LJ12A3-4-Z/BX inductive proximity switch (NPN) with ESP32

Supply 6-36 V Bus GPIO Measures proximity, presence

Pins and ESP32 wiring

Pin	Role	ESP32 pin	Notes
BROWN	Not wired to the ESP32	—	Supply + from an external 6 to 36 V supply (e.g. 12 V). Never to the ESP32
BLUE	Ground	GND	Supply 0 V. Connect to ESP32 GND too (common ground)
BLACK	Output (the part drives it)	D25	NPN output, LOW near metal. Some units pull it up to the supply: measure first, use an optocoupler or divider

Suggested wiring for the 30-pin ESP32 DevKit, avoiding flash, input-only and strapping pins. BoardPilot checks it for you as you wire.

void setup() {
  Serial.begin(115200);
  pinMode(25, INPUT);  // BLACK
}

void loop() {
  Serial.println(digitalRead(25));
  delay(100);
}

LJ12A3-4-Z/BX seller datasheet, Supply 6 to 36 V DC; NPN NO output; detects metal at 4 mm; brown +, blue 0 V, black signal

Part data: CC BY 4.0, free to reuse with credit to BoardPilot.