In harsh environments where factors such as temperature, pressure, humidity, vibration, noise, and electromagnetic fields are constantly changing, using general network technologies to build a monitoring system may suffer from limitations such as insufficient real-time performance, low sensitivity, high latency, short range, low reliability, and significant environmental constraints, making it impossible to achieve comprehensive, real-time, and effective security monitoring. However, with the rapid development of microelectronics, digital technology, network, and communication technologies, wireless sensor networks (WSNs) have gradually become the preferred choice for monitoring systems due to their advantages such as low cost, flexible networking, less geographical restriction, strong concealment, and unattended operation. Among WSNs, low-data-rate, short-range ZigBee technology is one of the preferred wireless communication technologies. This design, based on ensuring real-time security monitoring, utilizes ZigBee technology, using wireless sensor network nodes for wireless voice and image transmission. The ZigBee-based voice and image wireless monitoring system consists of two parts: bidirectional wireless voice transmission and wireless image transmission. This allows staff at the monitoring center to conveniently monitor harsh environments, promptly handle various operational incidents, and ensure operational safety. 1. ZigBee Technology for Wireless Voice Transmission ① Overall Structure of the Wireless Voice Transmission System The wireless voice transmission is achieved using an embedded microprocessor and an RF transceiver module as the core, supplemented by external amplifiers, filtering circuits, and audio codecs. The overall structure is shown in Figure 1. [align=center] Figure 1 Overall Block Diagram of Wireless Voice Transmission[/align] The operational amplifier is responsible for amplifying the voice signal received by the microphone and eliminating some interference; the audio codec completes the A/D and D/A conversion of the voice signal and the encoding and decoding of the audio signal; the embedded microprocessor is responsible for storing and processing the data it collects and the data sent by other nodes, and coordinating communication with other nodes; the RF transceiver module is responsible for wireless communication with other nodes, exchanging control information, and completing the reception and transmission of data; the power amplifier amplifies the analog voice signal after decoding and D/A conversion, restores it to the original data signal, and outputs it through the speaker. ② Selection of Devices for the Wireless Voice Transmission System The embedded microprocessor selected is the low-power fixed-point high-performance TMS320VC5416 from TI. This DSP uses a dual power supply, consisting of a 1.6V core power supply and a 3.3V I/O power supply. Key features include: a maximum speed of 160 MIPS; three 16-bit data memory buses and one program memory bus; one 40-bit barrel shifter and two 40-bit accumulators; one 17×17 multiplier and one 40-bit dedicated adder; a maximum 8M×16-bit extended address space; built-in 128K×16-bit RAM and 16K×16-bit ROM; three multi-channel buffered serial ports (McBSP); and a PCM 3002 low-power monolithic stereo audio codec for A/D and D/A conversion of voice signals. The RF transceiver module uses the IP-Link 1221-2264 compliant with the IEEE 802.15.4 standard. This module operates in the 2.4 GHz band, achieving a communication rate of up to 250 kb/s, providing high-efficiency long-range connectivity, high output power, and low signal sensitivity, making it suitable for long-range and harsh environment wireless communication solutions. This module includes general-purpose I/O ports, an asynchronous serial interface, a JTAG port, a USB port, and an external power supply interface. The USB port is responsible for communication with the PC and powering the node. The external power supply interface supports 2.7–3.6V DC power supply. It also includes two A/D converters and two D/A converters. The audio codec is the TI TLV320AIC23. Its core digital power supply voltage is 1.42–3.6V, and its analog power supply voltage is 2.7–3.6V, both compatible with the TMS320VC5416. This allows for direct connection between the TLV320AIC23 and TMS320VC5416 without the need for additional level conversion chips. It features a built-in headphone amplifier, supporting both stereo line input and microphone input, and programmable gain adjustment for both input and output. The TLV320AIC23 integrates its A/D and D/A conversion components internally, employing advanced sigma-delta oversampling technology to provide 16-bit, 20-bit, 24-bit, and 32-bit sampling within the 8–96kHz range. The output signal-to-noise ratios of the ADC and DAC can reach 90dB and 100dB, respectively. [align=center]Figure 2 System Hardware Circuit[/align] The operational amplifier consists of an amplification circuit and a filter circuit. The amplification circuit uses the low-power, low-cost LMV324 amplifier, along with an external low-pass filter circuit composed of resistors and capacitors (R and C). The power amplifier selected is the LM386. It is an integrated audio amplifier with advantages such as low power consumption, adjustable voltage gain, wide power supply voltage range, few external components, and low total harmonic distortion. By adding an external resistor and capacitor between pins 1 and 8, the voltage gain can be adjusted to any value between 20 and 200. ③ The hardware circuit of the wireless voice transmission system implements the amplification of the voice signal obtained by the microphone, which is then sent to the microphone input (MICIN) of the TLV320AIC23. After A/D conversion and audio encoding, control and communication are completed by two multi-channel buffered serial ports, McBSP0 and McBSP1. The McBSP2 of the TMS320VC5416 is expanded into an asynchronous serial interface, sending the signal to the asynchronous serial interface of the RF transceiver module. After modulation by the carrier signal, the signal is transmitted outward by the transmitting antenna. The receiving process is the reverse of the above process. The specific hardware circuit is shown in Figure 2. [align=center]Figure 3 Power Supply Circuit[/align] In the hardware circuit, two power supplies, 1.6V and 3.3V, are used. A dual-output LD0 regulator, TPS73HD301 (see Figure 3), is selected. The TPS73HD301 is a two-output power chip provided by TI, with one output voltage of 3.3V and the other adjustable from 1.2V to 9.75V. 2. ZigBee Technology for Wireless Image Transmission Wireless image transmission is achieved using an RF transceiver module as the core, supplemented by an external camera and level conversion chip. The image data output from the camera has been well compressed, with a rate of tens of kb/s. Therefore, this system uses an RS-232 serial port for communication. Due to the high level of the RS-232 serial port, it must be converted by a MAX3232 level before being sent to the asynchronous serial port of the RF transceiver module for modulation and transmission. The receiving RF transceiver module is directly plugged into the host computer via a USB port to achieve communication with the host computer and power supply to the node. Since the camera's power supply voltage is 12V and the RF transceiver module's power supply voltage is 2.7-3.6V, this system uses two power supplies: 12V and 3.3V. System Software Design In the system software design, the nodes adopt serial communication mode, using interrupts to complete data reception and transmission. Data transmission uses a master-slave node approach, utilizing a USB interface for communication with the PC. Data to be sent is packaged according to the maximum frame length specified by the Zigbee protocol, with network layer, media access control layer, and physical layer headers added. The data is then sent to the receiving end's RF transceiver module via the SPI bus, as required by the user. When the slave node sends an interrupt request to the master node, it automatically jumps to the interrupt service subroutine to receive information packets and process data. The data transmission and reception flow of this system is shown in Figure 4. [align=center]Figure 4 Data Transmission and Reception Flowchart[/align] Simulation Results and Applications in Industrial Control The monitoring and management software, written in Java, is used at the monitoring end. By adjusting parameters such as serial port, baud rate, delay time, infrared lights, image size, and image transmission time, monitoring commands are sent to the wireless sensor network, and sensor data is received. This enables the processing, reception, storage, and display of image data, presenting a large amount of sensor data from the wireless sensor network to the staff in an intuitive way. The simulation results are shown in Figure 5. [align=center]Figure 5 Simulation Results of Wireless Image Transmission[/align] With social progress and development, safety is paramount in industrial production. In hazardous industrial environments such as mines, nuclear power plants, and steel processing plants, this system can be used for process monitoring and safety inspections. On industrial automated production lines, this system can significantly improve factory operating conditions and drastically reduce the cost of equipment inspection. Simultaneously, because problems can be detected early, losses caused by production accidents can be reduced, production can proceed smoothly, equipment downtime can be shortened, efficiency can be improved, and equipment lifespan can be extended. Conclusion Simulation results show that the system can reliably achieve real-time wireless transmission of voice and images in harsh environments such as tunnels and coal mines. It is reliable, feature-rich, and offers high overall cost-effectiveness, demonstrating broad application prospects. It can also be applied to factories, banks, supermarkets, prisons, hotels, shopping malls, and other fields, making it worthy of widespread adoption.