Ijsea 2nd publication

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Published on March 15, 2014

Author: sheeladoss

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International Journal of Science and Engineering Applications Volume 2 Issue 4, 2013, ISSN-2319-7560 (Online) www.ijsea.com 94 Monitoring the Respiratory System using Temperature Sensor J.Sheela Arokia Mary Dept of EEE KCET, Anna University Cuddalore, India R.Divya Dept of CSE Mookambigai College of Engg Trichy, India Abstract:This paper proposes to monitor the breathing of the patients. The device calculates a patient's breathing rate by detecting changes in temperature when the patient breathes through a mask. The device includes an alarm through a piezoelectric speaker which goes off when the patient stops breathing and a low-battery indicator signal when the battery powering the device reaches a threshold voltage. Keywords:Thermistor, piezoelectric speaker, threshold voltage, Temperature sensor, breathing. 1. INTRODUCTION Many biomedical devices, such as commercially available respiratory monitors, are designed for the developed world and require a stable power-supply to operate. We implement a solution that is adaptable to different environments. Our implementation also includes various analog circuits for voltage regulation and signal amplification. Developing a robust and accurate respiratory monitor served to be a challenging, yet rewarding experience. 2. METHODOLOGY An analog-to-digital conversion is used to sample readings from both the thermistor and the battery, pulse-width modulation to generate a signal for the speaker, and timers to switch between tasks. 3. BLOCK DIAGRAM It requires four components Thermistor, Power, Display & Speaker. Figure 1. Block Diagram 3.1 Thermistor measurements The resistance over the thermistor drops when it’s surrounding temperature increases, and goes back down when the temperature decreases. The voltage also, accordingly drops when a person exhales and rises when a person inhales. We use an operational amplifier to make the changes in temperature more apparent. The output of the amplifier is read into the microcontroller's ADC channel 0. Since our device uses a 9V battery, a voltage divider is used to drop the voltage

International Journal of Science and Engineering Applications Volume 2 Issue 4, 2013, ISSN-2319-7560 (Online) www.ijsea.com 95 3.2 Power Our device can be powered through either a standard AC power supply or a single 9V battery. 3.3 Display To conserve power, the user must hold down a button to turn on the display to read the respiration rate. This prevents the user fromleaving the display on by mistake and draining the battery. Breathing rate is measured and displayed in breaths/min on an LCD. This allows whoever is monitoring the patient to see if the patient is breathing too fast or too slowly. 3.4 Speaker There are two different alarms for our device generated by a piezoelectric speaker. The first is higher in pitch and alarms if the patient is not breathing. The second is a signal that the device is running on low battery. While the first alarm is a continuous sound, the low-battery alert is a one second long tone. 4. DESIGN METHOD 4.1 Microcontroller When choosing a microcontroller for this project, we first wanted to find the smallest microcontroller possible so that it could be mounted right onto the device's mask, the AtMega1284p microcontroller is used. 4.2 Thermistor Thermistor of smaller size is used, because larger thermistors could not detect a "breath" nor had a very slow response time. 4.3 Display LCD screen is used for display. In order to reduce power usage, the LCD only receives power when the user presses the display button, which reduces the load on the battery. 5 SOFTWARE DESIGN & IMPLEMENTATION The C programming language was used to program the MCU using the AVR Studio version 4.15 and was compiled using the WINAVR GCC C compiler. The software for the respiratory monitor contains 5 different tasks and 2 interrupt service routines (ISR). The first ISR is the Timer0 Compare Match Vector. This ISR activates every 16.4 ms and decrements three different timeout counters whenever it activates. It also zeroes the variable count (used to measure respiration rate) to prevent it from overflowing. Since the clock of the MCU is 16 MHz, we set the presale to 1024 and OCR0A to 255. Setting OCR0A to 255 means the ISR will activate every 256 clk cycles. The second ISR used was the AC ISR. This ISR activates when the onboard AC outputs a 1. This ISR was used to measure the respiration rate of the person. 5.1Thermistor sampling Samples from the thermistor are taken through PINA0. First, the ADMUX register is set to turn on the left adjust result and external reference. The MCU then waits for a conversion to occur, and then sets the variable sample old to the current sample and the sample variable to the high bits from the ADC. The absolute value of the difference between sample old and sample is used to determine if the patient has stopped breathing. If this difference is less than or equal to 8, then this is considered a "no breath". If the MCU detects 10 consecutive "no breaths", a PWM signal is generated to produce a sound from the speaker. If the difference is above the tolerance, then the "no breath" counter variable c is reset to 0 and the PWM signal is set to be turned off. The tolerance for the difference between breaths was found through experimentation. Looking at the ADC values on the UART, the range of the sampled values was 6-8 when a person was not breathing. To compensate for this fluctuation, we compare the difference between consecutive thermistor samples against 8 instead of 0. We also decided to have a counter to keep track of the number of "no breaths" detected because depending on how a

International Journal of Science and Engineering Applications Volume 2 Issue 4, 2013, ISSN-2319-7560 (Online) www.ijsea.com 96 person is breathing, consecutive samples could fall into the tolerance range. Counting up to 10 consecutive "no breaths" drastically reduces the number of false positive alarms. DC sampling and PWM signal generation were concepts we learned earlier in the semester in Labs 2 and 3. 5.2 Battery sampling To take a sample from the battery, ADC channel 1 on PINA1 is turned on by setting the ADMUX register. The MCU waits for a conversion to occur and then sets the variable bat_samp to the high bits from the ADC. The sample is then compared to the ADC value that was found to correspond to a voltage of 7.6 V. During testing it was found that device operation becomes unstable at 7.5 V. Therefore, we decided to warn the user when the voltage of the battery becomes 7.6 VIf the battery sample is found to be less than or equal to the tolerance, then a PWM signal is generated, left on for about 1 second, and then is turned off. The PWM channel which produces a tone for a low-battery warning has a larger presale than the PWM channel to produce the alarm for when a patient is not breathing, making the low-battery tone lower in pitch. 5.3 Display task The display function is used to display the respiratory rate on the LCD when the user is holding down the LCD push button. This was achieved by having the display function activate when PinB1 was read as 1. When PinB1 is 1 the LCD is initialized and the value of the respiratory rate stored in the variable breath rate and written to the LCD buffer. This value was then displayed on the LCD. 6 CONCLUSION This paper has comprehensively addresses that the Piezoelectric speaker is activated when the patient is not breathing & different sounds are used if not breathing. Speaker is automatically turned off when the patient begins to breathe. Hence the device is portable and low cost, can be used everywhere. 7. REFERENCES [1] B. Manzanita, C. Lambert and J. de Bie, "Validation of an ECG-derived respiration monitoring method", Computers in Cardiology, vol. 30, pp.613-616. [2] S. Park, Y. Noh, S. Park and H. Yoon, "An improved algorithm for respiration signal extraction from electrocardiogram measured by conductive textile electrodes using instantaneous frequency estimation", Medical & Biological Engineering &Computing, vol. 46, no. 2, pp. 147-1 58. [3] P. Currishly and Rodriguez-Villegas, "Breathing detection: towards a miniaturized, wearable, battery- operated monitoring system", IEEE Transactions on Biomedical Engineering, vol. 55, no. 1, pp. 196- 204. [4] an o -Solar, J.A. Fez and J. Moreira, "Automatic detection of snoring signals: validation with simple snorers and OSAS patients", Proc. of the 22th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. pp. 3129-3131. [5] Z. Zhu, J. Fief and I. Pavlodar," Tracking human breath in infrared imaging", in Proceedings of the fifth Symposium on Bioinformatics and Bioengineering,IEEE Computer Society Washington, DC, USA, pp. 227-231. [6] Saatchi, R., Al-Halides, F.Q., Burke, D., Delphic, H. " Thermal image analysis of the skin surface centered on the tip of the nose for respiration monitoring", Invited paper, IEEE organized International Conference on Electronic Design and Signal Processing to be held between 10th- 12th of December, Mani pal, India. [7] R. Murthy, I. Pavlodar and P. Tsiamyrtzis, "Touch less monitoring of breathing function", Engineering in Medicine and Biology Society, 2004. IEMBS'04 26 [8 J. Fein, Z. Zhen and I. Pavlodar, "Imaging breathing rate in C02 absorption band", Proceedings of the 2005 IEEE Engineering in Medicine and Biology 27th Annual Conference, Shanghai, China, pp. 700-705. [9] I. Sato and M. Nakajima," Non-contact Breath Motion Monitoring System in Full Automation", Proceedings of the 2005 IEEE

International Journal of Science and Engineering Applications Volume 2 Issue 4, 2013, ISSN-2319-7560 (Online) www.ijsea.com 97 Engineering in Medicine and Biology 27th Annual Conference, Shanghai, China, pp. 3448- 345. [10] M. Frijole, J. Amati and J. Pages, "Vision Based Respiratory Monitoring System", Proceedings of the 10th Mediterranean Conference on Control and Automation - MED2002 Lisbon, Portugal, July 9-12.

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