Optical Non-invasive Heartbeat Measurement Device 1 st Khondoker Saad Bin Kalam dept. of EEE (CSP Major) Group: 02 ID: 1706110 1706110@eee.buet.ac.bd 2 nd Md Fahim Abid dept. of EEE (CSP Major) Group: 02 ID: 1706115 1706115@eee.buet.ac.bd 3 rd Md.Shamsur Rahman Bhuiyan dept. of EEE (CSP Major) Group: 02 ID: 1706122 1706122@eee.buet.ac.bd 4 th Sanath kumar das dept. of EEE (CSP Major) Group: 02 ID: 1706149 1706149@eee.buet.ac.bd 5 th Swapneel Sen dept. of EEE (CSP Major) Group: 02 ID: 1706185 1706185@eee.buet.ac.bd 6 th Aong Shay Sing Marma dept. of EEE (CSP Major) Group: 02 ID: 1706195 1706195@eee.buet.ac.bd Abstract —Our prototype device can measure heartbeat within 20s of inserting a finger and later update it in each following 4 seconds. It uses analog filtering and amplification of the transmitted IR light induced voltage, as well as digital filtering and processing afterwards. The prototype is based on Arduino and few basic circuit components. Index Terms —heartbeat, sensor, biomedical, bpm-counter, pulse, pulse-oximeter I. I NTRODUCTION Easy to use, fast, accurate and portable medical kits to measure and detect certain biomedical characteristics have been gaining lot of attention in recent times. Many diseases and physical disorder needs frequent routine check of certain properties such as heart rate, oxygen level, blood glucose level etc. If there exists such device that can reliably measure said characteristics, patient themselves can keep them in check and call medical emergency if required before anything severe happens. II. T ARGET D EMOGRAPHIC Heartbeat measuring device or bpmcounter has always been a very important device both in hospital and home use for people including whole age spectrum. Especially people with heart diseases may need to frequently check heartbeat rate as a precaution, thus requiring easy to use and reliable device at home. Such device is already available in the market. But they are very expensive and not easily acquirable. Our device is very inexpensive and very easy to use and fast. III. D EVICE C ONSTRUCTION Our prototype’s construction is very simple. All the circuit components have been hidden inside an enclosure. The indi- cator LED, LCD display and the IR sensor enclosure have been placed on the top of the enclosure. The power button have been placed to the side which connects a removable 9v battery to the Arduino’s Vin pin. The usb port of Arduino is also exposed to help debugging and experimentation. Fig. 1. Device Enclosure Fig. 2. Device Enclosure (top view) IV. IR S ENSOR E NCLOSURE C ONSTRUCTION The basic method to detect pulsating blood flow inside hu- man finger is to pass strong IR beam through skin and measure transmittance on the opposite end by using IR receiver. We have coupled two IR transmitter (salvaged from TCRT5000) to increase beam intensity and used one IR receiver. The upper part of the encloser contains the transmitter and the bottom part holds the receiver. There are matte black rupper coverings in the inside surfaces of the enclosure to reduce Fig. 3. Device Enclosure (without cover) Fig. 4. Sensor Enclosure (schematic) internal reflections of IR beam (Fig. 5). V. W ORKING M ETHOD The voltage generated by the IR receiver is passed through analog filter and amplifier circuit and then fed through Ar- duino’s analog pin where it is converted into digital signal for further digital processing and bpm counting. A. Amplifier and Filter Circuit The circuit at Fig. 6 contains two step ampification and Low pass filtering. Each amplification stage has gain 101; thus resulting in 10,000x boosting of the IR receiver voltage. The LPFs have cutoff at 2.34Hz which makes our circuit only capable of detecting bpm till 140. B. Digital Processing Another digital low pass filter (Moving average algorithm) was implemented to ease in and further denoise the pulsing wave to make it easy to count. C. Pulse Counting and Others We apply pulse counting algorithm (Fig. 8) on the output of the moving average filter. We detect pair of consecutive rising gradient and falling gradient and consider that a pulse. The amount of rising and falling gradient pair in 1 minute is actually the person’s heart rate in bpm. Fig. 5. Sensor Enclosure (construction) Fig. 6. Analog filtering and amplification circuit) Fig. 7. Using moving average algorithm VI. C OST B REAKDOWN The available heartbeat measurement devices on the market comes with as a package of heartbeat sensor and oximeter; those sells for around 2,500-5,000tk. Our prototype only costs 1300 tk, which can be drastically reduced my designing a marketable small frame, building PCB and having a compact design with massive production, thus the cost will easily go under 1,000 tk. Item Piece(s) Cost (TK) Arduino 1 800 LCD 1 250 Enclosure 1 50 LM358 2 20 IRs 3 60 9V Battery 1 60 Misc 60 Total 1300/- Fig. 8. Algorithm to count pulse and detect if finger is inserted) VII. F UTURE G OALS AND E XPERIMENTATIONS • Designing and transferring the breadboard circuit in PCB and using a suitable mictrocontroller/microprocessor in- stead of Arduino • Designing a single enclosure that can hold both the sensor area and the other components: circuit, LED, display etc. • Reducing power consumption to ensure long life on a single AA battery. • Manufacture the complete product in large scale. A CKNOWLEDGMENT Words cannot express our gratitude to your lab teachers, Shahed Ahmed and Md. Jahin Alam for their invaluable patience and feedback. R EFERENCES [1] Design and Performance Analysis of an Infra-Red Based Heart Rate Monitoring System. (2019). International Journal of Engineering and Advanced Technology, 8(6), 534–540. https://doi.org/10.35940/ijeat.e7313.088619 [2] A low cost optical sensor based heart rate monitoring system. (n.d.). A Low Cost Optical Sensor Based Heart Rate Monitor- ing System — IEEE Conference Publication — IEEE Xplore. https://ieeexplore.ieee.org/document/6572660