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Heart Beat Sensor

This application note demonstrates fundamental

implementations of the cost effective heart rate

monitor. The IR based heart beat pulse sensor gives

the output of low and high Pulse. Heart beat sensor is

designed to give digital output of heat beat when a

finger is inserted between the IR Transmitter and

Receiver. When the heart beat detector is working,

the beat LED flashes with each heart beat. This

digital output can be connected to microcontroller directly to measure the Beats Per Minute

(BPM) rate. It works on the principle of light modulation by blood flow through finger at each

pulse.

Working Principle

The sensor consists of an Infrared transmitter and Receiver. The Infrared ray emits from

the transmitter and received in the receiver. When the blood is pumped in between the

fingers correspondingly to the beats of the heart, the infrared rays are blocked in between

and released accordingly. With each heart pulse the detector signal varies. This variation is

converted into the electrical signals and given as output voltage as 0 or 5 Volts DC. The

output signal is indicated in LED which blinks on each heart beat.

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Introduction:

Heart and Functions The heart is the organ responsible for pumping blood throughout the body. It is located in the middle of the thorax, slightly offset to the left and surrounded by the lungs. The heart is composed of four chambers; two atriums and two ventricles. The right atrium receives blood returning to the heart from the whole body. That blood passes through the right ventricle and is pumped to the lungs where it is oxygenated and goes back to the heart through the left atrium, then the blood passes through the left ventricle and is pumped again to be distributed to the entire body through the arteries. Figure 1: How the heart functions electrically The heart's natural pacemaker - the SA node - sends out regular electrical impulses from the top chamber (the atrium) causing it to contract and pump blood into the bottom chamber (the ventricle). The electrical impulse is then conducted to the ventricles through a form of 'junction box' called the AV node. The impulse spreads into the ventricles, causing the muscle to contract and to pump out the blood. The blood from the right ventricle goes to the lungs, and the blood from the left ventricle goes to the body

Sensing Principle Sensor works on Infrared signal. It contains IR transmitter and Receiver. Between Transmitter and Receiver, the person has to insert his finger. When there was no finger, Receiver gets, IR signal and output of sensor is high 10 V. Now when there is no blood in finger then also IR passes through finger and output is 10V But when Heart pushes blood, blood comes to finger, and IR light is not able to pass though finger. So output of Sensor becomes 0V

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As micro controller can only accept voltage less than 5v, We are reducing the voltage of sensor using voltage divider circuit as shown (10 K resistors in series and parallel across Sensor). Now sensor Gives 5v when No blood in finger and gives 0V when blood comes to finger. So when blood comes to finger output goes from 5v to 0v. This is high to low pulse. This pulse can be applied as interrupt for microcontroller(pin 3.2-INT0). So microcontroller will get interrupt each time when blood comes and goes from finger. We can count number of interrupts generated in 1 minute. This count is heart beat rate

We start with a light source and a light detector. Here used an Infrared LED, and a

photodiode sensor. It’s important that the two devices are matched well, so that the light

wavelength output from the LED is detected strongly by the photodiode (see below for part

numbers). The photodiode is essentially a teeny tiny solar cell, just like the panels on

rooftops, but really small. It will generate a small voltage and current when it is blasted with

photons. The Infrared LED is what we will use for our photon blaster.

The next thing we need is a way to amplify the tiny signal coming off of the photodiode. Happily enough, the configuration of this circuit is well-known in analog electronics circles as a ‘Current to Voltage Converter’ and it is a classic

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Features Plastic Casing/PCB without casing

Heart Beat Indication by LED

Working Voltage 12 Volts DC

3 wire -Red Black Green

Connection

Red +12Volts DC Black GROUND GREEN (0Volt or 5Volt) Pulse OUTPUT Applications Digital Heart rate Monitor

Blood Pressure Monitoring

Patient Monitoring system

Bio-logical feedback for Robotics and controls

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Circuit Block Diagram

Digital Output

Graph Outputs

Graph Fig 1

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Graph 1 shows the output of a normal human being whose pulse amplitude increases more than 3 volts for every high impedance and goes down less than 1.8 volts for low impedance. The output can be directly integrated to microcontroller. Hence for every 5 volts peak the controller can take the high logic and for less than 1 volt the microcontroller will take the low output for counting.

Manual Heart Beat Pulse Sensing Part Heart beat monitoring through sensor

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Heart Beat Sensor

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////////////////////Following Program is According to ADC0809 and AT89s52 ////////////// #include <REGX51.H> sbit SOC =P0^3; sbit EOC =P0^5; sbit OUT_EN =P0^6; sbit CLOCK =P0^7; sbit ALE =P0^4; sbit CHAN_SEL0 =P0^0; sbit CHAN_SEL1 =P0^1; sbit CHAN_SEL2 =P0^2; unsigned char sensor_value=0X00; void adc_conversion(unsigned char ); void delay(); void sensor(); void delay_50ms (); void delay_nsec(char); void serial_init();

Heart Beat Sensor

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void main() { unsigned char i = 0; serial_init(); while(1) { sensor(); SBUF=0x0A; while(TI==0); TI=0; SBUF=0x0D; while(TI==0); TI=0; delay_nsec(2); } } void serial_init() { SCON=0x50; TMOD=0x20; TH1=0xfd; TL1=0xfd; TR1=1; } void delay_nsec(char n) { char i,j; for(j=0;j<n;j++) { for(i=0;i<20;i++) delay_50ms (); } } void delay_50ms (void) // Delay function using Timer 0 for 50ms. { TMOD &=0xF0; TMOD |=0x01; ET0 =0; TH0=0x4b;

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TL0=0xfc; TF0 =0; TR0 =1; while(TF0==0); TR0=0; } void sensor() { CHAN_SEL0=0; CHAN_SEL1=0; CHAN_SEL2=0; ALE=0; delay(); delay(); ALE=1; delay(); SOC=1; delay(); SOC=0; while (EOC!=1); OUT_EN=1; delay(); delay(); sensor_value=P1; OUT_EN=0; adc_conversion(sensor_value); } void delay() { unsigned char i; for(i=8;i>0;i--) { } } void adc_conversion(unsigned char a) { unsigned char x,y,z1,z2,z3; x=a; y=x/10; z1=x%10; z2=y%10; z3=y/10;

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z1+=0x30; z2+=0x30; z3+=0x30; SBUF=z3; while(TI==0); TI=0; SBUF=z2; while(TI==0); TI=0; SBUF=z1; while(TI==0); TI=0; } ////////////////////Following Program is According to AT89s52 ////////////// #include <REGX51.H> sbit sensor=P0^0; void delay(); void delay_50ms (); void delay_nsec(char); void serial_init(); void main() { serial_init(); while(1) { if(sensor==1) { ////Your Code SBUF=0x0A; while(TI==0); TI=0;

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SBUF=0x0D; while(TI==0); TI=0; SBUF='1';////Here is the output on Hyper terminal while(TI==0); TI=0; } else { ////Your Code SBUF=0x0A; while(TI==0); TI=0; SBUF=0x0D; while(TI==0); TI=0; SBUF='0';////Here is the output on Hyper terminal while(TI==0); TI=0; } delay_nsec(2); } } void serial_init() { SCON=0x50; TMOD=0x20; TH1=0xfd; TL1=0xfd; TR1=1; } void delay_nsec(char n) { char i,j; for(j=0;j<n;j++) { for(i=0;i<20;i++) delay_50ms (); } } void delay_50ms (void) // Delay function using Timer 0 for 50ms. {

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TMOD &=0xF0; TMOD |=0x01; ET0 =0; TH0=0x4b; TL0=0xfc; TF0 =0; TR0 =1; while(TF0==0); TR0=0; } } void delay() { unsigned char i; for(i=8;i>0;i--) { }