R305 Optical Fingerprint Sensor Module

Working Principle

The R305 (also sold as FPM10A) is an optical fingerprint sensor module. A CMOS camera illuminated by LEDs captures an image of the fingertip pressed against a glass prism. An on-board DSP extracts minutiae points (ridge endings and bifurcations) and stores them as a compact template. During verification, the sensor captures a new image, extracts minutiae, and compares against stored templates.

Analogy: Imagine taking a close-up photo of a fingerprint and circling every spot where a ridge splits or ends. Those circles become the "password." To unlock, a new photo is taken and compared — if enough circles match, access is granted.

Electrical Characteristics

Parameter	Value
Supply Voltage	3.6 V – 6.0 V
Interface	UART (57600 baud default)
Image Resolution	500 dpi
Template Capacity	162 fingerprints (on-board flash)
FAR (False Accept Rate)	<0.001%
FRR (False Reject Rate)	<1%
Match Time	<1 second (1:162)
Current	~120 mA during capture

Interfacing with an MCU

The R305 communicates via UART at 57600 baud (or configurable up to 115200). It has 4 wires: VCC, GND, TX, RX. Most modules use a JST connector or colour-coded wires (red=VCC, black=GND, yellow=TX, green/white=RX).

Calibration

The R305 is factory-calibrated for image capture. The enrollment workflow is the key setup step:

• Enrollment: Capture the same finger twice (two templates), then merge and store with an ID number.
• Security level: Adjustable 1–5 (1 = lenient, 5 = strict). Higher levels reduce FAR but increase FRR.
• Clean sensor: Wipe the glass surface regularly — oils and dust degrade image quality and match accuracy.

Code Example

/*
 * R305 Fingerprint Verification — Arduino
 * Requires: Adafruit_Fingerprint library
 * Wiring: TX→Pin2(RX), RX→Pin3(TX), VCC→5V
 */
#include <Adafruit_Fingerprint.h>
#include <SoftwareSerial.h>

SoftwareSerial mySerial(2, 3);  /* RX=2, TX=3 */
Adafruit_Fingerprint finger = Adafruit_Fingerprint(&mySerial);

void setup() {
    Serial.begin(9600);
    finger.begin(57600);
    if (finger.verifyPassword()) {
        Serial.println("Fingerprint sensor found!");
        Serial.print("Templates stored: ");
        finger.getTemplateCount();
        Serial.println(finger.templateCount);
    } else {
        Serial.println("Sensor not found! Check wiring.");
        while (1);
    }
}

void loop() {
    Serial.println("Place finger on sensor...");
    int id = getFingerprintID();
    if (id >= 0) {
        Serial.print("Match found! ID: "); Serial.println(id);
        Serial.print("Confidence: "); Serial.println(finger.confidence);
    }
    delay(1000);
}

int getFingerprintID() {
    uint8_t p = finger.getImage();
    if (p != FINGERPRINT_OK) return -1;
    p = finger.image2Tz();
    if (p != FINGERPRINT_OK) return -1;
    p = finger.fingerSearch();
    if (p == FINGERPRINT_OK) return finger.fingerID;
    return -1;
}

Real-World Applications

Limitations

• Optical limitations: Wet, dirty, or scarred fingers produce poor images and higher rejection rates.
• Small database: 162 templates is sufficient for small installations; larger systems need R307/R503 (1000+ templates).
• No liveness detection: Basic optical sensors can be spoofed by high-quality silicone fingerprint moulds — capacitive sensors are more secure.
• Power hungry: ~120 mA during capture makes it unsuitable for ultra-low-power battery applications.