Research on Temperature Monitoring System Based on ZigBee Technology

0 Introduction

At present, most areas in northern my country have greenhouses, and with the advancement of automated monitoring technology, greenhouses have entered the era of modern remote monitoring. The increase in agricultural product prices has made it possible for greenhouses to adopt further advanced technologies. In this context, we use ZigBee technology for data collection in the temperature and humidity monitoring system of greenhouses, so that the system can achieve distributed monitoring and reduce costs. After the data is aggregated, it is remotely transmitted to the greenhouse manager's computer through PTR2000, and the intelligent software processing of the background machine gives the manager real-time data and timely suggestions, so as to improve the quality of vegetables and increase the yield.

To conduct distributed monitoring, we must first establish a distributed network. The choice of network communication method is very important. According to the characteristics of the data transmitted in the system and the requirements that the system has many nodes, the price of communication nodes should be low, and wiring is not allowed, we chose a very new technology - ZigBee technology as the communication method of our wireless network. In terms of data communication, we chose the most cost-effective communication method.

1 Introduction to ZigBee

ZigBee is the commercial name for a wireless connection technology that focuses on solving low-cost, low-power, low-complexity, low-transmission-rate, and short-distance device networking applications.

The ZigBee standard is based on the 802.15.4 protocol stack and has powerful device networking capabilities. It supports three main types of self-organizing wireless networks, namely star structure, mesh structure and cluster structure. In particular, the mesh structure has strong network robustness and system reliability. ZigBee is a short-range wireless network technology that emphasizes extremely low power consumption and extremely low cost. The transmission speed is 20 k~250 kbps. ZigBee uses DSSS technology. The power consumption is lower. According to the ZigBee website, ZigBee products can be used for months to years with general battery power. It is very suitable for devices that need to replace batteries for a year or even longer. This is very suitable for meter reading systems.

2 Working principle of greenhouse distributed monitoring system and working architecture of zigBee network in the system

The working principle of the greenhouse distributed monitoring system is as follows: the mesh-distributed ZigBee nodes collect data through temperature sensors and humidity sensors and then transmit the data to the main node, which then transmits the summarized data to the host computer through PTR2000. The host computer stores the data in the ACCESS database table. The host computer software can display real-time data, historical data, process the data, make reasonable suggestions to managers, and analyze historical data to make intelligent management.

The mesh network is based on the ZigBee wireless sensor network, and its network architecture is shown in Figure 1.

The greenhouse distributed monitoring system based on the ZigBee wireless network platform has the following characteristics:

(1) There is no need to lay communication lines, and wireless automatic networking is achieved between devices, which reduces the system installation cost.

(2) As each module of the entire communication system has the advantages of high integration, high reliability, low power consumption, low cost, and small size, maintenance is very convenient.

(3) Excellent physical performance. The wireless frequency used by the entire network is the internationally accepted free frequency band (2.4-2.48 GHz ISM), and the transmission method is the direct sequence spread spectrum (DSSS) method with strong anti-interference ability.

(4) The network has strong self-organization and self-healing capabilities. ZigBee's self-organizing function: without human intervention, network nodes can sense the existence of other nodes and determine the connection relationship to form a structured network.

3 Network node design based on CC2430 chip

CC2430 is the latest RF transceiver launched by ChipconAs that complies with the 2.4G IEEE802.15.4 standard. Wireless communication devices developed using this chip support data transmission rates up to 250 kbps and can achieve multi-point to multi-point rapid networking.

The CC2430 chip only needs a few peripheral components to realize the signal receiving and sending functions. Figure 2 shows the hardware structure of the temperature detection terminal.

The circuit uses an unbalanced antenna. Connecting an unbalanced transformer can improve the antenna performance. The unbalanced transformer in the circuit is composed of capacitor C1 and inductors L1, L2, L3 and a PCB (printed circuit board) microwave transmission line. The entire structure meets the requirements of RF input/output matching resistance (50 Q). The internal T/R switching circuit completes the switching between LNA and PA. R1 and R2 are bias resistors. R1 is mainly used to provide a suitable working current for the 32 MHz crystal oscillator. A 32 MHz crystal oscillator circuit is formed by a 32 MHz quartz resonator (xTAL1) and two capacitors (C2 and C3). A 32.768 kHz crystal oscillator circuit is formed by a 32.768 kHz quartz resonator (XTAL2) and two capacitors (C4 and C5). The voltage regulator supplies power to all pins and internal power supplies that require 1.8 V voltage. Capacitors C6 and C7 are decoupling capacitors used to filter the power supply to improve the stability of the chip. The data input/output terminal DQ of the temperature sensor DS18B20 is connected to the P0-0 pin, which has an output drive capability of 4 mA.

The data transmission node uses PTR2000 chip for wireless remote transmission. PTR2000 is a new type of single-chip wireless transceiver data transmission MODEM module. This device is an ultra-small module device with ultra-low power consumption, high-speed (19.2 kb-ps) wireless transceiver data transmission function, excellent performance, and easy to use. The hardware connection of the data transmission node composed of PTR2000 and the single-chip microcomputer is shown in Figure 3.

The upper computer software adopts VB6.0, which has a friendly interface and can display historical data, real-time data, temperature, humidity curves, etc. The monitoring interface is shown in Figure 4.

4 Conclusion

Through the design of the system and the use of the CC2430 chip, I feel that the application prospects of ZigBee wireless sensor networks are very broad. The CC2430 chip is a real SOC chip, which makes it easier for us to develop ZigBee wireless sensor networks and greatly shortens the product development cycle.