RF BASED HEART RATE MEASUREMENT 2015

CHAPTER – 1

INTRODUCTION

Heart rate is the number of heartbeats per unit of time and is

usually expressed in beats per minute (bpm).

In adults, a normal heart beats about 60 to 100 times a minute

during resting condition. 

The resting heart rate is directly related to the health and fitness

of a person and hence is important to know.

feel a pulse with your fingers. The most common places are

wrist and neck.

You can count the number of pulses within a certain interval

(say 10 sec), and easily determine the heart rate in bpm.

This project describes a microcontroller based heart rate

measurement system that uses optical sensors to measure the

alteration in blood volume at fingertip with each heart beat.

The sensor unit consists of an infrared light-emitting-diode (IR

LED) and a photodiode, placed side by side as shown below.

The IR diode transmits an infrared light into the fingertip

(placed over the sensor unit), and the photodiode senses the

portion of the light that is reflected back.

The intensity of reflected light depends upon the blood volume

inside the fingertip.

1

RF BASED HEART RATE MEASUREMENT 2015

So, each heart beat slightly alters the amount of reflected

infrared light that can be detected by the photodiode.

With a proper signal conditioning, this little change in the

amplitude of the reflected light can be converted into a pulse.

CHAPTER – 2

BLOCK DIAGRAM

FIG:1 Block diagram of measurement device

Figure shows the block diagram of the proposed device. Basically, the

device consists of an infrared transmitter LED and an infrared sensor

photo-transistor.

2

Wireless Heart Beat Sensor

Sender (Patient Side)

Data Acquisition Unit – RF Tx

Microcontroller

RF Rx

Potential Divider

Relay Driver

If Abnormal Beat occurs, Medicine Alarm

RF Tx

RF BASED HEART RATE MEASUREMENT 2015

The transmitter-sensor pair is clipped on one of the fingers of the

subject. The LED emits infrared light to the finger of the subject.

The photo-transistor detects this light beam and measures the change

of blood volume through the finger artery.

This signal, which is in the form of pulses is then amplified and

filtered suitably and is fed to a low-cost microcontroller for analysis

and display.

The microcontroller counts the number of pulses over a fixed time

interval and thus obtains the heart rate of the subject.

Several such readings are obtained over a known period of time and

the results are averaged to give a more accurate reading of the heart

rate.

The calculated heart rate is displayed on an LCD in beats-per-minute

in the following format:

Rate = nnn bpm

Where nnn is an integer between 1 and 999.

The circuit diagram of the measurement device is shown in Figure 3.

The circuit basically consists of 2 operational amplifiers, a low-pass

filter, a microcontroller, and an LCD.

The first amplifier is set for a gain of just over 100, while the gain of

the second amplifier is around 560.

During the laboratory trials it was found necessary to use a low pass

filter in the circuit to filter out any unwanted high frequency noise

from nearby equipment.

The cut-off frequency of the filter was chosen as 2Hz. Figure 4 shows

the frequency and phase responses of the amplifier together with the

filter.

3

RF BASED HEART RATE MEASUREMENT 2015

The output time response of the amplifier and filter circuit is shown in

Figure which consists of pulses.

An LED, connected to the output of the operational amplifiers flashes

as the pulses are received and amplified by the circuit.

The output of the amplifier and filter circuit was fed to one of the

digital inputs of a PIC16F84 type microcontroller

In order to reduce the cost of the circuit the microcontroller is

operated from a 4MHz resonator.

The microcontroller output ports drive the LCD as shown in Figure .

The circuit operates when a push-button switch connected to RB1 port

of the microcontroller is pressed.

4

RF BASED HEART RATE MEASUREMENT 2015

CHAPTER-3

CIRCUIT DIAGRAM

FIG:2 CIRCUIT DIAGRAM

5

RF BASED HEART RATE MEASUREMENT 2015

The use of this device is very simple. Turn the power on, and you will

see all zeros on display for few seconds.

Wait till the display goes off. Now place your forefinger tip on the

sensor assembly, and press the start button. Just relaxed and don’t

move your finger.

You will see the LED blinking with heart beats, and after 10 sec, the

result will be displayed.

Figure shows for the output of this device which is calculating using

butter worth low pass filter and after calculating finally below result

can be done through this circuit.

FIG:3

6

RF BASED HEART RATE MEASUREMENT 2015

I am adding these paragraphs to provide further detail on the sensor

and signal conditioning part of this project.

The harder part in this project is the signal conditioning circuit that

uses active low pass filters using Op Amps to boost the weak reflected

light signal detected by the photo diode.

The IR transmitting diode and the photo diode are placed closely but

any direct crosstalk between the two is avoided.

Look at the following pictures to see how I have blocked the direct

infrared light from falling into the adjacent photo diode. Besides,

surrounding the sensor with an opaque material makes the sensor

system more robust to changing ambient light condition.

I have used separate IR diode and photo diode, but you can buy

reflective optical sensor systems that have both the diodes assembled

together.

The 150 Ω resistance in series with the IR diode is to limit the current

and hence the intensity of the transmitted infrared light.

The intensity of IR light should not be too high otherwise the reflected

light will be sufficient enough to saturate the photo detecting diode all

the time and no signal will exist.

The value of this current limiting resistor could be different for

different IR diodes, depending upon their specifications

Here’s my practical test circuit that I used to find the appropriate value

of theFirst I used a 68 Ω resistor with a 470 Ω potentiometer in series

with the IR diode.

7

RF BASED HEART RATE MEASUREMENT 2015

Placing a fingertip over the sensor assembly, I slowly varied the

potentiometer till I found the output LED blinking with heartbeat.

Then I measured the equivalent resistance R and replaced the 68 Ω and

the potentiometer with a single resistor closest to R.

But you can also keep the potentiometer in your circuit so that you can

always adjust it when needed.

You should keep your fingertip very still over the sensor while testing.

Once you see the pulses at the output of the signal conditioning circuit,

you can feed them to a microcontroller to count and display.

8

RF BASED HEART RATE MEASUREMENT 2015

CHAPTER – 4

PROGRAMING CODE

PIC16F628A at 4.0 MHz external clock, MCLR enabled*/Sbit IR TX at RA3_bit;Sbit DD0_Set at RA2_bit;Sbit DD1_Set at RA1_bit;Sbit DD2_Set at RA0_bit;Sbit start at RB7_bit;Unsigned short j, DD0, DD1, DD2, DD3;Unsigned short pulse rate, pulse count;Unsigned inti;//-------------- Function to Return mask for common anode 7-seg. displayUnsigned short mask (unsigned short num)

{ Switch (num) { Case 0: return 0xC0; Case 1: return 0xF9; Case 2: return 0xA4; Case 3: return 0xB0; Case 4: return 0x99; Case 5: return 0x92; Case 6: return 0x82; Case 7: return 0xF8; Case 8: return 0x80; Case 9: return 0x90; } //case end}

Void delay debounce (){ Delay ms (300);}

Void delay refresh ()

9

RF BASED HEART RATE MEASUREMENT 2015

{ Delay ms (5);}Void count pulse (){ IR TX = 1; Delay debounce (); Delay debounce (); TMR0=0; Delay ms (10000); // Delay 10 Sec IR_Tx = 0; Pulse count = TMR0; Pulse rate = pulse count*4;}Void display (){ DD0 = pulserate%10; DD0 = mask (DD0); DD1 = (pulse rate/10) %10; DD1 = mask (DD1); DD2 = pulse rate/100; DD2 = mask (DD2); For (i = 0; i<=180*j; i++) { DD0_Set = 0; DD1_Set = 1; DD2_Set = 1; PORTB = DD0; Delay _ refresh (); DD0_Set = 1; DD1_Set = 0; DD2_Set = 1; PORTB = DD1; delay_refresh (); DD0_Set = 1; DD1_Set = 1; DD2_Set = 0; PORTB = DD2; delay_refresh (); } DD2_Set = 1;}

10

RF BASED HEART RATE MEASUREMENT 2015

Void main () { CMCON = 0x07; // Disable Comparators TRISA = 0b00110000; // RA4/T0CKI input, RA5 is I/P only TRISB = 0b10000000; // RB7 input, rest output OPTION_REG = 0b00101000; // Prescaler (1:1), TOCS =1 for counter mode Pulse rate = 0; j = 1; Display (); Do { If (! start){ delay_debounce (); Count pulse (); j= 3; Display (); } } while (1); // Infinite loop}

11

RF BASED HEART RATE MEASUREMENT 2015

CHAPTER –5

COMPONENTS

5.1 COMPONENTS LIST:-

Micro controller

Seven segments led

Crystal

Resistors

Capacitors

Transistors

Photo diode

IR SENSOR

7805 IC

Switches

LED

Bettery

12

RF BASED HEART RATE MEASUREMENT 2015

5.2 Description of seven segment:-

Here are two types of LED 7-segment displays: common cathode (CC)

and common anode (CA).

The difference between the two displays is the common cathode has

all the cathodes of the 7-segments connected directly together and the

common anode has all the anodes of the 7-segments connected

together.

Shown below is a common anode seven segment.

FIG:4 As shown above all the anode segments are connected together.

13

RF BASED HEART RATE MEASUREMENT 2015

When working with a CA seven segment display, power must be

applied externally to the anode connection that is common to all the

segments.

Then by applying a ground to a particular segment connection (a-g),

the appropriate segment will light up.

An additional resistor must be added to the circuit to limit the amount

of current flowing thru each LED segment.

FIG:5

The above diagram shows the instance when power is applied to the

CA connection and segments b & c are grounded causing these two

segments to light up.

14

RF BASED HEART RATE MEASUREMENT 2015

A typical pin out for a seven segment common anode display is shown

below.

FIG:6

15

RF BASED HEART RATE MEASUREMENT 2015

5.3 Detail of IC 7805 :-

5.3.1 Features:-

Output Current up to 1A

Output Voltages of 5v

Thermal Overload Protection

Short Circuit Protection

5.3.2 Description :-

The MC78XX/LM78XX/MC78XXA series of three terminal positive

regulators are available in theTO-220/D-PAK package and with

several fixed output voltages, making them useful in a wide range of

applications.

Each type employs internal current limiting , thermal shut down and

safe operating area protection, making it essentially in destructible.

If adequate heat sinking is provided, they can deliver over 1A output

current.

Although designed primarily as fixed voltage regulator, these devices

can be used with external components to obtain adjustable voltages

currents.

16

RF BASED HEART RATE MEASUREMENT 2015

FIG:7

5.4 Detail of IC LM 358 :-

5.4.1 Features:-

Internally Frequency Compensated for Unity Gain

Large DC Voltage Gain: 100dB

Wide Power Supply Range: 3V~32V

Input Common Mode Voltage Range Includes Ground

Large Output Voltage Swing: 0V DC to Vcc -1.5V DC

Power Drain Suitable for Battery Operation.

5.4.2 Pin Diagram:-

17

RF BASED HEART RATE MEASUREMENT 2015

FIG:9

5.4.3 Description:-

The, LM358 consist 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 voltage.

Operation from split power supplies is also possible and the low

power supply current drain is independent of the magnitude of the

power supply voltage.

Application areas include transducer amplifier, DC gain blocks and all

the conventional OP-AMP circuits which now can be easily

implemented in single power supply systems.

18

RF BASED HEART RATE MEASUREMENT 2015

5.5 Detail of IR sensor:-

An infrared sensor is a device that emits and or receives infrared

waves in the form of heat.

An infrared wave is a type of electromagnetic wave that all objects

emit due to thermal waste.

While most infrared sensors transmit and receive infrared waves,

some can only receive them.

These types of infrared sensors are known as Passive infrared Sensors

(PIR sensors) and are usually in the form of motion detectors.

19

RF BASED HEART RATE MEASUREMENT 2015

FIG:9

5.5.1How Infrared Sensors Work :-

Though infrared sensors can be designed to perform different

functions, all infrared sensors are dependent on pyroelectric materials,

whether natural or artificial.

A pyro electric material produces an electrical voltage whenever it is

heated or cooled.

20

RF BASED HEART RATE MEASUREMENT 2015

Most infrared sensors are coated with either parabolic mirrors or

Fresnel lenses in order to retrieve infrared waves from an entire room

or area.

As infrared waves reach the sensor from different areas, they cause the

sensor to generate a voltage in different waves, which can be used to

trigger an alarm or activate another type of system.

5.5.2Applications:-

Infrared sensors can be used in many applications. Such applications

usually involve measuring distance, detecting motion, or transferring

data.

The most common infrared sensor types are found in televisions and

motion detectors.

21

RF BASED HEART RATE MEASUREMENT 2015

Infrared remotes activate televisions, while motion activates motion

detectors. Heat-seeking missiles also use infrared sensors to detect

their target.

In the case of a motion detector, an infrared sensor can be calibrated to

set an alarm off only if the object weighs over a certain amount,

usually forty to eighty pounds.

This is known as “desensitivization” and prevents false alarms due to

small pets, flashes of light, or natural temperature changes.

5.5.3 Advantages:-

Infrared sensors are advantageous because they use an electromagnetic

wave that is invisible to human eyes, harmless to users, and that all

objects naturally emit.

They are relatively inexpensive and provide the most efficient means

of detecting objects, especially while they are moving. Infrared

sensors are simple in design and are reliable for detection.

Additionally, infrared sensors are small and can be installed into

virtually any electronic device.

An example of this is an infrared remote, although they generally only

emit infrared waves, not receive them.

The signal conditioning circuit consists of two identical active low

pass filters with a cut-off frequency of about 2.5 Hz.

This means the maximum measurable heart rate is about 150 bpm.

22

RF BASED HEART RATE MEASUREMENT 2015

The operational amplifier IC used in this circuit is LM 358, a dual Op

Amp chip from Microchip.

It operates at a single power supply and provides rail-to-rail output

swing.

The filtering is necessary to block any higher frequency noises present

in the signal.

The gain of each filter stage is set to 101, giving the total

amplification of about 10000.

A 1 uF capacitor at the input of each stage is required to block the dc

component in the signal.

The equations for calculating gain and cut-off frequency of the active

low pass filter are shown in the circuit diagram.

The two stage amplifier/filter provides sufficient gain to boost the

weak signal coming from the photo sensor unit and convert it into a

pulse.

An LED connected at the output blinks every time a heart beat is

detected.

The output from the signal conditioner goes to the T0CKI input of

PIC16F628A.

23

RF BASED HEART RATE MEASUREMENT 2015

FIG:10

The control and display part of the circuit is shown below. The display

unit comprises of a 3-digit, common anode, seven segment module

that is driven using multiplexing technique.

The segments a-g are driven through PORTB pins RB0-RB6,

respectively.

The unit’s, ten’s and hundred’s digits are multiplexed with RA2, RA1,

and RA0 port pins.

A tact switch input is connected to RB7 pin. This is to start the heart

rate measurement.

Once the start button is pressed, the microcontroller activates the IR

transmission in the sensor unit for 15 sec.

During this interval, the number of pulses arriving at the T0CKI input

is counted.

The actual heart rate would be 4 times the count value, and the

resolution of measurement would be 4. 

You can see the IR transmission is controlled through RA3 pin of

PIC16F628A.

The microcontroller runs at 4.0 MHz using an external crystal.

A regulated +5V power supply is derived from an external 9 V battery

using an LM7805 regulator IC.

24

RF BASED HEART RATE MEASUREMENT 2015

5.6 TRANSISTORS:-

The transistor BC 547 is used in this project. it is used for switching and balancing of seven segment led.

5.6.1 Features:-

Low current.

Low voltage.

The design of a transistor allows it to function as an amplifier or a

switch. This is accomplished by using a small amount of electricity to

control a gate on a much larger supply of electricity, much like turning

a valve to control a supply of water.

Transistors are composed of three parts – a base, a collector, and an

emitter. The base is the gate controller device for the larger electrical

supply. The collector is the larger electrical supply, and the emitter is

the outlet for that supply.

25

RF BASED HEART RATE MEASUREMENT 2015

By sending varying levels of current from the base, the amount of

current flowing through the gate from the collector may be regulated.

In this way, a very small amount of current may be used to control a

large amount of current, as in an amplifier.

The same process is used to create the binary code for the digital

processors but in this case a voltage threshold of five volts is needed

to open the collector gate. In this way, the transistor is being used as a

switch with a binary function: five volts – ON, less than five volts –

OFF.

5.6.2 TYPES OF TRANSISTOR:-

There are two types of standard transistors, NPN and PNP, with

different circuit symbols.

26

RF BASED HEART RATE MEASUREMENT 2015

FIG.11 NPN & PNP TRANSISTOR

A junction transistor consists of a thin piece of one type of

semiconductor material between two thicker layers of the opposite

type. For example, if the middle layer is p-type, the outside layers

must be n-type. Such a transistor is an NPN transistor.

One of the outside layers is called the emitter, and the other is known

as the collector. The middle layer is the base. The places where the

emitter joins the base and the base joins the collector are called

junctions.

The layers of an NPN transistor must have the proper voltage

connected across them. The voltage of the base must be more positive

than that of the emitter. The voltage of the collector, in turn, must be

more positive than that of the base.

The voltages are supplied by a battery or some other source of direct

current. The emitter supplies electrons. The base pulls these electrons

from the emitter because it has a more positive voltage than does the

emitter. This movement of electrons creates a flow of electricity

through the transistor.

The current passes from the emitter to the collector through the base.

Changes in the voltage connected to the base modify the flow of the

current by changing the number of electrons in the base. In this way,

small changes in the base voltage can cause large changes in the

current flowing out of the collector.

Manufacturers also make PNP junction transistors. In these devices,

the emitter and collector are both a p-type semiconductor material

and the base is n-type. A PNP junction transistor works on the same

principle as an NPN transistor.

27

RF BASED HEART RATE MEASUREMENT 2015

But it differs in one respect. The main flow of current in a PNP

transistor is controlled by altering the number of holes rather than the

number of electrons in the base. Also, this type of transistor works

properly only if the negative and positive connections to it are the

reverse of those of the NPN transistor.

28

RF BASED HEART RATE MEASUREMENT 2015

5.6.3 Darlington pair:-

FIG.12 DARLINGTON PAIR

This is two transistors connected together so that the amplified

current from the first is amplified further by the second transistor. This

gives the Darlington pair a very high current gain such as 10000.

Darlington pairs are sold as complete packages containing the two

transistors. They have three leads (B, C and E) which are equivalent

to the leads of a standard individual transistor.

5.6.4 Function:-

Transistors amplify current, for example they can be

used to amplify the small output current from a logic

IC so that it can operate a lamp, relay or other high

current device.

In many circuits a resistor is used to convert the changing current to a

changing voltage, so the transistor is being used to amplify voltage.

29

RF BASED HEART RATE MEASUREMENT 2015

The amount of current amplification is called the current gain, symbol

hFE.

A transistor may be used as a switch (either fully on with maximum

current, or fully off with no current) and as an amplifier (always

partly on).

5.6.5 Characteristics:-

30

RF BASED HEART RATE MEASUREMENT 2015

FIG:13 Dc current gain for typical value

31

RF BASED HEART RATE MEASUREMENT 2015

5.7 RESISTORS:-

FIG:14 RESISTOR

Resistors are considered to be the most used and the most important

component of all the electronic circuits. Take a look at the working,

types and also use of resistors in the field of electronics.

We know that the basic idea of any electronic circuit is the flow of

electricity. This also is further categorized into two – conductors and

insulators. Conductors allow the flow of electrons, while insulators do

not. But the amount of electricity that we want to pass through them

depends on the resistors.

32

RF BASED HEART RATE MEASUREMENT 2015

If a high voltage is passed through a conductor such as a metal, the

whole voltage passes through it.

If resistors are introduced, the amount of voltage and current can be

controlled.

The resistor is a passive component that is opposed to the electrical

current dissipating heat, the higher the resistor value, the lower the

current.

This effect is called electrical resistance, while the component resistor

is popularly known as resistance.

Resistance: is the property of a material to oppose the flow of electric

current and dissipate power. Unit: Ω (Ohm).

5.7.1 Symbol of Resistor:

Resistor is a 2 terminal passive device. The symbol is given below.

Symbol of resistor

5.7.2 Utilities of resistors:-

Limiting the current that flows in a circuit

Control the loading speed of a capacitor.

33

RF BASED HEART RATE MEASUREMENT 2015

To make current and voltage dividers.

Transforming energy into heat.

When applying a voltage in a resistor, it creates a current that

passes through it.

The relation between the voltage and the current defines the

electrical resistance:

It’s a physical law and, therefore, will always work for any type of

electronic circuit.

Most of the resistors used in electronic obey this law, omic

resistors. Among them are the cluster of carbon resistors, metal

film and carbon film.

Practicing – Leds and resistors

To light up a LED we need to limit the current that flows through

it, for that we use resistors. If the current that flows through it is

higher than recommended, there is a high risk of burning the

component.

5.7.3 COLOUR CODING :

The value of the resistance is found out by colour coding. The

resistors have a band of colours shown in their outer covering. Here

are the steps to determine the value of the resistor.

34

RF BASED HEART RATE MEASUREMENT 2015

All resistors have three bands of colours, followed by a space and then

a fourth band of colour. The fourth band of colour will be brown, red,

gold or silver.

To read the colours turn it to the position such as the three consecutive

colours come on the left and then the space and the rest of the

colours. T

the first two colours from the left indicate the first two digits of the

value. The third colour represents the digital multiplier. That is, it

indicates how much you have to multiply the first two numbers with.

Thus if you have a resistance with the first three colours being brown,

black and red, the value of resistance is 10*100 = 1000 ohms or 1K.

The last band, after the space indicates the tolerance of the resistor

This indicates the range of accuracy of the resistor. Thus, along with

the three colours above, if the fourth colour is gold, it means you have

a tolerance between +/-5%. Thus the actual value of the resistance can

be between 950 Ohms and 1K. There can also be resistors with five

colours.

If so, the first three represents the digits, the fourth will be the

multiplier and the fifth will be the percentage of tolerance. This

indicates that a more precise value of the resistor used can be obtained

from a 5-colour resistor.

Take a look at the colours and their associated numbers given below.

35

RF BASED HEART RATE MEASUREMENT 2015

FIG.15 COLOUR CODING OF RESISTORS

The application of variable resistance is also helpful to us.

Our TV’s, radios, loud speakers and so on work on this

principle.

36

RF BASED HEART RATE MEASUREMENT 2015

5.8 CAPACITOR:-

FIG.16 CAPACITOR

Capacitors are components that are used to store an electrical charge

and are used in timer circuits. A capacitor may be used with a resistor

to produce a timer.

Sometimes capacitors are used to smooth a current in a circuit as they

can prevent false triggering of other components such as relays.

When power is supplied to a circuit that includes a capacitor the

capacitor charges up. When power is turned off the capacitor discharges

its electrical charge slowly.

A capacitor is a passive two terminal component which stores electric

charge. A capacitor is composed of two conductors separated

by an insulating material called a DIELECTRIC.

This component consists of two conductors which are separated by a

dielectric medium. The potential difference when applied across the

conductors polarizes the dipole ions to store the charge in the dielectric

medium.

37

RF BASED HEART RATE MEASUREMENT 2015

The circuit symbol of a capacitor is shown below:

The capacitance or the potential storage by the capacitor is measured

in Farads which is symbolized as ‘F’. One Farad is the capacitance

when one coulomb of electric charge is stored in the conductor on the

application of one volt potential difference.

The charge stored in a capacitor is given by 

Q = CV

Where Q - charge stored by the capacitor

o C - Capacitance value of the capacitor

o V - Voltage applied across the capacitor

The capacitor can be fixed or variable. They are categorized into two

groups, polarized or non-polarized. Electrolytic capacitors are

polarized. Most of the low value capacitors are non-polarized. The

symbol of capacitors from each group is shown below:

38

RF BASED HEART RATE MEASUREMENT 2015

FIG.22TYPES OF CAPACITOR

Capacitors are widely used in a variety of applications of

electronic circuits such as

store charges such as in a camera flash circuit

smoothing the output of power supply circuits

Coupling of two stages of a circuit.

Filter networks (tone control of an audio system).

Delay applications.

tuning radios to particular frequencies

Phase alteration.

39

RF BASED HEART RATE MEASUREMENT 2015

5.9 Light-emitting diode:-

5.9.1 General Decription:-

Light-emitting diode

Red, pure green and blue LEDs of the 5mm diffused type

40

RF BASED HEART RATE MEASUREMENT 2015

Type Passive, optoelectronic

Working principle Electroluminescence

Invented Nick Holonyak Jr. (1962)

Electronic symbol

Parts of an LED. Although not directly labeled, the flat bottom surfaces of the anvil and post embedded inside the epoxy act as anchors, to prevent the conductors from being forcefully pulled out from mechanical strain or vibration.

41

RF BASED HEART RATE MEASUREMENT 2015

LED retrofit "bulb" with aluminium heatsink, a diffusing dome and E27 base, using a build in powersupply working onmains voltage

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting. Introduced as a practical electronic component in 1962,[2]early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.

When a light-emitting diode is forward biased (switched on), electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. LEDs are often small in area (less than 1 mm2), and integrated optical components may be used to shape its radiation pattern.[3] LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, and faster switching. LEDs powerful enough for room lighting are relatively expensive and require more precise current and heat management than compact fluorescent lamp sources of comparable output.

Light-emitting diodes are used in applications as diverse as replacements for aviation lighting,automotive lighting (particularly brake lamps, turn signals and indicators) as well as in traffic signals. LEDs have allowed new text, video displays, and sensors to be developed, while their high switching rates are also useful in advanced communications technology.

 InfraredLEDs are also used in the remote control units of many commercial products including televisions, DVD players, and other domestic appliances.

Discoveries and early devices5.9.2 Practical use:-

The first commercial LEDs were commonly used as replacements for incandescent and neon indicator lamps, and in seven-segment displays,[19] first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs,

42

RF BASED HEART RATE MEASUREMENT 2015

radios, telephones, calculators, and even watches (see list of signal uses).

These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Readouts in calculators were so small that plastic lenses were built over each digit to make them legible. Later, other colors grew widely available and also appeared in appliances and equipment.

As LED materials technology grew more advanced, light output rose, while maintaining efficiency and reliability at acceptable levels.

development of the high power white light LED led to use for illumination, which is fast replacing incandescent and fluorescent lighting.[20][21] (see list of illumination applications).

Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1 packages, but with rising power output, it has grown increasingly necessary to shed excess heat to maintain reliability,[22] so more complex packages have been adapted for efficient heat dissipation. Packages for state-of-the-art high power LEDs bear little resemblance to early LEDs.

5.9.3 Continuing development:-

The first high-brightness blue LED was demonstrated by Shuji Nakamura of Nichia Corporation and was based on InGaNborrowing on critical developments in GaNnucleation on sapphire substrates and the demonstration of p-type doping of GaN which were developed by Isamu Akasaki and H.

Amano in Nagoya. In 1995, Alberto Barbieri at the Cardiff University Laboratory (GB) investigated the efficiency and reliability of high-brightness LEDs and demonstrated a very impressive result by using a transparent contact made of indium tin oxide (ITO) on (AlGaInP/GaAs) LED.

The existence of blue LEDs and high efficiency LEDs quickly led to the development of the first white LED, which employed

43

RF BASED HEART RATE MEASUREMENT 2015

a Y3Al5O12:Ce, or "YAG", phosphor coating to mix yellow (down-converted) light with blue to produce light that appears white

Nakamura was awarded the 2006 Millennium Technology Prize for his invention.[23]The development of LED technology has caused their efficiency and light output to rise exponentially, with a doubling occurring about every 36 months since the 1960s, in a way similar to Moore's law.

The advances are generally attributed to the parallel development of other semiconductor technologies and advances in optics and material science. This trend is normally called Haitz's Law after Dr. Roland Haitz. [24]

In February 2008, a luminous efficacy of 300 lumens of visible light per watt of radiation (not per electrical watt) and warm-light emission was achieved by using nanocrystals.[25]

In 2009, a process for growing gallium nitride (GaN) LEDs on silicon has been reported. Epitaxy costs could be reduced by up to 90% using six-inch silicon wafers instead of two-inch sapphire wafers.[26]

The LED consists of a chip of semiconducting material doped with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releasesenergy in the form of a photon.

The wavelength of the light emitted, and thus its color depends on the band gap energy of the materials forming the p-n junction.

Insilicon or germanium diodes, the electrons and holes recombine by a non-radiative transitionwhich produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to near-infrared, visible or near-ultraviolet light.

LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have enabled making devices with ever-shorter wavelengths, emitting light in a variety of colors.

44

RF BASED HEART RATE MEASUREMENT 2015

LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.

Most materials used for LED production have very high refractive indices. This means that much light will be reflected back into the material at the material/air surface interface. Thus, light extraction in LEDs is an important aspect of LED production, subject to much research and development.

5.9.4 Refractive index:-

Generally a flat-surfaced uncoated LED semiconductor chip will only emit light perpendicular to the semiconductor's surface, and a few degrees to the side, in a cone shape referred to as the light cone, cone of light,[29]or the escape cone.[27]

 The maximum angle of incidence is referred to as the critical angle. When this angle is exceeded photons no longer penetrate the semiconductor, but are instead reflected both internally inside the semiconductor crystal, and externally off the surface of the crystal as if it were a mirror.[27]

Internal reflections can escape through other crystalline faces, if the incidence angle is low enough and the crystal is sufficiently transparent to not re-absorb the photon emission.

But for a simple square LED with 90-degree angled surfaces on all sides, the faces all act as equal angle mirrors. In this case the light can not escape and is lost as waste heat in the crystal.[27]

A convoluted chip surface with angled facetssimilar to a jewel or fresnel lens can increase light output by allowing light to be emitted perpendicular to the chip surface while far to the sides of the photon emission point.[30]

The ideal shape of a semiconductor with maximum light output would be a microspherewith the photon emission occurring at the exact center, with electrodes penetrating to the center to contact at the emission point.

All light rays emanating from the center would be perpendicular to the entire surface of the sphere, resulting in no internal reflections. A

45

RF BASED HEART RATE MEASUREMENT 2015

hemispherical semiconductor would also work, with the flat back-surface serving as a mirror to back-scattered photons.

5.9.5 Transition coatings:-

Many LED semiconductor chips are potted in clear or colored molded plastic shells. The plastic shell has three purposes:

1. Mounting the semiconductor chip in devices is easier to accomplish.

2. The tiny fragile electrical wiring is physically supported and protected from damage

3. The plastic acts as a refractive intermediary between the relatively high-index semiconductor and low-index open air.

The third feature helps to boost the light emission from the semiconductor by acting as a diffusing lens, allowing light to be emitted at a much higher angle of incidence from the light cone, than the bare chip is able to emit alone.

5.9.6 Efficiency and operational parameters:-

Typical indicator LEDs are designed to operate with no more than 30–60 mW of electrical power. Around 1999, Philips Lumileds introduced power LEDs capable of continuous use at one watt.

These LEDs used much larger semiconductor die sizes to handle the large power inputs. Also, the semiconductor dies were mounted onto metal slugs to allow for heat removal from the LED die.

One of the key advantages of LED-based lighting sources is high luminous efficacy. White LEDs quickly matched and overtook the efficacy of standard incandescent lighting systems.

In 2002, Lumileds made five-watt LEDs available with a luminous efficacy of 18–22 lumens per watt (lm/W). For comparison, a conventional 60–100 W incandescent light bulb emits around 15 lm/W, and standardfluorescent lights emit up to 100 lm/W.

A recurring problem is that efficacy falls sharply with rising current. This effect is known as droop and effectively limits the light output of a given LED, raising heating more than light output for higher current.[33][34][35]

46

RF BASED HEART RATE MEASUREMENT 2015

In September 2003, a new type of blue LED was demonstrated by the company Cree Inc. to provide 24 mW at 20 milliamperes (mA). This produced a commercially packaged white light giving 65 lm/W at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as standard incandescents. In 2006, they demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. 

Nichia Corporation has developed a white LED with luminous efficacy of 150 lm/W at a forward current of 20 mA.Cree's XLamp XM-L LEDs, commercially available in 2011, produce 100 lumens per watt at their full power of 10 watts, and up to 160 lumens/watt at around 2 watts input power.

Practical general lighting needs high-power LEDs, of one watt or more. Typical operating currents for such devices begin at 350 mA.

Note that these efficiencies are for the LED chip only, held at low temperature in a lab. Lighting works at higher temperature and with drive circuit losses, so efficiencies are much lower.

 United States Department of Energy (DOE) testing of commercial LED lamps designed to replace incandescent lamps or CFLs showed that average efficacy was still about 46 lm/W in 2009 (tested performance ranged from 17 lm/W to 79 lm/W).

Cree issued a press release on February 3, 2010 about a laboratory prototype LED achieving 208 lumens per watt at room temperature. The correlated color temperature was reported to be 4579 K.

5.9.7 Lifetime and failure:-

Solid state devices such as LEDs are subject to very limited wear and tear if operated at low currents and at low temperatures.

Many of the LEDs made in the 1970s and 1980s are still in service today. Typical lifetimes quoted are 25,000 to 100,000 hours but heat and current settings can extend or shorten this time significantly. 

The most common symptom of LED (and diode laser) failure is the gradual lowering of light output and loss of efficiency. Sudden failures, although rare, can occur as well. Early red LEDs were notable for their short lifetime.

47

RF BASED HEART RATE MEASUREMENT 2015

With the development of high-power LEDs the devices are subjected to higherjunction temperatures and higher current densities than traditional devices.

This causes stress on the material and may cause early light-output degradation. To quantitatively classify lifetime in a standardized manner it has been suggested to use the terms L75 and L50 which is the time it will take a given LED to reach 75% and 50% light output respectively.

Like other lighting devices, LED performance is temperature dependent.

Most manufacturers’ published ratings of LEDs are for an operating temperature of 25 °C. LEDs used outdoors, such as traffic signals or in-pavement signal lights, and that are utilized in climates where the temperature within the luminaire gets very hot, could result in low signal intensities or even failure.

LED light output actually rises at colder temperatures (leveling off depending on type at around −30C.

Consequently, LED technology may be a good replacement in uses such as supermarket freezer lightingand will last longer than other technologies.

Because LEDs emit less heat than incandescent bulbs, they are an energy-efficient technology for uses such as freezers. However, because they emit little heat, ice and snow may build up on the LED luminaire in colder climates.

 This lack of waste heat generation has been observed to cause sometimes significant problems with street traffic signals and airport runway lighting in snow-prone areas, although some research has been done to try to develop heat sink technologies to transfer heat to other areas of the luminaire.

5.9.8 Ultraviolet and blue LEDs

Blue  LEDs.:-

48

RF BASED HEART RATE MEASUREMENT 2015

Current bright blue LEDs are based on the wide band gapsemiconductors GaN (gallium nitride) and InGaN (indium gallium nitride). They can be added to existing red and green LEDs to produce the impression of white light, though white LEDs today rarely use this principle.

The first blue LEDs using gallium nitride were made in 1971 by Jacques Pankove at RCA Laboratories. These devices had too little light output to be of practical use and research into gallium nitride devices slowed. In August 1989, Cree Inc. introduced the first commercially available blue LED based on the indirect bandgap semiconductor, silicon carbide.[53] SiC LEDs had very low effiency, no more than about 0.03%, but did emit in the blue portion of the visible light spectrum.

In the late 1980s, key breakthroughs in GaN epitaxialgrowth and p-type doping[54] ushered in the modern era of GaN-based optoelectronic devices.

Building upon this foundation, in 1993 high brightness blue LEDs were demonstrated. Efficiency (light energy produced vs. electrical energy used) reached 10%. High-brightness blue LEDs invented by Shuji Nakamura ofNichia Corporation using gallium nitride revolutionized LED lighting, making high-power light sources practical.

By the late 1990s, blue LEDs had become widely available. They have an active region consisting of one or more InGaN quantum wells sandwiched between thicker layers of GaN, called cladding layers.

By varying the relative InN-GaN fraction in the InGaN quantum wells, the light emission can be varied from violet to amber. AlGaN aluminium gallium nitride of varying AlN fraction can be used to manufacture the cladding and quantum well layers for ultraviolet LEDs, but these devices have not yet reached the level of efficiency and technological maturity of the InGaN-GaN blue/green devices. If the active quantum well layers are GaN, instead of alloyed InGaN or AlGaN, the device will emit near-ultraviolet light with wavelengths around 350–370 nm. Green LEDs manufactured from the InGaN-GaN

49

RF BASED HEART RATE MEASUREMENT 2015

system are far more efficient and brighter than green LEDs produced with non-nitride material systems.

With nitrides containing aluminium, most often AlGaN and AlGaInN, even shorter wavelengths are achievable

. Ultraviolet LEDs in a range of wavelengths are becoming available on the market. Near-UV emitters at wavelengths around 375–395 nm are already cheap and often encountered, for example, asblack light lamp replacements for inspection of anti-counterfeiting UV watermarks in some documents and paper currencies.

Shorter wavelength diodes, while substantially more expensive, are commercially available for wavelengths down to 247 nm. As the photosensitivity of microorganisms approximately matches the absorption spectrum of DNA, with a peak at about 260 nm, UV LED emitting at 250–270 nm are to be expected in prospective disinfection and sterilization devices.

Recent research has shown that commercially available UVA LEDs (365 nm) are already effective disinfection and sterilization devices.

Deep-UV wavelengths were obtained in laboratories using aluminium (210 nm),[50] boron nitride(215 nm)[48][49] and diamond (235 nm).

5.9.9 White light:-

There are two primary ways of producing high intensity white-light using LEDs. One is to use individual LEDs that emit three primary colors[58]—red, green, and blue—and then mix all the colors to form white light.

The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works.

Due to metamerism, it is possible to have quite different spectra that appear white.

RGB systems

50

RF BASED HEART RATE MEASUREMENT 2015

White light can be formed by mixing differently colored lights; the most common method is to use red, green and blue (RGB). Hence the method is called multi-colored white LEDs (sometimes referred to as Red Green Blue LEDs).

Because these need electronic circuits to control the blending and diffusion of different colors, these are seldom used to produce white lighting.

Nevertheless, this method is particularly interesting in many uses because of the flexibility of mixing different colors, and, in principle, this mechanism also has higher quantum efficiency in producing white light.

There are several types of multi-colored white LEDs: di-, tri-, and tetrachromatic white LEDs. Several key factors that play among these different methods, include costability, colorrendering capability, and luminous efficacy. Often higher efficiency will mean lower color rendering, presenting a trade off between the luminous efficiency and color rendering.

For example, the dichromatic white LEDs have the best luminous efficacy (120 lm/W), but the lowest color rendering capability. Conversely, althoughtetrachromatic white LEDs have excellent color rendering capability, they often have poor luminous efficiency. Dichromatic white LEDs are in between, having both good luminous efficacy (>70 lm/W) and fair color rendering capability.

Multi-color LEDs offer not merely another means to form white light, but a new means to form light of different colors. Most perceivable colors can be formed by mixing different amounts of three primary colors.

This allows precise dynamic color control. As more effort is devoted to investigating this method, multi-color LEDs should have profound influence on the fundamental method which we use to produce and control light color.

However, before this type of LED can play a role on the market, several technical problems need solving. These include that this type of LED's emission power decays exponentially with rising temperature,resulting in a substantial change in color stability. Such problems inhibit and may preclude industrial use.

51

RF BASED HEART RATE MEASUREMENT 2015

Thus, many new package designs aimed at solving this problem have been proposed and their results are now being reproduced by researchers and scientists.

Phosphor based LEDs have a lower efficiency than normal LEDs due to the heat loss from the Stokes shift and also other phosphor-related degradation issues.

However, the phosphor method is still the most popular method for making high intensity white LEDs. The design and production of a light source or light fixture using a monochrome emitter with phosphor conversion is simpler and cheaper than a complex RGB system, and the majority of high intensity white LEDs presently on the market are manufactured using phosphor light conversion.

The greatest barrier to high efficiency is the seemingly unavoidable Stokes energy loss.

However, much effort is being spent on optimizing these devices to higher light output and higher operation temperatures. For instance, the efficiency can be raised by adapting better package design or by using a more suitable type of phosphor.

Philips Lumileds' patented conformal coating process addresses the issue of varying phosphor thickness, giving the white LEDs a more homogeneous white light.[63] With development ongoing, the efficiency of phosphor based LEDs generally rises with each new product announcement.

The phosphor based white LEDs encapsulate InGaN blue LEDs inside phosphor coated epoxy. A common yellow phosphor material is cerium-doped yttrium aluminium garnet (Ce3+:YAG).

White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium-based red and blue emitting phosphors plus green emitting copper and aluminium doped zinc sulfide (ZnS:Cu, Al). This is a method analogous to the way fluorescent lamps work. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger, so more energy is converted to heat, but yields light with better spectral characteristics, which render color better. Due to

52

RF BASED HEART RATE MEASUREMENT 2015

the higher radiative output of the ultraviolet LEDs than of the blue ones, both methods offer comparable brightness.

A concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin.

Other white LEDs

Another method used to produce experimental white light LEDs used no phosphors at all and was based on homoepitaxially grown zinc selenide (ZnSe) on a ZnSe substrate which simultaneously emitted blue light from its active region and yellow light from the substrate.[64]

Quantum dot LEDs (experimental):-

Quantum dots (QD) are semiconductor nanocrystals that possess unique optical properties.[70] Their emission color can be tuned from the visible throughout the infrared spectrum.

This allows quantum dot LEDs to create almost any color on the CIE diagram. This provides more color options and better color rendering than white LEDs.[citation needed] Quantum dot LEDs are available in the same package types as traditional phosphor based LEDs.[citation

needed] One example of this is a method developed by Michael Bowers, at Vanderbilt University in Nashville, involving coating a blue LED with quantum dotsthat glow white in response to the blue light from the LED.

This method emits a warm, yellowish-white light similar to that made by incandescent bulbs.Quantum dots are also being considered for use in white light emitting diodes in liquid crystal display (LCD) televisions.

The major difficulty in using quantum dots based LEDs is the insufficient stability of Odds under prolonged irradiation.[citation needed] In February 2011 scientists at PlasmaChem GmbH could synthesize quantum dots for LED applications and build a light converter on their basis, which could efficiently convert light from blue to any other color for many hundred hours.[citation needed] Such QDs can be used to emit visible or near infrared light of any wavelength being excited by light with a shorter wavelength.

Miniature

53

RF BASED HEART RATE MEASUREMENT 2015

Different sized LEDs. 8 mm, 5 mm and 3 mm, with a wooden match-stick for scale.

These are mostly single-die LEDs used as indicators, and they come in various-sizes from 2 mm to 8 mm, through-holeand surface mount packages.

They usually don't use a separate heat sink.[74] Typical current ratings ranges from around 1 mA to above 20 mA. The small size sets a natural upper boundary on power consumption due to heat caused by the high current density and need for heat sinking.

Common package shapes include round, with a domed or flat top, rectangular wtih a flat top (as used in bar-graph displays), and triangular or square with a flat top The encapsulation may also be clear or tinted to improve contrast and viewing angle.

There are three main categories of miniature single die LEDs:

Low current — typically rated for 2 mA at around 2 V (approximately 4 mW consumption).

Standard — 20 mA LEDs at around 2 V (approximately 40 mW) for red, orange, yellow & green, and 20 mA at 4–5 V (approximately 100 mW) for blue, violet and white.

Ultra-high output — 20 mA at approximately 2 V or 4–5 V, designed for viewing in direct sunlight.

Five- and twelve-volt LEDs are ordinary miniature LEDs that incorporate a suitable series resistor for direct connection to a 5 V or 12 V supply.

Mid-range Medium power LEDs are often through-hole mounted and used when

an output of a few lumen is needed.

They sometimes have the diode mounted to four leads (two cathode leads, two anode leads) for better heat conduction and carry an integrated lens. An example of this is the Superflux package, from Philips Lumileds.

54

RF BASED HEART RATE MEASUREMENT 2015

These LEDs are most commonly used in light panels, emergency lighting and automotive tail-lights. Due to the larger amount of metal in the LED, they are able to handle higher currents (around 100 mA).

The higher current allows for the higher light output required for tail-lights and emergency lighting.

High power

See also: Solid-state lighting and LED lamp.

High power LEDs (HPLED) can be driven at currents from hundreds of mA to more than an ampere, compared with the tens of mA for other LEDs.

Some can emit over a thousand lumens. Since overheating is destructive, the HPLEDs must be mounted on a heat sink to allow for heat dissipation.

If the heat from a HPLED is not removed, the device will fail in seconds. One HPLED can often replace an incandescent bulb in a torch, or be set in an array to form a powerful LED lamp.

Some well-known HPLEDs in this category are the Lumileds Rebel Led, Osram Opto Semiconductors Golden Dragon and Cree X-lamp. As of September 2009 some HPLEDs manufactured by Cree Inc. now exceed 105 lm/W [77] (e.g. the XLamp XP-G LED chip emitting Cool White light) and are being sold in lamps intended to replace incandescent, halogen, and even fluorescent lights, as LEDs grow more cost competitive.

LEDs have been developed by Seoul Semiconductor that can operate on AC power without the need for a DC converter. For each half cycle, part of the LED emits light and part is dark, and this is reversed during the next half cycle.

The efficacy of this type of HPLED is typically 40 lm/W.A large number of LED elements in series may be able to operate directly from line voltage.

In 2009 Seoul Semiconductor released a high DC voltage capable of being driven from AC power with a simple controlling circuit. The low power dissipation of these LEDs affords them more flexibility than the original AC LED design.

55

RF BASED HEART RATE MEASUREMENT 2015

Application-specific variations

Flashing LEDs are used as attention seeking indicators without requiring external electronics. Flashing LEDs resemble standard LEDs but they contain an integrated multivibrator circuit which causes the LED to flash with a typical period of one second.

In diffused lens LEDs this is visible as a small black dot. Most flashing LEDs emit light of one color, but more sophisticated devices can flash between multiple colors and even fade through a color sequence using RGB color mixing.

Calculator LED display, 1970s.

Bi-color LEDs are actually two different LEDs in one case. They consist of two dies connected to the same two leads antiparallel to each other.

Current flow in one direction emits one color, and current in the opposite direction emits the other color. Alternating the two colors with sufficient frequency causes the appearance of a blended third color. For example, a red/green LED operated in this fashion will color blend to emit a yellow appearance.

Tri-color LEDs are two LEDs in one case, but the two LEDs are connected to separate leads so that the two LEDs can be controlled independently and lit simultaneously. A three-lead arrangement is typical with one common lead (anode or cathode).[citation needed]

RGB LEDs contain red, green and blue emitters, generally using a four-wire connection with one common lead (anode or cathode).

These LEDs can have either common positive or common negative leads. Others however, have only two leads (positive and negative) and have a built in tinyelectronic control unit.

Alphanumeric LED displays are available in seven-segment and starburst format. Seven-segment displays handle all numbers and a limited set of letters. Starburst displays can display all letters.

56

RF BASED HEART RATE MEASUREMENT 2015

Seven-segment LED displays were in widespread use in the 1970s and 1980s, but rising use of liquid crystal displays, with their lower power needs and greater display flexibility, has reduced the popularity of numeric and alphanumeric LED displays.

Power sources:-

Main article: LED power sources

The current/voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation).

This means that a small change in voltage can cause a large change in current.

If the maximum voltage rating is exceeded by a small amount, the current rating may be exceeded by a large amount, potentially damaging or destroying the LED.

The typical solution is to use constant current power supplies, or driving the LED at a voltage much below the maximum rating. Since most common power sources (batteries, mains) are not constant current sources, most LED fixtures must include a power converter

However, the I/V curve of nitride-based LEDs is quite steep above the knee and gives an If of a few milliamperes at a Vf of 3 V, making it possible to power a nitride-based LED from a 3 V battery such as a coin cell without the need for a current limiting resistor.

Electrical polarity:-

Main article: Electrical polarity of LEDs

As with all diodes, current flows easily from p-type to n-type material.[80] However, no current flows and no light is emitted if a small voltage is applied in the reverse direction.

If the reverse voltage grows large enough to exceed the breakdown voltage, a large current flows and the LED may be damaged. If the reverse current is sufficiently limited to avoid damage, the reverse-conducting LED is a useful noise diode.

57

RF BASED HEART RATE MEASUREMENT 2015

Safety and health

The vast majority of devices containing LEDs are "safe under all conditions of normal use", and so are classified as "Class 1 LED product"/"LED Klasse 1".

At present, only a few LEDs—extremely bright LEDs that also have a tightly focused viewing angle of 8° or less—could, in theory, cause temporary blindness, and so are classified as "Class 2". In general, laser safety regulations—and the "Class 1", "Class 2", etc. system—also apply to LEDs.

While LEDs have the advantage over fluorescent lamps that they do not contain mercury, they may cont+ain other hazardous metals such as lead and arsenic. A study published in 2011 states: "According to federal standards, LEDs are not hazardous except for low-intensity red LEDs, which leached Pb [lead] at levels exceeding regulatory limits (186 mg/L; regulatory limit: 5).

However, according to California regulations, excessive levels of copper (up to 3892 mg/kg; limit: 2500), Pb (up to 8103 mg/kg; limit: 1000), nickel (up to 4797 mg/kg; limit: 2000), or silver (up to 721 mg/kg; limit: 500) render all except low-intensity yellow LEDs hazardous.".[83]

Advantages

Efficiency: LEDs emit more light per watt than incandescent light Their efficiency is not affected by shape and size, unlike fluorescent light bulbs or tubes.

Color: LEDs can emit light of an intended color without using any color filters as traditional lighting methods need. This is more efficient and can lower initial costs.

Size: LEDs can be very small (smaller than 2 mm2[85]) and are easily populated onto printed circuit boards.

58

RF BASED HEART RATE MEASUREMENT 2015

On/Off time: LEDs light up very quickly. A typical red indicator LED will achieve full brightness in under a microsecond.[86] LEDs used in communications devices can have even faster response times.

Cycling: LEDs are ideal for uses subject to frequent on-off cycling, unlike fluorescent lamps that fail faster when cycled often, or HID lamps that require a long time before restarting.

Dimming: LEDs can very easily be dimmed either by pulse-width modulation or lowering the forward current.[87]

Cool light: In contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the LED.

Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt failure of incandescent bulbs.[88]

Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer.[89] Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000–2,000 hours.

Shock resistance: LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile.

Focus: The solid package of the LED can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner.

Disadvantages

High initial price: LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than most conventional lighting technologies. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed.

59

RF BASED HEART RATE MEASUREMENT 2015

Temperature dependence: LED performance largely depends on the ambient temperature of the operating environment. Over-driving an LED in high ambient temperatures may result in overheating the LED package, eventually leading to device failure. Adequate heat sinking is needed to maintain long life. This is especially important in automotive, medical, and military uses where devices must operate over a wide range of temperatures, and need low failure rates.

Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating. This can involve series resistors or current-regulated power supplies.[90]

Light quality: Most cool-white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white LED illumination than sunlight or incandescent sources, due to metamerism,[91] red surfaces being rendered particularly badly by typical phosphor based cool-white LEDs. However, the color rendering properties of common fluorescent lamps are often inferior to what is now available in state-of-art white LEDs.

Area light source: LEDs do not approximate a “point source” of light, but rather a lambertiandistribution. So LEDs are difficult to apply to uses needing a spherical light field. LEDs cannot provide divergence below a few degrees. In contrast, lasers can emit beams with divergences of 0.2 degrees or less.[92]

Blue hazard: There is a concern that blue LEDs and cool-white LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ANSI/IESNA RP-27.1–05: Recommended Practice for Photobiological Safety for Lamp and Lamp Systems.[93][94]

Blue pollution: Because cool-white LEDs (i.e., LEDs with high color temperature) emit proportionally more blue light than conventional outdoor light sources such as high-pressure sodium vapor lamps, the strong wavelength dependence of Rayleigh scattering means that cool-white LEDs can cause more light pollution than other light sources.

60

RF BASED HEART RATE MEASUREMENT 2015

The International Dark-Sky Associationdiscourages using white light sources with correlated color temperature above 3,000 K.[95][not in citation given]

Droop: The efficiency of LEDs tends to decrease as one increases current.[96][97][98][99]

Applications:-

LED lighting in the aircraft cabin of anAirbus A320 Enhanced.

A large LED display behind a disc jockey.

LED destination signs on buses, one with a colored route number.

LED digital display that can display 4 digits along with points.

Traffic light using LED

Western Australia Police car with LEDs used in its high-mounted brake light, its rear window and roof-mounted flashing Police vehicle lights and roof-mounted road user information display.

LED daytime running lights of Audi A4

LED Illumination

61

RF BASED HEART RATE MEASUREMENT 2015

LED lights reacting dynamically to video feed via AmBX.

In general, all the LED products can be divided into two major parts, the public lighting and indoor lighting.LED uses fall into four major categories:

Visual signals where light goes more or less directly from the source to the human eye, to convey a message or meaning.

Illumination where light is reflected from objects to give visual response of these objects.

Measuring and interacting with processes involving no human vision.[100]

Narrow band light sensors where LEDs operate in a reverse-bias mode and respond to incident light, instead of emitting light.

For more than 70 years, until the LED, practically all lighting was incandescent and fluorescent with the first fluorescent light only being commercially available after the 1939 World's Fair.

CHAPTER – 7

APPLICATIONS

It is use to count the heart beat, and display our heart rate on the LCD.

It is used to identify the person.

With the help of this device we known about any effect of heart.

62

RF BASED HEART RATE MEASUREMENT 2015

This project describes a microcontroller based heart rate measurement

system that uses optical sensors to measure the alteration in blood

volume at fingertip with each heart beat.

This device used to measurement our blood pressure.

CHAPTER – 8

ADVANTAGES

63

RF BASED HEART RATE MEASUREMENT 2015

The device has the advantage that it is microcontroller based and thus

can be programmed to display various quantities, such as the average,

maximum and minimum rates over a period of time and so on.

Another advantage of such a design is that it can be expanded and can

easily be connected to a recording device or a PC to collect and

analyzer the data for over a period of time.

The building cost of the proposed device is around $20.

CHAPTER – 9

DISADVANTAGE

64

RF BASED HEART RATE MEASUREMENT 2015

Instead of this device we can also use cosy communications. With no

extension capabilities costs around $100.

It is costly.

It is the heardierous our heart. So this device is not widely use.

CHAPTER –10

65

RF BASED HEART RATE MEASUREMENT 2015

CONCLUSION

During working on this project of heart rate measurement we get

knowledge about data of components which use in this circuit,

information about some sites like data sheet.com, electronics

project .com etc.And knowledge about how to measure our heart rate.

CHAPTER – 11

66

RF BASED HEART RATE MEASUREMENT 2015

Bibliography

1. Pulsar heart rate monitors, web site: http://www.heartratemonitor.co.uk 2. Copy Communications web site: http://cosycommunications.com 3 . Microchip web site: http://microchip.com PROTON+ User Guide, web site:

67

RF BASED HEART RATE MEASUREMENT 2015

68