Introduction Wireless sensor networks, as an emerging technology, have become a research hotspot at home and abroad. They have shown broad application prospects in military, environment, health, home, business, space exploration and disaster relief[1]. Many units at home and abroad have carried out research in related fields, but most of the work is still in the stage of wireless network protocol performance simulation and small-scale experimental design of hardware nodes. Wireless sensor networks do not require high transmission bandwidth, but require extremely low power consumption so that the devices in the wireless sensor network can work for a longer time. At the same time, low cost is also a major requirement for the popularization and application of wireless sensors. The ZigBee/IEEE 802.15.4 standard takes low power consumption and low cost as the main goals and provides a platform for interconnection and interoperability of wireless sensor networks. At present, the research and development of wireless sensor networks based on this technology has received more and more attention. This paper designs a general wireless sensor network hardware platform based on ZigBee technology, hoping to industrialize it and make a greater contribution to China's wireless sensor industry. The main advantages of ZigBee-based wireless sensor networks The word ZigBee comes from the fact that when bees find pollen, they tell their companions by dancing a zigzag dance to achieve the purpose of exchanging information. It can be said that a small animal achieves “wireless” communication in a simple way. People use this to refer to a short-range wireless network communication technology that focuses on low power consumption, low cost, low complexity, and low speed. It also has a metaphorical meaning. ZigBee technology is not a completely unique or new standard. Its physical layer, MAC layer and link layer adopt the IEEE 802.15.4 standard, but it has been improved and expanded on this basis. Its network layer, application convergence layer and high-level application specifications are formulated by the ZigBee Alliance. ZigBee has prominent features, especially in terms of low power consumption and low cost, mainly in the following aspects [2]. ① Low power consumption. In low power standby mode, two AA batteries can support one node to work for 6 to 24 months, or even longer. This is the outstanding advantage of ZigBee. In comparison, Bluetooth can only work for a few weeks and WiFi can only work for a few hours. ② Low cost. By significantly simplifying the protocol (less than 1/10 of Bluetooth), the requirements for the communication controller are reduced. Predictive analysis shows that, based on the 8-bit microcontroller of the 8051, a full-function master node requires 32 KB of code, while sub-functional nodes require as little as 4 KB. Furthermore, ZigBee is royalty-free. ③ Low data rate. ZigBee operates at a low data rate of 20–250 kbps, providing raw data throughput of 250 kbps (2.4 GHz), 40 kbps (915 MHz), and 20 kbps (868 MHz) respectively, meeting the application requirements for low-data-rate transmission. ④ Short range. The transmission range is generally between 10 and 100 m, which can be increased to 1–3 km by increasing RF transmission power. This refers to the distance between adjacent nodes. The transmission distance can be further increased through routing and relay communication between nodes. ⑤ Low latency. ZigBee boasts a fast response time, typically transitioning from sleep to active mode in just 15 ms and connecting to the network in only 30 ms, further conserving power. In comparison, Bluetooth requires 3-10 seconds, and WiFi requires 3 seconds. ⑥ High capacity. ZigBee can utilize star, patch, and mesh network structures, with one master node managing several child nodes, up to a maximum of 254 child nodes per master node; simultaneously, the master node can be managed by higher-level network nodes, creating a large network of up to 65,000 nodes. ⑦ Simple protocol and high security. The ZigBee protocol stack is only about 1/4 the length of Bluetooth on average; this simplification is crucial for low cost, interoperability, and maintainability. ZigBee technology provides data integrity checks and authentication functions, offering three security modes that allow for flexible determination of security attributes, effectively ensuring network security. ⑧ License-free frequency band. Direct sequence spread spectrum is used in the Industrial Science and Medical (ISM) band—2.4 GHz (global), 915 MHz (USA) and 868 MHz (Europe). From the above main technical features of ZigBee, it can be seen that: based on the IEEE 802.15.4 standard, mutual coordination and communication can be achieved between thousands of tiny sensors. In addition, the relay method is used to transmit data from one sensor to another via radio waves, which makes the communication efficiency very high. Compared with various existing wireless communication technologies, the low power consumption and low data rate of ZigBee technology are most suitable for wireless sensor networks. Wireless sensor network hardware design In a wireless sensor network, nodes are randomly scattered in the monitored area. The nodes form a network in a self-organizing form, and transmit the monitoring data to the sink node through a multi-hop relay method. Finally, the data in the entire area is transmitted to the remote center for centralized processing by means of long-distance or temporarily established sink links. Figure 1 shows the general form of wireless sensor network architecture [3]. For environmental and structural condition monitoring, we designed a general-purpose wireless sensor network hardware platform. This platform consists of several sensor nodes, a sink node with wireless receiving capabilities, and a computer. The wireless sensor nodes are distributed within the monitored area, performing data acquisition, processing, and wireless communication. The sink node receives data from each sensor and transmits it to the computer via a wired connection, as shown in Figure 2. Hardware Design of the Wireless Sensor Node A wireless sensor node generally consists of four parts: a sensor module, a data processing module, a data transmission module, and a power management module. The sensor module is responsible for collecting information from the monitored area and performing data conversion. The collected information may include temperature, humidity, light intensity, acceleration, and atmospheric pressure. The data processing module is responsible for controlling the node's processing operations, routing protocols, synchronous positioning, power consumption management, and task management. The data transmission module is responsible for wireless communication with other nodes or the sink node, exchanging control messages and transmitting and receiving collected data. The power management module selects the sensors used. The node power supply uses a miniature button battery to reduce the node's size. Our designed node implementation mechanism uses a ZigBee transmission module instead of a traditional serial communication module to wirelessly transmit the collected information data. This node includes a ZigBee wireless transmission module, a microcontroller module, a sensor module and interface circuits, a DC power supply module, and external memory. To reduce the cost and size of the sensor node, we use the highly integrated SoC chip CC2430 from Chipcon to implement the data transmission and processing functions of the sensor node. Figure 3 is a block diagram of the designed wireless sensor node. The following will introduce several main functional modules in the wireless sensor node. SoC Chip CC2430 The CC2430 chip continues the architecture of the previous CC2420 chip, integrating the ZigBee RF front-end, memory, and microcontroller on a single chip. It uses an 8-bit 8051 MCU with 128 KB of programmable flash memory and 8 KB of RAM, and also includes an analog-to-digital converter (ADC), several timers, an AES128 coprocessor, a watchdog timer, a sleep mode timer with a 32 kHz crystal oscillator, a power-on reset circuit, a power-down detection circuit, and 21 programmable I/O pins. The CC2430 chip is manufactured using a 0.18 μm CMOS process, with a current consumption of 27 mA during operation; in receive and transmit modes, the current consumption is below 27 mA and 25 mA, respectively. The CC2430's sleep mode and ultra-short transition time to active mode make it particularly suitable for applications requiring very long battery life. Thanks to the CC2430's high integration, its peripheral circuitry is very simple, requiring only a few inexpensive external components to complete the data transmission and processing functions of the wireless sensor node, thus significantly reducing costs. Sensor Module Different sensors are selected according to actual needs to detect physical signals such as temperature, humidity, vibration, sound, and light within the monitoring area. Photosensitive devices, digital format sensors, and electret microphones can be used to detect light intensity, temperature, vibration, and sound. The 5516 photoresistor is a light guide that operates based on the semiconductor photoelectric effect. It has extremely high sensitivity to light intensity. When exposed to light within a certain wavelength range, its resistance (light resistance) decreases sharply, and the current increases rapidly. The resistance of the photoresistor can be obtained by analog-to-digital conversion after voltage division using a reference resistor, and then the light intensity can be calculated. Maxim's DS18B20 is a one-wire digital temperature sensor. Measurement results can be output as 9-12 bits of serial data, with a measurement range of -55 to 125℃ and an accuracy of ±0.5℃ in the range of -10 to 85℃. The HX034P electret microphone is a condenser micromicrophone. The input signal is an audio signal, and the output signal is preamplified by a MAX4466 preamplifier circuit and then sampled by voltage A/D conversion. The processor's A/D sampling frequency can reach 200kHz, enabling the capture of audio signals. Analog Devices' ADXL202 is a biaxial accelerometer that utilizes advanced microelectromechanical systems (MEMS) technology. It etches a polysilicon-encoded micromechanical sensor onto a single silicon wafer, integrating precise signal processing circuitry to measure both static and dynamic acceleration. This sensor has wide applications in inertial navigation, earthquake monitoring, vehicle safety, and motion state testing of battery-powered devices. Wireless sensor network nodes using these sensors and sensing devices can accurately measure and detect temperature and acceleration (vibration). Photoresistors have their own spectral and temperature characteristics, therefore precise calibration is not required in the design. Furthermore, the capture and reproduction of sound signals requires extensive data processing. Considering energy utilization and the simplification of sensor node functions, the design uses a threshold setting to provide a Boolean output for sound and light intensity detection. Power Module This enables miniaturization of the node design. The node can be powered by a 3.6V rechargeable lithium-ion button battery (LIR2032). These batteries have a self-discharge rate of less than 10% per month, but their rated capacity is small, limiting the node's lifespan. Powering them with two AA batteries can extend their operating time. In network operation, by rationally configuring the node's transmitter's receiving, transmitting, and standby states, the node's lifespan can be effectively extended. For wireless sensor networks where node power supply units are difficult to replace, research into new energy solutions and low-power design of network systems are also noteworthy topics. The CC2430 impedance matching network uses a differential RF signal, with an optimal differential load impedance of 115 + j180Ω. The impedance matching circuit needs to be adjusted according to this value. This design uses a 50-ohm monopole antenna. Since the CC2430's RF port is differential with two ports, while the antenna is single-port, a balun is needed to convert between two ports and a single port. The balun circuit consists of inexpensive inductors and capacitors, as shown in Figure 4, including inductors L1, L2, and L3, capacitor C1, and two long transmission lines. Hardware Design of Sink Node The connection between information within a wireless sensor network and external networks or processing terminals is achieved through sink nodes. Sink nodes act as relay stations between wireless sensor networks and wired devices, responsible for sending upper-layer commands (such as queries and ID address allocation), receiving requests and data from lower-layer nodes, and possessing data fusion, request arbitration, and routing functions. They are the most crucial component of a wireless sensor network. Our designed sink node features both a USB data port and an RS232 data port, which can be switched via a switch to facilitate connection between the sink and external networks or processing terminals. Figure 5 shows the block diagram of our designed sink node, which still utilizes the highly integrated SoC chip CC2430 from Chipcon to implement the sensor node's data transmission and processing functions. The TTL to RS232 level conversion unit uses the MAX 3316 chip, which can achieve bidirectional level conversion with a 2.25–3.0V power supply and can directly operate the CC2430 chip's serial data and control lines. The peripheral circuit design of the CC2430 is the same as that of the sensor node. Conclusion ZigBee-based wireless sensor networks have significant advantages such as low power consumption, low cost, and small size, enabling signal acquisition, transmission, and processing within a monitoring area under special conditions. With the maturity of wireless ad hoc network technology and the emergence of new energy solutions, the application of wireless sensor networks will inevitably expand from military, environmental monitoring, healthcare, space exploration, and disaster prediction to all aspects of life. References: 1. Xia Li, Chen Xi, Zhao Qianchuan, et al., Introduction to Wireless Sensor Networks and Applications [J], Automation Expo, 2004, 1:34-37. 2. Yuan Yi, Su Honggen, Research on Wireless Network Applications Based on ZigBee Technology [J], Computer Applications and Software, 2004, (6):89-91. 3. Ren Fengyuan, Huang Haining, Lin Chuang, Wireless Sensor Networks [J], Journal of Software, 2003, 14 (7):1282-1291 Tags: Wireless Sensor Network; ZigBee; CC2430