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Microcontroller Based Heart Rate Meter
INTRODUCTION
1.1 OVERVIEW
Heart rate can be measured either by the ECG waveform or by the blood flow into the
finger (pulse method). The pulse method is simple and convenient. When blood flows
during the systolic stroke of the heart into the body parts, the finger gets its blood via the
radial artery on the arm. The blood flow into the finger can be sensed photo electrically.
To count the heart beats, here we use a small light source on one side of the finger
(thumb) and observe the change in light intensity on the other side. The blood flow
causes variation in light intensity reaching the light dependent resistor (LDR), which
results in change in signal strength due to change in the resistance of the LDR.
1.2 LITERATURE SURVEY
We have chosen MICROCONTROLLER BASED HEART RATE METER using
AT89C2051 as our minor project. We have practically seen heart rate meter in places
like hospital and Doctors clinics. From here we got the idea to make this project. For
making this project we have studied the microcontroller from the book An introduction
to microcontroller by Mazidi and Mazidi and the Basic electronics book which
was available in our institute RAD innovation where we had done training in
Embedded systems and the rest of the material we have searched from internet. Before
making this project we searched the various components to be required are available in
the market or not. The most important portion or we can say Heart of this project is
SENSOR without which it seems to be incomplete and could not work. The various
books and links which we have followed in our report are given below.
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1) The 8051 Microcontroller and Embedded Systems,(2nd Edition)by Muhammad Ali
Mazidi, All the basic fundamentals of programming of microcontroller 8051 were
studied from this book.
2) http://www.play-hookey.com/digital/experiments/seven_seg_led.html:-One common
requirement for many different digital devices is a visual numeric display. Individual
LEDs can of course display the binary states of a set of latches or flip-flops.
However, we're far more used to thinking and dealing with decimal numbers.
Therefore we have used a 7-segment for display purposes.
3) www.national.com/pf/LM/LM358.html:- The LM358 series consists of two
independent, high gain, internally frequency compensated operational amplifiers
which were designed specifically to operate from a single power supply over a wide
range of voltages.
1.3 OBJECTIVE
We the students of Chandigarh College of Engineering & Technology (CCET) are
going to be graduates in Electronics & Electrical Communication Engineering &
Technology, we should have the theoretical as well as practical knowledge of various
electronic components being used in various electronic circuits. The main objective of
making this project is to grab practical knowledge of electronic components. We have
done our minor project (Microcontroller based heart rate meter) in which we used
various electronic components like diodes, ICs etc. We have also practiced soldering,
disordering, testing of components & fabrication of components on PCB.
Another Objective behind choosing the project is to understand the use of
microcontroller in various electronic circuits.
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1.4 ORGANISATION OF REPORT
This report has been written in manner in which the development of the project has been
made. Certain modifications have been made in order to make the understanding simpler.
This report has been divided into various chapters. Brief description of these chapters is
discussed below:
Chapter 1
It deals with the general introduction of the project. It gives as overview to the project by
covering the literature that had been surveyed to get all relevant information. This chapter
ends with the objective of this project which also covers some practical aspects of the
projects.
Chapter 2
Thischapter deals with the description of various section of the project. Which type of
components were used in order achieve the desired target. How PCB is printed and make
sure its tracks are good enough for the conductivity.
Chapter 3
This chapter explains how the circuit is printed on a copper clad PCB using different
techniques and software thus helping to avoid any sort of short circuit in projects as there
are a lot of wire in general purpose PCBs.
Chapter 4
This chapter explains the hardware model of the project. This gives you an idea how
project will look like after completion and how will it work. How reading are observed
on it.
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MODULAR DESCRIPTION
1. Soldering
2. Power supply
3. Control Unit
4. Display Section
5. Circuit Description
6. PCB Designing
7. Testing
Fig 2.1 Block diagram of Heart Rate Meter
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2.1 Soldering
Soldering is a process in which two or more metal items are joined together by melting
and flowing a filler metal into the joint, the filler metal having a relatively low melting
point. Soft soldering is characterized by the melting point of the filler metal, which is
below 400 C (800 F). The filler metal used in the process is called solder.
2.1.1 Applications
One of the most frequent application of soldering is assembling electronic components toprinted circuit boards (PCBs). Another common application is making permanent but
reversible connections between copper pipes in plumbing systems. Joints in sheet metal
objects such as food cans, roof flashing, rain gutters and automobile radiators have also
historically been soldered, and occasionally still are. Jewelry components are assembled
and repaired by soldering. Small mechanical parts are often soldered as well. Soldering is
also used to join lead came and copper foil in stained glass work. Soldering can also be
used to effect a semi-permanent patch for a leak in a container cooking vessel.
2.1.2 Solders
Soldering filler materials are available in many different alloys for differing applications.
In electronics assembly, the eutectic alloy of 63% tin and 37% lead (or 60/40, which is
almost identical in performance to the eutectic) has been the alloy of choice. Other alloys
are used for plumbing, mechanical assembly, and other applications. Lead-free solders
are suggested anywhere children may come into contact (since children are likely to place
things into their mouths), or for outdoor use where rain and other precipitation may wash
the lead into the groundwater.
Common solder alloys are mixtures of tin and lead, respectively:
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63/37: melts at 183 C (361.4 F) (eutectic: the only mixture that melts at a point,
instead of over a range)
60/40: melts between 183190 C (361374 F)
50/50: melts between 185215 C (365419 F)
2.1.3 Flux
In high-temperature metal joining processes (welding, brazing and soldering), the
primary purpose of flux is to prevent oxidation of the base and filler materials. Tin-lead
solder, for example, attaches very well to copper, but poorly to the various oxides of
copper, which form quickly at soldering temperatures. Flux is a substance which is nearly
inert at room temperature, but which becomes strongly reducing at elevated temperatures,
preventing the formation of metal oxides. Secondarily, flux acts as a wetting agent in the
soldering process, reducing the surface tension of the molten solder and causing it to
better wet out the parts to be joined.
Fluxes currently available include water-soluble fluxes and 'no-clean' fluxes which are
mild enough to not require removal at all. Performance of the flux needs to be carefully
evaluated; a very mild 'no-clean' flux might be perfectly acceptable for production
equipment, but not give adequate performance for a poorly-controlled hand-solderingoperation.
2.1.4 Basic soldering techniques
Methods
Soldering operations can be performed with hand tools, one joint at a time, or en masse
on a production line. Hand soldering is typically performed with a soldering iron,
soldering gun, or a torch, or occasionally a hot-air pencil. Sheet metal work was
traditionally done with "soldering coppers" directly heated by a flame, with sufficient
stored heat in the mass of the soldering copper to complete a joint; torches or electrically-
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heated soldering irons are more convenient. All soldered joints require the same elements
of cleaning of the metal parts to be joined, fitting up the joint, heating the parts, applying
flux, applying the filler, removing heat and holding the assembly still until the filler metal
has completely solidified. Depending on the nature of flux material used, cleaning of the
joints may be required after they have cooled.
"Hard soldering" or "silver soldering" (performed with high-temperature solder
containing up to 40% silver) is also often a form of brazing, since it involves filler
materials with melting points in the vicinity of, or in excess of, 450 C. Although the
term "silver soldering" is used much more often than "silver brazing", it may be
technically incorrect depending on the exact melting point of the filler in use. In silver
soldering ("hard soldering"), the goal is generally to give a beautiful, structurally sound
joint, especially in the field of jewelry. Thus, the temperatures involved, and the usual use
of a torch rather than an iron, would seem to indicate that the process should be referred
to as "brazing" rather than "soldering", but the endurance of the "soldering" apellation
serves to indicate the arbitrary nature of the distinction (and the level of confusion)
between the two processes.
Induction soldering is a process which is similar to brazing. The source of heat in
induction soldering is induction heating by high-frequency AC current. Generally copper
coils are used for the induction heating. This induces currents in the part being soldered.
The coils are usually made of copper or a copper base alloy. The copper rings can be
made to fit the part needed to be soldered for precision in the work piece. Induction
soldering is a process in which a filler metal (solder) is placed between the faying
surfaces of (to be joined) metals.
The filler metal in this process is melted at a fairly low temperature. Fluxes are a
common use in induction soldering. This is a process which is particularly suitable for
soldering continuously. The process is usually done with coils that wrap around a
cylinder/pipe that needs to be soldered. Some metals are easier to solder than others.
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adjustable or fixed temperature
power source (electric or gas)
portable or bench use
I do not recommend soldering guns, as these have no temperature control and can get too
hot. This can result in damage to circuit boards, melt cable insulation, and even damage
connectors.
Wattage
It is important to realise that higher wattage does not necessarily mean hotter soldering
iron. Higher wattage irons just have more power available to cope with bigger joints. A
low wattage iron may not keep its temperature on a big joint, as it can loose heat faster
than it can reheat itself. Therefore, smaller joints such as circuit boards require a lesser
wattage iron - around 15-30 watts will be fine. Audio connectors need something bigger -
I recommend 40 watts at least.
Temperature
There are a lot of cheap, low watt irons with no temperature control available. Most of
these are fine for basic soldering, but if you are going to be doing a lot you may want to
consider a variable temperature soldering iron. Some of these simply have a boost button
on the handle, which is useful with larger joints, others have a thermostatic control so you
can vary the heat of the tip.
Figure Solder Iron
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If you have a temperature controlled iron you should start at about 315-345C (600-
650F). You may want to increase this however - I prefer about 700-750F. Use a
temperature that will allow you to complete a joint in 1 to 3 seconds.
Power
Most soldering irons are mains powered - either 110/230v AC, or benchtop soldering
stations which transform down to low voltage DC. Also available are battery and gas
powered. These are great for the toolbox, but you'll want a plug in one for your bench.
Gas soldering irons loose their heat in windy outside conditions more easily that a good
high wattage mains powered iron.
Figure Power Rating
Portability
Most cheaper soldering irons will need to plug into the mains. This is fine a lot of the
time, but if there is no mains socket around, you will need another solution. Gas and
battery soldering irons are the answer here. They are totally portable and can be taken and
used almost anywhere. They may not be as efficient at heating as a good high wattage
iron, but they can get you out of a lot of hassle at times.
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Figure
If you have a bench setup, you should consider using a soldering station. These usually
have a soldering iron and desoldering iron with heatproof stands, variable heat, and a
place for a cleaning pad. A good solder station will be reliable, accurate with itstemperature, and with a range of tips handy it can perform any soldering task you attempt
with it.
Solder
The most commonly used type of solder is rosin core. The rosin is flux, which cleans as
you solder. The other type of solder is acid core and unless you are experienced atsoldering, you should stick to rosin core solder. Acid core solder can be tricky, and better
avoided for the beginner.
Figure
Rosin core solder comes in three main types - 50/50, 60/40 and 63/37. These numbers
represent the amount of tin and lead are present in the solder,as shown below:
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Solder Type % Tin % Lead Melting Temp (F)
50/50 50 50 425
60/40 60 40 371
63/37 63 37 361
Any general purpose rosin core solder will be fine.
Soldering Accessories
Soldering Iron Tips
Try to use the right size tip whenever you can. Smaller wires and circuit boards require
small fine tips, and mic cable onto an XLR would need a larger tip. You can get pointed
tips, or flat tipped ones (sometimes called 'spade tips'). If you have a solder station with a
desolderer, you will also want a range of desoldering tips and cleaners.
Figure
Soldering Iron Stands
These are handy to use if you are doing several or more joints. It is a heat resistant cradle
for your iron to sit in, so you don't have to lie it down on the bench while it is hot. It
really is essential if you are planning to do a lot of bench soldering as it is only a matter
of time before you burn something (probably your elbow resting on the hot tip) if you
don't use one.
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figure
Clamps
I strongly recommend clamps of some sort. Trying to hold your soldering iron, the solder,
and the wire is tricky enough, but when you have to hold the connector as well it is
almost impossible. The are however, adjustable clamps that can be manipulated to hold
both the connector and the wire in place so you still have two free hands to apply the heatand the solder. These are cheap items, and I know mine have paid for themselves many
times over.
Magnifying glass
If you are doing work on PCBs (printed circuit boards) you may need to get a magnifying
glass. This will help you see the tracks on the PCB, and unless you have exceptional
sight, small chip resistors are pretty difficult to solder on well without a magnifying glass.
Once again, they are not expensive, and some clamps come with one that can mount on
the clamp stand.
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figure
Solder Wick
Solder wick is a mesh the you lie on a joint and heat. When it heats up it also melts thesolder which is drawn out of the joint. It is usually used for cleaning up solder from
tracks on a circuit board, but you will need a solder sucker to clean out the holes in the
circuit board. Place the wick on the solder you want to remove then put your soldering
iron on top of the wick. The wick will heat up, then the solder will melt and flow away
from the joint and into wick.
figure
Solder Suckers
If you don't have a solder station with desolderer, and you work on PCB's, you are going
to need one of these before too long. They are spring loaded and suck the melted solder
out of the joint. They are a bit tricky to use, as you have to melt the solder with your iron,
then quickly position the solder sucker over the melted solder and release the spring to
suck up the solder. I find solder wick to be easier to use and more effective.
figure
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Fume Extractors
Solder fumes are poisonous. A fume extractor will suck the fumes (smoke) into itself and
filter it. An absolute must for your health if you are setting up a soldering bench.
figure
2.1.7Soldering
This step can often be the easiest when soldering audio cables. You simply need to place
your soldering iron onto the contact to melt the solder. When the solder in the contact
melts, slide the wire into the contact. Remove the iron and hold the wire still while the
solder solidifies again. You will see the solder 'set' as it goes hard.
figure
This should all take around 1-3 seconds.
A good solder joint will be smooth and shiny.
If the joint is dull and crinkly, the wire probably moved during soldering.
If you have taken too long it will have solder spikes.
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figure
If it does not go so well, you may find the insulation has melted, or there is too much
stripped wire showing. If this is the case, you should desolder the joint and start again.
2.1.8 Tips and Tricks
1. Melted solder flows towards heat.
2. Most beginning solder tend to use too much solder.
3. Don't move the joint until the solder has cooled.
4. Keep your iron tip clean.
5. Use the proper type of iron and tip size.
2.1.9 Troubleshooting
If either of the parts you are soldering is dirty or greasy, the solder won't take (or 'stick')
to it. Desolder the joint and clean the parts before trying again. Another reason the solder
won't take is that it may not be the right sort of metal. For example you cannot solder
aluminium with lead/tin solder. If the joint has been moved during soldering, it may look
grainy or dull. It may also look like this if the joint was not heated properly while
soldering. If the joint was overheated the solder will have formed a spike and there will
be burnt flux residue.
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2.1.10 Power supply
Fig 2.2 Block diagram of a power supply
Fig 2.3 Requirements of a power supply
Above is the circuit of a basic unregulated dc power supply. A bridge rectifier D1 to D4
rectifies the ac from the transformer secondary, which may also be a block rectifier such as
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WO4 or even four individual diodes such as 1N4004 types. The principal advantage of a
bridge rectifier is you do not need a centre tap on the secondary of the transformer. A
further but significant advantage is that the ripple frequency at the output is twice the line
frequency (i.e. 50 Hz or 60 Hz) and makes filtering somewhat easier.
Resistors
Example: Circuit symbol:
Resistors restrict the flow of electric current, for example a resistor is placed in series
with a light-emitting diode (LED) to limit the current passing through the LED.
Resistors may be connected either way round. They are not damaged by heat when
soldering.
Resistor values - the resistor colour code
Resistance is measured in ohms, the symbol for ohm is an omega .
1 is quite small so resistor values are often given in k and M .
1 k = 1000 1 M = 1000000 .
Resistor values are normally shown using coloured bands.
Each colour represents a number as shown in the table.
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The Resistor
Colour Code
Colour Number
Black 0
Brown 1
Red 2
Orange 3
Yellow 4
Green 5
Blue 6
Violet 7
Grey 8
White 9
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Most resistors have 4 bands:
The first band gives the first digit.
The second band gives the second digit.
The third band indicates the number of zeros. The fourth band is used to shows the tolerance (precision) of the resistor, this
may be ignored for almost all circuits but further details are given below.
This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.
So its value is 270000 = 270 k . On circuit diagrams the is usually omitted and the
value is written 270K.
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Capacitors
The capacitor's function is to store electricity, or electrical energy.
The capacitor also functions as a filter, passing alternating current (AC), and blocking direct
current (DC).
This symbol is used to indicate a capacitor in a circuit diagram.
The capacitor is constructed with two electrode plates facing eachother, but separated by an
insulator.
When DC voltage is applied to the capacitor, an electric charge is stored on each electrode.
While the capacitor is charging up, current flows. The current will stop flowing when the
capacitor has fully charged.
figure
When a circuit tester, such as an analog meter set to measure resistance, is connected to a 10
microfarad (F) electrolytic capacitor, a current will flow, but only for a moment. You can
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confirm that the meter's needle moves off of zero, but returns to zero right away.
When you connect the meter's probes to the capacitor in reverse, you will note that current
once again flows for a moment. Once again, when the capacitor has fully charged, the
current stops flowing. So the capacitor can be used as a filter that blocks DC current. (A
"DC cut" filter.)
However, in the case of alternating current, the current will be allowed to pass. Alternating
current is similar to repeatedly switching the test meter's probes back and forth on the
capacitor. Current flows every time the probes are switched. The value of a capacitor (the
capacitance), is designated in units called the Farad(F).The capacitance of a capacitor is
generally very small, so units such as the microfarad (10-6F), nanofarad (10-9F), and
picofarad (10-12F) are used.
Recently, an new capacitor with very high capacitance has been developed. The Electric
Double Layer capacitor has capacitance designated in Farad units. These are known as
"Super Capacitors."
Sometimes, a three-digit code is used to indicate the value of a capacitor. There are two
ways in which the capacitance can be written. One uses letters and numbers, the other uses
only numbers. In either case, there are only three characters used. [10n] and [103] denote
the same value of capacitance. The method used differs depending on the capacitor supplier.
In the case that the value is displayed with the three-digit code, the 1st and 2nd digits from
the left show the 1st figure and the 2nd figure, and the 3rd digit is a multiplier which
determines how many zeros are to be added to the capacitance. Picofarad ( pF ) units are
written this way. For example, when the code is [103], it indicates 10 x 10 3, or 10,000pF =
10 nanofarad( nF ) = 0.01 microfarad( F ).
Diodes
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Example:
figure
Circuit symbol:
figure
Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol
shows the direction in which the current can flow. Diodes are the electrical version of a
valve and early diodes were actually called valves.
figure
Light Emitting Diodes (LEDs)
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Example:
Circuit symbol:
LEDs emit light when an electric current passes through them.
figure
LEDs must be connected the correct way round, the diagram may be labelled a or+ for
anode and kor- for cathode (yes, it really is k, not c, for cathode!). The cathode is the
short lead and there may be a slight flat on the body of round LEDs. If you can see inside
the LED the cathode is the larger electrode (but this is not an official identification
method). LEDs can be damaged by heat when soldering, but the risk is small unless you
are very slow. No special precautions are needed for soldering most LEDs.
2.1.2 ULN 2003:
DESCRIPTION:
The ULN2003 is a high voltage, high current darlington array containing seven open
collector darlington pairs with common emitters. Each channel rated at 500mA and can
withstand peak currents of 600mA. Suppression diodes are included for inductive load
driving and the inputs are pinned opposite the outputs to simplify board layout.
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The versions interface to ULN2003A 5V is TTL, CMOS. These versatile devices are
useful for driving a wide range of loads including solenoids, relays DC motors; LED
displays filament lamps, thermal print heads and high power buffers. The ULN2003 is
supplied in 16 pin plastic DIP packages with a copper lead frame to reduce thermal
resistance.
Fig 2.4 ULN2003
Features:-
Output Voltage up to 50 V
Input Voltage up to 30 V
Continuous Collector Current - 500 mA
Continuous Base Current - 25 mA
Operating Ambient Temperature Range - 20 to 85 C
Storage Temperature Range - 55 to 150 C
Junction Temperature 150 C
WORKING:
Voltage regulator limits the voltage that passes through it. Each regulator has a
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voltage rating; For example, the 7805 IC (these regulators are often considered to be ICs)
is a 5-volt voltage regulator. What that means is that no matter how many volts you put
into it, it will output only 5 volts. This means that you can connect a 9-volt battery, a
12-volt power supply, or virtually anything else that's over 5 volts, and have the 7805
give you a nice supply of 5 volts out. There are also 7812 (12-volt) and 7815 (15-volt)
three pin regulators in common use.
The pin-out for a three pin voltage regulator is as follows:
1. Voltage-in
2. Ground
3. Voltage out
For example, with a 9-volt battery, you'd connect the positive end to pin 1 and the
negative (or ground) end to pin 2. A 7805 would then give you +5 volts on pin 3.Voltage
regulators are simple and useful. There are only two important drawbacks to them: First,
the input voltage must be higher than the output voltage. For example, you cannot give a
7805 only 2 or 3 volts and expect it to give you 5 volts in return. Generally, the input
voltage must be at least 2 volts higher than the desired output voltage, so a 7805 would
require about 7 volts to work properly. The other problem: The excess voltage isdissipated as heat. At low voltages (such as using a 9-volt battery with a 7805), this is not
a problem. At higher voltages, however, it becomes a very real problem and you must
have some way of controlling the temperature so you don't melt your regulator. This is
why most voltage regulators have a metal plate with a hole in it; That plate is intended for
attaching a heat sink to-Do not confuse three-pin voltage regulators with a device known
as a TRIAC (short for triode AC switch). It is easy to associate them with each other,
since they look similar (both have three pins) and they both regulate power. However, the
78XX types of regulators are used for regulating DC current, while TRIACs are used for
AC current.
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2.2 Control Unit:
Microcontroller is used to control our hardware using programs which we make
according to our requirement. In our project the devices connected with the
Microcontroller are:a) Display unit
b) Heart Rate monitoring unit
c) Switches.
Output of IC is given to microcontroller and as per our requirement controller controls
the hardware according to heart rate and side by side it displays the heart beat in decimal
number system on Common anode 7-seg display.
2.3 Display Section
Common anode 7-segment display is used for display purpose. These are finding
widespread use in various applications. A seven-segment display, or seven-segment
indicator, is a form of electronic display device for displaying decimal numerals that is
an alternative to the more complex dot-matrix displays. Seven-segment displays are
widely used in digital clocks, electronic meters, and other electronic devices for
displaying numerical information. They are preferred because of ease of programming for
characters and numbers. We have used LT542 3 common anode 7-seg display.
2.4 Circuit Description
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Fig.2.5 Circuit Diagram
The setup uses a 6V electric bulb for light illumination of flesh on the thumb
behind the nail and the LDR as detector of change in the light intensity due to the flow of
blood. The photo-current is converted into voltage and amplified by operational amplifier
IC LM358 (IC1). The detected signal is given to the non-inverting input (pin 3) and its
output is fed to another non-inverting input (pin 5) for squaring and amplification. Output
pin 7 provides detected heartbeats to pin 12 of the microcontroller. Preset VR1 is used for
sensitivity and preset VR2 for trigger level settings.
Microcontroller IC AT89C2051 (IC2) is at the heart of the circuit. It is a 20-pin,8-bit
microcontroller with 2 kB of Flash programmable and erasable read-only memory
FEROM), 128 bytes of RAM, 15 input/output (l/O) lines, two 16-bit timer/counters, a
five-vector two-level interrupt architecture, a full duplex serial port, a precision analogue
comparator, on-chip oscillator and clock circuitry.
Port-1 pins P1.7 through P1.2, and port-3 pin P3.7 are connected to input pins 1
through 7 of IC ULN2003 (IC3), respectively. These pins are pulled-up with 10-kilo-ohm
resistor network RNW1. They drive all the segments of the 7-segment display with the
help of inverting buffer IC3.
The displays are selected through port pins P3.0, P3.1 and P3.2 of the
microcontroller (IC2). Port pins P3.0 down through P3.2 are connected to the base of
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transistors T3 through T1, respectively. Pin 6 of IC2 goes low to drive transistor T1 into
saturation and provide supply to the common-anode pin (either pin 3 or pin 8) of DIS1.
Similarly, transistors T2 and T3 drive common-anode pin 3 or 8 of 7-segment
displays DIS2 and DIS3, respectively. Only three 7-segment displays are used. IC2
provides segment-data and display-enable signals simultaneously in time-division-
multiplexed mode for displaying a particular number on the 7-segment display unit.
Segment- data and display-enable pulses for the display are refreshed every 5 ms. Thus
the display appears to be continuous/ even though it lights up one by one.
Switch S2 is used to manually reset the microcontroller, while the power on reset
signal for the microcontroller is derived from the combination of capacitor C4 and
resistor R8. An 11.0592MH2 crystal is used to generate the basic clock frequency for the
microcontroller. The circuit is powered by a 6V battery. Port pin P3.6 of the
microcontroller is internally available for software checking. This pin is actually the
output of the internal analogue comparator, which is available internally for comparing
the two analogue levels at pins 12 and 13. As pins 12 and 13 of IC2 can work as an
analogue comparator, these are used for sensing the rise and fall of the pulse waveform
and thereby evaluate the time between two peaks and hence the beat rate.
The output of the pulse pick-up preamplifier is fed to pin 12 of the microcontroller. Pin
13 of the microcontroller is connected to the preset for reference-level setting of the
comparator.
Thus voltages at pins 12 and 13 are always compared. The signal rise and the fall
at pin 12 are sensed by the program. The internal timer of the microcontroller is used to
find the time taken for one wavelength. This time is converted into the heart beat rate in
beats per minute by a pre-calculated look-up table. The program notes the time between
the high to low and low-to-high transitions of the wave. This time in microseconds is
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converted in steps of 4 ms for comparison with the values already stored in the look-up
table.
This number is used to find (from the look-up table) the heart rate in beats per
minute. The number so obtained is converted into a 3-digit number in binary-coded
decimal (BCD) form. The same is output to the 7-segment LED displays in a multiplexed
manner. The display shows the rate for a while and proceeds to another measurement.
Thus beat rates obtained from time to time are visible on the Display.
2.5 Programming of microcontroller
2.5.1 Beginning
a. Open Keil from the Start menu
b. The Figure below shows the basic names of the windows referred in this document
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2.5.2 Starting a new Assembler Project
a. Select New Project from the Project Menu
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b. Name the project Toggle.a51
c. Click on the Save Button.
d. The device window will be displayed.
e. Select the part you will be using to test with. For now we will use the Dallas
Semiconductor part DS89C420.
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f. Double Click on the Dallas Semiconductor.
g. Scroll down and select the DS89C420 Part
h. Click OK
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2.5.3 Creating Source File
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a. Click File Menu and select New.
b. A new window will open up in the Keil IDE.
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c. Copy the example to the Right into the new window. This file will toggle Ports 1
and 2 with a delay.
d. Click on File menu and select Save As
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e. Name the file Toggle.a51
f. Click the Save Button
2.5.4 Adding File to the Project
a. Expand Target 1 in the Tree Menu
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b. Click on Project and select Targets, Groups, Files
c. Click on Groups/Add Files tab
d. Under Available Groups select Source Group 1
e. Click Add Files to Group button
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f. Change file type to Asm Source file(*.a*;*.src)
g. Click on toggle.a51h. Click Add button
i. Click Close Button
j. Click
button
return to Target,
Groups, Files
dialog box
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k. Expand the Source Group 1 in the Tree menu to ensure that the file was added to the
project
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2.5.5 Creating HEX for the Part
a. Click on Target 1 in Tree menu
b. Click on Project Menu and select Options for Target 1
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c. Select Target Tab
d. Change Xtal (Mhz) from 50.0 to 11.0592
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e. Select Output Tab
f. Click on Create Hex File check box
g. Click OK Button
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h. Click on Project Menu and select Rebuild all Target Files
i. In the Build Window it should report 0 Errors (s), 0 Warnings
j. You are now ready to Program your Part
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PCB DESIGNING
Printed Circuit Board Etching:-
Etching is where the excess copper is removed to leave the individual tracks or traces as
they are sometimes called. Buckets, bubble tanks, and spray machines lots of different
ways to etch, but most firms currently use high pressure conveyerised spray equipment.
Spray etching is fast, ammoniacal etching solutions when sprayed can etch 55 microns of
copper a minute. Less than 40 seconds to etch a standard 1 oz, 35 micron circuit board.
Many different chemical solutions can be used to etch circuit boards. Ranging from slow
controlled speed etches used for surface preparation to the faster etches used for etching
the tracks. Some are best used in horizontal spray process equipment while others are
best used in tanks. Etchents for PTH work have to be selective and be non aggressive to
tin / tin lead plating, which is used as the etch resist. Copper etching is normally
exothermic, where high speed etching is carried out solution cooling is normally required.
This is normally done by placing titanium water cooling coils into the etchent. Almost all
etching solutions liberate toxic corrosive fumes, extraction is highly recommended. All
etchents are corrosive and toxic, mainly due to the high metal content. P.P.E. Personal
Protection Equipment must always be used, spent solutions should always be disposed of
properly and not down local drains, where they pollute local sewage works and rivers.
Ferric Chloride.
An old favorite, also very good at staining fingers, clothing, etc brown. Etch rate can be
very high but is dependant on solution movement over the surface of the board and
temperature. At 70C using Spray etching 1oz copper is removed in a little under a
minute, normal etching temperature is more likely to be 45C. When etching circuits if up
to 5% of HCL is added it, increases etch rate, helps to stop staining, and reduces the risk
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of the solution sludging. Ferric especially with extra HCL makes a very good stainless
steel etchent.
When Ferric crystals are mixed with water some free HCL produced through hydrolysis.
FeCl3 + 3H2O > Fe(OH)3 + 3HCL
The basic etching reaction takes place in 3 stages. First the ferric ion oxidizes copper to
cuprous chloride, which is then further oxidized to cupric chloride.
FeCl3 + Cu > FeCl2 + CuCl
FeCl3 + CuCl > FeCl2 + CuCl2
As the cupric chloride builds up at further reaction takes place,
CuCl2 + Cu > 2CuCl
The etch rate quickly falls off after about 17oz/gallon (100g/l of copper has been etched.
For a typical solution containing 5.3lb/gallon (530g/l) of ferric chloride.
PCB Etching
Since the introduction of laser printers making your own PCBs (Printed Circuit Boards)
has become fairly easy. The method described here assumes you want to make a PCB
from an electronics magazine PCB layout - so you can copy it with a copier - or you are
able to print your own PCB layouts from a PCB design package or have them available in
electronic format and you can print them with a laser printer.
I am using the described method below successfully since 1996. I was forced to find an
etching method to be used at home after the company I worked for dumped their
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prototype PCB production tools. A short version of the `greasy' etching method has been
published August 2000 in the newsletter `Vijgeblaadje' from the Dutch FIG (HCC Forth
gebruikersgroep).
PCB Layout
PCB Preparation
PCB UV Exposure
PCB Development
PCB Etching
Trouble shooting
More Examples
PCB Layout
The PCB layout is a mirrored positive one - black on white. Mirrored as viewed from the
silkscreen top (component) side. The PCB layout is printed 1:1 on paper by means of a
laser printer or copier machine. The laser printer or copier toner will not run out when it
gets wet or oily. The ink of an inkjet paper print does run out and inkjet printers are
therefore useless with the described method.
I have used several types of HP laser printers (LaserJet Series II, 5L, 4000 and 1100).
These printers work fine. It might be possible that the toner texture on the layout prints
from your used laser printer is not dense enough and passes too much light. However,
results might be improved by setting the toner density to maximum. Generally printer
driver properties allow to set the toner density.
PCB Preparation
The PCB layout paper is drenched with sunflower-seed oil. Sunflower-seed oil is
common available from your local grocery or wall market. Superfluous oil should be
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removed carefully with tissue paper. The sunflower-seed oil is used to make the white
part of the layout paper transparent for light.
If you prefer to use the PCB layout more than once let the drenched PCB layout paper
dry at least 48 hours. The layout paper should be carefully dried on forehand as much as
possible with tissue paper. Sunflower-seed oil is a `drying' oil. Exposed to the air over a
number of hours, the layout paper becomes rigid again. A kind of polymerization takes
place. You will get a lot less or no greasy fingers anymore afterwards.
Other mineral or vegetable oils might work as well to obtain light transparency.
However, they might not be `drying' oils. When I started experimenting, sunflower-seed
oil was the first oil I used and it worked fine. So I didn't try any other oils. Using water
does not work. The layout paper crumples up a bit.
Drench layout with sunflower-seed oil
Layout fully drenched
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Greasy layout
PCB UV Exposure
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The protective plastic layer is removed - peeled back - from the photosensitive PCB. The
toner side of the greased layout is placed on the copper of the PCB. Captured air-bubbles
are gently pressed away from underneath the layout. The PCB with the layout is now
covered with an appropriate sized windowpane and placed on a piece of plain polished
tile or marble. The tile or marble absorbs the heat coming from the UV bulb, which is
significant. Three to four minutes 300W bulb UV exposure from a distance of 30-40 cm
will do the photo process. Take care when finished and removing the PCB, it gets hot!
Home-built UV exposure box with 300W UV bulb, polished tile and
window pane
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PCB with partly peeled back protective plastic layer and `dried' la
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Place layout with toner side on copper of the PCB
Cover PCB and layout with window-pane
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Exposure
PCB Development
The PCB is developed with a 1% solution of sodium hydroxide NaOH. You can make
this solvent by adding 10 gram ofsodium hydroxide pellets to 1 liter of water and mix it
until everything is dissolved. Use a brush to speed up the developing and clean the PCB
during this process if the PCB is still greasy due to the applied sunflower-seed oil. The
developing process takes about 1 minute. It is sometimes difficult to guess when the
developing is finished. The traces should become clear and the exposed photosensitive
layer has dissolved (during the brushing you see darker `cloud' coming off the PCB
surface).
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Gently brush the PCB Almost developed, some traces are not
clear yet
PCB Etching
The developed PCB is etched with a 220 g/l solution of ammonium peroxydisulfate
(NH4)2S2O8 a.k.a. ammonium persulfate, 220 gram added to 1 liter of water and mix it
until everything is dissolved. Theoretically it should be possible to etch slightly more
than 60 grams of copper with 1 liter etching solution. Assume an 50% efficiency, about
30 grams of copper. With a thickness of 35 m copper on your PCB this covers a copper
area of about 1000 cm2. Unfortunately the efficiency of the etching solution degrades,
dissolved ammonium peroxydisulfate decomposes slowly. You better make just enough
etching solution you need to etch. For an etching tray of about 20 x 25 cm a minimum
practical amount is 200-250 ml solution. So you dissolve about 44 grams ammoniumperoxydisulfate into 200 ml or 55 grams into 250 ml water.
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Etching at ambient temperature might take over an hour, it is better to heat up the etching
solvent to about 35-45 degrees Celcius. The etching solution heating up could be done in
a magnetron, this takes about 40 to 60 seconds in a 850W magnetron depending on the
initial temperature of the etching solution (hint: first try this with just water to determine
the timer setting of the magnetron). The etching - rocking the etching tray - takes about
15-30 minutes at this temperature. If you have a heated, air-bubble circulated etching
fluid tank available, this is probably the fastest way to etch. At higher temperatures the
etching performance decreases. The etching process is an exothermic reaction, it
generates heat. Take care, cool your etching tray when necessary! You should minimize
the amount of copper to etch by creating copper area in your PCB layout as much as
possible. When starting the etching process and little to etch it is difficult to keep the
etching solution at 35-45 degrees Celcius. It helps to fill for example the kitchen sink
with warm water and rock the etching tray in the filled kitchen sink.
When the ammonium peroxydisulfate is dissolved it is a clear liquid. After an etching
procedure it gradually becomes blue and more deeper blue - the chemical reaction creates
dissolved copper sulfate CuSO4. Compared to other etching chemicals like hydrated iron
(III) chloride FeCl3.6H2O a.k.a. ferric chloride or the combination ofhydrochloric acid
HCL and hydrogen peroxide H2O2, using ammonium peroxydisulfate is a clean and safe
method. Did you ever spilled dissolved iron chloride on your clothes or your assumed
stainless steel kitchen sink? Do you really want to keep concentrated hydrochloric acid
and hydrogen peroxide at home? So, without doubt ammonium peroxydisulfate is the best
choice for etching at home. However, copper sulfate is a poisonous substance and should
be treated as chemical waste.
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Rock the etching tray The epoxy of the PCB becomes visible
Almost finishedThe etching solution colors slighty blue
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Finished
Trouble shooting
The above mentioned exposure timing should be determined experimentally. But even
when the exposure timing is correct PCB etching failures could happen because of low
quality or too old photosensitive PCB, the photosensitive layer has aged despite the
protective plastic layer. Other possible causes are too high concentration of development
solution causing the photosensitive part not exposed to light to be dissolved by the
sodium hydroxide solution as well. When developing too short not all of the copper of the
PCB will be etched. Developing might take some experimenting to get used to it and
know what to expect. Furthermore set the toner density of your laser printer driver always
to maximum.
More examples
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Exposure
Development
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Etching Finished
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HARDWARE IMPLEMENTATION AND TESTING
4.1 Construction and testing
An actual-size, single-side PCB for the microcontroller-based temperature meter and its
component layout is shown in Fig. 2.6. Wire the circuit on the PCB. Use bases for ICs
AT8951. Program the AT89S51 with suitable programmer and put into the IC base after
soldering all the components and checking +5V at each Vcc point of the circuit. Also
check continuity between respective connections using a multimeter. An actual- size,
single-side PCB for the microcontroller based heart rate meter and component layout is
shown in shown below:
Fig.2.6 Component layout for the PCB
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The arrangement for heart beat rate detection is shown in Fig. 2. Purchase a plastic T
tube is used to fit LEDs and the LDR sensor. The tube should be about 5cm long and
have a diameter of 1.5 cm. House the electric bulb into the left tube and the LDR (sol-
dered on a small PCB) into the right tube. Fit shields on both sides of the tube to maintain
darkness for better performance. Connect the 6V battery supply to the bulb and the LDR
to the circuit board via a shielded cable.
Fig 2.7: T Tube with finger inserted
For heart beat detection, which can be seen on a cathode ray oscilloscope (CRO), insert
your thumb with the nail facing the LDR inside the T-tube. Shaking the thumb will
change the level of signal from the previous value, and it will keep oscillating. Therefore
you have to hold the thumb firmly between the light bulb and the LDR while the
measurement is being made.
Hold the thumb steady and observe the heart beat rate on the display. The rate may vary
and may not be exactly steady. For instance, normally, the rate can vary between 60 and
100.
Since this is a beat-to-beat measurement and not an average over a time period of one
minute, variation is expected. However, when the reading shows high value at times, say,
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140, it may be due to unusual mains hum picked up by the transducer. To suppress it,
place a separate capacitor of 100 F across the 5V supply.
This is how the project will look like after completion and reading are observed on it:
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CONCLUSION
The minor project which is used to test the technical skills of the student is the only way
to get the technical knowledge. While working on this project we are in a position to
conclude some of the points. The project has been rigorously tested and is found to work
under all practically possible situations.
Our project Microcontroller Based Heart Rate Meter is just a kind of practice work
and although we gave our hundred percent but still many more advancements can be
realized in future. Some of which are:
1. The results of the project can be displayed on CRO.
2. The heart beat can be listened using headphones.
3. This can be implemented on a large scale with the running cost turing out to be
very less.
This project has made us familiar with actual situations being faced in the projects. We
know that it was difficult task to establish at various points but we managed each and
every thing collectively. Now we are familiar with microcontroller programming, and we
have worked on many components that have been used in this project which otherwise
are difficult to be studied from the text books.
Troubleshooting which is an inherent part of any engineering project has widened our
thinking capacity. Main problem that we found was in software development. Although
we also faced problem in hardware, when some of components like LDR sensor using
finger etc were not working, and when we were not able to implement the correct
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algorithm for the working of the project but guidance of many faculty members, our
friends and parents encouragement made this whole experience extremely wonderful.
REFERENCES
[1] Muhammad Ali Mazidi, Janice GillispieMazidi, Rolin D. McKinlay , The 8051
Microcontroller & Embedded Systems, Pearson Education Inc. 2nd Edition, 2008.
[2] The 8051 Microcontroller by Kenneth Ayala
[3] www.atmel.com/dyn/resources/prod_documents/doc2487.pdf
[4] http://pdf1.alldatasheet.com/datasheet-pdf/view/77085/MITEL/MT8870.html
[5] http://www.datasheetcatalog.org/datasheets/105/366825_DS.pdf
[6] http://www.futurlec.com
[7] Yashwant Kanetkar,Let Us C++. 5
th
Edition
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APPENDIX A
List of components
S.No. Code Name Value
1 R1,R4
R2,R3,R5-R8Resistor n/w
VR1-VR2
Resistors 330 ohms
10k10k
10k
2 C4,C5
C6
C2
C3C1
Capacitors 22Pf150pF
0.1F
10F2200F
3 IC1
IC2
IC3IC4
D1-D4
LED1,LED2
Microcontroller
OP-AMP
Regulator
Diode
LED
AT89S51
LM358
ULN2003LM7805
1N4007
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4 X1
Xtal
Transformer
Crystal
7-Segment
230V,500mA
11.0592MHz
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APPENDIX B :
DATASHEETS