................................. 26

4.1 Introduction................................................................................................................ 26

4.2 Design Requirements of the Project .......................................................................... 26

4.3 Hardware Details of the Project ................................................................................. 27

4.3.1 Sensor ................................................................................................................. 28

4.3.2 Power Supply ...................................................................................................... 32

4.3.3 Interfacing of PIC16F877A to various Components .......................................... 33

4.3.4 PID based Heater Circuit for Baby Chamber ..................................................... 34

4.3.5 Operation of Heater Circuit ................................................................................ 36

4.3.6 Operation of humidity control system ............................................................... 37

4.4 Software Details of the Project .................................................................................. 37

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4.4.1 PIC16F877A microcontroller ............................................................................. 37

4.4.2 Flowcharts for Software Development ............................................................... 38

5 Results and Discussions .................................................................................................... 45

5.1 Results: ...................................................................................................................... 45

5.2 Discussions ................................................................................................................ 50

5.2.1 Temperature PID control .................................................................................... 50

5.2.2 stepper motor ..................................................................................................... 50

5.2.3 Without water in reservoir .................................................................................. 50

5.2.4 With water in reservoir and without control of humidity ................................... 51

5.2.5 With water in reservoir and controlled humidity ................................................ 51

5.2.6 Cautions .............................................................................................................. 51

6 Conclusion ........................................................................................................................ 52

6.1 Conclusion ................................................................................................................. 52

6.2 Problems .................................................................... Error! Bookmark not defined.

6.3 Future Scope Of work ................................................................................................ 52

References………………………………………………………………………………....57

Appendix A The Code …………………………………………………………………..A-1

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LIST OF TABLES

Table 3-1: Typical Characteristics for Voltage Output Circuit At Vcc 5V - 25°C) ......... 20

Table 3-2 Components ......................................................................................................... 24

Table 4-1 Project Requirements .......................................................................................... 26

Table 4-2 Pin Connection for Application........................................................................... 32

Table 4-3 Pin Connection of TRIAC in the Circuit ............................................................. 35

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LIST OF FIGURES

Figure 2.1: Infant Incubator ................................................................................................... 3

Figure 2.2:Heat losses sources ............................................................................................... 5

Figure 2.3: High and Low Cutback ..................................................................................... 17

Figure 3.1: LM35 temperature sensor ................................................................................. 18

Figure 3.2 Capacitive humidity sensor Figure 3.3 Capacitive humidity sensor ............ 19

Figure 3.4 Typical response curve of HS 1101 in humidity ................................................ 20

Figure 3.5 40-Pin PDIP PIC16f877A microcontroller ...................................................... 21

Figure 3.6 BT 136 ................................................................................................................ 21

Figure 3.7 Stepper Motor Unipolar ..................................................................................... 22

Figure 3.8 220V Fan ............................................................................................................ 23

Figure 3.9 ULN2003A ......................................................................................................... 23

Figure 3.10 Buzzer............................................................................................................... 24

Figure 4.1 Block diagram of microcontroller based temperature and humidity controller . 27

Figure 4.2 LM35 sensor interface to PIC16F877A microcontroller ................................... 29

Figure 4.3Temperature sensor simulation circuit ................................................................ 29

Figure 4.4 Internal Block Diagram ...................................................................................... 30

Figure 4.5 HS 1101 sensor interface to PIC16F877A microcontroller ............................... 31

Figure 4.6 Humidity sensor circuit simulation .................................................................... 31

Figure 4.7 Power Supply Schematic .................................................................................... 32

Figure 4.8 Interfacing of PIC16F877A ................................................................................ 33

Figure 4.9 Heater Circuit for Baby Chamber ...................................................................... 34

Figure 4.10 MOC 3011Schematic ....................................................................................... 35

Figure 4.11 Auto tuner ......................................................................................................... 36

Figure 4.12 Humidity control mechanism ........................................................................... 37

Figure 4.13 General Flowchart of the project ...................................................................... 39

Figure 4.14 Temperature Reading Algorithm ..................................................................... 41

Figure 4.15 Humidity Reading Algorithm .......................................................................... 42

Figure 4.16 Flowchart for ON-OFF Control of mobile window of Water reservoir ........... 43

Figure 4.17 Flowchart for PID Control of heater ................................................................ 44

Figure 5.1 Microcontroller Based Temperature and Humidity Controller .......................... 45

Figure 5.2 Circuit of The Microcontroller ........................................................................... 46

Figure 5.3 Humidity Sensor ................................................................................................. 46

Figure 5.4 Temperature Sensor............................................................................................ 47

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Figure 5.5 Stepper Motor ..................................................................................................... 47

Figure 5.6 Heatrr and Fan .................................................................................................... 48

Figure 5.7 Heater and Fan Driver Circuit ............................................................................ 48

Figure 5.8 Infant Incubator Model....................................................................................... 49

CHAPTER 1 INTRODUCTION

1

Chapter1

1 INTRODUCTION

1.1 Overview

An 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. In addition to these, the

incubator environment provides a homogeneous and stable temperature, a relative

humidity (RH) level and oxygen gas concentration that is needed especially for

intensive care of the premature baby [1] .

Temperature is one of the most important parameters that need to be maintained

to provide suitable environment for infants especially premature born infants. It is

important that the temperature that is set by the doctor is maintained with out

significant variation over time. The product that has been developed here uses

proportional integral and derivative (PID) controllers together with pulse width

modulation (PWM) and switching to provide accurate temperature maintenance with

reference to the input temperature. It further discusses the sensor that is used in order

to get the required temperature feedback for the control [2].

1.2 Problem Statement and Motivation

Baby Incubator is one of the quite essential life supportive equipment for the

premature babies in the hospitals. Unfortunately, there is a lack of low cost infant

incubators in the developing world.

―The aim of the thesis is to design and develop a microcontroller based

temperature control using PID concept and humidity control in an infant incubator‖.

Advances in electronic techniques coupled with economical prices make humidity and

temperature control cost-effective with highly accurate and stable performance.

CHAPTER 1 INTRODUCTION

2

1.3 Project Objectives

In this work main focus will be to:

i. Design and develop hardware for temperature and humidity control.

ii. The development of software using PIC16F877A microcontroller.

The developed system should be accurate, economical and must provide the

required environment for the growth of the premature baby.

1.4 Report Layout

Chapter 2: (Theory and Literature Review) this chapter reviews the

fundamental concepts and principles that the project relies on.

Chapter 3: (Materials and Tools) this chapter talks about all tools and

materials used in the project implementation mentioning brief description of the main

features for each component.

Chapter4: (Design And Implementation) this chapter is about the design in

details. All hardware and software design steps are considered here including all

physical requirements, algorithms, circuits block diagrams, flowcharts, and etc.

also in this chapter describes implementation details of the system modules

described in the design.

Chapter5: (Results And Discussion) this chapter constitutes the real work in

order to achieve the project objectives and disscuss different things may results or

difference between traditional and advanced method and so on.

Chapter6: (Conclusion) this chapter contains the conclusion, comments on the

results of the project, the accuracy test, the main problems the project faced, and

finally the recommendations for the future work.

References

Appendix A: includes C code for PIC16F877A microcontroller.

CHAPTER 2 THEORY AND LITERATURE REVIEW

3

Chapter2

2 Theory and Literature Review

2.1 Introduction

A neonatal intensive care unit, usually shortened NICU and also called a

Special Care Nursery, newborn intensive care unit, intensive care nursery (ICN), and

special care baby unit , is a unit of a hospital specializing in the care of ill or

premature newborn infants.

The problem of premature and congenitally ill infants is not a new one, by any

means. For centuries, people have attempted to save infants that had previously died

from lack of care.

A NICU is typically directed by one or more neonatologists and staffed by

nurses, nurse practitioners, pharmacists, physician assistants, resident physicians, and

respiratory therapists. Many other ancillary disciplines and specialists are available at

larger units [3].

Figure ‎2.1: Infant Incubator

CHAPTER 2 THEORY AND LITERATURE REVIEW

4

2.2 Premature Infant

Premature infants are babies born prior to the normal 36 or 37 weeks of

gestation within the womb. As a result, their physiological systems are

underdeveloped making the infant vulnerable to a number of health complications.

Some common problems include jaundice caused by an immature liver, respiratory

complications caused by fragile, underdeveloped lungs, and hypoglycemia, hypoxia

and even death caused by an immature response of the nervous system to cold stress.

These inadequate thermoregulations, wherein their physiology is not able to

compensate for the heat they lose from the body are by far the leading causes of death

in premature infants. Heat is lost via evaporative, conductive, convective and radiative

means. Premature infants lack muscle mass, which allows adults to shiver and

produce heat when necessary, as well as heat generating brown fat, which makes up

about 5% of the body weight in preterm infants. This heat loss is enhanced by their

large surface area to volume ratio (about 4 times the adult ratio). Furthermore, their

immature skin allows for excessive water loss from the body causing a considerable

evaporative heat loss and a potentially fatal imbalance of salts and acids in the infant’s

system. In evaporative heat loss, moisture from the body first diffuses across the

epidermis (general outer layer of skin). Then it evaporates off from the skin’s surface

cooling the infant.

Premature infants have a thin, underdeveloped stratum corneum, or the rough,

outer layer of the epidermis which protects the skin from external agents, that enables

excess of water to diffuse out. Evaporative heat losses make up a significant fraction

of the total heat loss of a premature infant [4].

2.3 Thermal Protection in New Born

Thermal protection of the newborn is the series of measures taken at birth and in

the first days of life to ensure that the newborn does not become either cold or

overheated and a normal body temperature of 36.5-37.5°C (97.7-99.5°F). Since the

consequences of an environment that is too cold or too warm are serious, it is

important to know what is the optimal — i.e. the most suitable — thermal

environment for the new born baby. This is the range of thermal conditions under

which a new born baby can maintain normal body temperature. The range is narrow,

CHAPTER 2 THEORY AND LITERATURE REVIEW

5

especially in low birth weight or sick babies. Basically speaking, the smaller and more

premature the new born is, the less it tolerates cold and heat. Thus there is no single

environmental temperature that is appropriate for all sizes, gestational ages and

conditions of new born babies. What is appropriate for a healthy baby is too cold for a

preterm baby, and what is appropriate for the preterm baby is too hot for the preterm

infant. The newborn cannot regulate its temperature as well as an adult. It therefore

cools down or heats up much faster and is able to tolerate only a limited range of

environmental temperatures. The smaller the new born, the greater the risk. Thermal

stability improves gradually as the baby increases in weight.

The temperature inside the mother's womb is 38°C (100.4°F). Leaving the

warmth of the womb at birth, the wet new born finds itself in a much colder

environment and immediately starts losing heat thus the thermal protection of

newborns is very important but not difficult. The basic principles are the same

whether the baby is born at home or in an institution. As most cooling of the newborn

occurs during the first minutes after birth, it is important to act quickly to prevent heat

loss. The new born baby loses heat in four different ways. Heat loss is mainly due to

evaporation of amniotic fluid from the baby's body. But loss of body heat also occurs

by conduction if the baby is placed naked on a cold surface (e.g. a table, weighing

scale or cold mattress); by convection if the naked new born is exposed to cooler

surrounding air; and by radiation from the baby to cooler objects in the vicinity (e.g. a

cold wall or a window) even if the baby is not actually touching them.

Figure ‎2.2:Heat losses sources

CHAPTER 2 THEORY AND LITERATURE REVIEW

6

Heat loss increases with air movement, and a baby risks getting cold even at a

room temperature of 30°C (86°F) if there is a draught. Most cooling of the new born

occurs during the first minutes after birth. In the first 10-20 minutes, the new born

who is not thermally protected may lose enough heat for the body temperature to fall

by 2-4°C (3.6- 7.2°F), with even greater falls in the following hours if proper care is

not given. If heat loss is not prevented and is allowed to continue, the baby will

develop hypothermia, i.e. a body temperature below normal. A hypothermic baby,

especially if it is small or sick, is at increased risk of developing health problems and

of dying. However, if heat loss is prevented, the new born will stay warm and will

have a much better chance of remaining healthy, or of surviving if it is already sick. In

trying to keep babies warm, it is important to make sure they do not become

overheated. The mechanisms described above may act in reverse and cause

hyperthermia, i.e. a body temperature above normal. Although less common,

hyperthermia is as dangerous as hypothermia [5].

2.4 Cold Stress or Hypothermia

Cold stress in the neonatal period can be defined as a body temperature

measurement less than 36.5° C (97.6° F) rectally with system wide associated. The

normal responses to cold stress for the adult are either not present or not adequately

effective for the neonate. Full term neonates have a very limited ability to shiver to

produce heat and preterm infants have none. Additionally, preterm neonates have

unstable vasomotor responses and therefore cannot vasoconstrict adequately to slow

down heat losses. Preterm infants have limited stores of brown fat and therefore

inadequately produce heat metabolically.

While in the adult model, control of body temperature is achieved by a complex

system which via negative feed-back basically creates a balance between heat

production, heat gain and heat loss. The key of this system is a central controller

located in the hypothalamus and limbic system, which based on information from

central and peripheral thermo receptors (multiple-input), controls the action of the so-

called effectors: thermo genesis, the vasomotor system, sweat secretion and

thermoregulatory behavior, through the efficient nervous system. Body temperature

CHAPTER 2 THEORY AND LITERATURE REVIEW

7

therefore is the result of the combined action of the detectors, controller system and

the effectors. In the case of newborn infants, especially preterm infants, immaturity of

the thermoregulatory system makes the infant more vulnerable to changes of

environmental temperature. In the infant model, the physiology of the response to

cold stress is related to the oxidation of brown fat or brown adipose tissue. In full term

newborn infants, non-shivering thermogeneisis (oxidation of brown adipose tissue) is

the major route of a rapid increase of heat production in response to cold exposure.

The figure 6 represents the metabolic response to cold stress [6].

The consequences of cold stress can be quite severe. As the body temperature

decreases, the baby becomes less active, lethargic, hypotonic, sucks poorly and their

cry becomes weaker. Respiration becomes shallow and slow and the heart-beat

decreases. Sclerema – hardening of skin with redness – develops mainly on the back

and the limbs. The face can also become bright red. As the condition progresses it

causes profound changes in body metabolism resulting in impaired cardiac function,

hemorrhage (especially pulmonary), jaundice and death [7].

2.4.1 Management of Cold Stress

Newborns found to be hypothermic must be rewarmed as soon as possible. The

temperature of the room where the rewarming takes place should be at least 25°C

(77°F). Cold clothes should first be removed and replaced with pre-warmed clothes

and a cap. The newborn should be quickly rewarmed; if a warming device is used, the

baby should be clothed and its temperature should be checked frequently during the

rewarming process. It is very important to continue feeding the baby to provide

calories and fluid. Breast-feeding should resume as soon as possible. If the infant is

too weak to breast feed, breast milk can be given by nasogastric tube, spoon or cup. It

is important to be aware that hypothermia can be a sign of infection. Every

hypothermic newborn should therefore be assessed for infection. In hospital a

diagnosis of hypothermia is confirmed by measuring the actual body temperature with

a low-reading thermometer, if available. The method used for rewarming depends on

the severity of the hypothermia and the availability of staff and equipment. In cases of

mild hypothermia (body temperature 36.0-36.4°C/96.8-97.5°F), the baby can be

rewarmed by skin-to-skin contact, in a warm room (at least 25°C/77°F). In cases of

CHAPTER 2 THEORY AND LITERATURE REVIEW

8

moderate hypothermia (body temperature 32-35.9°C/89.6-96.6°F) the clothed baby

may be rewarmed:

under a radiant heater;

in an incubator, at 35-36°C (95-96.8°F);

by using a heated water-filled mattress;

in a warm room: the temperature of the room should be 32-34°C/89.6-

93.2°F(more if the baby is small or sick); in a warm cot: if it is heated

with a hot water bottle or hot stone, these should beremoved before the

baby is put in;

If nothing is available or if the baby is clinically stable, skin-to-skin

contact withthe mother can be used in a warm room (at least

25°C/77°F).

The rewarming process should be continued until the baby's temperature

reaches the normal range. The temperature should be checked every hour, and the

temperature of the device being used or the room adjusted accordingly. The baby

should continue to be fed.

In cases of severe hypothermia (body temperature below 32°C/89.6°F), studies

suggest that fast rewarming over a few hours is preferable to slow rewarming over

several days. Rapid rewarming can be achieved by using a thermostatically controlled

heated mattress set at 37-38°C (98.6-100.4°F) or an air-heated incubator, with the air

temperature set at 35-36°C (95-96.8°F). If no equipment is available, skin to- skin

contact or a warm room or cot can be used. Feeding should continue, to provide

calories and fluid and to prevent a drop in the blood glucose level which is a common

problem in hypothermic infants. If this is not possible, monitoring blood glucose

becomes important and an intravenous line should be set up to administer glucose if

needed. Once the baby's temperature reaches 34°C (93.2°F), the rewarming process

should be slowed down to avoid overheating. The temperature of the incubator and

the baby's body temperature should be checked every hour [5].

CHAPTER 2 THEORY AND LITERATURE REVIEW

9

2.5 Hyperthermia

Hyperthermia can be defined as a rectal temperature greater than 37.0°C

(98.6°F). Determination of an external source of heat gain versus an actual febrile

state can be made by observing for peripheral vasoconstriction as demonstrated by a

higher rectal temperature versus a distal temperature of the foot. In the presence of

over heating, the opposite would occur [6]. Hyperthermia should not be confused with

fever, which is a raised body temperature in response to infection with

microorganisms or other sources of inflammation. However, it is not possible to

distinguish between fever and hyperthermia by measuring the body temperature or by

clinical signs, and when the newborn has a raised temperature it is important to

consider both causes. Infection should always be suspected first, unless there are very

obvious external reasons for the baby becoming overheated [5]

.Hyperthermia can cause increased metabolic demands for the neonate. The

neonate may have increased oxygen requirements, apnea, dehydration, metabolic

acidosis and in worse case scenarios heat stroke, brain damage, shock and death [6].

2.5.1 Management of Hyperthermia

The baby should be moved away from the source of heat, and undressed

partially or fully, if necessary. If the baby is in an incubator, the air temperature

should be lowered. It is important that the baby be breast-fed more frequently to

replace fluids. Every hyperthermic baby should be examined for infection. When

hyperthermia is severe i.e. body temperature above 40°C(104°F°) the baby can be

given a bath. The water should be warm. If it is possible to measure the water

temperature, it should be about 2°C (3.6°F) lower than the baby's body temperature.

Using cooler or cold water is dangerous. It may not achieve the desired effect and the

baby may very quickly become hypothermic. If the baby cannot breast-feed extra

fluids should be given intravenously or by tube.

CHAPTER 2 THEORY AND LITERATURE REVIEW

10

2.6 Measurement of Body Temperature

Obtaining a body temperature is the only reliable method available to evaluate

thermal stability. Accepted temperature ranges for the neonate are dependent upon the

site from which the body temperature is obtained.

2.7 Devices for Thermal Protection in Preterm Infants

Low birth weight or sick newborns are at greater risk of developing

hypothermia or hyperthermia than normal weight babies because they regulate body

temperature even less well. To keep low birth weight or sick newborn babies warm,

the same principles apply as for other newborns, but these babies require extra

warmth over a longer period of time.

Moreover the baby's temperature and the temperature inside the device should

be monitored frequently. No heating device can function efficiently in a cold room,

because heat loss by radiation to the cold environment may exceed heat generated by

the device.

All equipment should therefore be used in room temperatures of at least 25°C

(77°F). The method used to keep the baby warm will depend on its weight, gestational

age, and health, which can be taken care by various devices such as:

1. Infant Incubators

2. Radiant Warmers

2.8 History of Infant Incubators

Before the industrial revolution, premature and ill infants were born and cared

for at home and either lived or died without medical intervention. In the mid-

nineteenth century, the infant incubator was first developed, based on the incubators

used for chicken eggs. Dr. Stephane Tarnier is generally considered to be the father of

the incubator (or isolette as it is now known), having developed it to attempt to keep

premature infants in a Paris maternity ward warm. Other methods had been used

before, but this was the first closed model, additionally, he helped convince other

CHAPTER 2 THEORY AND LITERATURE REVIEW

11

physicians that the treatment helped premature infants. France became a forerunner in

assisting premature infants, in part due to their concerns about a falling birth rate.

Dr. Pierre Budin, followed in Tarnier’s footsteps after he retired, noting the

limitations of infants in incubators and the importance of breastmilk and the mother’s

attachment to the child. Budin is known as the father of modern perinatology, and his

seminal work The Nursling (Le Nourisson in French) became the first major

publication to deal with the care of the neonate.

Another factor that contributed to the development of modern neonatology was

thanks to Dr. Martin Couney and his permanent installment of premature babies in

incubators at Coney Island. A more controversial figure, he studied under Dr. Budin

and brought attention to premature babies and their plight through his display of

infants as sideshow attractions at Coney Island and the World’s Fair in New York and

Chicago in 1933 and 1939, respectively.

2.8.1 Early years

Doctors took an increasing role in childbirth from the eighteenth century

onwards. However, the care of newborn babies, sick or well, remained largely in the

hands of mothers and midwives. Some baby incubators, similar to those used for

hatching chicks, were devised in the late nineteenth century. In the United States these

were shown at commercial exhibitions, complete with babies inside, until 1931. Dr A.

Robert Bauer MD at Henry Ford Hospital in Detroit, MI successfully combined

oxygen, heat, humidity, ease of accessibility, and ease of nursing care in 1931. It

wasn't until after the Second World War that special care baby units (SCBUs) were

established in many hospitals. In Britain, early SCBUs opened in Birmingham and

Bristol. At Southmead Hospital, Bristol, initial opposition from obstetricians lessened

after quadruplets born there in 1948 were successfully cared for in the new unit. More

resources became available - the first unit had been set up with £100. Most early units

had little equipment and relied on careful nursing and observation.

Incubators were expensive so the whole room often was kept warm instead.

Cross-infection between babies was greatly feared. Strict nursing routines involved

staff wearing gowns and masks, constant hand washing and minimal handling of

CHAPTER 2 THEORY AND LITERATURE REVIEW

12

babies. Parents were sometimes allowed to watch through the windows of the unit.

Much was learned about feeding - frequent, tiny feeds seemed best - and breathing.

Oxygen was given freely until the end of the 1950s, when it was shown that the high

concentrations reached inside incubators caused some babies to go blind. Monitoring

conditions in the incubator, and the baby itself, was to become a major area of

research. Although incubators provided oxygen and warmth, science in the 1950s was

limited and it was not until later that technology played a larger role in the decline of

infant mortality. The development of surfactant is the most important development in

neonatology to date, allowing the oxygenation and ventilation of underdeveloped

lungs.

2.8.2 Increasing technology

By the 1970s NICUs were an established part of hospitals in the developed

world. In Britain, some early units ran community programmes, sending experienced

nurses to help care for premature babies at home. But increasingly technological

monitoring and therapy meant special care for babies became hospital-based. By the

1980s, over 90% of births took place in hospital anyway. The emergency dash from

home to the NICU with baby in a transport incubator had become a thing of the past,

though transport incubators were still needed. Specialist equipment and expertise

were not available at every hospital, and strong arguments were made for large,

centralised NICUs. On the downside was the long travelling time for frail babies and

for parents. A 1979 study showed that 20% of babies in NICUs for up to a week were

never visited by either parent. Centralised or not, by the 1980s few questioned the role

of NICUs in saving babies. Around 80% of babies born weighing under 1.5 kg now

survived, compared to around 40% in the 1960s. From 1982 in Britain pediatricians

could train and qualify in the sub-specialty of neonatal medicine.

Not only careful nursing, but also new techniques and instruments now played a

major role. As in adult intensive care units, the use of monitoring and life support

systems became routine. These needed special modification for small babies, whose

bodies were tiny and often immature. Adult ventilators, for example, could damage

babies lungs and gentler techniques with smaller pressure changes were devised. The

many tubes and sensors used for monitoring the baby's condition, blood sampling and

artificial feeding made some babies scarcely visible beneath the technology.

CHAPTER 2 THEORY AND LITERATURE REVIEW

13

Furthermore, by 1975, over 18% of newborn babies in Britain were being admitted to

NICUs. Some hospitals admitted all babies delivered by Caesarian section, or under

2500g in weight. The fact that these babies missed early close contact with their

mothers was a growing concern. As in other area of medicine, the 1980s saw

questions being raised about the human, and the economic costs of too much

technology. Admission policies gradually changed. In addition, treating low birth

weight infants is expensive, especially when there are much cheaper ways of ensuring

healthy babies. The key is prevention. Money can be spent on programs educating

mothers on staying healthy during their pregnancy. One program (one that encourages

women to stop smoking) is one third the price of neonatal intensive care and has been

proven to work. During this program, a significant number of women often quit.

2.8.3 Changing priorities

NICUs now concentrate on treating very small, premature, or congenitally ill

babies. Some of these babies are from higher-order multiple births, but most are still

single babies born too early. Premature labour, and how to prevent it, remains a

perplexing problem for doctors. Even though medical advancements allow doctors to

save low birth weight babies, it is almost invariably better to delay such births.

over the last 10 years or so, SCBUs have become much more 'parent friendly',

encouraging maximum involvement with the babies. Routine gowns and masks have

gone and parents are encouraged to help with care as much as possible. Cuddling, and

skin-to-skin contact, also known as Kangaroo care, are seen as beneficial for all but

the frailest (very tiny babies are exhausted by the stimulus of being handled, or larger

critically ill infants). Less stressful ways of delivering high-technology medicine to

tiny patients have been devised - sensors to measure blood oxygen levels through the

skin, for example, and ways of reducing the amount of blood taken for tests.

Some major problems of the NICU have almost disappeared. Exchange

transfusions, in which all the blood is removed and replaced, are rare now. Rhesus

incompatibility (a difference in blood groups) between mother and baby is largely

preventable, and was the most common cause for exchange transfusion in the past.

Breathing difficulties, intraventricular hemorrhage, necrotizing enterocolitis and

CHAPTER 2 THEORY AND LITERATURE REVIEW

14

infection still claim many infant lives and are the focus of many current research

projects.

The long term outlook for premature babies saved by NICUs has always been a

concern. From the early years, it was reported that a higher proportion than normal

grew up with disabilities, including cerebral palsy and learning difficulties. Now that

treatments are available for many of the problems faced by tiny or immature babies in

the first weeks of life, long-term follow-up, and minimising long-term disability, are

major research areas.

Besides prematurity and extreme low birth weight, common diseases cared for

in a NICU include perinatal asphyxia, major birth defects, sepsis, neonatal jaundice,

and respiratory distress syndrome due to immaturity of the lungs. The leading cause

of death in NICUs is generally necrotizing enterocolitis. Complications of extreme

prematurity may include intracranial hemorrhage, chronic bronchopulmonary

dysplasia (see Infant respiratory distress syndrome), or retinopathy of prematurity. An

infant may spend a day of observation in a NICU or may spend many months there.

Overall survival rates, for all gestational ages lumped together, are roughly 70%.

Neonatology and NICUs have greatly increased the survival of very low birth

weight and extremely premature infants. In the era before NICUs, infants of birth

weight less than 1400 grams (3 lb, usually about 30 weeks gestation) rarely survived.

Today, infants of 500 grams at 26 weeks have a fair chance of survival.

The NICU environment provides challenges as well as benefits. Stressors for

the infants can include continual light, a high level of noise, separation from their

mothers, reduced physical contact, painful procedures, and interference with the

opportunity to breastfeed. A NICU can be stressful for the staff as well. A special

aspect of NICU stress for both parents and staff is that infants may survive, but with

damage to the brain or eyes.

NICU rotations are essential aspects of pediatric and obstetric residency

programs, but NICU experience is encouraged by other specialty residencies, such as

family practice, surgery, Pharmacy, and emergency medicine.

CHAPTER 2 THEORY AND LITERATURE REVIEW

15

2.9 Functions of a neonatal incubator

Oxygenation, through oxygen supplementation by head hood or nasal cannula,

or even continuous positive airway pressure (CPAP) or mechanical ventilation. Infant

respiratory distress syndrome is the leading cause of death in preterm infants, and the

main treatments are CPAP, in addition to administering surfactant and stabilizing the

blood sugar, blood salts, and blood pressure.

Observation: Modern neonatal intensive care involves sophisticated

measurement of temperature, respiration, cardiac function, oxygenation,

and brain activity.

Protection from cold temperature, infection, noise, drafts and excess

handling: Incubators may be described as bassinets enclosed in plastic,

with climate control equipment designed to keep them warm and limit

their exposure to germs.

Provision of nutrition, through intravenous catheter or NG tube.

Administration of medications.

Maintaining fluid balance by providing fluid and keeping a high air

humidity to prevent too great a loss from skin and respiratory

evaporation.

2.10 Types of Incubators

2.10.1 Manually controlled incubators

The temperature in an incubator may be controlled by a thermostat. This keeps

the environment at a set temperature and allows one to monitor the neonate's

temperature. The temperature is set to provide a neutral thermal environment.

2.10.2 Servo-Controlled incubators

The servo control system adjusts the environmental temperature to keep the skin

temperature constant. Changes in incubator temperature must be observed since the

neonate's skin temperature will not change. Air-heated incubators are widely used for

the care of very small and sick newborns. They provide a clean, warm environment,

CHAPTER 2 THEORY AND LITERATURE REVIEW

16

where the temperature and humidity can be controlled and oxygen can be supplied if

necessary.

2.10.3 3. Transport Incubators

A transport incubator is an incubator and the most necessary neonatal

instruments in a transportable format, and is used when a sick or premature baby is

moved, e.g., from one hospital to another, as from a community hospital to a larger

medical facility with a proper neonatal intensive care unit. It usually has a miniature

ventilator, cardio-respiratory monitor, IV pump, pulse oximeter, and oxygen supply

built into its frame.

2.11 PID Control

PID control is referred to as ―Three-term‖ control. The three terms are:

1. P for Proportional

2. I for Integral

3. D for Derivative

The output of the controller is the sum of the above three terms.The combined

output is a function of the magnitude and duration of the error signal, and the rate of

change of the temperature or process value.

2.11.1 PID Terms

1. The Proportional term delivers an output which is proportional to the size of

the error signal. In the example below, the proportional band is 10°C and an error of

3°C will produce an output of 30%.Proportional only controllers will not, in general,

control precisely at set point, but with an offset corresponding to the point at which

the output power equals the heat loss from the system.

2. The Integral term removes steady state control offsets by ramping the output

up or down in proportion to the amplitude and duration of the error signal. The ramp

rate (Integral time constant) must be longer than the time constant of the process to

avoid oscillations.

CHAPTER 2 THEORY AND LITERATURE REVIEW

17

3. The Derivative term is proportional to the rate of change of the temperature

or process value. It is used to prevent overshoot and undershoot of the set point and to

restore the process value rapidly to the set point if there is a sudden change in

demand.

2.11.2 High and Low Cutback

While the PID parameters are optimized for steady state control at or near the

set point, high and low cutback parameters are used to reduce overshoot and

undershoot for large step changes in temperature. They respectively set the number of

degrees above and below set point at which the controller will start to decrease or

cutback the output power.

Figure ‎2.3: High and Low Cutback

CHAPTER 3 MATERIALS AND TOOLS

18

CHAPTER 3

3 Materials and Tools

3.1 Introduction

The incubator is considered as an air conditioned room with special specification which we

can control it with respect to the condition of baby incubator. Incubators are designed to provide

an optimal environment for newborn babies with growth problems (premature baby) or with

illness problems. The incubator is isolated area environment with no dust, bacteria, and has the

ability to control temperature and humidity to remain them in acceptable levels such as (36°C-

38°C) for temperature and (70%-75%) for humidity . The incubator is provided with motor and

fan that sucks the air through it. Then the air-pass on to a heating grid followed by a water

evaporator to gain the required humidity. If it is necessary oxygen can be added [8].

3.2 Hardware Components

3.2.1 LM35 Temperature Sensor

The LM35DZ is precision integrated-circuit temperature sensor, is 3-pin device, give out

an analog voltage of typically 10 mV/C which is directly proportional to the celsius (Centigrade)

temperature.

This sensor is rated for full -55° to +150°C range with linear +10.0 mV/°C scale factor, it

operates from 4 to 30 V [9].

Figure ‎3.1: LM35 temperature sensor

CHAPTER 3 MATERIALS AND TOOLS

19

An infant incubator usually has two modes of temperature control:

skin temperature

air temperature

so there are two temperature sensors are used [8].

3.2.2 Humidity Sensor

A capacitive humidity sensor change its capacitance based on the relative humidity (RH)

of the surrounding air.as the relative humidity increases the capacitance also increases. Figure

3.2 shows HS 1101, capacitive type relative humidity.

Figure ‎3.2 Capacitive humidity sensor Figure ‎3.3 Capacitive humidity sensor

Relative humidity is the percentage of actual vapor pressure (P) compared to saturated

vapor pressure (Ps).

[8]

Vout=Vcc*(0.00474*%RH+0.2354)

CHAPTER 3 MATERIALS AND TOOLS

20

Table ‎3-1: Typical Characteristics for Voltage Output Circuit At Vcc 5V - 25°C)

Figure ‎3.4 Typical response curve of HS 1101 in humidity

3.2.3 PIC16F877A Microcontroller

A microcontroller is a single chip microprocessor system ,PIC is a family of Harvard

architecture microcontrollers made by Microchip Technology.

The name PIC initially referred to "Peripheral Interface Controller". It features up to 200

ns instruction execution, 256 bytes of EEPROM data memory, self programming, an ICD, 2

Comparators, 8 channels of 10-bit Analog-to-Digital converter, 2 capture/compare/PWM

functions, 3 timers, a synchronous serial port that can be configured as either 3-wire SPI or 2-

wire I2C bus, a USART, and a Parallel Slave Port [10].

CHAPTER 3 MATERIALS AND TOOLS

21

Figure ‎3.5 40-Pin PDIP PIC16f877A microcontroller

3.2.4 BT 136 or TRIAC

bidirectional triode thyristor is a solid-state device that acts like two SCRs that have been

connected in parallel with each other (inversely) so that one SCR will conduct the positive half-

cycle and the other will conduct the negative half-cycle. This means that the triac can be used for

control in ac circuits which is required in our circuit so that we can get optimum automatic

control of infant’s temperature.

Figure ‎3.6 BT 136

CHAPTER 3 MATERIALS AND TOOLS

22

3.2.5 MOC 3011 or Optotriac

family of non-zero crossing triac drivers consist of an aluminum gallium arsenide infrared

LED, optically coupled to a silicon detector chip these two chips are assembled in a 6 pin DIP

package, providing 7.5 KV ac(peak) of insulation between the LED and the output detector.

These output detector chips are designed to drive triac controlling loads on 115 and 220 V AC

power lines the detector chip is a complex device which functions in the same manner as a small

triac, generating the signals necessary to drive the gate of a larger triac. Basically, MOC30XX

family of opto-isolators is capable of controlling large power triacs with a minimum number of

additional components.

3.2.6 12-Volt Unipolar Stepper Motor

Stepper motors are electromechanical devices that convert a pattern of inputs and the rate-

of-change of those inputs into precise rotational motion. The rotational angle and direction for

each change (step) is determined by the construction of the motor as well as the step pattern

input. four-phase unipolar stepper motor that is easily controlled when buffered with an

appropriate high-current driver ULN2003.

Figure ‎3.7 Stepper Motor Unipolar

CHAPTER 3 MATERIALS AND TOOLS

23

3.2.7 220V Fan

An infant incubator in which the heater for heating the air circulated through the incubator

and the speed of the fan which forces air across the heater to circulate through the incubator are

controlled to increase the temperature of the heated air and delivery of the heated air to the space

in which an infant has been placed for treatment when an access door of the incubator has been

opened []

Figure ‎3.8 220V Fan

3.2.8 ULN2003A

The ULN2003A is high-voltage high-current Darlington transistor arrays. Each consists of

seven npn Darlington pairs that feature high-voltage outputs with common-cathode clamp diodes

for switching inductive loads. The collector-current rating of a single Darlington pair is 500 mA.

Figure ‎3.9 ULN2003A

3.2.9 Buzzer:

Is mechanical device which produce sound via a magnetized arm repeatedly striking a

diaphragm. These devices operate with a DC voltage and the current requirement is small,

CHAPTER 3 MATERIALS AND TOOLS

24

generally in the region of lO mA. Buzzers generate a `buzzing' noise (single tone) in the

frequency range 300 to 500 Hz.

Figure ‎3.10 Buzzer

3.2.10 Power Supply

This part of the hardware provides the required energy for working of the various

integrated circuits that has been developed. The schematic of power supply circuit is as shown in

details in next chapter.

3.2.11 Other Small Components

These include the components that are either basic requirement for the above components

or employed for unnecessary purpose. Table 3-2 summarizes theses components.

Table ‎3-2 Components

Components Usage

USB PIC programmer (UP00A) Downloads hex files into PIC chip

4 MHz crystal oscillator Required by PIC16f877A microcontroller

22 pF capacitors Required by crystal oscillator

Transformer step down the voltage level from 220 V AC

5 V, DC regulator (7805) regulates the voltage to 5 V DC

CHAPTER 3 MATERIALS AND TOOLS

25

3.3 Software Tools

MikroC compiler is used to edit and compile C code for PIC16F877A. Only hex.file is

downloaded into programmer in the microcontroller chip.

Proteus simulator is used to design and simulate electronic circuits.also help to testing the

code.

CHAPTER 4 DESIGN AND IMPELEMENTATION

26

Chapter4

4 Design and Implementation

4.1 Introduction

Temperature and humidity are two very important parameters that need to be monitored

continuously in the infant incubator chamber so that similar environment can be replicated for

the pre-term infant or new born baby. Temperature can be displayed in terms of degree Celsius

(0C) and humidity in terms of relative humidity which is expressed as % Relative Humidity

(%RH).

4.2 Design Requirements of the Project

The various design requirements of the system are given in Table

Table ‎4-1 Project Requirements

Mode of System Operation Automatic Control

Temperature Range 28 0C-38 0C

Relative Humidity >70 % R.H

Temperature of Skin 37 0C

Mode of Temperature Control Air Temperature Control

Display LCD

CHAPTER 4 DESIGN AND IMPELEMENTATION

27

4.3 Hardware Details of the Project

The block diagram of microcontroller based temperature and humidity controller in the

infant incubator is shown in Figure 4.1.

Figure ‎4.1 Block diagram of microcontroller based temperature and humidity

controller

The details of the various components are given below:

CHAPTER 4 DESIGN AND IMPELEMENTATION

28

4.3.1 Sensor

Sensor is the front end device which comes directly in contact with the quantity being

measured. In microcontroller based infant incubator, the choice of transducer or sensor to

measure the temperature of baby, temperature of water reservoir and humidity of baby chamber

is very critical.So we require two types of sensors:

1. Temperature Sensor

2. Relative Humidity Sensor

Temperature sensor

The requirements of the temperature measurement are given below:

Temperature Sensor (1) for measurement of body temperature of an infant in the

range of 28 0C-38 0C.

Temperature Sensor (2) for measurement of air temperature.

The transducer should have following properties:

i. Accuracy

ii. High Output

iii. Repeatability

iv. Long term stability

v. High Input Impedance

vi. Linearity

vii. Self Heating

viii. Temperature Compensation

ix. Small Size

CHAPTER 4 DESIGN AND IMPELEMENTATION

29

Figure ‎4.2 LM35 sensor interface to PIC16F877A microcontroller

Figure ‎4.3Temperature sensor simulation circuit

CHAPTER 4 DESIGN AND IMPELEMENTATION

30

Humidity Sensor

Humidity sensor should provide humidity level in the incubator in terms of relative

humidity (%RH) in the range of 0-100%RH.The humidity sensor must have the following

properties:

i. Accuracy

ii. Temperature Range

iii. Repeatability

iv. Long term stability

v. High Input Impedance

vi. Linearity

vii. Humidity Range

Figure ‎4.4 Internal Block Diagram

CHAPTER 4 DESIGN AND IMPELEMENTATION

31

Figure ‎4.5 HS 1101 sensor interface to PIC16F877A microcontroller

Figure ‎4.6 Humidity sensor circuit simulation

CHAPTER 4 DESIGN AND IMPELEMENTATION

32

Table ‎4-2 Pin Connection for Application

PIC16F877A Pins Pins of other Components

Port A ( pin 2,3,4,7,10) Sens1 ,sens2, sens3, buzzer and fan

Port B( pin 33,34,35,36,37,38) LCD

Port C ( pin 16) Heater

Port D ( pin 19,20,21,22) Stepper motor

4.3.2 Power Supply

The schematic of power supply circuit is as shown figure……

Figure ‎4.7 Power Supply Schematic

The power supply circuit converts the 220 V AC into 5 V DC at which various integrated

circuits can work efficiently.

Hence it can be achieved by using various components such as:

i. Transformer which step down the voltage level from 220 V AC to required voltage level.

CHAPTER 4 DESIGN AND IMPELEMENTATION

33

ii. Full Wave Rectifier is composed of four diodes (IN4007) which are placed as shown in

Figure 4.7. It converts the alternating voltage to a unidirectional voltage.

iii. Capacitor of 1000 AF is used for ripple rejection of the unidirectional voltage obtained

at rectifier end.

iv. LM 7805 is a regulator which regulates the voltage to constant supply which is 5 V DC

in this case. It has three pins i.e. Vin, GND, Vout as as shown in Figure 4.7.

4.3.3 Interfacing of PIC16F877A to various Components

The connection of microcontroller with various components of temperature and humidity

control in baby chamber is shown below in detail in Figure 4.8

Figure ‎4.8 Interfacing of PIC16F877A

CHAPTER 4 DESIGN AND IMPELEMENTATION

34

4.3.4 PID based Heater Circuit for Baby Chamber

Temperature of infant is the most important parameter which is maintained by switching

ON and OFF of the heater at desired temperature level and hence for this purpose the concept of

PID has been developed in the software. This concept switches the heater On and OFF for

particular time intervals by calculating the error and hence requires high speed switching ON and

OFF and heater which cannot be achieved by devices such as relay because it can give away at

such high speed and hence TRIAC has been used. The implementation of this concept requires a

compatible hardware which can be seen in the Figure 4.9.

Figure ‎4.9 Heater Circuit for Baby Chamber

This circuit has two main components

CHAPTER 4 DESIGN AND IMPELEMENTATION

35

BT 136 or TRIAC

MOC 3011

Figure ‎4.10 MOC 3011Schematic

The description of various pins used in triac is given in Table 4-3.

Table ‎4-3 Pin Connection of TRIAC in the Circuit

Kp, Ti and Td are found by using auto tuning program, can be seen in Figure 4.11.

CHAPTER 4 DESIGN AND IMPELEMENTATION

36

Figure ‎4.11 Auto tuner

4.3.5 Operation of Heater Circuit

This circuit makes the monitoring of infants temperature in the incubator much more

precise and accurate based on PID concept employed in the software thereby taking careof:

i. Overshoots

ii. Reduce energy wastage.

As seen in Figure 4.9 one terminal of heater is connected to 220V source directly while the

other terminal is connected to this source through MOC 3011 and BT136.The current from

source to terminal 2 of triac doesn’t reach MOC 3011 till gate pin of BT 136 gets high which is

connected to pin6 of MOC 3011 and this high pulse is received according to software

instructions from pin 0.6 (bch) of microcontroller. When high pulse is received gate gets into

active mode and current blocked at pin 2 of BT136 is passed on to pin1 of BT136 and hence

circuit gets completed and heater is switched ON and similarly according to pulse it gets

switched OFF.

CHAPTER 4 DESIGN AND IMPELEMENTATION

37

4.3.6 Operation of humidity control system

The humidity control system is based on the microcontroller PIC16Fb77A of the

Microchip, was developed for newborn incubator using a step motor, to maintain the relative

humidity inside a band of comfort established by the standard (40 % to 60 %), turning in a shut

mesh control system. Figure 4.6 can shows the block diagram.

The driver is the interface that makes switching voltage of 12 volts required by the

unipolar motor from the voltage of work of the microcontroller that is 5 V.

Figure 4.6 shows the mechanism that was inserted in the water reservoir of the newborn

incubator with the objective to control the relative humidity.

In this mechanism, the step motor receives a sign of the microcontroller then moving the

window of the humidity reservoir of coupled to his axle whenever the value of the humidity will

be out of a belt prearranged with the finality of maintaining it inside the belt of comfort

established in the standard .

Figure ‎4.12 Humidity control mechanism

4.4 Software Details of the Project

4.4.1 PIC16F877A microcontroller

Software is an integral part of any control system; it interacts with hardware to carry out

different functions which are responsible for the control of parameters. In the given problem the

software can be divided into following subparts:

CHAPTER 4 DESIGN AND IMPELEMENTATION

38

i. To assign different ports (pins) of microcontroller (PIC16F877A) to different

ii. components of the system.

iii. To display different input values.

iv. To accept the set point input value of air temperature of infant chamber.

v. To compare the real time values to input values and perform necessary control action.

vi. To display the results.

PIC16F877A microcontroller is the main brain of the infant incubator, so the algorithm

inside it must be capable to control and perform all operations including reading the sensor

outputs, processing these readings.

4.4.2 Flowcharts for Software Development

Flowcharts has been developed in this section depicting step by step development of the

software which issue instructions to various components of the hardware thereby making

monitoring and control of parameters efficient and automatic.

General Flowchart

CHAPTER 4 DESIGN AND IMPELEMENTATION

39

Figure ‎4.13 General Flowchart of the project

CHAPTER 4 DESIGN AND IMPELEMENTATION

40

Temperature Reading Algorithm

The ADC module in PIC16F877A has eight inputs, it also has high and low voltage

references which are always in our code set to 5 V and 0 V, respectively. LM35 temperature

sensor analog voltage output is applied to channel 0 (AN0) of PIC16F877A which is pin 2

(RA0/AN0). Hence the algorithm to read temperature will be:

i. Initialize the microcontroller:

ADC configuration: ADC channels are (AN0 and AN1), resolution is 10 bit, and

voltage references are 0 V and 5 V.

Clock = 4 MHz.

ii. Set ADC channel for AN0 and AN1. Read ADC value.

iii. Calibrate the obtained digital value to actual temperature reading using:

. ° = ∗500/1024

Then the flow chart of the algorithm will be as in Figure 4.14

CHAPTER 4 DESIGN AND IMPELEMENTATION

41

Figure ‎4.14 Temperature Reading Algorithm

CHAPTER 4 DESIGN AND IMPELEMENTATION

42

Humidity Reading Algorithm

the flow chart of the algorithm will be as in Figure 4.15

Figure ‎4.15 Humidity Reading Algorithm

CHAPTER 4 DESIGN AND IMPELEMENTATION

43

Water Reservoir Subroutine

As humidity is an important parameter which helps in maintaining heat loss to minimum at

high relative humdidty level, hence its indirectly controlled by switching ON-OFF of mobile

window of water reservoir which is responsible for humidity in baby chamber.

Figure ‎4.16 Flowchart for ON-OFF Control of mobile window of Water reservoir

CHAPTER 4 DESIGN AND IMPELEMENTATION

44

PID Subroutine

Figure ‎4.17 Flowchart for PID Control of heater

CHAPTER 5 RESULTS AND DISCUSSION

45

Chapter5

5 Results and Discussions

5.1 Results:

Figure 4.8 shows the Simulation results of complete circuit carried out using Proteus

software. The results obtained from the PIC16F877A microcontroller interfaced with two

temperature sensors, humidity sensors, an LCD and LED’s. The LCD is used to monitor the

sensor readings. The LED’s are also connected for identification of the sensor working properly.

The performance of the system depends on working of each individual unit. Hence overall

performance of the unit has been checked and which has been satisfactory.

Figure ‎5.1 Microcontroller Based Temperature and Humidity Controller

CHAPTER 5 RESULTS AND DISCUSSION

46

Figure ‎5.2 Circuit of The Microcontroller

Figure ‎5.3 Humidity Sensor

CHAPTER 5 RESULTS AND DISCUSSION

47

Figure ‎5.4 Temperature Sensor

Figure ‎5.5 Stepper Motor

CHAPTER 5 RESULTS AND DISCUSSION

48

Figure ‎5.6 Heatrr and Fan

Figure ‎5.7 Heater and Fan Driver Circuit

CHAPTER 5 RESULTS AND DISCUSSION

49

Figure ‎5.8 Infant Incubator Model

CHAPTER 5 RESULTS AND DISCUSSION

50

5.2 Discussions

5.2.1 Temperature PID control

An accurate regulation of the temperature inside the canopy is compulsory in order to

fulfill the clinical needs and to limit the health diseases caused by temperature changes. For

maintaining the internal temperature constant and close to the setting temperature, a control

system is required. A Proportional-Derivative and Integral (PID) control unit is applied in

contrast to the servo control unit which is built on the electronic board, because in PID the

opportunity exists to optimize or ―tune‖ the control loop to achieve the best possible accuracy in

each case.

Proportional-Derivative and Integral (PID) control unit is generally adopted, in an attempt

to reduce wide variations in incubator temperature.

5.2.2 Stepper Motor

Passive humidity control system consists of a reservoir with water whose surface is

crossed on the part of the air flow generated for weathercock. A greater or minor humidity of air

can be gotten regulating the air flow. This humidity of air occurs for the passive diffusion of the

water for the air that passes for the reservoir, not existing a shut mesh control mechanism

because the relative humidity of air is not measured nor controlled, The disadvantages of the use

of this system inhabit in low the quality of the humidity control rate and the necessity of a very

rigorous asepsis. This system used in most of the newborn incubator cannot reach high and

constant levels of humidity to develop the system for newborn incubator using a step motor, to

maintain the relative humidity inside a band of comfort established by the standard (40 % to 60

%) turning in a shut mesh control system.

5.2.3 Without water in reservoir

The relative humidity of the air inside in newborn incubator, without water in humidity

reservoir, if it kept inside of the band of comfort established for the norm

CHAPTER 5 RESULTS AND DISCUSSION

51

5.2.4 With water in reservoir and without control of humidity

The relative humidity of the air inside of the newborn incubator that used water in

humidity reservoir, without control of humidity, go out from the band of comfort if it kept above

of the greatest limit established by standard

5.2.5 With water in reservoir and controlled humidity

The relative humidity of the air inside of the newborn incubator that used water in

humidity reservoir, with control of humidity, if it kept inside of a band preset in agreement with

the norm.

It was verified, with this study, necessity of use water in the humidity reservoir of newborn

incubator used in this work, as well as, to maintain humidity controlled. The expectation is that

the presented results will be able to provoke reflections in the professionals of the health area in

the sense of using water in humidity system of the newborn incubator and that the control of this

humidity could contribute to the thermo-neutral of the environment and to improve the quality of

life of the premature newborns.

5.2.6 Cautions

Air filter

Air filter should be changed at least every three months for the sake of the baby health.

Cleaning

The incubator should be clean every time and specially after the incubation of every baby.

CHAPTER 6 CONCLUSION

52

Chapter 6

6 Conclusion

6.1 Conclusion

The Goal of my thesis was to design and develop microcontroller based humidity and

temperature controller for infant incubator. To achieve this, hardware was developed with

compatible software in mikroc, so that the above mentioned parameters can be monitored for the

normal growth of the infant.

This system can provide optimum automatic control of temperature of the infant using PID

control technique which has been implemented in the software. Moreover it controls the heater,

according to air temperature in the infant chamber. The control of relative humidity in chamber

is required to reduce the thermal loss from the infant’s body.

6.2 Future Scope Of work

Some of the future aspects of the work in terms of its improvements are discussed below:

1. Presently only air temperature control mode which measures temperature from infant’s

chamber air has been used. We can enhance the accuracy of system by introducing skin

temperature control mode.

2. Parameters such as pulse measurement can also be introduced for close monitoring.

3. Oxygen connector which allows delivering supplemental oxygen to the baby, if

necessary.

4. Wireless transfer of data regarding parameters from infant’s unit to the nurse monitoring

station can be very beneficial for the doctors and nurses in critical monitoring of each infant in

the nursery.

5. Webcam that helps the mother and the doctor to see the baby to make sure about his

health condition.

6. Low internal noise level (below the 60 dB limit during normal operation).

53

References

1. Journal of Medical Engineering & Technology, Volume 26, Number 2. March/April

2002.

2. Parameters Modelling and Fuzzy Control System of Neonatal Incubators. Available

from: http://ieeexplore.ieee.org//xpls/abs_all.jsp?arnumber=4250258

3. Neonatal intensive care unit. Available from:

http://en.wikipedia.org/wiki/Neonatal_intensive_care_unit.

4. Prasanga D., H.L., Yael Maguire, Aileen Wu, Design of a Passive Incubator for

Premature Infants in the Developing World. 2002, Massachusetts Institute Of

Technology, Cambridge, U.S.A.

5. Thermal Protection of newborn: a practical guide, World Health Organization, Maternal

or newborn health/ Safe motherhood unit, Division of reproductive health (Technical

Support) Geneva, (WHO/RHT/MSM/1997, 2nd Edition).

6. RobertaWeber, C. Neonatal Thermoregulation. Available from:

www.continuingeducation.com/ nursing/thermoreg/thermoreg.pdf.

7. Andrew Lyon, P.P. Thermo monitoring. Available from: www.draeger.com.

8. Available from: http://www.philadelphia.edu.jo/academics/kaubaidy/uploads/ref50.pdf.

9. Available: http://mech207.engr.scu.edu/SensorPresentations/Nibbelink%20-%20Capacitive%20Humidity%20Sensor%20Combined.pdf

10. http://www.noise.physx.u-

szeged.hu/DigitalMeasurements/Sensors/RelativeHumidity/HIH3610.pdf.

A-1

Appendix A The Code

Appendix A: C code for PIC16F877A sbit LCD_RS at RB4_bit; sbit LCD_EN at RB5_bit; sbit LCD_D4 at RB0_bit; sbit LCD_D5 at RB1_bit; sbit LCD_D6 at RB2_bit; sbit LCD_D7 at RB3_bit; sbit LCD_RS_Direction at TRISB4_bit; sbit LCD_EN_Direction at TRISB5_bit; sbit LCD_D4_Direction at TRISB0_bit; sbit LCD_D5_Direction at TRISB1_bit; sbit LCD_D6_Direction at TRISB2_bit; sbit LCD_D7_Direction at TRISB3_bit; float x; float volt; int air_temp; char air_temptxt[16]; float xs; float volts; int skin_temp; char skin_temptxt[16]; void measure(){ x=adc_read(0); volt=x*0.00489; air_temp=volt*100; inttostr(air_temp,air_temptxt); lcd_out(1,1,"air_temp="); lcd_out_cp(air_temptxt); delay_ms(2000); } void measures(){ xs=adc_read(1); volts=xs*0.00489; skin_temp=volts*100; inttostr(skin_temp,skin_temptxt); lcd_out(2,1,"skin_temp="); lcd_out_cp(skin_temptxt); delay_ms(2000); } int h;

A-2

int hm; char htxt[16]; void hu(){ h=adc_read(2); hm=h/40; inttostr(hm,htxt); lcd_out(2,1,"hum="); lcd_out_cp(htxt); delay_ms(2000); } int errorNOW; int PWMon ; int PWMoff ; int errorLAST ; void PID (){ errorNOW = 37 -air_temp; PWMon= PWMon + (0.49 * errorNOW ) + (0.98 * (errorNOW - (0 *

(errorNOW - errorLAST)))); errorLAST = errorNOW; if (PWMon > 190) PWMon = 190; //maximum on time if (PWMon < 10) PWMon =10; //minimum on time PWMoff = 200 - PWMon; } void main() { trisc=0; trisd=0; lcd_init(); lcd_cmd(_lcd_cursor_off); while(1){ PWM2_Start(); measure(); lcd_cmd(_lcd_clear); hu(); lcd_cmd(_lcd_clear); measures(); PID(); if (air_temp<37) { porta.b7=1 ; PWM2_Set_Duty(50);} else { porta.b7= 0 ; PWM2_Set_Duty(0); } if (air_temp>39) porta.b5=1 ; else porta.b5=0; if (hm<80) {portd= 0x0c; delay_ms(100); portd = 0x06; delay_ms(100); portd = 0x03; delay_ms(100); portd = 0x09; delay_ms(100); }

A-3

else portd=0x00; } }