1. Introduction Gas detection systems are essential safety equipment in industrial and mining enterprises, public utilities, and environmental protection sectors. After decades of development, significant improvements have been made in key technical indicators such as the types of gases that can be detected, measurement range, accuracy, stability, and lifespan. With the development of large-scale integrated circuit technology, instruments are evolving towards miniaturization, multi-parameter combinations, and intelligence. A new methane gas detection system should possess intelligent features, be able to operate under certain interference from other gases, and may employ an electronic nose. The system structure identifies methane gas using pattern recognition methods. Based on a miniaturized electronic nose system, the design of a methane gas detection system should consider reducing system size, simplifying the gas injection device, and improving circuitry to meet low power consumption requirements. Furthermore, the operators of portable detection systems are typically field personnel, who are not professionals; therefore, the system's operation should not be complex, and the design of the system's human-machine interface should also be emphasized. Traditional metal oxide-based gas sensors suffer from low gas selectivity and poor anti-interference capabilities. Detection systems using a single sensor are prone to similar responses and misjudgments when other gases interfere with detection. This paper discusses a high-sensitivity methane detection system based on a microcontroller. This portable system uses a microstructured metal oxide gas sensor array as the sensing element and combines pattern recognition technology for methane gas detection. The entire system consists of a four-unit sensor array, a gas injection device, and a signal processing circuit with a high-speed microcontroller as its core. It boasts excellent performance characteristics such as small size, high accuracy, and strong anti-interference capability. This paper introduces the working principle and design of the detection system, focusing on the design of low-power circuitry. 2. Basic Structure of the Detection System The gas injection section consists of a thin conduit, a micro-pump, and a small gas chamber. The control and signal acquisition processing circuits are based on a microcontroller, and the system also includes display, keyboard, and PC interface circuits. Application software for training artificial neural networks runs on a PC, as shown in Figure 1. The gas detection system operates as follows: the microcontroller controls the pump to draw the gas to be detected into the gas chamber, simultaneously acquiring the response signal from the gas sensor array, converting it, and storing it in the data memory. Then, the microcontroller extracts feature values ​​from the stored data, the recognition network performs gas identification, and the result is output to the LCD display screen. To address the characteristics of portable systems, the detection system is designed with a small size and low power consumption processing circuit. Figure 1 shows the schematic diagram of the methane detection system. The fabrication technology of the low-power sensor array: A microstructured metal oxide gas sensor array manufactured using MEMS technology is employed as the gas sensing element of the detection system. The characteristics of the microstructured metal oxide gas sensor array are discussed in the introduction. The selected array device is small in size, with a device area of ​​3 x 3 mm². 2 x 2 sensor units are integrated within the same diaphragm, and the operating power consumption of each unit is less than 50 mW. A corresponding sensitive thin film is deposited on each unit using a mask sputtering method. The film resistance of each unit can change to varying degrees in response to changes in the concentration of a specific gas at a certain operating temperature. The change in the film resistance of the sensor unit's sensitive thin film can rapidly reflect the changes in gas composition and concentration in the gas chamber. After being converted into a voltage signal, it can be acquired and quantized by a microcontroller through an A/D circuit into data suitable for pattern recognition. Furthermore, since the portable system is battery powered, the power consumption requirements of each part of the circuit are relatively strict. Therefore, low-voltage, low-power components are used in the circuit, and the power management function is optimized to ensure that it can work for a long time when powered by battery. 3 Detection System Circuit 3.1 Introduction to Cygnal C805lF020 Microcontroller [align=center] Figure 2 Block Diagram of Methane Detection System[/align] The Cygnal C805lF020 with built-in A/D circuit is an 8-bit microcontroller 1201 with 8052 core, which belongs to high-speed mixed signal system-on-a-chip. It can well meet the design requirements of the methane detection system, so the system uses it as the processing and control core. Figure 2 is the block diagram of the composition principle of the detection system circuit. The functions of each part of the circuit are described in detail below. 3.2 Circuit Design 3.2.1 Signal Acquisition and Control Circuit First, the operating temperature of each unit of the array needs to be regulated by the heating voltage to ensure good response characteristics. One 12-bit D/A converter of the C8051F020 uses an analog switch 4052 to cyclically output the heating voltage required by each unit of the sensor array. This voltage is then directly driven to each unit by a high-current output operational amplifier chip MAX4069, reducing the power output circuitry. After each unit of the sensor array heats up to its operating temperature and stabilizes, the microcontroller controls a miniature air pump via an air pump control circuit to draw in the gas to be detected. The signal acquisition interface circuit for the sensor array and system circuit is similar to the data acquisition circuit in the previous chapter, except that the signal isolation follower circuit uses a single-supply low-power operational amplifier OP491. The response signals from the four sensor units are acquired by the microcontroller's internal A/D converter at regular intervals, and the acquired data is stored in the SRAM chip IDT71V124SA. The IDT71V124SA is a low-power 3.3V operating voltage static CMOS random access memory chip capable of storing 128KB of data. As an extended data unit for the microcontroller, it significantly compensates for the insufficient RAM space of the microcontroller. However, this device requires 100mA of current during read/write operations, while it only draws 10mA in non-chip select mode. Therefore, to reduce power consumption, the chip select control signal should be released when the microcontroller is not reading data. 3.2.2 Input/Output Interface Circuit Secondly, a good display and operation interface is essential for a portable system. This system uses an HS12232 graphic dot-matrix LCD module with a 122x32 resolution as the display screen to show prompts and processing results. The display interface is designed with a multi-layer menu mode. The main menu includes options such as methane detection, sensor operating voltage setting, sampling data upload, and identification network update. Various operations are performed by selecting menus via keyboard input. Simultaneously, another D/A output from the microcontroller drives a buzzer to emit a prompt sound. According to the design requirements of the detection system, convenient and flexible communication with a computer is also very important. Currently, the USB standard is widely used, so USB communication is chosen. USB is a universal serial bus, characterized by reliable use, plug-and-play functionality, and low cost. The USB interface chip used in the detection system circuit is the Philips PDUSBDI2 chip, which supports the USB 1.1 protocol. The microcontroller sends commands and data to the PDIUSBDI2 via a parallel I/O port to read and write data to the USB interface. Since the data transfer volume in this system is not large, interrupt-driven asynchronous transmission is used. In the USB protocol, the USB bus is divided into host and device parts. The USB controller on the computer is the host device, and the PDIUSBDI2 is the device device. Figure 3 shows the interface diagram between the PDIUSBDI2 and the microcontroller. [align=center] Figure 3 Schematic diagram of the PDUSBDI2 interface circuit[/align] 3.2.3 System Power Management Circuit Finally, the power supply selection needs to be considered. As a portable system, the methane detection system is powered by a battery with a supply voltage of approximately 5V. However, some components in the circuit operate at lower voltages, such as the microcontroller, SRAM, and USB chip, which operate at 3.3V. This necessitates designing a 5V-3.3V voltage conversion circuit in the circuit. By comparison, using the DC-DC device LM2S74 for voltage conversion (Figure 4) to convert the 5V supply voltage to 3.3V can meet the operating requirements of low-voltage devices, reduce additional power consumption, and achieve good voltage regulation and linear output through a well-designed filter circuit. Regarding power reduction, CMOS devices and low-power surface-mount components were selected throughout the system design, resulting in a smaller system size and reduced circuit power consumption. Furthermore, the software design incorporates a power-saving operation mechanism with standby and power-down functions, and some devices have a Shutdown function, allowing them to enter power-saving mode during idle periods, further reducing power consumption. [align=center] Figure 4 Power Supply Voltage Conversion Circuit[/align] 4 Detection System Circuit Debugging After determining the overall hardware design and individual component design of the system circuit, an experimental circuit board was fabricated, and preliminary debugging of the circuit was performed. The power supply uses four NiMH rechargeable batteries connected in series. After debugging, each heating voltage drive circuit can output a maximum voltage of 4.5V. While heating the sensor, data acquisition and storage are performed simultaneously, and the total current can be controlled within 250mA. Of this, the microcontroller circuit accounts for approximately 120mA, the sensor array heating current does not exceed 80mA, and the pump circuit operates below 50mA, meeting the low-power design target. After the hardware circuit of the detection system is debugged, gas identification and other functions can be implemented in the detection system by writing microcontroller programs and computer application programs. 5. Software Design of Methane Detection System After the detection system circuit is debugged, it needs to be combined with identification software to perform gas detection. This paper mainly focuses on the software design, proposing a network identification algorithm suitable for the microcontroller system. The paper discusses network construction and training in both microcontroller and PC software aspects, and also explains other functional programs of the system. Since the C8051 series microcontroller has a complete 8052 core and is fully compatible with MCS-51 instructions, a standard 805x compiler can be used for software development. In the microcontroller software design of this detection system, the Cygnal C51IDE development environment was used. The program was debugged through the JTAG interface reserved in the circuit. Based on the different functional requirements of the detection system, a modular design was adopted, dividing the program into several main functional modules. Figure 5 shows the module diagram of the microcontroller program. [align=center] Figure 5 Module Diagram of the Microcontroller Program for the Detection System[/align] As can be seen from Figure 5, after system initialization, the microcontroller's main program enters the main menu interface and waits for keyboard input. When a key input is detected, the key value is read, the required operation is determined, and then the corresponding subroutine module is called. The author's innovation: The low-power, high-sensitivity methane detection system based on a microcontroller designed in this paper uses an integrated micro-sensor array to extract the cross-response signal of the array units. 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