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I'm trying to connect a fingerprint sensor (Adafruit type) to my ESP32 (DOIT ESP32 Devkit V1), but the Serial Monitor remains completely blank, even though I'm using Serial.begin(9600) and printing debug messages like "Starting setup...".

Here's what I have:

Board: DOIT ESP32 Devkit V1

Port: COM6 (shows up as "Silicon Labs CP210x USB to UART Bridge")

Wiring:

3.3V → VCC

GND → GND

GPIO16 (RX2) → TX of sensor

GPIO17 (TX2) → RX of sensor

Code :

#include <Adafruit_Fingerprint.h>
#include <HardwareSerial.h>



#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..
HardwareSerial mySerial(2);

#else
// On Leonardo/M0/etc, others with hardware serial, use hardware serial!
// #0 is green wire, #1 is white
#define mySerial Serial1

#endif


Adafruit_Fingerprint finger = Adafruit_Fingerprint(&mySerial);

void setup()
{
  Serial.begin(9600);
  Serial.println("התחלתי את setup");

  delay(100);
  Serial.println("\n\nAdafruit finger detect test");
  mySerial.begin(57600, SERIAL_8N1, 16, 17);
  // set the data rate for the sensor serial port
  finger.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");
      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!");
  } else if (p == FINGERPRINT_PACKETRECIEVEERR) {
    Serial.println("Communication error");
    return p;
  } else if (p == FINGERPRINT_NOTFOUND) {
    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;
}

I verified the port is correct and the board is selected properly in the Arduino IDE. But the Serial Monitor stays empty. I even added early Serial.println() calls, and nothing appears.

What could be causing this issue?

2
  • "I verified the port is correct ..." - How did you do that? Did you perform a loopback test? Did you verify that the voltages are compatible between this mystery "fingerprint sensor" and your ESP board? Do you have an oscilloscope to check signals? Commented May 5 at 19:31
  • Also posted at arduino.stackexchange.com/q/97643/40646. The problem is the wrong #ifdef and wrong Serial port used. Commented May 6 at 1:40

1 Answer 1

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Replace

#if (defined(__AVR__) || defined(ESP8266)) && !defined(__AVR_ATmega2560__)
    HardwareSerial mySerial(2);
#else
    #define mySerial Serial1
#endif

with

HardwareSerial mySerial(2);  // UART2, cocok untuk ESP32

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