Biometric Access Control: DIY Arduino Fingerprint Scanner with LCD & LED Indicators

Biometric Access Control: DIY Arduino Fingerprint Scanner with LCD & LED Indicators

Biometric security systems provide reliable access control by replacing traditional keys and passwords with unique physical traits. In this project, you will build a complete fingerprint verification system using an AS608 optical fingerprint sensor, an Arduino Uno, a 16×2 I2C LCD screen, and status LEDs. The system scans stored fingerprint templates, provides visual updates on the LCD, and triggers a green LED for authorized access or a red LED for unrecognized prints.

Components Needed

  • Arduino Uno
  • AS608 Optical Fingerprint Sensor Module
  • 16×2 LCD Display with I2C Interface (PCF8574 adapter)
  • Blue LED (Authorized access indicator)
  • Red LED (Unauthorized access indicator)
  • 200Ω Resistors (Current limiting for LEDs)
  • Breadboard & Jumper Wires

Circuit Schematic & Wiring Connection

ComponentComponent PinArduino Uno PinNotes
AS608 SensorVCC5VPower input
S608 SensorGNDGNDGround
AS608 SensorTXPin 2SoftwareSerial RX
AS608 SensorRXPin 3SoftwareSerial TX
I2C LCDVCC5VPower input
I2C LCDGNDGNDGround
I2C LCDSDAA4I2C Data
I2C LCDSCLA5I2C Clock
Green LEDAnode (+)Pin 7via 200Ω Resistor
Red LEDAnode (+)Pin 6via 200Ω Resistor
LEDsCathode (-)GNDCommon Ground

Required Libraries

Adafruit Fingerprint Sensor Library by Adafruit

LiquidCrystal_I2C by Frank de Brabander

Arduino Code

#include <Adafruit_Fingerprint.h>
#include <SoftwareSerial.h>
#include <Wire.h>
#include <LiquidCrystal_I2C.h>

#define Green_LED 7    // Green LED pin for authorized access
#define red_LED 6      // Red LED pin for unauthorized access

// RX (Pin 2) connects to AS608 TX, TX (Pin 3) connects to AS608 RX
SoftwareSerial mySerial(2, 3);
Adafruit_Fingerprint finger = Adafruit_Fingerprint(&mySerial);

// Initialize 16x2 LCD at address 0x27 (use 0x3F if display doesn't respond)
LiquidCrystal_I2C lcd(0x27, 16, 2);

void setup() {
  Serial.begin(9600);
  while (!Serial);
  delay(100);

  lcd.init();
  lcd.backlight();
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Fingerprint Init");

  pinMode(Green_LED, OUTPUT);
  pinMode(red_LED, OUTPUT);
  digitalWrite(Green_LED, LOW);
  digitalWrite(red_LED, LOW);

  finger.begin(57600);
  delay(5);
  
  if (finger.verifyPassword()) {
    Serial.println("Found fingerprint sensor!");
    lcd.setCursor(0, 1);
    lcd.print("Sensor detected :)");
  } else {
    Serial.println("Did not find fingerprint sensor :(");
    lcd.setCursor(0, 1);
    lcd.print("Sensor error :(");
    while (1) { delay(1); }
  }

  finger.getTemplateCount();
  Serial.print("Sensor contains "); 
  Serial.print(finger.templateCount); 
  Serial.println(" templates");

  delay(2000);
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Place Finger...");
}

void loop() {
  uint8_t result = getFingerprintID();

  if (result == 1) {
    digitalWrite(Green_LED, HIGH);
    digitalWrite(red_LED, LOW);
    Serial.println("Authorized fingerprint!");

    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Authorized Finger:");
    lcd.setCursor(0, 1);
    lcd.print("ID: ");
    lcd.print(result);
    delay(1500);
  } 
  else if (result == 0xFF) {
    // Idle state: No finger detected or error during scan
    digitalWrite(Green_LED, LOW);
    digitalWrite(red_LED, LOW);
  } 
  else {
    // Unregistered print or mismatch
    digitalWrite(Green_LED, LOW);
    digitalWrite(red_LED, HIGH);
    Serial.println("Unauthorized fingerprint!");

    lcd.clear();
    lcd.setCursor(0, 0);
    lcd.print("Unauthorized");
    lcd.setCursor(0, 1);
    lcd.print("Finger");
    delay(1500);
  }

  digitalWrite(Green_LED, LOW);
  digitalWrite(red_LED, LOW);
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("Place Finger...");
  delay(200);
}

// Custom function to query fingerprint matching status
uint8_t getFingerprintID() {
  uint8_t p = finger.getImage();
  if (p != FINGERPRINT_OK) return 0xFF;

  p = finger.image2Tz();
  if (p != FINGERPRINT_OK) return 0xFF;

  p = finger.fingerFastSearch();
  if (p != FINGERPRINT_OK) return 0xFE;  // No match found in flash memory

  // Match found
  Serial.print("Found ID #"); Serial.print(finger.fingerID);
  Serial.print(" with confidence "); Serial.println(finger.confidence);
  return finger.fingerID;
}

How it works

Initialization: In setup(), SoftwareSerial initializes the I2C LCD screen at address 0x2 and connects with the AS608 sensor at a 57,600 baud rate.7. The code uses a finger to confirm the connection.verifyPassword() and shows the LCD’s sensor status.

Image Capture & Conversion: The getFingerprintID() method triggers the finger during loop().To take an optical picture, use getImage(). Finger if there is a print.The original image is transformed into a feature template using image2Tz().

Authorized Print (ID match): The method returns the ID if it finds a template that matches, such as ID 1. The user’s ID number is shown on the LCD for 1.5 seconds while the blue LED illuminates.

Unauthorized Print: getFingerprintID() returns 0xFE if there isn’t a match in memory. When the red LED illuminates, the LCD shows “Unauthorized Finger.”

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