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Telemedicine System: Development of Wireless Healthcare Units with GSM and Bluetooth Link

Zainudin Kornain MIEEE, Muhammad Rosli Abdullah & Mohd Azlan Abu 1Universiti Kuala Lumpur British Malaysian Institute

Gombak, Selangor, Malaysia Email : [email protected], [email protected]

Abstract—Telemedicine has a potential used with the advancement in electronic and computer. It requires sensors for a health indicators and units to communicate between patients and the doctors. This promote a flexible solution to a home telecare or ICU by develop units for measuring vital signs which are wirelessly connected to a master unit with a Bluetooth link to a personal digital assistant (PDA). These independent units consist of a PIC microcontroller, GSM modem, RF and Bluetooth transceiver plus transducers for the body temperature, bodyweight, pulse rate and blood pressure measurement. Later, these measurements are sent as SMS via a GSM module and to the PDA via a 2.4 GHz Bluetooth transceiver. The data transmission is optimized up to 100 meter distance with accuracy of ± 0.1 ºC body temperature, ≤ 150 Kg bodyweight, 0~260 mmHg blood pressure and 40~180 BPM pulse rate. A voice synthesizer promotes a user friendly approach for alarming and guiding user when this system is in use

Keywords- Telemedicine, Home telecare, Microcontroller, Bluetooth, PDA, Oscillometric

I. INTRODUCTION Normally, Malaysian doctors are still practice a traditional

method for monitoring patients from one bed to another [1]. In advance countries, telemedicine has overcome shortage of the doctors to patient ratio [2]. It also helps overloaded doctors with patient’s treatment, monitoring and diagnosis. Administration of pre-hospital care and patient monitoring techniques also could be improved [3]. In Malaysia, telemedicine is not much used due to its non-effectuated legislation act [4].

The early works of telemedicine began with the National

Aeronautics and space (NASA) instrumentation pack to monitor astronaut’s vital signs [5]. It contains an endoscope, ophthalmoscope, lens, ECG, automatic blood pressure, stethoscope, oximeter and a computer [6]. Since then telemedicine has increased quality, efficiency and expand the access of health-care delivery system [7].

Recent design incorporates palmtop computers, Personal

Diary Assistance (PDA) and even high-end mobile phones as information devices that are equipped with data acquisition capabilities [8,9]. Hence, many researches have been carried out to integrate PDA in the telemedicine applications [10-18]. An availability of Bluetooth technology fully furnishes a

modern communication with a piconet and adhoc communication up to 100 meter away at a baud rate of 1M bps [19]. Furthermore, combination of Bluetooth technology with PDA can be adapted in the telemedicine without generate interference to other medical equipment [20]. Medical equipment also becomes less cumbersome since physical wiring from the patients to medical instruments will be wirelessly replaced.

II. METHODOLOGY The block diagram of system seen in Figure 1 consist of

the Slaves and Master unit.

Figure 1. Block diagram of Telemedicine system

Slave1: Body temperature measurement based on NTC thermistor was chosen due to its high sensitivity. As stated in Equation 1, an exponential response is appropriate for measuring body temperature (37 ºC to 39 ºC).

( )1 100 T TRT R eβ −

=

(1)

In Figure 2, it was simplified with the use of a voltage regulator (LM317T) for setting the ADC reference (Vref+). It was set to 4 V for enhancing the on-board ADC resolution of PIC16F873A. Once the ADC conversion is obtained, it will be

2012 IEEE Symposium on Industrial Electronics and Applications (ISIEA2012), September 23-26, 2012, Bandung, Indonesia

978-1-4673-3005-3/12/$31.00 ©2011 IEEE 72

displayed on a LCD and then transmitted on air via RF transceiver module.

Figure 2. Body temperature measurement circuit

Slave2: Bodyweight was measured via quadruple load cell as shown in Figure 3. AD524 Instrumentation Amplifier (IA) is choosed as a perfect solution for amplifying noisy strain gauge’s signal [21]. An economical system of single IA to amplify quadruple strain gauge signals was achieved by interface AD524 to a serial analogue multiplexer (MAX349). It is controlled by the PIC16F877A with Serial Protocol Interface (SPI) via time division switching technique.

Figure 3. Bodyweight data acquisition circuit

Referring to the Figure 4, a 16 Hz passive low-pass filter

with a voltage buffer (LM124) is cascaded to attenuate 50 Hz power line interference and noise such as artefact, environment and natural randomness. The ADC result was sample about 200 times then displayed and calibrated on the

LCD before transmitted on air via RF transceiver module (ER900TRS).

Slave3: An oscillometric technique is applied in which limb and vasculatures are compressed with an inflatable cuff [22]. As shown in Figure 5, a 0-5 psi pressure transducer (ASDX005G24R) which satisfies 0-260 mmHg was split into two paths. It was digitized by the on-board PIC16F877A ADC and also filtered by the two bandpass filter to give large voltage gain at 1 Hz to 4 Hz [23].

Figure 4. Filtering and buffering circuit

Note:

Bp1= Bandpass Filter1 Bp2=Bandpass Filter2

Figure 5. Blood pressure measurement circuit As the pump is deflated from 160 millimetre mercury (mmHg), pulse rate will be sampled in a PIC16F877A timer 0 routine at interval of 10 milliseconds. This process continues for 15 seconds duration and the detected pulse is multiplied by 4 to give an average pulse rate at beat per minute. An empirical method is used to determine systolic (SBP) and diastolic (DBP) that infer to a mean arterial pressure (MAP) [24]. This relates to the Oscillometric method as a maximum oscillation function of a parabolic curve in Figure6 [25].


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Figure 6. Blood pressure measurement parabolic curve

Once MAP is found, Equation 2 and Equation 3 are referred to determine the SBP and DBP.

( )Systolic map map a= + (2)

( )Diastolic map map b= − (3)

Variation duty cycle of pulse width modulation (PWM) generated by the PIC16F877A is applied to the valve to ensure a linear release rate at 5 mmHg per second [26]. This allows the PIC16F877A to capture the oscillation amplitude for determining the MAP. Optical coupler 4N26 which is electrically isolated was used to prevent electromagnetic interference from the pump.

Master: The Telemedicine system began with the keypad entry on the Master unit in Figure 7 for setting a date and time in a Real Time Clock (DS1302). Then the microcontroller polls the measurements data from slave units at 19.2 kbps baud rate via radio frequency (RF) transceiver operated at 433-434MHz. Upon RF data reception, master unit will display slave’s data on the LCD and record it in the EEPROM according to the Real Time Clock (RTC). The communication mode can be set either via GSM or Bluetooth module. A Bluetooth transceiver is used to send the biomedical data, time and date to the mobile phone within a radius of 100 meters away. If the GSM mode is set, the PIC microcontroller will send AT commands for sending SMS to the respective medical specialist.

Figure 7. Master unit circuit diagram

III. EXPERIMANTAL RESULTS The NTC thermistor response over a temperature

(0°C~100°C) had been tested and result in Figure 8 was obtained with β=3.86K. The ADC resolution was reduced at 3.9 mV and successfully to updates ADC conversion at 0.1º C such as shown in the Figure 9. A calibration formula as stated in the Equation 4 was applied for the Body temperature measurement.

0.0735 23.436Y X= − (4)

Therefore in Figure 10, if X/ ADC=581 then Y/ Body temperature=19.26 °C.

Figure 8. Thermistor resistances Vs. Temperature

Figure 9. 3.9 mV ADC resolution at 0.1º C changes

Figure 10. Displaying the body temperature

The strain gauge response in a compressive force had

been conducted from a resting state until 10 Kg. A linear result in Figure 11(a) was obtained and represented by the Equation 5.

0.1 10.9y x= + (5)


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Therefore, given x=150 Kg × 0.1mV, y=25.9 mV and as noted in Equation 6 when Vout= 5 V, Vin= 25.9 mV then AV=193.

VoutAV Vin= (6)

Figure 11(b) indicates an instrumentation amplifier (IA)

voltage output from 10 g to 150 Kg of applied weight. A significant voltage output had change from 10 Kg onwards which is relevant to the adult bodyweight measurement. As expressed in the Equation 7, a small change of the strain gauge will cause a tiny output voltage of Wheatstone bridge circuit.

VexRxRxVout ⎥⎦

⎤⎢⎣⎡Δ=Δ

2

(7)

(a) (b)

Figure 11. Weight Vs Voltage Therefore, given Rx=1 kΩ, ΔVout=0.1 mV, Vex=5 V thus ΔRx=0.04 Ω. Therefore, at every 1 kg, 1 kΩ strain gauge will change at 0.004 %. As a result, at 150 kg, ΔRx=6 Ω and ΔVout= 15 mV + 10.9 mV (strain gauge at resting state) is equal to 25.9 mV. Finally at 150 kg, the Equation 5 and Equation 7 will lead to the same result. In Figure12a to 12d shows the averaging result over fluctuation caused by the natural randomness. The lower LCD row represents the 200 samples of the ADC fluctuated result while the upper LCD row is its consistent average value.

Figure 12. The averaging result on LCD

An acceptance test was conducted in Figure 13 with the

bodyweight result was displayed on the LCD before transmission to the master unit on air via the RF transceiver.

Figure 13. Body weight measurement system testing

An ASDX005G24R experimental result as shown in Figure14 was initially tested for an Oscillometric blood pressure measurement.

Figure 14. ASDX005G24R experimental result

The ASDX005G24R output is then processed by the first and second bandpass filter at specified cutoff frequency as shown in Figure 15 and Figure 16.

Figure 15. 0.3Hz~6.6Hz of 1st bandpass filter


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Figure 16. 0.3Hz~19.8 Hz of 2nd bandpass filter

The two stages of bandpass filter had been cascaded for a

better roll-off at a gain factor of 400. The bandpass filter output in Figure 17 shows the oscillation signal at 1 Hz (Bottom waveform) riding on the Cp signal at ≤ 0.04 Hz (Top waveform). Finally, the system accuracy was carried out with a Non Invasive Blood Pressure (NIBP) analyzer as shown in Figure18. As displayed on 40x4 LCD, a Master unit in Figure19 indicates successful wireless data reception from the slaves system. As a home telecare, measured data could be sent via SMS to the respective medical specialist. A functionality of GSM module had been tested with a PIC microcontroller simulator in Figure 20. In Figure 21, the Graphical User Interface in Microsoft Visual Basic (VB) was programmed for receiving, sending, profiling, analyzing and logging SMS data from the Master unit.

Figure 17. Finding the MAP

Figure 18. Accuracy test with the nibp analyzer

Figure 19. Master to PDA communication test

Figure 20. PIC16F877A simulation for sending SMS

Figure 21. GUI in VB for receiving and sending SMS


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IV. CONCLUSION In this paper, a working concept of telemedicine system had been developed under the factors of cost and applications in Malaysia. The wireless slaves unit are successfully promote a patients comfort without haywire the analytical equipment. The enumeration process on wireless slaves/ Master communication provides unlimited number of hardware connectivity. A flexible approach was offered either from a long or short distance communication via GSM or Bluetooth module. A Bluetooth communication within 100m radius is appropriate for monitoring patients in the small area such as hospital ward. Meanwhile, a GSM communication is more suitable to be used as a home telecare. Patients are advised for taking number of measurement in a day and their health profile will be monitored remotely. Those with a low health profile will be contacted by their respective doctor immediately. Effectively, cases such as heart failure and stroke could be managed and pre-hospital care will be improved with this telemedicine system. As a home telecare, hospitalized cost could be reduced and doctor to patient ratio also will be improved. Hence, the way of healthcare delivery in Malaysia will be change as what had been practiced in some countries.

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