Design of Circuit Module of Fingerprint Time Attendance System Based on ARM7

Single chip microcomputer STM32L151CCU6

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The attendance system has become a must-have device for many companies, but the traditional attendance system is prone to replace punching and swiping. The new fingerprint attendance machine completely avoids this situation. In this paper, we introduce the scheme of designing a fingerprint attendance machine with ARM7 chip as the core. This product has two basic functions: fingerprint attendance and credit card attendance. Biometric technology relies on the uniqueness and reliability of its identification. After nearly ten years of development, its application has become more and more extensive and mature. At present, fingerprint recognition technology has become popular in the civilian market, and fingerprint attendance machine is one of its main applications. A powerful fingerprint attendance machine is designed with the powerful S33C44B0X processor, which has great advantages in function, interface and price.

System hardware design

The main CPU of this system adopts Samsung's S3C44B0X processor, which has many advantages such as multi-function, low power consumption, fast calculation speed and low price. The hardware design mainly includes three parts: fingerprint acquisition, credit card collection, and power management. The memory is externally connected, and is connected to the 64M HY57V641620HG SDRAM and the 16M 39VF1601 flash. The voice prompt module uses an AP8921A chip with a total length of 21S recording time. The host computer communicates through the CH341 chip to the asynchronous serial port to the USB1.1 interface, and the user can use the normal USB interface externally, eliminating the troublesome serial port. The system uses the MAX1508 chip to charge the lithium battery through the USB interface. It is usually powered by a battery. After plugging in the USB interface, it can supply power to the system through the USB interface and charge the lithium battery. There are three buttons in total, one is the system's on/off button, and the other two are the real-time clock settings button and direction button.

Fingerprint acquisition circuit module

The fingerprint acquisition sensor adopts OV7620, and realizes the information exchange with the CPU by the data transmission mode of I2C bus and DMA. Figure 2 shows the fingerprint acquisition interface.

Figure 2 fingerprint capture interface

J1 is the interface of the acquisition head. There are mainly 15 pins. Pin 8 to pin 15 are data output interfaces, which are connected to the latch and finally connected to the data bus. Pins 6 and 7 are I2C bus. Initialize the sensor register; pins 3 to 5 are the sensor's clock signal, line sync signal, and frame sync signal. The frame sync signal is directly connected to the general-purpose I/O port GPF3 of the CPU, and the line sync signal and the clock signal are input to the external DMA request of the NAND gate to the nXDREQ1.

When the nXDREQ1 output goes from a high level to a low level, the sensor has data output and the data can be maintained until the next identical process. This is in line with the requirements of the single-step mode of 44B0's external DMA request. So naturally you can use DMA to read the data. The final data read is done through the chip select latch. Since the DMA method does not interfere with the CPU, it also greatly increases the speed of reading.