Gas based on ZigBee wireless monitoring system hardware design

Introduction

As computers and wireless communications technology, computer, wireless communication technology has begun to mine safety and production monitoring, broadly related to the computer application technology, wireless communication technology, sensor technology, information transfer technology, electrical explosion protection technology, applied chemistry technology, control technology, optical technology and embedded technology and other techniques.

ZigBee is a short distance, low complexity, low power, low data rate, low-cost two-way wireless communication technology, the complete protocol stack only 32KB, you can embed all kinds of equipment, while supporting the geolocation feature. These characteristics determine ZigBee technology is ideally suited for applications in wireless sensor networks. And existing wireless communication technology, the ZigBee technology in power consumption and costs are relatively low, there is a great advantage. This article on the design of coal mine gas wireless monitoring system is based on ZigBee technology for wireless sensor networks for real-time monitoring of coal mine methane concentration in the air, the realization of system reliability, easy installation, low-cost, efficient and practical feasibility and thus give coal production work smoothly with a certain degree of protection, as mine disaster prevention, mitigation and improve production efficiency play a certain role.

Coal mine methane wireless monitoring system overall design

This system is composed of multiple autonomous power supply of ZigBee nodes, each composed of ZigBee node can conduct surrounding environmental data acquisition, a simple calculation as well as with the other nodes and external communications, which makes many of the sensor can work together to conduct high-quality sensing, constitute a fault-tolerant better acquisition system.

The system mainly includes ZigBee node and ZigBee base station node, the overall system architecture is shown in Figure 1, where the main base station node ZigBee for combining various sensor node data available, as well as responsible for the communication with the outside world, the node based on embedded systems. This system uses a partial mesh (Partial Mesh) topology, its main advantage is that each node of the range are multiplied expands, there is no maximum communication distance limitations, because it all nodes is used as a Repeater or router. In Figure 1, the node path by following A signal transmitted to ZigBee base station node: A-B-ZigBee base station node, another alternative path is: A-E-F-ZigBee base station node, there are several other redundant paths.

1 ZigBee node design

ZigBee node's main function is to capture the gas concentration data and sends the data to each node of the Group of ZigBee base station.

ZigBee node is mainly composed of sensor modules, MSP430F149 module, CC2420 transceiver modules, enclosure and power management module five parts, including the power supply module led/switches, sensor module interface, USB interface, antenna interface, etc.

ZigBee node of the sensor module is responsible for monitoring regional information acquisition and data transformation, the design of the sensor module using gas sensor and temperature and humidity sensors; MSP430F149 module is responsible for controlling the entire node handling operations, routing protocols, synchronous positioning, power management, task management, etc., MSP430F149 processor itself has A/D function, from the sensor to get analog signal can be directly sent to MSP430F149, ADC and low power consumption; CC2420 transceiver module for wireless communication with other nodes to exchange control messages and send and receive data acquisition, offers SPI interface and MSP430F149 communication without MSP430F149 connect keyboard, display, and other human-computer interaction interface, sensors, controllers, etc.; enclosure is responsible for the storage of the data collected; power management module provides energy, gated used sensor, two-section 1.5V alkaline batteries.

① M S P 430 F 149 module

MSP430F149 module, that is, the MCU Module, using TI company MSP430F149, as shown in Figure 2.

TI's MSP430 microcontroller series is an ultra low-power, mixed-signal controllers at low voltages to ultra low-status jobs; their controller with powerful processing capabilities and rich on-chip peripherals; with FLASH memory chip can also be easily and efficiently carry out on-line simulation and programming. MSP430F149 is MSP430X1XX series of the most powerful single chip, and MSP430F149 operating environment temperature range is-40 ° c to + 85 ° c, can adapt to all kinds of bad environment.

② C C 355 transceiver modules

CC2420 is the first company to launch Chipcon complies with the IEEE 802.15.4 standard 2.4GHz RF transceiver.

The device is the first product for Zigbee RF devices. It's based on Chipcon SmartRF03 technology to MCU μ m CMOS process, just very few external components, stable performance and low power consumption. CC2420 selectivity and sensitivity index exceeds the IEEE 802.15.4 standard, ensures the effectiveness of short-distance communication and reliability. Use this chip development of wireless communications devices support data transfer rates up to 250Kb/s, you can implement multiple point-to-multipoint network quickly. Its peripheral circuits including crystal oscillator clock circuit, radio frequency input/output matching circuits, and microcontroller interface circuit three parts. Chip local oscillator signal by external Active Crystals provide, can also be provided by an internal circuit. Provided by an internal circuit is required plus crystal oscillator and two, capacitance load capacitance of size depends on the frequency and type of Crystal capacitance and other parameters. CC2420 transceiver modules of peripheral circuit shown in Figure 3.

③ enclosure

Storage module using STMicrolectronics company 1 MB serial EE

PROM chip M24M01, tiny SO8N package M24M01, encapsulate shell width only 150mil (3.8mm), built-in I2C Twin-wire serial interface that is saved parameters often modified ideal for mass data storage density from 1Kb ~ 1Mb. M24M01 support 100kHz and 400kHz clock frequency, fully compatible with I2C specification, wide 1.8 ~ 5.5V working power supply voltage. 128Kb8 storage structure, to support the bytes and pages-and-write mode, the write operation very soon, 256B write below 5ms. Data capacity for over 40 years, resistant to scratches and writing not less than 100 million times erased cycle, temperature range-40 ° c ~ + 85 ℃. Save the module as shown in Figure 4.

④ sensor module

There are many kinds of sensors that can detect the temperature and humidity, lighting, noise, vibration, magnetic field, acceleration, gas concentrations and other physical quantity.

This system uses a sensor module using gas sensor and temperature and humidity sensors.

Temperature and humidity sensor with the SHTxx series support the low-power mode, the acquisition data automatically into sleep mode, A current of less than 1 μ.

This design uses SHT11 SHT11 humidity sensor, is Switzerland Scnsirion company launched a digital temperature and humidity sensor chip. The chip is widely used in HVAC, automotive, consumer electronic, automatic control and other fields. SHT11 humidity sensor using SMD (LCC) surface mount package, the interface is very simple, as shown in Figure 5.

Gas sensor using Beijing Oriental jihua technology co., Ltd. production of gas sensor KGS-20 low power consumption, as shown in Figure 6.

KGS-20 to Tin oxide as a basic of sensitive materials, specifically for gas concentration measurement of a semiconductor gas sensor. Its basic features are: very high sensitivity and extremely fast response speed and low power consumption. KGS-20-type gas sensor suitable for gas and other gas concentrations of detection for gas detectors, gas detectors, gas detectors, etc. The sensor is small size, low power consumption, simple alarm application circuit as methane concentration ≥ 1 per cent, response time, recovery time of ≤ 20s 30s, ≤ of working temperature range of-15 ℃ ~ + 50 ℃, humidity ≤ 97% RH, power dissipation for 150mW, alarm State power 300mW, supply voltage is 3 ~ 5VDC. Sensor sensitive components of resistance RS changes appearance to the load resistance voltage changes on RL. Drive voltage VH, load resistor RL and detection voltage VD value references the typical information provided by the company, so that the sensor is in top working condition.

Sensor power supply circuit design on the sensor module is very important for energy consumption.

Work for low current sensor (A few hundred μ) that can be used by the processor I/O port direct drive; when do not have the sensor, the I/O port is set to input. Such external sensor input without energy, there will be no energy consumption.

⑤ power management module

There are many kinds of battery, battery storage size and shape, the proliferation of active ion, select etc electrodes.

Wireless sensor network node to replace the battery in General, it is important to select a cell, the efficiency of the DCDC module is also critical. This design incorporates 2 section 5 AA battery.

2 design of base station node ZigBee

ZigBee base station node, mainly by ARM module, enclosure (NAND Flash, 64MB-1GB optional), CC2420 transceiver modules, sensor module and power management module.

ARM module using ST company STR710FZ2T6 microprocessor, STR710FZ2T6 ARM7-based instruction set of the ARM processor, chip has 256KB Flash and 64 KB of SRAM, besides the processor integrates many peripheral interface, including USB2.0 interface and Ethernet interface. ZigBee base station node design diagram as shown in Figure 7.

Coal mine methane wireless monitoring system architecture

General length of the coal mine in the layout above, required 10km 100 over ZigBee node, the node is a battery-powered, Executive networking, perception, sampling and preliminary data processing tasks that require all nodes can communicate with each other and with strong collaborative capacity, by forwarding the information between nodes, node is pose many jump between communication networks.

This item design network using MESH mesh network, ensuring the reliability of data transfer, and in a regional setting a base-station node ZigBee (network Terminal), base station through ZigBee node will be the data through the network to the control center.

Conclusions of the

This system combines the current mine safety production and ZigBee technology development status, application of low-power microprocessor MSP430F149, combined with appropriate external circuit design ZigBee node, to capture the gas temperature, humidity, and test data, and can pass the ZigBee base station node to the host computer.

ZigBee technology as a short distance, low complexity, low power, low data rate, low-cost wireless network technology, as the technology develops further, become wireless monitoring system for the best applications and trends.