Senior Design I - ECE 4512 Mississippi State University Department of Electrical Engineering

1. Heart Monitor Senior Design I - ECE 4512 Mississippi State University Department of Electrical Engineering

2. Advisor: Dr. Lori Bruce bruce@ece.msstate.edu Team Leader: Todd Peacock tpp1@ece.msstate.edu K’lvin Sui kvs1@ece.msstate.edu Craig Williamson lcw1@ece.msstate.edu Chong Meng Teh ct3@ece.msstate.edu Team Members

3. Individual Contributions • Todd Peacock • Filter • Comparator • Micro-controller frequency detection • Optical Signal generation and detection • Matlab and P-Spice simulation • Documentation • Craig Williamson • Filter • Comparator • Optical Signal generation and detection • Matlab and P-Spice Simulation • Documentation • Voon Siong K’lvin Sui • Filter • Micro-controller LCD programming • Matlab and P-Spice Simulation • Documentation • Chong Meng Teh • Web page • 5 min. presentation • Documentation

4. Motivation • A heart rate monitor that is accurate, affordable, and easy to use is essential to ensure one’s health quality • Current heart rate monitors are either too expensive, inaccurate, or not user friendly

5. Problem Statement • Design a heart rate monitor that is accurate, inexpensive, safe, and easy to use • To achieve better accuracy than current optical technology • Compete with the prices of current optical heart monitors • Provide a safe and non-invasive design • Technical problems: • Detecting the pulse using optical techniques • Extracting the pulse signal • Digitizing the signal • Obtaining an accuracy rating of +/- 10 % to compete with current optical technology • Power the device using a 3v lithium battery

6. Design Requirements 1. Pulse acquisition: • Light Transmitter: The transmitter will be a red LED light source to reflect the pulse signal from changes in reflectivity caused by changes in blood flow in the index finger. • Pulse Receiver: The receiver will be a photo-sensor that will detect the pulse signal, by sensing attenuations from the transmitted light through an index finger, and create an output voltage in the range of 10 mVpp.

7. Design Requirements • 2. Signal Extraction:A low pass filter and amplifier will be designed to remove noise from ambient light and level detection distortions. • Cutoff frequency of 4 Hz (200 BPM max heart rate) • SNR of –14 dB before filtering • Need an SNR of 20 dB for the comparator to operate • Roll off rate of 40 dB/dec (second-order butterworth) • Attenuation of 60 Hz noise by 47 dB • Amplification of pass-band frequencies by 40 dB

8. Design Requirements • 3. Pulse Digitization:The conditioned signal will be analyzed by a comparator to produce a digital pulse. • 1 Vpp output digital pulse • Time between rising pulse edges corresponds to heart rate period • 4. Display:The heart rate will be displayed on a 3-digit LCD display. • Pulse rates measured between 0 < pulse rate < 200

9. Design Requirements • 5. Accuracy:Due to noise, there will be distortion. Currently available optical heart monitors have a range of +/- 10-15% error. • The design will measure heart rate with no more than +/- 10% error. • Dynamic pulse averaging is used to give a better distribution of accuracy over the full range of pulses. • 6. Power: • The device will consume less than 30 mA • 3 volt lithium battery with a capacity of 1000 mAh • The battery will last 1 year with typical usage. • A watch battery will be used to compact the design.

10. Design Requirements • 7. Durability: • Operating temperature of –30 C to 80 C • Shock resistant • Water resistant • 8. Physical Packaging: • Design will be close to the size of a standard stopwatch. • Final packaged dimensions will not exceed 2.5” x 1.7” x 1” (H x W x D). ( rectangular shaped plastic enclosure)

11. Design Requirements 9. Cost:The component cost should not exceed $30.00. The production cost should not exceed $90.00.

12. Optical Signal Transmitter Optical Signal Receiver Low Pass Filter & Amplifier A/D Micro- Controller Display 82 Design Flow-Chart

13. Design Explanation • Optical Transmitter and Receiver • PSPICE was used to simulate the output voltage of the the pulse receiving part of the design • Signal Analysis • Matlab was used to conduct filter tests and to simulate the comparator • PSPICE was used to simulate the amplifier, filter, and comparator

14. With Noise Without Noise Sensor Design

15. Filter Design Fc = 4 Hz 60Hz Noise -47 dB 120Hz Noise -127 dB

16. Comparator Design Requires 20dB SNR

17. Simulation

18. FFT Filtered Raw Signal 87 BPM v v t Hz FFT FFT Hz Hz Comparator Output Matlab Simulation: Low Noise

19. Raw Signal Filtered v v FFT t FFT FFT 96 BPM Hz Hz Hz Comparator Output Matlab Simulation: Noisy

20. Microcontroller & Display

21. Microcontroller Flow-Chart If TMR<5 else Start Reset TMR N + 1 If Reset Display BPM Calculate Frequency BPM = 12Na

22. Conclusions/Future Work • Through the use of P-Spice and Matlab, the simulated data shows that the design will work • Light generates a lot of noise which distorts the pulse signal. The packaged design will have the photo-sensor placed so that the light will not highly distort the signal • Our future work will be to construct a working design to meet our design requirements