Use of Ultrasonic Signal Coding and PIR Sensors to Enhance the Sensing Reliability of an Embedded Surveillance System

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1 Use of Ultrasonic Signal Coding and PIR Sensors to Enhance the Sensing Reliability of an Embedded Surveillance System Ying-Wen Bai, Chen-Chien Cheng and Zi-Li Xie Department of Electrical Engineering, Fu Jen Catholic University, New Taipei City, Taiwan, 242, R.O.C. Abstract In this paper we design and implement an embedded surveillance system by use of ultrasonic coding of ultrasonic sensors with multiple pyroelectric infrared sensors (PIR) to detect an intruder in a home or a storehouse. The PIR sensors are placed on the ceiling, and the ultrasonic sensor module consists of a transmitter and a receiver which are placed in a line direction; however, ultrasonic sensors with the same frequency are subject to interference by crosstalk with each other and have a high miss rate. To overcome these disadvantages of the ultrasonic sensor, our design reduces the miss rate from the environmental interference by using an ultrasonic coding. Both ultrasonic sensors and PIR sensors are managed by the majority voting mechanism (MVM). Keywords Embedded Surveillance System; Majority Voting Mechanism; PIR Sensor; Ultrasonic Sensor I. INTRODUCTION Recently surveillance systems have become more important for everyone s security. The embedded surveillance system, frequently used in a home, an office or a factory [1-3], uses a sensor triggered to turn on a camera [4-5]. Some designs use different types of sensors to achieve reliability by means of the different features of each sensor [6-7]. In this paper we extend our previous design not only by using both multiple PIR sensors and ultrasonic sensors as a sensor group, but also by using the MVM. Ultrasonic receivers and transmitters are located at opposite ends [8-9]. However, to reduce the interference from other frequencies in ultrasonic s, we use a coding to enhance the ability to distinguish the random interference [10]. To enhance system reliability in the experiment, we focus on how to improve the shortcomings of the ultrasonic sensor. Some research explores the influence of attenuation in air and crosstalk of ultrasonic s by using a coding [11-12], while some provides improvement of the ultrasonic by using different coding types [13-14]. Other research uses the application of a coding to increase resolution and contrast of images [15]. Yet another approach build a 3D image with an ultrasonic sensor in the PN code that solves the problem with time delay [16]. To enhance the reliability of the ultrasonic sensors group, we propose adding to the number of bits with coding to reduce the probability of code breaking. II. SYSTEM ARCHITECTURE Fig. 1 shows our design which contains several ultrasonic and PIR sensor groups. In the modules of the ultrasonic sensor groups the transmitter and the receiver are separated. The transmitter circuit generates a multi-frequency square waveform, and the receiver circuit amplifies the received s and filters out any noise. When a transmitter transmits an ultrasonic coding, the ultrasonic receiver determines whether there is an intruder passing through the sensing area. If there is no intruder, the MCU (Micro Controller Unit) will use the predefined ultrasonic pattern to decode the received. Use of relay stations and frequency conversion extends the sensing range. Our design reduces the environmental interference with the ultrasonic. All sensing s are input to the embedded surveillance system by the GPIO (General purpose input and output), and the MVM program counts the number of sensing states to determine whether to adopt the MVM. The PIR sensor groups obtain the sensing s from human temperature. If the voting results of ultrasonic and PIR sensor groups pass the criteria, the embedded surveillance system starts the Web camera to capture images. Figure 1. Embedded surveillance system with ultrasonic coding /13/$ IEEE 287

2 A. Software modules We choose Embedded Linux as our operating system. The program of the majority voting mechanism contains a detection of the GPIO function, a counting and majority voting function, an image captured function and a Web server. Fig. 2 shows the detection software flowchart of the embedded system. The embedded system scans the GPIO sockets, which are connected to external PIR sensors and ultrasonic sensors. To verify the state of each PIR and ultrasonic sensor, the embedded system reads the voltage levels of the GPIO sockets. When the system reads 5V from a GPIO socket, we learn that the ultrasonic sensors or the PIR sensors have been triggered and will execute the majority voting program by counting the state of each ultrasonic and PIR sensor. Majority voting is achieved by the sensor groups of the different GPIO sockets. The embedded system, when interrupted by the detection procedure, starts the Web camera to capture images. When this is finished, the embedded system starts the detection procedure over again. If the intruder is still in the monitoring area, the count of the GPIO sockets voltage levels continues the majority voting mechanism, and the embedded system again starts the Web camera to capture images. The embedded system uploads the captured images by means of both the Web server and the streaming server through the Internet. No Enter the detection mode Scan GPIO sockets Detect intruder Yes A Detect intruder Figure 3. Block diagram of PIR module. Fig. 3 shows the ultrasonic transmitter circuit which uses a pulse width modulation (PWM) function in the MCU to send out the desired frequency of the ultrasonic. The ultrasonic transducer transforms the voltage waveform into an ultrasonic transmission, and the transducer of the receiver transforms the ultrasonic transmission into the voltage waveform. Figure 4. Ultrasonic transmitter circuit. Fig. 4 shows the ultrasonic receiver circuit. We use a two-stage amplifier to enlarge the ultrasonic waveform, and the filter suppresses any undesired frequency. The MCU comparator determines the level of the ultrasonic waveform, which is the method used for the ultrasonic transmission, whether blocked. When there is no intruder, the MCU changes the transmitting frequency of the ultrasonic to avoid any crosstalk for the next stage. We also design several ultrasonic receivers to receive the ultrasonic transmission and to activate the majority voting mechanism (MVM) to improve the sensing reliability in long distance sensing [6]. The receiving states of all receivers are input to the embedded home surveillance system, which, depending on the results from the ultrasonic receivers, uses the MVM. No Adopt the MVM Upload images on the internet A Yes Figure 2. Turn on the camera and capture images END Detection software flowchart of embedded system. B. Hardware modules We use two groups of the external hardware circuits, the PIR and the ultrasonic sensor group. As the PIR sensor produces a weak voltage, we input the sensed to a two-stage OP amplifier to amplify the weak voltage by about 1000 times. Since the amplified changes between positive and negative voltage, we input this to the absolute value circuit, and then we input it to the adjustable comparator to compare the sensing voltage and the reference voltage which are set according to the environment temperature. Fig. 2 shows the block diagram of the PIR module. Figure 5. Ultrasonic receiver circuit. Table I shows our comparison of the sensing characteristics of both the ultrasonic sensor and the PIR sensor [6]. We have found that the ultrasonic sensor and the PIR sensor can both compensate each other and enhance the overall sensing probability in our design. TABLE I. Sensor Ultrasonic PIR COMPARISON OF CHARACTERISTICS OF PIR SENSOR AND ULTRASONIC SENSOR Condition for trigger Moving block Temperature change Influence of environment temperature Independence Dependence Sensing type Line direction Projection area Disadvantages Noise interference Slow speed and heat insulation 288

3 III. ULTRASONIC INTERFERENCE Ultrasonic transmission is a sound transmission which is easily interfered with by other frequencies from the random ultrasonic s. The interference causes difficulties in setting up the reference voltage. Therefore we propose the coding to increase the reliability of the system. According to the features of the coding our design enhances the ultrasonic pattern to distinguish the random ultrasonic interferences. IV. FEATURES OF CODING SIGNAL In this paper we use a coding to increase the reliability of the ultrasonic sensor group. Equation (1) is the function of probability of code breaking. Equation (2) is the function of reliability. Fig. 5 shows the results, when the number of bits increases, the reliability approaches 1. According to Eqs. (1) and (2) we know that with one bit if the probability of code breaking is 0.5, the reliability would be 0.5. To increase the number of bits of the ultrasonic code is to increase the reliability. (1) (2) Figure 7. Ultrasonic interfered by another frequency. In Fig. 8 we see that the has been coded by our system. The coded is not affected by another frequency because our design receives a through the code instead of through its s frequency. Figure 6. Relationship between reliability and number of bits of the ultrasonic code. In our design we use an 8-bit number coding. Using (1) and (2), we know that if the number of bits is the probability of code breaking is The reliability is equal to Figure 8. Our ultrasonic coding in the scope. Fig. 9 shows the judgment of our experiment. When judging a coding, one method of our design counts the rising edge number. If the rising edge number is equal to two, it means the is correct. Lines A and B of Figure 9 show a coding interval. V. IMPLEMENTATION AND EXPERIMENT RESULTS In the experiment results we found that an ultrasonic would be affected by environment sounds and the amplitude of the reference voltage. Those factors affect the transmission distance and the error rate of detecting. We therefore put the transmitter and the receiver on both ends of the sensing area and make sure the intruder passes through if the outside group has detected an individual. Fig. 6 shows an ultrasonic being interfered with by another ultrasonic frequency. As ultrasonic interference causes difficulties in setting up the amplitude of the reference voltage of the circuit, therefore we use the coding to reduce ultrasonic interference based on the characteristics of the ultrasonic. Figure 9. Judgement from received ultrasonic coding. 289

4 Fig. 10 shows our design that consists of the internal software module and the home embedded system software module. When an intruder has been detected, the MCU wakes up the majority decision to test the threshold and then turns on the power supply for the indoor sensors. If the indoor sensors detect no intruder when the outdoor sensors are misjudging, the MCU turns off the power of the indoor sensors and goes back to the alert state. If the indoor sensors detect an intruder, the MCU turns on the Web camera to capture images in keeping with the decision of the MVM. In the experiment the ultrasonic of the receiver has the same direction as the transmitter, and we find that if the amplitude of the voltage waveform has been reduced to approximately the same as the comparator's reference voltage our design can work normally. The scattering causes the amplitude of the voltage waveform to become gradually lower than the reference voltage. To increase the amplitude of the voltage waveform we place a PET bottle at the front end for focusing. Fig. 11 shows the distribution of scattering after adding a PET bottle focus. We have found that the ultrasonic increases at the central point and achieves the focusing effect m 6m 5m 4m 3m Figure 12. Curves showing distribution of scattering after adding PET bottle focus. Figure 10. Software flowchart of embedded surveillance system [11]. After the intruder has been detected outdoors, the MCU software submodule of the ultrasonic coding is executed as shown in Fig. 11. Our design transmits the ultrasonic coding, and the receiver checks whether the coding is correct. If the coding is correct, the ultrasonic sensor group continues for some seconds to make sure that there is no intruder. If the coding is not correct, our design also starts the majority voting mechanism (MVM) to make sure whether there is any detection. Fig. 12 shows the arrangement of our experimental environment that detect intruders in a suitable place. We place the PIR sensor on the ceiling or above the detection area. Transmitter and receiver of the ultrasonic sensor module are placed in a line direction. When an intruder enters the detection area, the ultrasonic coding will be blocked and the PIR sensors will detect temperature changes. Figure 13. Arrangement of our experimental environment. Figure 11. Flowchart of detection by ultrasonic coding. Table II compares our coding and noncoding. The coding is not interfered with by other frequencies unless their patterns are similar. It is easier to break a noncoding than a coding. When we add to the bits of the ultrasonic coding, the message type rise with. A noncoding transmits just two types of messages, 0 and 1. N means number of bits. With more message types, 290

5 more codes can be used in the same design to decrease the probability of breaking a. In our design, when N is equal to 8, the message conbination of the ultrasonic coding is 128 times better than that of noncoding, and the reliability is enhanced from 0.5 to as shown in Eq. (1). TABLE II. COMPARISON OF OUR CODING SIGNAL AND NONCODING SIGNAL Ultrasonic patterns Interference by other ultrasonic Probability of breaking Message combination Reliability Coding Low Low High Noncoding High High 2 Low VI. CONCLUSION Our experiment shows two different types of sensors which are enhancing the overall sensing probability by using the MVM to reduce the shortcomings of both the ultrasonic sensors and the PIR sensors. By adding an ultrasonic coding our design reduces the miss rate of the receiver with ultrasonic sensors by different patterns, improving the reliability of the overall system. REFERENCES [1] Jun Hou, Chengdong Wu, Zhongjia Yuan, Jiyuan Tan, Qiaoqiao Wang and Yun Zhou, Research of Intelligent Home Security Surveillance System Based on ZigBee, International Symposium on Intelligent Information Technology Application Workshops, Shanghai, Dec. 2008, pp [2] Xiangjun Zhu, Shaodong Ying and Le Ling, Multimedia sensor networks design for smart home surveillance, Control and Decision Conference, 2008, Chinese, 2-4 July 2008, pp [3] L. Lo Presti, M. La Cascia, Real-Time Object Detection in Embedded Video Surveillance Systems, Ninth International Workshop on Image Analysis for Multimedia Interactive Services, 7-9 May 2008, pp [4] Wen-Tsuen Chen, Po-Yu Chen, Wei-Shun Lee and Chi-Fu Huang, Design and Implementation of a Real Time Video Surveillance System with Wireless Sensor Networks, VTC Spring IEEE Vehicular Technology Conference, May 2008, pp [5] Mikko Nieminen, Tomi Raty, and Mikko Lindholm, Multi-Sensor Logical Decision Making in the Single Location Surveillance Point System, Fourth International Conference on Systems, France, 1-6 March 2009, pp [6] Ying-Wen Bai, Li-Sih Shen and Zong-Han Li, Design and Implementation of an Embedded Surveillance System by Use of Multiple Ultrasonic Sensors, The 28 th IEEE International Conference on Consumer Electronics, Las Vegas, Nevada, USA, Jan. 2010, , pp [7] Yang Cao, Huijie Zhao, Na Li and Hong Wei Land-Cover Classification by Airborne LIDAR Data Fused with Aerial Optical Images, International Workshop on Multi-Platform/Multi-Sensor Remote Sensing and Mapping (M2RSM), Jan. 2011, pp [8] Hai-Wen Zhao, Hong Yue, and He-Gao Cai, Design of a Distributed Ultrasonic Detecting System Based on Multiprocessor for Autonomous Mobile Robot, Proceedings of tbe 2007 WSEAS Int. Conference on Circuits, Systems, Signal and Telecommunications, Gold Coast, Australia, January 17-19, 2007, pp [9] Zi-LI Xie and Zong-Han Li, Design and implementation of a home embedded surveillance system with ultra-low alert power, IEEE Transactions on Consumer Electronics, Feb. 2011, pp [10] Francesco Alonge, Marco Brancifortem and Francesco Motta, A novel method of distance measurement based on pulse position modulation and synchronization of chaotic s using ultrasonic radar systems, IEEE Transactions on Instrumentation and Measurement, Feb.2009, pp [11] Shraga Shoval and Johann Borenstein, Using Coded Sognals to Benefit from Ultrasonic Sensor Crosstalk in Mobile Robot Obstacle Avoidance, IEEE International Conference on Robotics and Automation, Seoul, Korea, May, 2001, vol.3, pp [12] Hannes Elmer, and Herbert Schweinzer, High Resolution Ultrasonic Distance Measurement in Air Using Coded Signals, The 19 th IEEE Conference on Instrumentation and Measurement Technology Conference, Anchorage, AK, USA, May, 2002, vol.2, pp [13] Rodrigo Pereira Barretto da Costa-Felix and Joao Carlos Machado, P1G-9 Stepped Sine Versus Coded Pulse As Excitation Signals for Ultrasonic Transducer Calibration in a Non-Linear Propagation Field, IEEE Conference on Ultrasonics symposium, 2-6 Oct, 2006, pp [14] Fernando J. Alvarez, A. Jesus Urena, varo Hermamdez, Ana Jimenez, Carlos de Marziano, M. Jose Villadangos, and M. Varmen Perez, Detecting Ultrasonic Signals in a Turbulent Atmosphere Performance of Different Codes, IEEE International Symposium on Intelligent Signal Processing, 3-5 Oct, 2007, pp [15] Jose R. Sanchez, Marko Orescanin and Michael Oelze, Improving image contrast using coded excitation for ultrasonic imaging, IEEE International Conference on Electro/Information Technology, May, 2010, pp.1-6. [16] Hongbo Zhu, Hiroki Inubushi, Noriyuki Takahashi and Kenji Taniguchi, An ultrasonic 3D image sensor employing PN code, The 5 th IEEE conference on Sensors, Daegu, Korea, Oct, 2006, pp