Portable USB fingerprint collector based on MC68HC908JB8

Chapter 1 Introduction

Fingerprints refer to the stripes on human fingers. Their formation depends on the environment and genetics during embryonic development. There are almost no two identical fingerprints in the world. Due to the stability, uniqueness and easy collection of fingerprints, they have always been considered one of the most reliable bases for identity identification using biometrics.

With the advancement of computer technology, the development of image processing and pattern recognition methods, fingerprint processing technology has become more mature and has gone through three stages of development: manual processing, semi-automatic processing and automatic processing. The United States first conducted research on fingerprint recognition software in 1963, followed by Japan (1975). China started relatively slowly (starting around 1981). In 1975, the United States launched the first commercial system Printrak250, while Japan's NECAFIS was not put into use until 1982. In recent years, China has also launched its own fingerprint recognition systems. Fingerprint imaging technology,

which is the first step in fingerprint processing, has also become increasingly mature, making the collected fingerprint data more real, the image clearer, the processing results more reliable, and the credibility of the identification results stronger. At present, there are methods to obtain fingerprint images using optical total reflection technology, silicon crystal capacitance sensing technology, ultrasonic scanning technology, etc.

Moreover, with the development of modern society, security has become the primary consideration of many systems. Fingerprints have become a reliable means of identification due to 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.

USB is the abbreviation of Universal Serial Bus. This is a new serial interface technology that has been gradually 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 ability, can be bus-powered, low-cost, and has strong peripheral connection capabilities. Therefore, the USB interface is used to transmit the collected fingerprint image, which can communicate with the computer more conveniently and flexibly, and has good application prospects.

Chapter 2, Design Overview

The purpose of the design is to realize a high-performance fingerprint collector that uses a USB interface to communicate with the host. The fingerprint chip uses the silicon crystal capacitive sensor FPS110 from Veridicom, and the main control chip uses the single-chip microcomputer MC68HC908JB8 with integrated USB module from Motorola. 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.

Figure 1. Fingerprint collection scheme diagram

The host software design is mainly divided into two parts: USB driver and demonstration interface.

1. Use Jungo's Windriver software to develop the USB driver for the WINDOWS platform.
2. Use Microsoft's VC6.0 software to develop the demonstration platform and some simple fingerprint processing programs.

Chapter 3, System Hardware Design

3.1, Main Chip Features

1. MC68HC908JB8, the main control chip of the fingerprint collector with integrated USB module

MC68HC908JB8 is a cost-effective single-chip microcomputer of the MC68HC08 series of Motorola. 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 a silicon crystal capacitive sensor from Veridicom. The sensor uses advanced semiconductor CMOS technology and is only the size of a stamp. It has many advantages, such as high sensitivity, high reliability, high resolution (500DPI), low power consumption, and low price. It is particularly suitable for commercial and outdoor fingerprint application systems.

3.2 Fingerprint collector system hardware design

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

Figure 2. Basic principle diagram of fingerprint collector [page]

1. Power supply design

MC68HC908JB8 and FPS110 can both support 5V power supply, and MC68HC908JB8 can also provide the 3.3V reference voltage required by 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 separate power supply.

2. Clock design

MC68HC908JB8 and FPS110 supply clocks respectively. MC68HC908JB8 uses a 6M crystal connected between OSC1 and OSC2, and FPS110 uses a 12M crystal connected between XTAL1 and XTAL2. 3. Interface design of FPS110 and MC68HC908JB8
MC68HC908JB8 has five sets of general interfaces PTA, PTB, PTC, PTD, PTE. In the design, PTB port and PTC port are selected to connect to FPS110. PTB port is used for data communication and PTC port is used for control. The specific connection is shown in Figure 3.

Figure 3. Interface design diagram of FPS110 and MC68HC908JB8

4. USB interface design.

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

Figure 4. Low-speed USB interface design

Chapter 4, System Software Design

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

4.1 USB firmware design on MC68HC908JB8

The development environment of the microcontroller uses Metrowerks' CodeWarrior studio integrated development software, and the online simulation and programming tool uses P&E Microcomputer Systems' MON08MULTILINK. The

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

Figure 5. USB firmware basic flow chart

4.2 Fingerprint collection program design

MC68HC908JB8 uses the general interface PTB and PTC to connect with FPS110. By controlling the row register and column register in the FPS110 chip, it is very convenient to complete the collection of the entire fingerprint or part of the fingerprint. The basic process of fingerprint collection is shown in Figure 6. [page]

Figure 6. Basic flow chart of fingerprint collection

4.3, USB driver design under WINDOWS platform

Windriver is a tool software for writing hardware drivers produced by Jungo Corporation of the United States. It is mainly used for driver development of ISA cards, PCI cards and USB. The 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 Driver Wizard that can help developers perform hardware diagnosis and automatically generate code. Therefore, using Windriver can enable electronic engineers to develop easy-to-use and compatible drivers for homemade hardware in a short time. Using Windriver to design USB drivers, as shown in Figure 7, actually just calls the API function provided by the Windriver universal driver in user mode, and does not need to write a WDM driver.

Figure 7 Windriver application structure diagram

Basic calling process: When the program is running, first call the WDU_INI function to initialize various variables and wait for the callback function result; if the callback is successful, call WDU_TRANSFER and other functions to complete the data transmission and reception; and when the program is finished, call WDU_UNINIT to release variables, handles, etc. to obtain resources.

4.4, Demonstration program design under WINDOWS platform The

demonstration program on the computer mainly includes simple control of the computer and MC68HC908JB8 communication, 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, and Figure 8 is an example of a demonstration interface.

Figure 8, demonstration interface

Chapter 5, Conclusion

This paper introduces a portable USB fingerprint acquisition solution based on MC68HC908JB8. Experiments show that this solution fully utilizes the advantages of USB, such as plug-and-play support, strong error correction capability, and bus power supply, simplifies the design, reduces costs, and realizes flexible and reliable fingerprint image transmission, which has a good application prospect. (end)