Exercise Bracelet with Bluetooth

Exercise Bracelet with BluetoothLow Energy Module and Accelerometerfor Sporting EventsJung-Tang Huang,Wen-Chia Chao,and Chia-Hsiang LeeAbstract While the wireless Bluetooth4.0technology has been introduced,this study focuses on its low power consumption and quick connection features to develop a system used in sporting events.The system includes a user bracelet, signal reading stations,and individual positioning program by using of the RSSI (received signal strength indication).The proposed system does effectively and accurately capture user’s location,with different characteristics from regular posi-tioning system as GPS and Wi-Fi,which can be applied in indoor and outdoor environments.Due to sporting events,the venue must maintain a certain space for movement,and the loss of multipath fading effects in the open spaces is much lower.Thus,the attenuation of the signal strength is much less,and it will more effectively target the user’s position.The positioning method is similar to Zigbee by using the triangulation algorithm,but the biggest difference is the cellular phones in the market support Bluetooth rather than ZigBee.Keywords Bluetooth4.0•Positioning•Exercise bracelet1IntroductionThis study adopts Bluetooth4.0technology for short distance transmission.For the different sporting events,we designed a bracelet and read station for the event’s timing and combined a3-axis accelerometer to record the movement information of the bracelet wearer,with the algorithm designed to calculate the movement distance,speed,and other information for trainer to refer and match the analysis. Due to the spacious space of the sport event,the phenomenon of multipath fading J.-T.Huang(*)•W.-C.Chao•C.-H.LeeDepartment of Mechanical Engineering,National Taipei University of Technology,Taipei10608,Taiwane-mail:jthuang@.tw657 J.Juang and Y.-C.Huang(eds.),Intelligent Technologies and Engineering Systems,Lecture Notes in Electrical Engineering234,DOI10.1007/978-1-4614-6747-2_76,#Springer Science+Business Media New York2013658J.-T.Huang et al. effects is not obvious when wearing the bracelet.Thus,after users pass by the reading station,it could use the RSSI(received signal strength indicator)value to locate their positions.But,due to the RSSIfloatingfigures and the absolute value with noise[1],the distance information of the blind node must use at least three masternodes doing the positioning[2].And we design algorithms to mitigate the error value to increase the positioning accuracy.Comparing with the previous studies,the regular positioning technology using GPS(Global Positioning System)employs satellite to obtain the coordinates of the target[3].However,this method is only available in the outdoor areas but not in the indoor area.Therefore,many different wireless locating methods based on Zigbee, RFID,Bluetooth,Wi-Fi,etc.[4–6]are developed for indoor positioning,which have their own pros and cons for selection and evaluation.In this study,the novel Bluetooth4.0(BT4)technology only using a3V coin cell battery[7]is proposed to operate the positioning system for sporting competition.In this release version,the literature article pointed out that the master and slave devices can keep connection and periodically transmit packets on one CR2032coin cell battery to maintain the utilization rate nearly a year[8],with sending a small amount of data and transfer rates reaching to1Mbps.So the use of BLE in competition can effectively reduce the transmission of data time and thus record the accurate timing.Sporting events and training were analyzed by using a3-axis accelerometer for several years[9].And the combined gyroscope can identify the direction and restore the more accurate positioning information of the subjects[10].Using the original accelerometer values with the algorithm designed for motion analysis, the system can be applied to running,bicycle riding,swimming,and other activity [11]in terms of3-axis data of the action,speed,and acceleration.With the information kept inside theflash memory of the MCU chip.After the sports,one can place the bracelet device near to the computer/mobile phone to transmit and record user’s activity information and use these methods to build a personal exercise model which is used in sporting events and training program.2System DesignOur system is composed of static receiving read station and the bracelet sender worn by the user.The system reads the information from the bracelet at each station then transmits to the cloud database and unifies the integrated timing and informa-tion.Inside each bracelet,there is a control unit which is a microcontroller of CC2540[12]from Texas Instruments.This microcontroller is a complete SoC (system on chip),which is a combination of a BLE transceiver and an8051 microcontroller.And due to its6Â6mm size,it significantly reduces the designed area of the bracelet.The system reading station is accompanied with computer/phone for transceiving action.The PC portion is using the USB dongle designed by Texas Instrument as shown in Fig.1.And the Bluetooth board developed by our researchteam will be applied in bracelet circuit.Since Bluetooth communication is a built-in function for the mobile devices,it is straightforward to develop the application program on the iOS/Android mobile phone operating system.Finally,through Wi-Fi/3G network supported by the computer/phone,data is sent to the cloud database and integrated into useful information and stored as part of the personal database,which builds up a health management program for reference analysis of the exerciser.The circuit of the bracelet is worn by the user,shown in Fig.2;the battery is placed in the back of the circuit board with the accelerometer (CMA 3000-D [13]VTI Technology)which contains SPI and I 2C interface for fast transfer.The chip’s power consumption is quite small and can maintain for a long time.According to the referenced article [14],the analysis of physical activity by accelerometer is different from wear positions of the individual body parts,usually worn on the hands,waist and leg are the more appropriate locations for this device.One Fig.1Bluetooth 4.0board Fig.2Exercise braceletExercise Bracelet with Bluetooth Low Energy Module and Accelerometer ...659example in this study is to let the bracelet be worn on the upper arm for measure-ment,which is expected to have less irregular jitter and vibration than wrist.And the position makes users feel less uncomfortable.Also,the fixed method is impor-tant,and because the value of the accelerometer will be impacted from different placement and gravity,the design of the bracelet should make the board to be attached nicely,without unnecessary shaking [15].When sports bracelet is worn in a different location,the gravity (3-axis value)caused by the earth’s gravitation will be various.In accordance with the CMA3000datasheet,in the original flat state,there will be +1g gravity offset along the Z axis.Therefore,for the position of wear in this study,the X -axis yields +1g gravity offset,which is compensated with the data processing to obtain the correct accelerometer values.3Experimental SetupThe demonstrations of experimental test use the circular track and a swimming pool as shown in Fig.3,for example.We set the starting point,relay station,and final point on the track.The set number of relay station depends on the distance of the track.When players pass the starting point,the starting point starts reading the players time data via Bluetooth for timing.As the players pass,relay station will record the individual player time.The final station records the time data,which is then employed to subtract from the records of previous few stations and get the total time period spent by the players.As shown in Fig.4,at the indoor swimming pool,for example,due to the short distance of the track,the implementation way of our system is different.The short distance of back-and-forth track will not allow setting up relay stations.Both sides of the read station will be combined as the start and final function,then calculation of the two station time gets the players’time.While in large outdoor swimming,implementation method will be the same as to the general track-and-fieldevents.Fig.3Track-and-fieldeventdiagramFig.4Swimmingevent diagram660J.-T.Huang et al.The overall operation of Fig.5shows the user enters the scope of the read station.Reader station will work with the user Bluetooth bracelet device to quickly obtain information for record.The read station with Wi-Fi/3G network spread to cloud database.Therefore,it can increase the multi-record station and alternately record to avoid data missing,if a considerable number of users enter the range.The Bluetooth 4.0can offer fast scanning service in 10ms [16].In game/training session,the user can go to the USER Login station game/training memory to record the original 3-axis accelerometer values sent to the USER Login station.4Experimental ResultsWhile the Bluetooth wireless communications is used in sporting events/training,the wireless signal is highly sensitive to the surrounding environment inference and the signal strength is also vulnerable to air medium decay.However,according to the accurate RSSI offered by the Bluetooth 4.0,positioning or tacking of the blind node is possible and can be applied to indoor and outdoor sports occasions,mostly due to the smaller of the changing environment in open space.As shown in Fig.6,the test in the free space,the RSSI is taken eight times at the same location,then recalculated in smooth algorithm to filter the original read RSSI values.It can be found obviously from the figure that the original RSSI value is beating severely and the ideal distance ratio is not so obvious.After smoothing,the RSSI value is closer to the ideal propagation curve.Therefore,we confirmed that this smoothing method can indeed improve the accuracy of the RSSI and increase its usability too.As described previously,RSSI is a fluctuating value,which means every measured value has inherent error and the error range has proportional relationship with the distance as shown in Fig.7.Therefore,take the circular track as an example,it has eight running tracks and its width is about paring with ideal RSSI in Fig.7,the RSSI at distance of 10m has error up to Æ3dBm.In order to cover the whole width of the eight tracks and alleviate the large error of the RSSI,the read stations are installed along the two sides of the track;hence,the maximum reading distance is reduced from 10to 5m,which indicates that the RSSI error is around Æ2dBm accordingly and the positioning accuracy isenhanced.Fig.5System configuration diagramExercise Bracelet with Bluetooth Low Energy Module and Accelerometer (661)Considering the fast rhythm of the sporting contest,Bluetooth 4.0just can provide a quick scanning function to fetch data of several nodes in very short period.In this study,the read station can scan each target node and obtain its several RSSI values in a period of 100ms,which are calculated to get the distance through algorithm in [17].As shown in Fig.8,three final read stations of C1,C2,and C3can Fig.6Smoothed RSSI and original RSSIcomparisonFig.7Actual RSSI and errors comparison662J.-T.Huang et al.read the RSSI value from the target node,respectively,and upload the data to the cloud database for computing the coordinates of the target node through triangula-tion algorithm [18,19].As shown in Table 1,we performed several experiments by setting up three reading stations at the vertices of the right triangle.Two cases of 3and 5m between each reading station are tested.The results indicate the error between the estimated and the actual location is less than 1m.As described previously,in the near distance,the variance of the RSSI is smaller.Mostly the runners run on the inner track in a circular track so that their BT4bracelet will be close to the read station installed near the side,and thus the RSSI is stronger to have higher accurate positioning.5ConclusionIn this chapter,we describe the personal bracelet with Bluetooth 4.0communica-tion module and the backhaul system for sporting events.We implemented the new Bluetooth 4.0communication based on the CC2540SoC solution architecture,which can effectively reduce the area.In the sporting event system,throughthe Fig.8Triangulation diagramTable 1Compare the actual and estimate resultRange (m)Actual position Estimate position SQRT ΔX þΔY j j ðÞ3(2,1.1)(2.3,1.5)0.773(1.9,1.8)(1.4,2.7) 1.185(3.5,2.9)(2.9,3.2)0.945(3,0.4)(3.1,1)0.83Exercise Bracelet with Bluetooth Low Energy Module and Accelerometer (663)664J.-T.Huang et al. fast communication between the user bracelet and read station,it can record the user’s time and position when the user is entering the range of read station. 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