Theory of Operation

Introduction

The patient monitoring system is a state-of-the-art system that provides the user the capability to monitor a patient’s heart-beat, body temperature and blood pressure using Bluetooth technology. The patient wears the evaluation board with sensors along with a host controller to monitor his health conditions.

At the heart of the system lies the Freescale MC9S12C62 microcontroller. The other components include a temperature sensor, a heart beat sensor and a blood pressure sensor, an LCD display, and a Bluetooth module. The sensors, interfaced to the microcontroller, periodically (once every five minutes) send signals to the microcontroller which are first processed and then encoded to be sent over 2.4 GHz frequency using the Bluetooth module. The information is received on a compatible Bluetooth PDA displaying and informing the examiner about the patient’s health conditions. The system also contains a speaker that can beep whenever the patient’s health becomes critical (heart beat or temperature exceed normal value). The system also allows patients to monitor their own health by regularly checking the LCD display panel strapped around their chests.

Theory of Operation

Microcontroller:

The microcontroller used for the project is the Freescale MC9S12C32. This microcontroller has all the peripherals (ATD, Timer, UART, PWM) required for our design. The general purpose I/O pins of port A are intended for use with the LCD while the ATD pin is used to get the analog signal from the comparator connected to the heart- rate receiver circuit. The ‘TXD’ pin of the SCI is used to communicate with the RF transmitter while the general purpose I/O pins of Port B are intended for use with the temperature sensor and the boomer. The microcontroller first collects data from the temperature sensor and heart-rate receiver circuit. It then displays the information on the LCD connected through the 4 data I/O pins. It also transmits this data serially over to the RF transmitter using the TXD pin of the SCI peripheral. The data received by the microcontroller is also compared to a range of heart rate (35 – 120 pulse/min) and body temperature (30 – 40 degrees C) values. If the received values are found to lie outside this range, an emergency, in the form of an alarm, is sounded through the boomer connected to the MCU. An emergency signal is then also sent to the terminal computer over RF that keeps flashing on the screen. The microcontroller operates at 5V, which is supplied by the linear regulator powered by 4AA batteries

Radio Frequency:

The RF transmitter and receiver used for the purpose is Linx Technologies TXM-433-LC and RXM-433-LC-S respectively. The Linx transmitter interfaces to the microcontroller using the single ‘Data In’ pin. This pin is connected to the microcontroller through the

SCI peripheral. As the transmitter only transmits the received data, it will be interfaced to the ‘TXD’ pin of the microcontroller. Data sent serially to the transmitter will be sent to the ‘RF Out’ pin of the TXM-433-LC through a 50 Ohm RF antenna. The transmitter uses the CPCA (Carrier-Present Carrier-Absent) modulation scheme and is capable of sending serial data at upto 5kb/s. The transmitter has a wide operating voltage and operates anywhere between 2.7 – 5.0 V. The The MC9S12C32 will be operating at approximately 5V, due to which we will not have to worry about any DC-DC converters.

Heart-Rate receiver circuit: The Heart-Rate receiver circuit is designed to receive the electromagnetic signals emitted by the Polar transmitter belt worn by the patient around his/her chest. The transmitter belt emits these signals and the receiver circuit containing a resonator resonates at a frequency of 5kHz. These signals picked by the resonator are passed through a low pass filter to filter out noise and the high frequency components which is then fed into the LM393N comparator. The voltage fed into the comparator is a low 0.3V input. This input is then compared to a voltage divider circuit generating 0.3V to finally produce a 5V output. The output generated from the comparator is analog due to which it is interfaced to the ATD pin of the microcontroller to give a digital output.

LCD Display:

The function of the LCD is to constantly display the current body temperature and the heart-rate of the patient. A 16*2 LCD with a 4-bit interface is used for the purpose. The

LCD contains two 8-bit registers, one for data entry and the other for control. The LCD has three control signals R/W (read/write), RS (register select) and E (enable). The RS pin is connected to one of the I/O pins of Port A and is used to select between either the data or the control register. The E (enable) signal acts as the strobe signal is also connected to one of the I/O pins of Port A. The R/!W (read/write) pin is grounded as data is always written into the LCD and never read from it. The LCD requires a supply voltage of 5V which is provided by the 4AA batteries through the linear regulator that provides a 5V regulated supply. To operate the backlight, the LCD requires approximately 130mA of current which is again provided by the batteries which lowers operation time due to the large current draw. Temperature Sensor

The function of the temperature sensor is to measure the body temperature of the patient. It should be placed in direct contact with the patient’s skin/body to avoid heat loss through air and the effect of the surrounding temperature. The DS18S20 temperature sensor requires only 1 port pin for communication. It is directly connected to the microcontroller through the DQ bus using a 4.7 kOhm resistor. It is powered with 3.0 – 5.0 V and measures temperatures between –67°F to +257°F. The Maxim DS18S20 temperature sensor gives a digital output due to which it is connected to any I/O port pin. The temperature sensor output has a 9-bit resolution, which corresponds to 0.5_C steps. It converts temperature in 750 ms and uses an automatic alarm system to inform the microcontroller whenever the body temperature exceeds the normal value. In addition, the sensor derives power directly from the data line and eliminates the need for an external power supply. The sensor powers-up in a low-power idle state and needs to be initiated to measure the temperature. The A-to-D conversion of the temperature is stored in a 2-byte temperature register in the memory after which the sensor returns to its idle state. List of References

[1]. Crystalfontz CFAG12232D-YYH-N LCD Screen: http://www.crystalfontz.com/products/character-menubar.gif [2]. Maxim DS18S20 Digital Thermometer: http://pdfserv.maxim-ic.com/en/ds/DS18S20.pdf [3]. Salutron 2000 Heartbeat Sensor: http://www.salutron.com/product-pcba.html [4]. National Semiconductor LMX9820 Bluetooth Module: http://www.national.com/ds.cgi/LM/LMX9820.pdf [5]. Freescale MC9S12C62 Microcontroller: http://www.freescale.com/webapp/sps/site/prod_summary.jsp? code=MC9S12C64&nodeId=0162468636K100 [6]. Atmel ATmega64 Microcontroller: http://www.atmel.com/dyn/products/product_card.asp?part_id=2016 [7]. Polar F-1 Heart Rate Monitor http://www.polar-usa.us/polar-f1.html [8]. Maxim DS1620 Digital Thermometer: http://pdfserv.maxim-ic.com/en/ds/DS1620.pdf [9]. Crystalfontz CFAG12232D-NYG-N LCD Screen http://www.crystalfontz.com/products/12232d/CFAG12232DNYGN.pdf [10]. Crystalfontz 632 Serial LCD Module: http://www.crystalfontz.com/products/632/632full.pdf [11]. Texas Instruments S2000 Micro Reader: http://www.ti.com/tiris/docs/manuals/pdfSpecs/RI-STU-MRD1.pdf