Currently, most image-based security devices use CCD or CMOS sensors for imaging and DSP processing at the back end, performing human detection based on differential calculations of sequential images. This method is easily affected by external factors such as changes in light, swaying tree branches, and rain or snow, often resulting in false alarms. To eliminate these interferences, specific algorithms are needed, increasing the complexity of the system design. This paper introduces a high-performance, low-cost human detection system implemented using an infrared sensor and a CMOS camera. Furthermore, the entire system operates using solar energy, making it environmentally friendly and energy-saving. [b]System Working Principle[/b] The system structure is shown in Figure 1. When a human enters the detection range of the infrared sensor, the sensor emits a high-level alarm signal. This signal is amplified by the infrared signal processor and sent to the CPLD. The CMOS imaging chip VC0701 has motion detection capabilities; any change in the external environment within its field of view will trigger an alarm signal. When both alarm signals are valid simultaneously, the CPLD selects a buzzer to sound an alarm. If the image output of the VC0701 is set to digital format, the image data during the alarm period will be stored in 16MB of SDRAM. Figure 1 System Principle Block Diagram [align=center]Component Selection and System Design[/align][b]Imaging Module Design[/b] Since the entire system is powered by a solar battery, when selecting components, power consumption should be as low as possible while ensuring performance. This system uses the VC0701 TV imaging chip from Vimicro. The VC0701 has motion detection capabilities and integrates a 240,000-pixel CMOS image sensor, digital image processor, video encoder, and analog-to-digital converter. The VC0701 has functions such as automatic exposure, automatic gain, automatic white balance, and backlight compensation, and supports multiple video image output formats. The chip's operating parameters can be set by external pin pull-up or pull-down, or programmed and controlled via E2PROM or I2C interface. [b]Infrared Sensing Module Design[/b] The human body temperature is generally constant at around 37℃, and the emitted infrared wavelength is around 10µm. The passive pyroelectric infrared sensor consists of three parts: an interference filter, an infrared sensing element, and a field-effect transistor matching circuit. Interference filters are responsible for filtering out infrared radiation from light, sunlight, etc., allowing only infrared radiation within a specific wavelength range to pass through, and focusing this infrared radiation onto the infrared sensing element. The infrared sensing element is a pyroelectric material; when the intensity of the infrared radiation it receives from the human body changes, it loses its charge balance and begins to release current. The field-effect transistor matching circuit converts the current signal into a voltage signal for output. Infrared sensing has two types: active infrared detection and passive infrared detection. Active infrared detection has a wider range but is more expensive. In this system, the infrared sensor used is the NICERA RE46B passive infrared sensor. The RE46B has four infrared sensing elements connected in series, and the Fresnel lens on its surface only allows infrared radiation with a wavelength range of 0.2-20 μm to pass through, improving the sensitivity to human presence while suppressing ambient temperature disturbances and light source interference. The RE46B has a unique omnidirectional structure, which can effectively avoid false alarms caused by small animals. The effective detection range of the RE46B is 8 meters. Because the alarm signal output by the RE46B is very weak, typically a pulse signal with an amplitude of only a few mV, it cannot be directly used by the backend. During the design, an infrared sensor signal processor—BISS0001—was connected in series between the RE46B and the CPLD. [b]CPLD and SDRAM[/b] In this system, the CPLD configures the VC0701, which outputs a PAL-format color television signal, which can be directly output to a regular television for display. The CPLD also provides 8-bit RGB/YCbCr data lines, a vertical sync signal VSYNC, a horizontal sync signal HSYNC, a pixel clock PCLK, and an I2C bus interface, allowing for further digital image processing in the future. The CPLD used is the Altera MaxII EPM240, which is packaged in a TQFP package and has 80 available I/O ports, compatible with 1.5/1.8/2.5/3.3V. When a human body is within the detection range of the infrared sensor, the alarm signal emitted by RE46B is amplified by BISS0001, compared, and then sent to the CPLD; at the same time, the motion detection signal generated by VC0701 also enters the CPLD. After the two alarm signals are ANDed, the buzzer is driven to sound an alarm. If the output of VC0701 is a digital image, the image data will be stored in SDRAM during the alarm period. The 16MB SDRAM can store up to 16M/(514×484) = 67 images, which can be accessed through the data port reserved by the CPLD. [b]Conclusion[/b] This system utilizes VC0701 and the passive pyroelectric infrared sensor RE46B working together for human body detection. VC0701, which performs motion detection based on image content, solves the problem of false alarms caused by infrared sensors when the ambient temperature is close to human body temperature; while RE46B, which detects based on human body temperature, effectively overcomes the problem of false alarms caused by non-human factors such as ambient light and disturbances. The VC0701's flexible configuration and rich video output formats significantly reduce development difficulty and cost. Experimental results show that this system achieves an accuracy rate of over 90% for human targets within a 6m radius. Especially outdoors, its accuracy is higher than ordinary DSP-based human detection devices, and it can also detect stationary or low-speed moving human targets. Editor: He Shiping