指纹传感器是应用广泛的感知元件，本项目以R502/R503电容式指纹传感器为例，演示如何通过Arduino开发板录入和检测指纹。项目BOM清单如下：
Arduino开发板 1
指纹传感器R503 1
杜邦线 20
面包板 1
了解电容式指纹传感器
与光学指纹传感器的创建指纹图像不同，电容式产品采用微电容电路组成的阵列来收集数据。当手指按压到采集面上时，手指的脊和谷在表皮和芯片之间产生不同的微小电容,芯片通过测量空间中的不同的电磁场得到完整的指纹信息，并通过运放和ADC进行处理。例如，R502/R503就能识别干、湿指纹，而前者更轻巧。
以R503为例，该传感器内嵌指纹识别算法和协议，具有指纹采集、比对、搜索和模板存储等功能。R503图像大小192*192，分辨率达508 DPI，可存储200个指纹，FRR≤0.01%，FAR≤0.00001%，支持Arduino、Android、Windows、Linux等。
R503支持低功耗手指检测，工作电压3.3V，采集电流不超过18mA，平均待机电流仅2uA。R503通过RS232 UART接口，通讯速率达57600bps，用于电脑外设、指纹门锁、指纹挂锁、保险柜等。
把R502/R503与Arduino连接，电电路很简单。
把R502/R503的VCC、GND、Tx (黄线)、Rx (绿线)四个引脚分别连接到Arduino开发板的3.3V、GND、D2、D3引脚.，蓝色的中断线不用连接，白色引线接到3.3V引脚上。
源代码及编程
Github仓库有Adafruit编写的关于R502/R503指纹传感器的Arduino库文件。指纹录入和阅读是分开的，录入代码保存在EEPROM存储器中，阅读代码从EEPROM中读取数据并与扫描到的指纹数据校验匹配。
指纹录入代码如下：
#include#if (defined(__AVR__) || defined(ESP8266)) && !defined(__AVR_ATmega2560__)// For UNO and others without hardware serial, we must use software serial...// pin #2 is IN from sensor (GREEN wire)// pin #3 is OUT from arduino(WHITE wire)// Set up the serial port to use softwareserial..SoftwareSerial mySerial(2, 3);#else// On Leonardo/M0/etc, others with hardware serial, use hardware serial!// #0 is green wire, #1 is white#define mySerial Serial1#endifAdafruit_Fingerprint finger = Adafruit_Fingerprint(&mySerial);uint8_t id;void setup(){Serial.begin(9600);while (!Serial);// For Yun/Leo/Micro/Zero/...delay(100);Serial.println("\n\nAdafruit Fingerprint sensor enrollment");// set the data rate for the sensor serial portfinger.begin(57600);if (finger.verifyPassword()) {Serial.println("Found fingerprint sensor!");} else {Serial.println("Did not find fingerprint sensor : (");while (1) { delay(1); }}Serial.println(F("Reading sensor parameters"));finger.getParameters();Serial.print(F("Status: 0x")); Serial.println(finger.status_reg, HEX);Serial.print(F("Sys ID: 0x")); Serial.println(finger.system_id, HEX);Serial.print(F("Capacity: ")); Serial.println(finger.capacity);Serial.print(F("Security level: ")); Serial.println(finger.security_level);Serial.print(F("Device address: ")); Serial.println(finger.device_addr, HEX);Serial.print(F("Packet len: ")); Serial.println(finger.packet_len);Serial.print(F("Baud rate: ")); Serial.println(finger.baud_rate);}uint8_t readnumber(void) {uint8_t num = 0;while (num == 0) {while (! Serial.available());num = Serial.parseInt();}return num;}void loop() // run over and over again{Serial.println("Ready to enroll a fingerprint!");Serial.println("Please type in the ID # (from 1 to 127) you want to save this finger as...");id = readnumber();if (id == 0) {// ID #0 not allowed, try again!return;}Serial.print("Enrolling ID #");Serial.println(id);while (!getFingerprintEnroll() );}uint8_t getFingerprintEnroll() {int p = -1;Serial.print("Waiting for valid finger to enroll as #"); Serial.println(id);while (p != FINGERPRINT_OK) {p = finger.getImage();switch (p) {case FINGERPRINT_OK:Serial.println("Image taken");break;case FINGERPRINT_NOFINGER:Serial.println(".");break;case FINGERPRINT_PACKETRECIEVEERR:Serial.println("Communication error");break;case FINGERPRINT_IMAGEFAIL:Serial.println("Imaging error");break;default:Serial.println("Unknown error");break;}}// OK success!p = finger.image2Tz(1);switch (p) {case FINGERPRINT_OK:Serial.println("Image converted");break;case FINGERPRINT_IMAGEMESS:Serial.println("Image too messy");return p;case FINGERPRINT_PACKETRECIEVEERR:Serial.println("Communication error");return p;case FINGERPRINT_FEATUREFAIL:Serial.println("Could not find fingerprint features");return p;case FINGERPRINT_INVALIDIMAGE:Serial.println("Could not find fingerprint features");return p;default:Serial.println("Unknown error");return p;}Serial.println("Remove finger");delay(2000);p = 0;while (p != FINGERPRINT_NOFINGER) {p = finger.getImage();}Serial.print("ID "); Serial.println(id);p = -1;Serial.println("Place same finger again");while (p != FINGERPRINT_OK) {p = finger.getImage();switch (p) {case FINGERPRINT_OK:Serial.println("Image taken");break;case FINGERPRINT_NOFINGER:Serial.print(".");break;case FINGERPRINT_PACKETRECIEVEERR:Serial.println("Communication error");break;case FINGERPRINT_IMAGEFAIL:Serial.println("Imaging error");break;default:Serial.println("Unknown error");break;}}// OK success!p = finger.image2Tz(2);switch (p) {case FINGERPRINT_OK:Serial.println("Image converted");break;case FINGERPRINT_IMAGEMESS:Serial.println("Image too messy");return p;case FINGERPRINT_PACKETRECIEVEERR:Serial.println("Communication error");return p;case FINGERPRINT_FEATUREFAIL:Serial.println("Could not find fingerprint features");return p;case FINGERPRINT_INVALIDIMAGE:Serial.println("Could not find fingerprint features");return p;default:Serial.println("Unknown error");return p;}// OK converted!Serial.print("Creating model for #");Serial.println(id);p = finger.createModel();if (p == FINGERPRINT_OK) {Serial.println("Prints matched!");} else if (p == FINGERPRINT_PACKETRECIEVEERR) {Serial.println("Communication error");return p;} else if (p == FINGERPRINT_ENROLLMISMATCH) {Serial.println("Fingerprints did not match");return p;} else {Serial.println("Unknown error");return p;}Serial.print("ID "); Serial.println(id);p = finger.storeModel(id);if (p == FINGERPRINT_OK) {Serial.println("Stored!");} else if (p == FINGERPRINT_PACKETRECIEVEERR) {Serial.println("Communication error");return p;} else if (p == FINGERPRINT_BADLOCATION) {Serial.println("Could not store in that location");return p;} else if (p == FINGERPRINT_FLASHERR) {Serial.println("Error writing to flash");return p;} else {Serial.println("Unknown error");return p;}return true;}
上传代码后，打开Serial Monitor，监视器将询问位于1-127之间的指纹ID 。
现在Serial Monitor显示屏中输入ID号，并发送，然后按照屏幕指令提示录入指纹。
把希望录入的手指放在传感器上。
一个手指录入成功后，你也可以按照同样的方式再录入其他几个手指的指纹。
指纹读取代码如下：
#includeint u=0;int relay=5;#if (defined(__AVR__) || defined(ESP8266)) && !defined(__AVR_ATmega2560__)// For UNO and others without hardware serial, we must use software serial...// pin #2 is IN from sensor (GREEN wire)// pin #3 is OUT from arduino(WHITE wire)// Set up the serial port to use softwareserial..SoftwareSerial mySerial(2, 3);#else// On Leonardo/M0/etc, others with hardware serial, use hardware serial!// #0 is green wire, #1 is white#define mySerial Serial1#endifAdafruit_Fingerprint finger = Adafruit_Fingerprint(&mySerial);void setup(){pinMode(relay,OUTPUT);Serial.begin(9600);while (!Serial);// For Yun/Leo/Micro/Zero/...delay(100);Serial.println("\n\nAdafruit finger detect test");// set the data rate for the sensor serial portfinger.begin(57600);delay(5);if (finger.verifyPassword()) {Serial.println("Found fingerprint sensor!");} else {Serial.println("Did not find fingerprint sensor : (");while (1) { delay(1); }}Serial.println(F("Reading sensor parameters"));finger.getParameters();Serial.print(F("Status: 0x")); Serial.println(finger.status_reg, HEX);Serial.print(F("Sys ID: 0x")); Serial.println(finger.system_id, HEX);Serial.print(F("Capacity: ")); Serial.println(finger.capacity);Serial.print(F("Security level: ")); Serial.println(finger.security_level);Serial.print(F("Device address: ")); Serial.println(finger.device_addr, HEX);Serial.print(F("Packet len: ")); Serial.println(finger.packet_len);Serial.print(F("Baud rate: ")); Serial.println(finger.baud_rate);finger.getTemplateCount();if (finger.templateCount == 0) {Serial.print("Sensor doesn't contain any fingerprint data. Please run the 'enroll' example.");}else {Serial.println("Waiting for valid finger...");Serial.print("Sensor contains "); Serial.print(finger.templateCount); Serial.println(" templates");}}void loop() // run over and over again{getFingerprintID();delay(50);//don't ned to run this at full speed.}uint8_t getFingerprintID() {uint8_t p = finger.getImage();switch (p) {case FINGERPRINT_OK:Serial.println("Image taken");break;case FINGERPRINT_NOFINGER:Serial.println("No finger detected");finger.LEDcontrol(FINGERPRINT_LED_OFF, 0, FINGERPRINT_LED_BLUE);finger.LEDcontrol(FINGERPRINT_LED_OFF, 0, FINGERPRINT_LED_RED);return p;case FINGERPRINT_PACKETRECIEVEERR:Serial.println("Communication error");return p;case FINGERPRINT_IMAGEFAIL:Serial.println("Imaging error");return p;default:Serial.println("Unknown error");return p;}// OK success!p = finger.image2Tz();switch (p) {case FINGERPRINT_OK:Serial.println("Image converted");break;case FINGERPRINT_IMAGEMESS:Serial.println("Image too messy");return p;case FINGERPRINT_PACKETRECIEVEERR:Serial.println("Communication error");return p;case FINGERPRINT_FEATUREFAIL:Serial.println("Could not find fingerprint features");return p;case FINGERPRINT_INVALIDIMAGE:Serial.println("Could not find fingerprint features");return p;default:Serial.println("Unknown error");return p;}// OK converted!p = finger.fingerSearch();if (p == FINGERPRINT_OK) {Serial.println("Found a print match!");finger.LEDcontrol(FINGERPRINT_LED_FLASHING, 25, FINGERPRINT_LED_PURPLE, 10);delay(1000);if(u==0){digitalWrite(relay,HIGH);u=1;}else if(u==1){digitalWrite(relay,LOW);u=0;}} else if (p == FINGERPRINT_PACKETRECIEVEERR) {Serial.println("Communication error");return p;} else if (p == FINGERPRINT_NOTFOUND) {finger.LEDcontrol(FINGERPRINT_LED_FLASHING, 25, FINGERPRINT_LED_RED, 10);delay(1000);Serial.println("Did not find a match");return p;} else {Serial.println("Unknown error");return p;}// found a match!Serial.print("Found ID #"); Serial.print(finger.fingerID);Serial.print(" with confidence of "); Serial.println(finger.confidence);return finger.fingerID;}// returns -1 if failed, otherwise returns ID #int getFingerprintIDez() {uint8_t p = finger.getImage();if (p != FINGERPRINT_OK)return -1;p = finger.image2Tz();if (p != FINGERPRINT_OK)return -1;p = finger.fingerFastSearch();if (p != FINGERPRINT_OK)return -1;// found a match!Serial.print("Found ID #"); Serial.print(finger.fingerID);Serial.print(" with confidence of "); Serial.println(finger.confidence);return finger.fingerID;}
一旦指纹录入成功，就可以上传上述代码，以读取存储在指纹数据库中的指纹信息，通过比对匹配实现门禁、考勤、开机等操作。
作者：硬之城Allchips， 来源：面包板社区
链接：https://mbb.eet-china.com/blog/3975615-433079.html
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