Portable USB fingerprint collector based on MC68HC908JB8

With the advancement of computer technology and the development of image processing and pattern recognition methods, fingerprint processing technology has become increasingly mature and has been widely used in many fields. Fingerprint collection is the first step in fingerprint processing. This article introduces a portable USB fingerprint collection solution based on MC68HC908JB8, which can conveniently and flexibly collect high-quality fingerprint images. The system hardware and related drivers and applications are discussed in detail. the design of.

Fingerprints refer to the striped lines that appear on human fingers. Their formation depends on the environment and genetics during embryonic development. There are almost no two identical fingerprints in the world. Because fingerprints are stable, unique, and easy to collect, they have always been considered one of the most reliable bases for identification using biometric characteristics.

With the advancement of computer technology and the development of image processing and pattern recognition methods, fingerprint processing technology has become increasingly mature and has gone through three development stages: manual processing, semi-automatic processing and automatic processing. The United States first carried out research on fingerprint recognition software in 1963, and then Japan (1975) also started work in this area. my country developed it more slowly (started in about 1981). The United States launched the first commercial system Printrak250 in 1975, while Japan's NECAFIS was put into use in 1982. In recent years, China has also launched its own fingerprint recognition system.

Fingerprint imaging technology, which is the first step in fingerprint processing, is also increasingly mature, which makes the collected fingerprint data more realistic, the image clearer, the processing results more reliable, and the credibility of the identification results stronger. Currently, there are methods to obtain fingerprint images using optical total reflection technology, silicon crystal capacitive sensing technology, ultrasonic scanning technology, etc.

Moreover, with the development of modern society, security has become the primary consideration for many systems. Fingerprints have become a reliable means of identifying identities because of their non-replicable and irreplaceable characteristics. In recent years, research on automatic fingerprint recognition and authentication has become a hot topic in the fields of pattern recognition, image processing and computer vision. Fingerprint recognition has been widely used in banking, insurance, public security, access control, attendance, etc.

This article introduces a portable USB fingerprint collection solution based on MC68HC908JB8. Experiments show that this solution makes full use of USB's plug-and-play support, strong error correction capabilities, and bus power supply. It simplifies the design and reduces the cost. Cost-effective, flexible and reliable fingerprint image transmission is achieved, and has good application prospects.

USB is the abbreviation of Universal Serial Bus, which is a new serial interface technology that has gradually been widely used in the PC field in recent years. Compared with traditional computer interface methods such as parallel port and serial port, USB has many obvious advantages. It supports plug and play, has strong error correction capabilities, can be bus powered, is low-cost, and has strong peripheral connection capabilities. Therefore, using the USB interface to transmit the collected fingerprint images can communicate with the computer more conveniently and flexibly, and has good application prospects.

Design overview

The purpose of the design is to implement a high-performance fingerprint collector that uses a USB interface to communicate with the host. The fingerprint chip uses Veridicom's silicon crystal capacitive sensor FPS110, and the main control chip uses Motorola's microcontroller MC68HC908JB8 with integrated USB module. The basic working mode is shown in Figure 1. MC68HC908JB8 controls FPS110 to collect fingerprints, and then sends the data to the computer for storage and post-processing through the USB module integrated on the MC68HC908JB8 chip.

The host software design is mainly divided into two parts: USB driver and demonstration interface: Jungo Company's Windriver software is used to develop the USB driver for the WINDOWS platform; Microsoft Company's VC6.0 software is used to develop the demonstration platform and some simple fingerprint processing programs.

System hardware design

1.Main chip characteristics

1) Fingerprint collector main control chip MC68HC908JB8 with integrated USB module

MC68HC908JB8 is a cost-effective microcontroller of Motorola's MC68HC08 series. The chip has 256 bytes of on-chip RAM and 8K bytes of on-chip FLASH. In addition to traditional timers, keyboard interrupts, serial ports, and other I/O devices, Its main feature is the integration of a low-speed USB module with a communication rate of 1.5MB.

2) Fingerprint collection chip FPS110

FPS110 is Veridicom's silicon crystal capacitive sensor. This sensor uses advanced semiconductor CMOS technology and has an area the size of a postage stamp. It has many advantages such as high sensitivity, high reliability, high resolution (500DPI), low power consumption, and low price. , especially suitable for commercial and outdoor fingerprint application systems.

2. Fingerprint collector system hardware design

The basic principle of the fingerprint collector is shown in Figure 2, which mainly includes power supply design, microcontroller application design, and fingerprint chip application design.

1) Power supply design

Both MC68HC908JB8 and FPS110 can support 5V power supply, and MC68HC908JB8 can also provide the 3.3V reference voltage required for the USB interface, so the entire board only uses an external 5V power supply. In order to facilitate debugging, the design provides three sets of optional 5V power inputs, namely USB power supply, emulator interface power supply, and independent power supply.

2) Clock design.

MC68HC908JB8 and FPS110 supply clocks respectively. MC68HC908JB8 uses a 6M crystal to connect between OSC1 and OSC2, and FPS110 uses a 12M crystal to connect between XTAL1 and XTAL2.

3) FPS110 and MC68HC908JB8 interface design.

MC68HC908JB8 has five sets of general interfaces PTA, PTB, PTC, PTD, PTE. In the design, the PTB port and the PTC port are selected to connect to the FPS110. The PTB port is used for data communication and the PTC port is used for control. The specific connection is shown in Figure 3

4) USB interface design.

MC68HC908JB8 integrates a 1.5MB low-speed USB module on the chip. According to the USB protocol, a 1.5k pull-up resistor needs to be added to D- to 3.3 volts. The connection is shown in Figure 4.

System software design

The system software design is divided into four parts, namely USB firmware design on MC68HC908JB8, fingerprint collection program design, USB driver design on the computer and demonstration program design

1.USB firmware design on MC68HC908JB8

The development environment of the microcontroller is CodeWarriorstudio integrated development software of Metrowerks, and the online simulation and programming tool is MON08MULTILINK of P&EMicrocomputerSystems.

MC68HC908JB8 integrates a low-speed USB module that complies with the USB1.1 specification on-chip. The module has three endpoints. Endpoint 0 supports control transceiver transmission, endpoint 1 supports interrupt data transmission and transmission, and endpoint 2 supports interrupt data reception and transmission. The corresponding ones include USB control register, USB interrupt register, USB data register, and USB status register. In order to achieve normal USB communication between MC68HC908JB8 and the computer, USB firmware must be designed in MC68HC908JB8. As shown in Figure 5, USB firmware mainly includes control transmission and USB standard request command processing, endpoint data read and write processing, and other interrupt processing.

2. Fingerprint collection program design

MC68HC908JB8 uses the general interfaces PTB and PTC to connect to the FPS110. By controlling the row registers and column registers in the FPS110 chip, it can easily complete the collection of the entire fingerprint or part of the fingerprint. The basic process of fingerprint collection is shown in Figure 6.

3. USB driver design under WINDOWS platform

Windriver is a tool software produced by the American company Jungo for writing hardware drivers. It is mainly used for driver development of ISA plug-in cards, PCI plug-in cards and USB. The main advantage of using Windriver to develop drivers is that you don't need to know too much about operating systems and drivers, and Windriver comes with a powerful wizard called DriverWizard, which can help developers perform hardware diagnosis and automatically generate code. Therefore, using Windriver allows electronic engineers to develop easy-to-use and compatible drivers for home-made hardware in a short period of time. Using Windriver to design a USB driver, as shown in Figure 7, is actually only called in user mode. The API functions provided by the Windriver universal driver do not require writing a WDM driver.

Basic calling process: When the program is running, it first calls the WDU_INI function to initialize various variables and waits for the callback function result; if the callback is successful, it calls functions such as WDU_TRANSFER to complete sending and receiving data; and when the program ends, it calls WDU_UNINIT to release variables, handles, etc. to obtain resources.

4. Demonstration program design under WINDOWS platform

The demonstration program on the computer mainly includes simple control of the communication between the computer and MC68HC908JB8, display of the collected fingerprint image, and some simple processing of the fingerprint image such as thinning and binarization. The tool used is VC6.0, Figure 8 is an example of a demonstration interface.

Conclusion

This article introduces a portable USB fingerprint collection solution based on MC68HC908JB8. Experiments show that this solution makes full use of USB's plug-and-play support, strong error correction capabilities, and bus power supply. It simplifies the design and reduces the cost. Cost-effective, flexible and reliable fingerprint image transmission is achieved, and has good application prospects.