Proceedings of the 16th IEEE Symposium on Computer-Based Medical Systems (CBMS’03)
`1063-7125/03 $17.00 © 2003 IEEE
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`Recent publication of Pettichis et al., 2002 [4] showed an overview of Wireless
`Telemedicine Systems. The overview highlighted the use of wireless technologies in
`telemedicine areas such as emergency, tele- cardiology and remote monitoring.
`Some of the above mentioned systems use the GSM technology in medical devices to
`acquire the data via the IrDA, which are transmitted and received at the other end by PC(cid:173)
`based server networks for further process. This requires sending all measured data to the
`server via a public networks which may take long time and is subjected to error.
`This paper describes the design of a stand-alone single chip microcontroller with
`embedded software algorithm to monitor two parameters, the human temperature (Temp)
`and Blood pressure (BP). The patient may wear the embedded system-GSM modem as a
`wrist watch or attached to his/her belt. The device can transmit the parameters to and
`receive commands from a mobile phone/s. Section two describes the hardware architecture
`followed by the device software algorithm. Section four discuses the accuracy and related
`error sources. The last section of the paper is roadmap for future work and conclusion.
`
`2. Device hardware architecture:
`
`The device hardware architecture consists of several modules: sensors pack and signal
`conditioning circuits, 8-bit microcontroller with two lines of LCD display, GSM modem
`and SIM card.
`
`2.1. Sensors pack and signal conditioning circuits.
`
`The sensor pack has two transducers to measure the temperature and pressure.
`Thermocouple is a temperature sensor with signal conditioning circuit .It has a low power
`operational amplifier and a couple of resistors. The output of the thermocouple will provide
`a 0-volt for 0 degrees centigrade and a 5-volt output for 50 degrees centigrade.
`For the values between the two extremes, there is a linear relationship between output
`voltage and sensed temperature. The signal conditioning circuit, SCC, is used to make the
`sensor output compatible with the microcontroller built-in analog-to-digital converter. The
`relationship between the sec input and output is linear and can be described using the
`following equation:
`
`Where:
`
`Y=mX+B
`
`(1)
`
`Y = dependent output variable and can be expressed by decimal value of the digital output.
`This output is the SCC output. It is fed to ADC channel zero (AnO) of the microcontroller's
`built-in ADC.
`M = slope or conversion gain (m = l/LSB).
`LSB =the least significant bit of the analog-to-digital converter.
`X = Independent variable (analog input voltage to the SCC and the output of the
`temperature sensor in volts).
`B = Y-axis intercept or zero offset. It is assumed as zero in this application. Substituting B
`with zero in equation l gives the following result:
`
`Y=mX.
`
`(2)
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`Proceedings of the 16th IEEE Symposium on Computer-Based Medical Systems (CBMS’03)
`1063-7125/03 $17.00 © 2003 IEEE
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`The above equation can be realized using the LM 335 temperature sensor which has the
`following transfer function:
`VT= lOmV 1°c
`(3)
`Where is VT the temperature sensor analog output. This output swings between o° C to 50
`° C temperatures and between 0 -500 m V voltages. A signal conditioning circuit is designed
`to provide gain of 2.56. This will make the output voltage swing between O- l .28V and it is
`equivalent to 0 °c to 50 °c. An ADC reference voltage is supplied to provide resolution of
`0.1 °c. The output of the temperature ' s SCC is connected to channel 0 of the ADC (AnO).
`The pressure sensor has an input-output relationship that is similar to the temperature
`sensor. The output ranges from 14-300 mmhg. For the values between the two extremes,
`there is a linear relationship between output voltage and sensed temperature. SCC is used to
`make the sensor output compatible with the microcontroller built-in analog-to-digital
`converter. It is connected to channel 1 of the ADC (Anl).
`An offset and gain adjustments feature has been added to both temperature and pressure
`signal conditioning circuits. Both adjustments are needed to offset the long time gain and
`offset drift due to environment or components mismatching.
`The pressure sensor cuff is inflated by its compressing Digital output (DO) and deinflating
`using digital output (D 1 ). The pressure sound indicator is connected to analog signal (An2).
`
`2.2. The microcontroller:
`
`The microcontroller consists of an 8-bits processor that has 8-channels analog to digital
`converter (ADC) and several digital input/output ports. The ADC resolution is designed to
`have 0.1 °c and x mmhg. The built-in EPROM is used to host the embedded software
`algorithm that takes care of the parameters acquisition, processing, displaying, transmitting
`and receiving. The built-in EEPROM is used to save the online measured parameters along
`with their hourly and daily averages. The RS-232 is utilized for the GSM modem
`communication to upload and download messages that contain related patient's information
`and status.
`
`2.3. The GSM modem:
`
`The GSM modem offers high speed wireless connection. It is attached to the data adapter
`RS-232 and can be used as a stand-alone modem. Via the RS232, it can be connected to a
`personal computer or other devices such microcontroller. It supports five technologies for
`wireless data transfer, which can be used where GSM networks is available. The GSM
`modem is used as a short message server (SMS) device. It can send and receive messages
`containing a maximum of 160 characters. It supports call forwarding, call restriction, call
`transfer, multiparty calling and security options such as call barring [5] .
`
`In this application, The GSM modem is interfaced with the 8-bit microcontroller via RS-
`232 adapter. The modem receives a message from the microcontroller that contains the
`patient's information such as Name, ID, current temperature and pressure. It will then
`transmit the information as an SMS to pre-stored mobile phones. The receiver can be a
`health care personnel such as on call physician, nurse or/and emergency aid worker. Also, it
`can receive SMS messages from any one of the health care personnel acquiring more
`the following section, a detailed embedded software algorithm for
`information. In
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`Proceedings of the 16th IEEE Symposium on Computer-Based Medical Systems (CBMS’03)
`1063-7125/03 $17.00 © 2003 IEEE
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`parameters acqumng, processing, displaying, transm1ttmg and receiving are developed.
`Figure 1 shows the hardware layout of the proposed device.
`
`3. Device software development
`
`The embedded software is written using the microcontroller native language. Based on
`reset or power up, the microcontroller start to inflate the cuff with air and the blood pressure
`sound indicator is monitored until it fades away. One second later the microcontroller stops
`inflating the cuff and enable the release actuator to start deflating the cuff air pressure
`slowly. Meanwhile, the microcontroller starts the ADC conversion process and reads the
`pressure value every 16 µ-sec along with the indicating pressure signal. This process
`enabled again . When the trigger level of the
`continues until the indicating signal is
`indicating signal is reached it implies that the cuff air pressure is equivalent to the systolic
`blood pressure. This value will be stored as current systolic blood pressure. Along with this
`reading, the system will save the current value of the temperature. Microcontroller keeps
`listening to the indicating signal. Once it fades and is no longer heard, the value of the
`diastolic blood pressure is registered and saved along with the current temperature.
`The above process is a real-time interrupt driven event. The main program, the acquired
`and processed values are converted to BCD then displayed on the LED. If the acquired
`blood pressure and or temperature exceed a pre- stored warning level, the following
`sequence of events will take place:
`• A SMS message will be transmitted to the attached GSM modem via the RS232
`with the following information:
`Patient Name and ID.
`Current value of the blood pressure and temperature.
`Mobile number to dial to: one of the healths personnel.
`• The GSM modem then calls the attached mobile number and sends the above
`SMS to the first priority mobile number in the list.
`• Once the message is read, the reader must acknowledge by replying to the
`system. Otherwise, the system sends the above message to the second priority
`mobile number in the list.
`If there is no acknowledgement within two minutes, it will send the message to
`the third priority mobile and wait for acknowledgement.
`• The system repeats the above chain of commands until an acknowledgment is
`received.
`• Worst case scenario, the system repeats the above procedure x number of times,
`if there is no answer and the patient status is getting worse then it will call 911.
`Assuming 911 has SMS message center.
`Once the health personnel receive the SMS message, he/she can acquire more parameters
`from the system by sending SMS message such as the pressure and temperature average
`values for the last hour and day. The health personnel may send SMS or calls the patient
`direct for further instructions.
`
`•
`
`4. Accuracy and error analysis:
`
`The system accuracy depends on several factors. The signal conditioning circuits'
`components mismatching, aging factor, output offset and environment effect, the ADC
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`Proceedings of the 16th IEEE Symposium on Computer-Based Medical Systems (CBMS’03)
`1063-7125/03 $17.00 © 2003 IEEE
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`quantization error and rounding error due to the reminder from the fraction division. Some
`delay time that may be caused by the the interrupt procedure. The subjects of this error are
`under investigation and
`further work will be carried out to enhance the device accuracy
`and stability. It is worth mentioning that the major objective of this paper is the GSM(cid:173)
`microcontroller integration that enhance the mobility of the patient and communicate with
`the health personal from anywhere anytime.
`
`5. Future development and conclusion
`
`A prototype of GSM-based mobile patient has been design, developed and tested using
`off-the-shelf components. The device gives more freedom for patients to roam around the
`GSM-Network coverage area and allow the health personnel to keep in touch with patient
`without being around the hospital bedside. The system is scalable and extended to have up
`to eight different signals from the patient.
`
`6. References
`
`[I] B. Woodward, R S. H. Istepanian and C. I. Richards, "Design of a Telemedicine System Using A mobile
`Telephone. IEEE Transactions on Information Technology, Vol, 5, No. I, March 200 I. pp. 13-15.
`[2] Bauer, P. ; Sichitiu, M.; Istepanian, R.; Premaratne, K.; "The mobile patient: wireless distributed sensor
`networks for patient monitoring and care", Proceedings of the Information Technology Applications in
`Biomedicine-IEEE EMBS International Conference, 2000, Pp: 17 -21
`[3] A. T. S. Chen, " WWW + Smart card: towards a mobile health care management system", International
`Journal of Medical Informatics", Vol. , 57, Issue 2-3 , July 2000, pp. 127-137.
`[4] S. Pattiches, E. Kyriacou, et., " Wireless Telemedicine Systems: An Overview", IEEE Antenna's&
`Propagation Magazine, Vol. 44, No., April 2002, pp 143-153.
`[5] Nokia 30 GSM Connectivity Terminal User's Guide for modem use, 2002 Nokia Corporation,
`www.noka.com.
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`Proceedings of the 16th IEEE Symposium on Computer-Based Medical Systems (CBMS’03)
`1063-7125/03 $17.00 © 2003 IEEE
`
`IEEE~
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`:~\
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`\
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`.
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`Emerglncy's Phone
`
`Nurse's Phone
`
`Dr.'s Phone
`
`Ante;nna
`
`GSM.Modem
`
`Pressure Sound Indicator Si nol
`
`Embedded ~sf em-Based Mobile Patient Monitoring Device • Block Diagram
`
`Figure 1. Device block diagram
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`Proceedings of the 16th IEEE Symposium on Computer-Based Medical Systems (CBMS’03)
`1063-7125/03 $17.00 © 2003 IEEE
`
`IEEE~
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`COMPUTER
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