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Sensors and Actuators A 172 (2011) 315– 321

Contents lists available at ScienceDirect

Sensors and Actuators A: Physical

jo u rn al hom epage: www.elsev ier .com/ locate /sna

smart medication system using wireless sensor network technologies

en-Wei Changa, Tung-Jung Sungb, Heng-Wei Huanga, Wei-Chih Hsua, Chi-Wei Kuoa,he-Jhao Changb, Yi-Ting Houb, Yi-Chung Lana, Wen-Cheng Kuoc, Yu-Yen Lina, Yao-Joe Yanga,∗

National Taiwan University, Taiwan, ROCNational Taiwan Univ. of Sci. and Tech., Taipei, Taiwan, ROCNational Kaohsiung First Univ. of Sci. and Tech., Kaohsiung, Taiwan, ROC

r t i c l e i n f o

rticle history:eceived 30 September 2010eceived in revised form 4 February 2011ccepted 11 March 2011vailable online 17 March 2011

a b s t r a c t

In this work, a smart medication system, which employs the wireless sensor network (WSN) technologies,is designed, implemented and demonstrated. The primary functions of the system include medicationreminding, pill-dispensing assisting, and medication recording for the patients with chronic diseases.The proposed system, which can be easily deployed in a nursing home where many elderly people livetogether, consists of a master panel (MP) and seven portable smart pill-boxes (SPBs). An MP serves as

eywords:ireless sensor networkagnetic sensingealthcare systemhree-state detectionigBee

a network gateway/database for the SPBs registered under the MP. Each SPB, which stores user’s dailydoses of pills, can independently remind the user to take medicines at specified times. The star topologyis used for the communication between an MP and its seven affiliated SPBs. The tree topology is employedas the routing network among the MPs. Moreover, by using magnetic sensors, a pill-detection module isproposed for detecting the existence of pills in an SPB’s pill-cell. A WSN communication configuration,which can effectively reduce packet-loss rates, is also proposed. The relationship between round-trip

nts is

times (RTTs) and hop cou

. Introduction

The recent rapid progress in wireless communications andicrosystems has enabled the realization of low-cost miniatur-

zed wireless sensor devices [1,2]. These sensor devices, which arelso called sensor nodes, can be networked together over a wire-ess medium to form a wireless sensor network (WSN) for sensing,

easuring and gathering information from the environment [3–5].he applications of WSN technologies have been demonstrated inealthcare areas [6–9]. In [6,7], the WSN applications for patientonitoring are proposed. The monitored signals include heart rate

HR), electrocardiogram (ECG), blood pressure, blood glucose, ando on. A wearable healthcare system integrated with wireless sen-or networks for monitoring elderly patients with chronic diseasesas proposed in [8]. In [9], qualitative research was carried out for

tudying the perceptions, attitudes and concerns of elderly personsowards WSN technologies in healthcare applications.

Furthermore, the average human life has been extended dur-ng the past decades. Therefore, aging society is one of the mainssues for many countries in the world. Elderly patients frequentlyake wrong pills due to the complexity of prescribed medication,

∗ Corresponding author at: Mechanical Engineering, National Taiwan University,o. 1 Roosevelt Rd. Sec. 4, Taipei, Taiwan, ROC. Tel.: +886 2 33662712.

E-mail address: yjy@ntu.edu.tw (Y.-J. Yang).

924-4247/$ – see front matter © 2011 Elsevier B.V. All rights reserved.oi:10.1016/j.sna.2011.03.022

measured.© 2011 Elsevier B.V. All rights reserved.

or waste medicines due to the neglect of taking medications. Theformer might cost a life at certain critical conditions, and the lat-ter might waste significant healthcare resources. In this work, wedevelop a WSN smart medication system which is designed to pro-vide various functions to assist the medication for elderly patientswith chronic diseases.

The proposed smart medication system includes a masterpanel (MP) and seven smart pill-boxes (SPBs). The primary func-tions of the system include medication reminding, pill-dispensingassisting, and medication recording. An MP serves as a networkgateway/database as well as the charging dock for the SPBs regis-tered under the MP. Each SPB, which stores a user’s daily dose ofpills, can independently remind the user to take right medicinesat the specified times. A database is implemented and installed inthe MP for managing the prescription and medication records forusers. Also, this database is essential for users to correctly refill pillsin each pill-cell of SPBs. A three-state magnetic pill-detection mod-ule is proposed for detecting the existence of pills in a pill-cell. AnRF chip which complies with the ZigBee/IEEE 802.15.4 standards[10,11] is employed. The networks of the tree topology and the startopology are implemented in the system. Furthermore, network

performances, such as round-trip times and packet-loss rates, willalso be measured and discussed.

The rest of this paper is organized as follows. Section 2 describesthe hardware architecture of the proposed WSN smart medicationsystem. Section 3 presents the proposed network configuration.

316 W.-W. Chang et al. / Sensors and Actuators A 172 (2011) 315– 321

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provides the CSMA/CA [14] capability for avoiding packet collisions[15,16]. The sensor chip SHT11 (by Sensirion®) is employed as thetemperature and humidity sensor [17]. The sensed physical signalsof the SHT11 were converted into digital signals by the sensor chip

Fig. 1. Master panel: (a) the front view, and (b) the rear view.

ection 4 presents the measured results. The discussion of the mea-ured performance will also be provided. Section 5 concludes thisaper.

. Hardware architecture

Fig. 1 shows the smart medication system which includes anP and seven SPBs plugged in the MP’s charging dock. The pictures

f an SPB are shown in Fig. 2. Table 1 lists the dimensions of theP and the SPB. In principle, an SPB stores the doses of pills for a

atient to take in one day. In our current design, an SPB has fourill-cells, each of which is designed for storing pills of single dose.

f the medication requires five or more doses per day, two SPBs wille used for a single-day medication. The capacity of the lithium-ionattery used in each SPB is 330 mAh, and the typical life time of theattery is about 10 days. The speakers on the SPBs and the MP cane used to remind patients by voices. Also, the LED indicators on thePBs are used to indicate the pill-cells in which the pills should beaken. The LCD touch-screen on the MP is employed to assist usersor the medicine dispensing (refilling) process on a weekly basis.uring the dispensing process, interactive graphic instructions on

he LCD screen will guide users to pick up right pills, and put themnto the SPBs’ pill-cells whose LED indicators are on.

The hardware architectures of the MP and the SPB are shown inig. 3. Both the MP and the SPB use the RF modules which are com-osed of an RF transceiver chip (UZ2400, UBEC® [12]) and a 16-biticrocontroller chip (MSP430F1611, Texas Instruments® [13]). The

able 1imensions of the master panel and the smart pillbox.

Devices Length Width Height

Master panel 9 mm 28.5 mm 7.4 mmSmart pill-box 10.6 mm 6.2 mm 2.8 mm

Fig. 2. Smart pill-box: (a) the top view, and (b) the bottom view.

UZ2400 chip complies with the ZigBee/IEEE 802.15.4 standards and

Fig. 3. The hardware architecture sponge.

W.-W. Chang et al. / Sensors and Actuators A 172 (2011) 315– 321 317

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ig. 4. (a) The picture of the three-state pill detection module. (b) The operationalrinciple of the module. (c) The magnetic flux generated by the two permanentagnets.

tself. Then, the signals were digitally transferred to the microcon-roller by using the I2C bus. The performances and specificationsf the sensor chip can be found in the datasheet. Also, the for-ulas describing the relationships between the “converted digital

ignals” and the “measured physical quantities” (i.e., temperaturend humidity) are also provided in the datasheet.

In addition, a three-state pill detection module is proposed foretecting the existence of pills of an SPB’s pill-cell. As shown inig. 4(a), a movable plate is clipped into the cavity of the cover of

pill-cell. Two magnets are glued on the inner side of the mov-ble plate. Also, a small block of sponge, which serves as a durableoft spring, is installed inside the cavity between the cover and theovable plate. In addition, a magnetic sensor (MMC212Xmg, byEMSIC [18]), which is soldered on a printed circuit board, is placed

nder the pill-cell. Similar to the temperature and humidity sensorhip, the magnetic sensor communicates with the microcontrollery using the I2C bus.

Fig. 4(b) shows the operational principle of pill detection. Ashown in Fig. 4(b)-(i), when the cover of a pill-cell is closed witho pills inside, the magnetic flux “loop” generated by the two per-anent magnets (see Fig. 4(c)) is relatively close to the magnetic

Fig. 5. The schematics of the magnetic flux induced by (a) the single-magnet con-figuration, and (b) the proposed dual-magnet configuration.

sensor, so the detected magnetic field is relatively strong. As thecover is closed with pills inside the cell (Fig. 4(b)-(ii)), the detectedmagnetic field is smaller than the case in Fig. 4(b)-(i), since the mov-able plate as well as the magnets are pushed away from the sensorby the pills. When the cover is wide open (Fig. 4(b)-(iii)), apparentlythe detected magnetic field should be the smallest compared withprevious two cases.

By carefully designing the relative locations/orientations of themagnets and the magnetic sensor, this module can detect threestates: cover-closed-with-no-pills (CC-NP), cover-closed-with-pills(CC-P), and cover-open (CO). In addition, the status of each pill-cellwill be transmitted to the master panel (right after the status ischanged), and will be stored in the database (MySQL) running inthe master panel. We can judge whether the user (patient) takesthe medicines (pills) by the status of each pill-cell. For example, ifthe CC-P status (cover-closed with pills) of a pill-cell is detectedafter the medication time is passed, the master panel will receivethis status from the pill-box, and will record that the patient forgotto take the medication at the right time.

Note that the dual-magnet configuration (see Fig. 4(c)), whichconfines the magnetic flux on a two-dimensional plane (i.e., theplane aligned with the surface plane of the movable plate), canimprove the accuracy of detecting these three states. The schemat-ics of the magnetic flux induced by a single-magnet configurationand the proposed dual-magnet configuration are shown in Fig. 5. Ifsingle magnet is used, the magnetic field lines will be cylindricallysymmetric to the magnet. Therefore, the �Z (i.e., the thickness ofthe volume with substantial magnetic field intensity) is not very

small. For the dual-magnet configuration, since most of the mag-netic field lines are confined on the x–y plane, not only �Z is smallerthan the single-magnet configuration, but also the magnetic inten-sity is stronger. Therefore, the “contrast” of the field intensity in

318 W.-W. Chang et al. / Sensors and Actuators A 172 (2011) 315– 321

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ig. 6. (a) The star topology employed between a master panel and the sevenmart pill-boxed registered under the master panel. (b) The tree topology employedetween master panels.

-direction is much larger, so the magnetic sensor should differen-iate the position of the movable plate more accurately.

. Network configuration

This system establishes the networking by combining two typesf network topologies: the star topology and the tree topology. Thetar topology is used for the communication between an MP andhe seven SPBs registered under the MP, as shown in Fig. 6(a). EachPB in the star topology initializes the communication with theP. SPBs stay at the sleeping mode for most of the time, then wake

p periodically (i.e., at the normal mode) for requesting commandsrom the MP. Therefore, the power consumption of each SPB can be

inimized.The CSMA/CA [14] capability of the UZ2400 chip can prevent

acket collisions. However, the bandwidth contention problem,hich will also result in packet loss, might become significanthen the medication systems are deployed in a nursing home or

hospital. For example, if 20 users are using the medication sys-ems simultaneously in the same building, more than 160 pillboxessensor nodes) will share the wireless channels. In order to reduceandwidth contention in the star topology, we propose a simpli-ed time division method (STD) for time synchronization: the timeeriod for each communication cycle (i.e., the cycle when SPBs aret the normal mode) is divided into many time slots with specificags of synchronization [19], so that each SPB can communicateith the MP at a specific time slot. Note that the tag of the time slot

or each SPB is assigned when the SPB first joins the star network

f the MP.

The routing network among the MPs is constructed using theree topology [20–23], as shown in Fig. 6(b). The coordinator is inharge of initializing, organizing and maintaining the network [21].ach MP also serves as a router for relaying the data to the speci-

Fig. 7. The procedure of joining a tree topology.

fied destination. Fig. 7 describes how an MP joins a tree-topologynetwork. Firstly, Rn sends a beacon to request for joining a network(Step 1). Then, Rn receives the beacon responses from R5 and R6(Step 2). In Step 3, Rn chooses R5 and requests to become R5’s child.Then, R5 agrees the request and responds to Rn (Step 4). Finally, Rnbecomes one of the R5’s children (Step 5).

Since the tree topology is based on a hierarchical structure,transmission distance increases with the hop count, which is alsoproportional to the packet transmission time. If the waiting time forreceiving a packet is less than the transmission time of the packet,packet losses possibly occur. However, increasing the waiting timealso increases power consumption due to longer RF operating time.Since the numbers of the hop count are pre-determined in a treetopology, the waiting time for receiving a packet can be estimated.Therefore, by using the tree topology, the power consumption ofthe SPB will be nominal due to accurate estimation of the waitingtime as well as no requirement of computing routing paths. It isworthy to mention that the number of hops is determined by howthe tree topology network is formed in a building (e.g., a hospital).In other words, it will strongly depend on the locations of the roomswhere the MPs are located, the total number of MPs, and so on.

Under this network architecture including the star and the treetopologies, the user’s prescription, the records of medicine taking,as well as the sensed temperature/humidity data, can be wirelesslysynchronized between an MP and its affiliated SPBs. Also, an MP cansend/receive the information of its SPBs to/from the coordinatorthrough other MPs in the tree topology.

4. Experiment results and discussions

4.1. Pill detection

Fig. 8 is the measured results of the three-state pill detectionmodule. As shown in the figure, DMP is the vertical distance betweenthe magnets and the magnetic sensor. When the cover is closed, DMPis about 3 mm if there is no pill inside the cell (see Fig. 4(b)-(i)). At

W.-W. Chang et al. / Sensors and Actuators A 172 (2011) 315– 321 319

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CFG-2(enable CSMA/CA)

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ig. 8. The relationship between the measured magnetic field intensity and theertical displacement of the movable plate.

his condition (i.e., CC-NP), the detected magnetic field intensity isery strong and the output of the magnetic sensor saturates at about

G. When the cover is closed and pills are placed inside the cell, theills displace the movable plate upward. The minimum thickness ofypical pills is about 2 mm, and the maximum depth of the pill-cells 15 mm. Therefore, the value of DMP which is between 5 mm and8 mm can be considered as the CC-P state. When the cover of theill-cell is wide open, the measured field intensity is even smaller,ot only because DMP is larger, but also the tilting angle (see Fig. 4(b)-iii)) of the movable plate further increases the distance betweenhe magnetic sensor and the magnetic flux. At this condition (theO state), the magnetic field intensity is close to earth’s magneticeld [24].

.2. Network performance

We also measured the performance of three wireless commu-ication configurations, CFG-1, CFG-2 and CFG-3. In CFG-1, theSMA/CA capability is disabled. In CFG-2, the CSMA/CA is enabled.

n CFG-3, the CSMA/CA is enabled and the time division method ismployed. Fig. 9 shows the schematic of the experiments. An MP

s placed at the center, and SPB(s) are placed on the circular cir-umference with a radius of 1 m. The number of the SPB increasesrom 1 to 14. Each SPB sends a packet of 100 bytes to the MP every00 ms. When the MP receives a packet from the SPB, the MP will

Fig. 9. The schematic diagram of the experiment of packet-loss rate.

1 8765432 109 11 12 13 14

Number of Smart Pill-Box

Fig. 10. The relationship between packet-loss rates and numbers of smart pill-box.

send a packet of 100 bytes back to the SPB immediately for acknowl-edging a successful data transmission. The packet-loss rate can becalculated by:

Packet Loss Rate = TSP − TRP

TSP

where TSP is the total number of packets sent, and TRP is the totalnumber of packets received. As shown in Fig. 10, it is obvious thatthe packet loss rate of CFG-2 is better (i.e., smaller) than that of CFG-1. However, the packet-loss rates of both configurations increasewith the number of SPBs. For example, as the number of SPBs is 14,the packet-loss rate of CFG-2 is as high as 38%. Fig. 10 also showsthat the packet-loss rate of CFG-3 is about 5% when 14 SPBs areregistered in the network. In other words, CFG-3 not only reducesthe possibility of the packet collision but also reduces the band-width contention, and thus further provides higher transmissionperformance. Note that in the experiment, TSP is 1000.

In order to estimate the transmission time under different hopcounts, the relationship between round-trip times (RTTs) and hopcounts is measured. RTT represents the total time for a packetto travel from a source to a destination and then travel back tothe source again [25]. For the RTT measurement, the coordinatorsends a packet to a specific MP (router) through a specified routingpath, and the MP (router) sends the packet back to the coordina-tor through the same path. The cases with packet lengths of 60

bytes and 120 bytes are measured. As shown in Fig. 11, the rela-tionship between RTT and hop counts is quite linear for both cases.As the number of hop counts increases, RTT also increases due tothe increase of the transmission distance. Since the routing paths

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n a tree topology is pre-determined, the linear characteristic ofhe measured results can be utilized to accurately estimate theequired RF waiting time when an RF module is waiting for receiv-ng a packet, which can optimize the power consumption of theystem.

. Conclusion

In this work, we developed a smart medication system whichmploys the wireless sensor network (WSN) technologies. Theunctions of medication reminding, pill-dispensing assisting and

edication recording have been implemented and demonstrated.he proposed system consists of a master panel (MP) and sevenortable smart pill-boxes (SPBs). A tree topology network waspplied to the smart medication systems, which can be expandednto a multi-user system deployed in a nursing home or a hospital.

wireless communication configuration for reducing the proba-ility of packet-loss rate was also proposed. In the condition of 14PBs, each SPB sends one 100-byte packet every 200 ms, more than5% packets can be transmitted correctly with the proposed simpleime-division method and CSMA/CA. The relationship between RTTnd hop count was also measured. Furthermore, a three-state pilletection module was designed and implemented. The module canccurately detect if pills exist in a pill-cell, as well as if the cover ofhe pill-cell is opened.

cknowledgement

This research is sponsored by the National Science Council,aiwan, R.O.C. (Contract number: NSC 98-2218-E-002-016).

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Biographies

Wen-Wei Chang received his B.S. degree in Mechanical Engineering at NationalTaiwan University, Taiwan in 2009. Currently he is a graduate student in theMechanical Engineering Department. His research interests include wireless sensornetworks, blue-tooth technologies and embedded systems for biomedical applica-tions.

Tung-Jung Sung holds BSc and MA in Industrial Design and PhD in Management, andis currently an Associate Professor of the Department of Industrial and CommercialDesign at National Taiwan University of Science and Technology, Taiwan. Dr. Sunghad worked for Philips Electronics Industries (Taiwan) Ltd. in project and productmanagers for several years. He has also been the Patent Examiner of the IntellectualProperty Office in Taiwan for a number of years. His recent design and researchinterests focus on intelligent product design for elderly, service design, and designmanagement. His research articles are accepted for publication in the InternationalJournal of Technology Management and Design Studies.

Heng-Wei Huang is an undergraduate student in Mechanical Engineering atNational Taiwan University. His research interests include wireless sensor network,bi-stable microactuators, and sensor technologies.

Wei-Chih Hsu received his B.S. degree and M.S. degree in mechanical engineeringat National Taiwan University, Taiwan in 2008 and 2010, respectively. His researchinterests include wireless sensor network and embedded system for biomedicalapplications.

Chi-Wei Kuo received his B.S. degree and M.S. degree in Mechanical Engineeringat National Taiwan University, Taiwan in 2005 and 2007, respectively. His researchinterests include reduced order modeling for microsystems, wireless sensor net-work and parallel computing.

Jhe-Jhao Chang received his B.S. degree and M.S. degree in Industrial Design atNational Taiwan University of Science and Technology, Taiwan in 2005 and 2007,respectively. Currently he is a doctoral student of the department. His researchinterests include product design, user experience and ethnography, and informationdesign.

Yi-Ting Hou received his B.S. degree in Industrial Design at National Taiwan Univer-sity of Science and Technology, Taiwan in 2009. Currently he is a graduate studentof the department. His research interests include product design and design man-agement.

Yi-Chung Lan received his B.S. degree in Mechanical Engineering at National TaiwanUniversity, Taiwan in 2009. Current he is a graduate student in the department.His research interests include sensor technologies, carbon nanotubes assembly andnanotechnologies.

Wen-Cheng Kuo received the M.S. degree in Mechanical Engineering from Chiao-Tung University, Hsinchu, Taiwan in 1993 and the Ph.D. degree in MechanicalEngineering from National Taiwan University, Taipei, Taiwan in 2006. He has con-ducted the postdoctoral research in micro-electromechanical system (MEMS) atNational Taiwan University, Taipei, Taiwan from 2006 to 2007 and Caltech Micro-machining Laboratory, Pasadena, USA from 2007 to 2008 respectively. Currently,he is an Assistant Professor in the Department of Mechanical and Automationat National Kaohsiung, First University of Science and Technology in Kaohsiung,Taiwan. His research interests are in MEMS, including analysis, design and fabrica-tion of micro/nano structures, and sensors and actuators for optical applications.

Yu-Yen Lin received her B.S. degree in Mechanical Engineering from Chung YuanChristian University in 1993, and M.S. degree in Mechanical Engineering the National

Taipei Univerity of Technology in 2001. Ms. Lin has been one of members of thetechnical staff in the Department of Mechanical Engineering at the National TaiwanUniversity since 1992. Currently, she is the Technical Specialist of the department.Her expertise includes CAD, CNC programming, and process design.

Yao-Joe Joseph Yang received his M.S. and Ph.D. degrees in Electrical Engineer-ing from the Massachusetts Institute of Technology (MIT). Also, he received his

nd Act

Mb(mCHt

W.-W. Chang et al. / Sensors a

.S. degree from UCLA and his B.S. degree from the National Taiwan University,

oth in mechanical engineering. From 1999 to 2000, he joined the Coventor IncCambridge, MA) as a senior application engineer. Since 2000, he joined the Depart-

ent of Mechanical Engineering at the National Taiwan University, Taipei, Taiwan.urrently he is a professor, and serves as the associate chair of the department.e is also the director for CAD Technology in the NTU NEMS Center. From 2005

o 2009, he serves as the deputy Secretary General of the Chinese Institute of

uators A 172 (2011) 315– 321 321

Automation Engineering (CIAE). Currently he is the board member of the Institute.

His research interests include microelectromechanical systems, nanotechnology,high-precision micromachining, flexible sensing arrays, sensor network, parallelprocessing, and semiconductor devices and vacuum microelectronics modeling.He has been consulted by more than three US-based companies and four Taiwan-based organizations. Dr. Yang is a member of IEEE. He is also the recipient of theOutstanding Young Researcher Award of the National Science Council.