Design of Temperature and Humidity Data Acquisition System by Using ZigBee Technology

At present, there are greenhouses in most parts of northern China, and with the advancement of automated monitoring technology, greenhouses have come to the age of modern remote monitoring. The increase in agricultural product prices makes it possible for greenhouses to adopt further advanced technologies. We are in this context. The use of ZigBee technology for data collection of temperature and humidity monitoring systems in greenhouses enables the system to achieve distributed monitoring and reduce costs. After the data is aggregated, it is remotely transmitted to the greenhouse manager's computer through PTR2000 and through the background machine. The intelligent software processing gives managers real-time data and timely suggestions, so that the quality of vegetables is better and the yield is higher.

For distributed monitoring, a distributed network must be established first. The choice of network communication mode is very important. According to the characteristics of the data transmitted in the system and the number of system nodes, the price of communication nodes should be low, and the requirements for wiring cannot be selected. A very new technology-ZigBee technology as a communication method for our wireless network. In terms of data communication, the most cost-effective communication method was selected.

1.Introduction to ZigBee

ZigBee is a commercial name for a wireless connection technology that mainly addresses low-cost, low-power, low-complexity, low-transmission-rate, and close-range device networking applications.

The ZigBee standard is based on the 802.15.4 protocol stack and has a powerful device networking function. It supports three main types of self-organizing wireless networks, namely star structure, mesh structure, and cluster structure. tree), especially 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 low cost. The transmission speed is 20 k ~ 250 kbps. ZigBee uses DSSS technology. The power consumption is lower. According to the ZigBee website, in terms of general battery power, ZigBee products can be used for months to years. It is ideal for devices that require a year or more to replace the battery. This is very suitable for the meter reading system.

2.Greenhouse

The working principle of the distributed monitoring system and the working structure of the zigBee network in the system The working principle of the distributed monitoring system in a greenhouse is that the network-distributed ZigBee nodes collect data through temperature sensors and humidity sensors and then transmit the data to the master node. The master node then transmits the aggregated data to the upper computer through PTR2000. The upper computer stores the data in the ACCESS database table. The software of the upper computer can display real-time data, historical data, and process the data. Provide reasonable suggestions to the manager. , 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.

Design of Temperature and Humidity Data Acquisition System by Using ZigBee Technology

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

(1) There is no need to set up communication lines, and wireless automatic network connection is achieved between various devices, which reduces the system installation cost.

(2) Because each module of the entire communication system has the advantages of high integration, high reliability and 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 a free international frequency band (2.4 to 2.48 GHz ISM). The transmission method is a direct sequence spread spectrum method (DSSS) with strong anti-interference ability. .

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

3. Design of network node based on CC2430 chip

CC2430 is the latest RF transceiver from ChipconAs that complies with the 2.4 GIEEE 802.15.4 standard. The wireless communication equipment developed by using this chip supports data transmission rate up to 250 kbps and can realize multi-point to multi-point fast networking.

CC2430 chip only needs a small number of peripheral components to achieve the function of transmitting and receiving signals. FIG. 2 is a hardware structure of the temperature detection terminal.

Design of Temperature and Humidity Data Acquisition System by Using ZigBee Technology

The circuit uses an unbalanced antenna. Connecting an unbalanced transformer can make the antenna perform better. The unbalanced transformer in the circuit is composed of capacitor C1 and inductors L1, L2, L3 and a PCB (printed 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 exchange of LNA and PA. R1 and R2 are bias resistors. R1 is mainly used to provide a suitable operating current for a 32 MHz crystal. A 32 MHz crystal resonator (xTAL1) and two capacitors (C2 and C3) are used to form a 32 MHz crystal circuit. A 32.768 kHz crystal resonator (XTAL2) and two capacitors (C4 and C5) are used to form a 32.768 kHz crystal oscillator circuit. The voltage regulator supplies power to all pins that require a voltage of 1.8 V and the internal power supply. Capacitors C6 and C7 are decoupling capacitors used to filter the power supply to improve the stability of the chip's operation. 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 adopts PTR2000 chip for wireless remote transmission. PTR2000 is a new type of single-chip wireless transceiver digital modem module. This device is an ultra-small module device with ultra-low power consumption and high speed (19.2 kb-ps). The wireless transmission and reception data transmission function, and excellent performance, easy to use, PTR2000 and the single chip microcomputer data transmission node hardware connection shown in Figure 3.

Design of Temperature and Humidity Data Acquisition System by Using ZigBee Technology

The host computer software uses VB6.0, with a friendly interface, which can display historical data, real-time data, and temperature and humidity curves. 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 prospect of ZigBee wireless sensor network is very broad. The CC2430 chip is a true SOC chip, which makes it easier for us to develop ZigBee wireless sensor network, and the product development cycle will be greatly Shorten, if necessary, please contact iJUNCO engineers for consultation.