Identification System Based on Fingerprint Sensor AT77C101B

1 Fingerprint Recognition Principle

　　Capacitive sensor is a type of fingerprint recognition sensor. It captures fingerprint images through electronic measurement design. The surface is an insulating layer, and the inside is a sensor that combines about 100,000 conductive metal arrays. When the user's finger is placed on it, the skin forms the other side of the capacitor array. Due to the different distances between the fingerprint ridge (near) and the fingerprint valley (far), different capacitance values ​​are formed. This capacitance value array forms a fingerprint image. After the fingerprint image is collected, it is preliminarily processed through the original image to make it clearer, and then the fingerprint feature database is established through the fingerprint recognition software.

　　2 AT77C101B Introduction

　　AT77C101B is a member of the fingerprint sensor family, as shown in Figure 1 and Figure 2. It is a FingerChip series sensor chip developed by Atmel, manufactured using COMS technology, with small size, good performance and low cost. AT77C101B can acquire different numbers of images within 1 s, and its area is much larger than that of a sliding fingerprint sensor. The integrated A/D converter can establish a digital interface between AT77C102B and EPP, USB or MCU, making this device easily applicable to any identification application system. The scanned image is 8×280=22.4 million pixels with a resolution of up to 2 GHz, equivalent to 1 780 frames/s, and one million fingers can be read without failure; it has the advantage of low power consumption, 4.5 mA during image acquisition, 1.5 mA during navigation, and less than 10μA in sleep mode. Its functions are shown in Table 1.

Because the image itself has a huge storage capacity, the system needs an external memory to ensure that there is enough storage space to store the image on a USB flash drive. At the same time, the system can also be connected to the network through a data cable to achieve remote control function.

　　

 

　　4 Software Design

　　The software design is shown in Figure 4. When no one touches the screen, the MCU is placed in power-saving sleep mode. Once the user has input, the system exits the low-power state and enters the normal execution state. The control software determines the user's needs and executes the corresponding functions.

　　

 

　　5 Experimental simulation

　　The data simulation was performed using the Matlab 7.0 image processing box from The MathWorks. The computer configuration was Intel 3.06 GZH CPU and Kingston 2GZH memory. The average simulation time for one image data was 0.53 s, and the recognition rate error was less than 1/310 000, which was completely in line with the requirements. Figure 5 is a random thumb fingerprint image, and Figure 6 is the corresponding image collected from the fingerprint library.

　　

 

　　

 

　　6 Conclusion

　　The AT77C101B fingerprint collector is used to collect data. When the user's fingerprint does not match the preset fingerprint in the fingerprint library, the user is refused to use. It can be used to identify the user's identity or replace manual password input, and has a wide range of application prospects.