Heartbeat Sensor

Introduction: Heart beat sensor is designed to give digital output of heat beat when a finger is placed on it. When the heart beat detector is working, the beat LED flashes in unison 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.The sensor consists of a super bright red LED and light detector. The LED needs to be super bright as the maximum light must pass spread in finger and detected by detector. Now, when the heart pumps a pulse of blood through the blood vessels, the finger becomes slightly more opaque and so less light reached the detector. With each heart pulse the detector signal varies. This variation is converted to electrical pulse. This signal is amplified and triggered through an amplifier which outputs +5V logic level signal. The output signal is also indicated by a LED which blinks on each heart beat.

Materials used: Breadboard LM358 IC IR LED Pair Ceramic Capacitor (100nF) Electrolytic Capacitor (4.7uF) Resistors(220,10k,680k,6.8k,47k) 9v Battery 5mm LED Specification and working of the project: The heartbeat sensor is based on the principle of photoplethysmography. It measures the change in volume of blood through any organ of the body which causes a change in the light intensity through that organ (avascular region). In the case of applications where the heart pulse rate is to be monitored, the timing of the pulses is more important. The flow of blood volume is decided by the rate of heart pulses and since light is absorbed by the blood, the signal pulses are equivalent to the heartbeat pulses.

LM358 IC: The LM358 IC is a low power and easy to use dual channel op-amp IC. It is designed and introduced by national semiconductor. It consists of two internally frequency compensated, high gain, independent op-amps. This IC is designed for specially to operate from a single power supply over a wide range of voltages. The LM358 IC is available in a chip sized package and applications of this op amp include conventional op-amp circuits, DC gain blocks and transducer amplifiers. LM358 IC is a good, standard operational amplifier

IR Transmitter and Receiver(TSOP1738: TSOP1738 is an IR receiver with an amplifier that acts as a switch and converter within a circuit. It has one input and output which only acts on the base of the input IR signal. The basic purpose of TSOP1738 is to convert the IR signal to electric signals. Every IR receiver has a special frequency to operate. TSOP1738 operates on 38KHz IR frequency. Working: The basic heartbeat sensor consists of a light-emitting diode and a detector like a light detecting resistor or a photodiode. The heartbeat pulses cause a variation in the flow of blood to different regions of the body. When tissue is illuminated with the light source, i.e. light emitted by the led, it either reflects (a finger tissue) or transmits the light (earlobe). Some of the light is absorbed by the blood and the transmitted or the reflected light is received by the light detector.

The amount of light absorbed depends on the blood volume in that tissue. The detector output is in the form of the electrical signal and is proportional to the heartbeat rate. Two Ways to Measure a Heartbeat Manual Way: Heartbeat can be checked manually by checking one’s pulses at two locations- wrist (the radial pulse) and the neck (carotid pulse). The procedure is to place the two fingers (index and middle finger) on the wrist (or neck below the windpipe) and count the number of pulses for 30 seconds and then multiplying that number by 2 to get the heartbeat rate. However, pressure should be applied minimum and also fingers should be moved up and down till the pulse is felt. Using a sensor: Heart Beat can be measured based on optical power variation as light is scattered or absorbed during its path through the blood as the heartbeat changes.

Circuit Diagram:

Advantages of heart beat sensors: Can be implemented in medical devices Can be used in smart watches Used for anxiety monitoring Affordable and accurate The design is compact

Disadvantages of heart beat sensor: The main disadvantage of this sensor is that the distance between the skin and the sensor affects a lot, also the shade of the skin varying from while to dark reduces the light entering into the blood vessels. The pulse rate sensor sometimes shows inappropriate reading and can sometimes change the average of the data also may arise a problem Conclusion: The objective of this project was to build a low power, low cost, reliable, non-intrusive, and non-invasive monitoring system that would accurately measure the vital signs. The resulting system was also low in power and cost, noninvasive, and provided real time monitoring. It is also easy to use and provides accurate measurements. For medical purpose the accuracy is always before cost of the device but for the

countries like India there is huge scope of experiments and work on the medical devices to make them cheaper still equally reliable. Given the scope of this project the heart rate measurement circuits accurately measure the heart rate signal and body. Reference: https://support.polar.com/en/support/what_are_the_pros _and_cons_of_wrist_based_heart_rate_measurement_and_ measuring_heart_rate_with_a#:~:text=Cons%3A-,Not%20n ecessarily%20accurate%20in%20sports%20where%20you% 20move%20your%20hands,sensor%20with%20a%20chest% 20strap. https://images.app.goo.gl/y4vBYK26Ro5FAUoc9 https://youtu.be/PODrFeHFirs