1. Optical Heart Monitor/Jump Drive Sponsor: Calit2 Mentor: Paul Blair Ph.D. Team: Matt Chandrangsu, Jeffrey Chi, Kari Nip ECE 191 – Group 6 Fall 2008

2. Agenda Project Background and Objective Design Summary Approach and Methodology Results Conclusions

3. Background and Objective There is increasing interest within the medical community in studying an individual’s heart rate variability. Existing data collection systems are cumbersome and report heart rate rather than the variations of each heart beat. There are not many applications that allow users to save their heart rate data to view later for medical purposes. Our objective is to develop a small, reliable device capable of conveniently reporting a person's heart rate variability and storing the data for later use.

4. Design Summary Pulse Oximeter Sensor Digital Signal Filtering Flash Memory AVR Microprocessor AT90USB1287 Computer Database 2 Stage Amplifier

5. Approach and Methodology Research and familiarize with Atmel AVR Microcontrollers Understand heart rate monitor work from previous quarters Research FAT12 file systems Write digital signal processing code that detects time differences between heart beats from a raw signal Write code that properly writes data to microcontroller flash memory and verify data is read on PC Write interrupt driven AVR Microcontroller code to properly run application integrating all components

6. Pulse Oximeter Sensor Purpose: Indirectly measures the oxygen saturation of a patient's blood to find heart beat wave Typically a 2 LED system: -One red LED (660nm) -One infrared LED (910nm). We only use 1 LED: -Only care about finding peaks of heart beat signal, not oxygenation levels or accuracy of waveform -Implemented using 1 SFH487 infrared LED transmitter and 1 SFH309 photodetector light

7. 2 Stage Amplifier Schematic

8. 2 Stage Amplifier Operational Amplifier Chip LM358 used Circuit amplifies input signal and also filters out higher frequency noise components –Gain of circuit is ~ 9.4 Potentiometer functions as “volume control” – dials up or down output voltage Analog filter output signal is fed into ADC port of the microcontroller to undergo digital signal processing

9. Oscilloscope Views

10. Inside the AVR Microcontroller Interrupt-driven AVR Microcontroller code structure Timer 1 LED ON Start Timer 0ADC ON ADC OFF LED OFF

11. Digital Signal Processing Find time between peaks to determine heart rate variability High frequencies make determining the time between beats difficult Approach: Matched filtering to improve signal- to-noise ratio

12. Matched Filtering Convolve input signal with template pulse to detect the presence of the template in the obtained signal

13. Inside the Microcontroller Data from ADC inputted into an array Array filtered using template signal array Time between beats is saved to buffer array for later storage onto flash memory

14. Storing the heart rate variability to flash memory Modifications of working storage C code to implement. As data flows into a buffer array, it is read and stored into a single file on the flash memory. New data is appended to the same file.

15. FAT Filesystem Boot Sector –Describes structure of file system File Allocation Table –Acts as a map of the data region Root Directory (aka Directory Table) –Displays name and information about the files stored in memory Data Region –Actual file storage

16. File locations in the flash memory Directory Table = Sector 0x20 (32) First File in Data Region = Sector 0x40 (64)

17. Inside the Microcontroller Digital Filtering Output Array = 1010 900 1300 … ASCII Conversion = 31 30 31 30 00 39 30 30 00 31 33 30 30 00 Storage in USB filesystem at sector 40 = 31 30 31 30 00 39 30 30 00 31 33 30 30 00 00 00 00 00 00 00 … Preparation for Conversion = 1 0 1 0 NULL 9 0 0 NULL 1 3 0 0 NULL Store to intermediate buffer

18. Conclusion Completed: –Pulse oximeter sensor –2 stage analog amplification element –Digital filtering code that detects peaks and computes time differences –Code for writing bytes to a file system and transferring to PC via USB –Interrupt driven code infrastructure in place Future Development: –Integrate all individual code elements into one cohesive program and test and fine tune for functionality –Mill PCB of amplifier circuit along with surface-mountable AVR microcontroller chip and other circuit components to have a standalone module

19. Questions??