The Design of the Sensor Node of IOT Based on SIM20 KUANG Xinghong 1, a,yao Zheyi 1, b, Huo haibo 1, c, Li junjun 1, d, Wu yanxiang 1, e

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1 Advanced Materials Research Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland The Design of the Sensor Node of IOT Based on SIM20 KUANG Xinghong 1, a,yao Zheyi 1, b, Huo haibo 1, c, Li junjun 1, d, Wu yanxiang 1, e 1 Department of Automation Shanghai Ocean University Shanghai , China a xhkuang@shou.edu.cn, b zyyao@shou.edu.cn, c hbhuo@shou.edu.cn, d,jjli@shou.edu.cn, e yxwu@shou.edu.cn Keywords: The Internet of Things (IOT); Sensor Networks; SIM20. Abstract. The sensor node is important component part of the Internet Of Things. The sensor node circuit based on SIM20 module was implemented in the paper. The design of the wireless RF circuit and the energy management circuit were described in detail. The reliable link between the sensors and the gate are achieved by the developed product. 1.Introduction The Internet of Things is a network integrated by the objects, which have the identity, perception and intelligent processing capabilities with the help of communication technology. Without manual intervention and coordination, it achieves the synergy and interaction. It is new network technology which integrated sensor technology, micro-electromechanical systems technology, wireless communication technology and distributed information processing technology. The processed information will be send to the interested network users when the information was obtained by the nodes. Wireless sensor networks become an extension of the Internet from the virtual world to the physical world and become a bridge between the logical world and the real physical world. So, WSN worked as an important part of the Internet of Things. It is widely used in remote environment monitoring, remote fault diagnosis, the military battlefield, medical and health, disaster response, public places, security and other fields [1-3]. This paper describes the design of the sensor node based on the Internet of Things. The node is responsible for receiving the data from the internal network and sending the data to MCU unit of the gateway. and the same time, the node is also responsible for sending the gateway s command to the other nodes in the network through the short-range RF. 2. The overall block diagram of sensor node The design of the sensor nodes based on the IOT described in the paper includes the embedded microprocessors, peripheral hardware devices, applications software and other components. The structure of system circuit is shown in Fig. 1. Interface of sensor circuit Interface of gateway circuit Crystal circuit MCU SIM20-RF RESET Circuit JTAG Circuit ENERGY MANAGEMENT UNIT Fig 1 The structure of the node All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-08/05/16,22:52:22)

2 2376 Advanced Designs and Researches for Manufacturing The microprocessor system includes many parts such as the crystal oscillator, reset circuit, and MCU. MCU is fully compatible with 8051 s CIP-51 microprocessor core. It can work in the maximum system clock frequency of 25M, he peak speed of up to 25 MIPS. The MCU do not need to expand the storage unit with integrated internal RAM and ROM unit. So it can simplify the system s hardware design [4]. AD interface of the sensor: it was used to obtain the data from the sensor. According to the different IOT application occasion, the node can obtain different type of data when we use different sensor such as the temperature sensor, Humidity sensor, PH sensor, and luminosity sensor, etc. RF circuit: It is a key circuit in the system. it is used to accomplish the communication between the nodes, node and the gateway. JTAG debug circuit: It is used to debug the hardware and the software. Energy Management Unit: In order to reduce the energy and prolong the lifecycle of the network. The unit is used to manage the energy of the node. 3 The hardware design of the node based on the IOT We will describe the key technology of the node based on SIM20 module in detail such as the interface circuit of the node and the energy management circuit. 3.1 The design of the RF circuit The designed node s RF circuit uses the SIM20 module. SIM20 designed for global marked is a highly-integrated, semi-duplex, multi-channel, low power and wireless communication module. It includes high speed MCU and perfect performance RF chip, so it has the perfect receiving sensitivity, programmable transmitting power and data rate. SIM20 supports the multi-channel choice, transparent date transfer without complex user settings, it also supports UART,II,SPI interface. SIM20 module supports Transparent Mode which is a special data mode for receiving and sending data. Once the local module (TX side) is switched to this special data mode -- Transparent Mode, all data received from serial port will be treated as data packets which will be transferred later, similarly all data received from remote module (RX side) will be sent to serial port directly. The module is widely used in mobile device field and the industry field. The General features: Supply voltage range: 3.0~3.6 V, Low power consumption, Maximum transmit power: 18 dbm Receive sensitivity: Transmission distance:1500 Frequency bands support: SIM20-A is 433~434.79MHz, Sleep current consumption: 1uA, Rx current consumption: 26mA, Tx current consumption: 80mA@18dBm, peak value. Support peer to peer transmission and broadcasting transmission [5]. The circuit is shown in Fig.2. Fig 2. The design of the node based on SIM20

3 Advanced Materials Research Vols SIM20 has two normal work modes: data mode and command mode, these two modes can be switched via C2D pin. The default status of SIM20 C2D pin is at high level and SIM20 is in data mode after powered on. When C2D pin is open or connected to high level (via Resistor > 4.7K) SIM20 will work in data mode. When C2D pin is pulled down to GND, SIM20 will be switched to command mode. Once SIM20 is switched to command mode, all AT commands can be used. The receive pin and the send pin are connect to the MCU by the 100R register. The data communication is implemented by the two lines. The components R4, C6 and C7 are the matching circuit from RF output to the antenna connector. If the RF characteristic is not perfect, these three components value can be adjusted. The default value of R4 is 0ohm; C6 and C7 are not connecting (NC). 3.2 Energy control circuit The node s power of the IOT is supplied by the battery. It is difficult or impossible to replace the battery because of the environment. In order to prolong the lifetime of the network, we must take full account of the energy needs according to the hardware and the software. In the node s energy consumption, the RF energy consumption is the largest. Hence, the control of the RF energy consumption is the node key to energy conservation. The energy management circuit is shown in Fig. 3 Fig. 3 Energy management circuit The node s energy management circuit uses the chip XC6221 to control the energy supply. We can control the PIN of the XC6221 to control the whole energy consumption. When the node is not sleep, we can enable the CE PIN of the chip XC6221B332. Otherwise, we disable the PIN. 4, The software design of the node based on the IOT We use Keil C51 debugging environment, it is an online and a full-speed debug method. The debugging environment support for the breakpoints, watchpoints, single step debug method. The application software is implemented by microcontroller language (C51 ).The main function work as Multi-task cycle way. The communication between the nodes and the data collection can be implemented in the software. The frame of the main software can be described as following: Creat_All_Task(); //create the task while(1) { SENSOR_SIM20_Test_SEND();//send the SENSOR s test data Delay_Time(500); temp_sample();//measure the real-time data //send the obtained data SENSOR_SIM20_Sample_SEND();//start to send the data Multi_Task(); }

4 2378 Advanced Designs and Researches for Manufacturing The communication of the wireless RF is implemented through the interrupt method: 1) in the receive interrupt program when the SIM20 module receive the data from other module. In the interrupt program, the data was received and put in the buffer. 2)the MCU send the data to the other node when the node want to send the command or the data to the other node. It also implemented in the send interrupt program. 5 Experiments the communication protocol of the IOT node is a short protocol such as Zigbee. The ad hoc method must used when it need long distance communication, also, if the data must be send to the internet, the gateway also should used. The communication distance can reach to 300m. If there are some walls between the nodes, the communication distance is less than 100m. So the function of the node is good for the IOT. Three nodes and one gateway are used to test the network in our research laboratory, the temperature sensors are set on the node. In the user terminate, we receive the data from the nodes. The experiments validate the design of the node. Fig.4 The experiment frame of the network We list some data obtained in the list below experiment 7E A F 11 1F 03 C0 A A 0E F2 03 EA B B B E We can see the data in the user terminate: B ; 6 Conclusions SIM20 module is a short range communication module manufactured by the SIMCOM Corporation. Compare to the existed node, it simplified the complexity of the system. The use can choose different sensors according to the different application occasion. This paper described the circuit and software in detail. At last, the experiments validate the design of the node. Acknowledgments: This work is supported by Marine Renewable Energy 2011 (SHME2011GD01) Reference: [1] Akyildiz I, Su W, Sankarasubramaniam Y, Cayirci E, A survey on sensor networks, IEEE Communications Magazine, 2002 (8): [2] Tilak S, Abu-Ghazaleh NB, Heinzelman W, A taxonomy of wireless micro-sensor network models, Mobile Computing and Communications Review, 2002, 1(2):1-8 [3] LI Jian-Zhong1, LI Jin-Bao etc. Concepts, Issues and Advance of Sensor Networks and Data Management of Sensor Networks, Journal of Software, 2003,14(10): [4] Cignal C8051 DatasheetNew China Dragon Electronic Co., Ltd,2005 [5] SIM20 Hardware Design Datasheet,SIMCOM(China) Co., Ltd,2010

5 Advanced Designs and Researches for Manufacturing / The Design of the Sensor Node of IOT Based on SIM /