Poster Abstract: An Extremely Long Standby Time Wireless Sensor System for Debris Flow Monitoring Teng-Chieh Chan, Kai-Hsiang Ke, Yao-Min Fang+, Bing-Jean Lee+, Huang-Chen Lee* Department of Communications Engineering, and the Advanced Institute for Manufacturing with High-tech Innovations (AIM-HI), National Chung-Cheng University, Taiwan +GIS Research Center, Feng-Chia University, Taiwan *

[email protected]

ABSTRACT The one of the major difficulties in deploying a wireless sensor to monitor debris flow in the real world is power consumption. Frequently replacing the battery of a sensor that is located in a remote mountainous area is not practical. In this study we examine the newly-introduced wireless debris flow sensor, SMARTCONE, which is designed to minimize the standby power consumption, but still keep alert to detecting debris flow. During standby periods, SMARTCONE turns off all major components and uses an accelerometer to sense vibration generated by moving debris flow, and it wakes up SMARTCONE for collecting the parameters of a moving debris flow. Multiple SMARTCONEs need to change operation modes between standby and wake up, collect physical parameters, and transmit data simultaneously, and these issues are kept in mind while designing the system. The performance of vibration detection, data transmission and records of GPS trajectories are evaluated to ensure the accuracy of the design.

Categories and Subject Descriptors C. 3 [Special-Purpose and Application-Based Systems]: Real-time and Embedded Systems

General Terms Design, Experimentation, Measurement, Performance

Keywords: Debris flow, Low Power, Wireless Sensor

1. PRELIMINARY DESIGN AND RESULTS

Server SMARTCONE

Fig. 1 System Architecture Fig. 1 depicts the system architecture. The SMARTCONEs are deployed on the river bed to detect the occurrence of debris flow. The basic architecture is as in our previous study [1]. The collected data of SMARTCONE will be transmitted to the server

on the river bank for later analysis. Fig. 2 shows the deployment of a SMARTCONE on dry riverbed of a potential stream of debris flow.

Fig. 2 SMARTCONE deployed on a dry riverbed for waiting debris flow. While debris flow occurs, the SMARTCONE will be moved and triggered to measure the internal parameters of debris flow. For INSIDER, the previous model debris flow sensor, the CPU and accelerometer remained on in standby period to detect the occurrence of debris flow. However, this consumes substantial energy and decreases its lifetime. Energy harvesters such as solar panels were seriously considered to supply energy in this design, but they create other reliability issues, such as the need to clean dirt on solar panels, or faulty rechargeable batteries. The Li-ion battery is the most reliable power source for this type of application and it is used in this design. Keeping the above issues in mind and hoping to achieve longer standby time with limited energy, we designed the wireless sensor SMARTCON, the hardware architecture of which is shown in Fig. 3. Fig. 4 shows the prototype PCB. SMARTCONE is based on a ARM M0 based Nuvoton microcontroller (MCU), NANO102SC2AN. In addition, a proprietary RF transceiver Nordic NRF24L01+PA with a 3-dbi unidirectional antenna is used to transmit data between SMARTCONE and its server on riverside. The SMARTCONE also integrates a low-power MEMS accelerometer ADXL345, a low-power temperature and humidity sensor SHT-21, and a GPS module FMP04-TLP for providing its location while being moved by debris flow.

Switch circuit

GPS module FMP04-TLP

Power supply Li-ion Battery

MCU NANO102SC2AN

Wireless transceiver NRF24L01+PA

Battery fuel gauge bq27441

Accelerometer ADXL345

Temperature and Humidity Sensor SHT-21

internal battery and control the power supplies for the powerhungry wireless transceiver and GPS module. In this prototype SMARTCONE, an 18650 Li-ion battery (4.2V/3400mAh) was used to power up the unit, and it can stay in SLEEP mode for more than 3400mAh/0.05ma = 2833 days (or about 7.7 years). During this time, SMARTCONE is still able to be awakened by external vibration forces and receive commands from the SERVER. The power consumption of SMARTCONE is ten times lower than our previous design, the INSIDER.

Fig. 3 SMARTCONE's hardware architecture

SMARTCONE moving direction 100m

Fig. 4: The prototype PCB of SMARTCONE (left: top-view, right: bottom-view.) Server

MCU

RF

GPS

Accelero.

SHT/ BQ

power consumption

REGISTER

4MHz

v

x

Standby

v

24.702mA

IDLE

4MHz

v

x

Standby

v

24.701mA

DETECT

4MHz

x

x

Measure

v

3.35mA

ACTIVE

16MHz

v

v

Measure

v

68.3mA

SLEEP

x

x

x

Interrupt

x

0.050mA

Fig. 5: The SMARTCONE's power consumption Referring to Fig. 5, SMARTCONE is working in five operation modes and its measured power consumption, on/off components for each is shown. (1) In REGISTER mode, which the initial mode of a SMARTCONE powers-on and awaits the beacon message from the server. (2) In IDLE mode, the SMARTCONE waits for a command from the server. (3) In DETECT mode, the SMARTCONE detects the vibrations and returns the computed variances to the server to analyze whether debris flows are occurring. (4) In ACTIVE mode, the SMARTCONE collects internal parameters including vibration, location, temperature, humidity, and battery voltage and sends them back in raw data format. (5) In SLEEP mode, the SMARTCONE turns off all components, sets the accelerometer to detect vibration, and wakes up the system if significant vibration is detected. In this design, SMARTCONE turns off the CPU, wireless transceiver, GPS, temperature, and humidity sensors during the SLEEP mode, (which is a standby mode), and senses the vibration generated by a moving debris flow. A predefined vibration threshold of ADXL345 is configured to generate an interrupt to wake up MCU from power-down mode. In order to achieve ultralow power consumption in standby time and other modes, a battery fuel gauge TI BQ27441 is used to monitor the status of its

Fig. 6: GPS Moving trajectories collected by five SMARTCONEs. Next, we executed an experiment to test the performance of the SMARTCONE to detect debris flow, collect data and transmit back to server. The above figure shows five SMARTCONEs that were carried by a trailer in the campus, to simulate being moved by debris flows. Moving duration is about 10 seconds and speed is about 10 m/s, to simulate a typical debris flow for which the speed is about 2 to 20 m/s. The five SMARTCONEs were awakened from SLEEP mode and switched into ACTIVE mode to measure all their internal parameters (acceleration, temperature, humidity, GPS moving trajectories) and wirelessly transmit their collected data back to the server simultaneously. In this design the server (the red triangle in Fig. 6) actively polls the data from every SMARTCONE; therefore, data collisions between SMARTCONEs are avoided. The GPS moving trajectories are shown in Fig. 6. In this experiment, the package delivery ratio for all SMARTCONEs to the server are 100%. This experiment verified multiple SMARTCONEs can stand by in extreme low energy consumption, be awakened in time and wireless transmit their data back to SERVER reliably.

2. ACKNOWLEDGMENTS The authors acknowledge support from the Ministry of Science and Technology, Taiwan ROC, under grant 103-2221-E-194-037 and 104-2622-E-194-007-CC3, and Nuvoton Technology. The authors would also like to thank research assistants Mr. Pei-Jyi Kuo and Mrs. Pin-Chen Kuo for their excellent technical assistance.

3. REFERENCE [1] Huang-Chen Lee; Banerjee, A.; Yao-Min Fang; Bing-Jean Lee; Chung-Ta King, "Design of a Multifunctional Wireless Sensor for In-Situ Monitoring of Debris Flows," in Instrumentation and Measurement, IEEE Transactions on , vol.59, no.11, pp.2958-2967, Nov. 2010