4-20 mA to voltage converter module (HW-685) with ESP32

Supply 7-36 V Bus ANALOG Measures current

Pins and ESP32 wiring

Pin	Role	ESP32 pin	Notes
VCC	Not wired to the ESP32	—	External 7 to 36 V supply (e.g. 12 or 24 V). Never to the ESP32. Pin order varies
GND	Ground	GND	Connect to ESP32 GND too (common ground)
VOUT	Analog output	D34	Set the span trimmer so 20 mA gives 3.3 V or less before connecting. To an ADC pin (prefer ADC1: GPIO 32 to 39)
I+	Not wired to the ESP32	—	Current loop in, from the transmitter
I-	Not wired to the ESP32	—	Current loop out

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); }

void loop() {
  int mv = analogReadMilliVolts(34);  // VOUT on GPIO 34
  Serial.println(mv);
  delay(200);
}

HW-685 seller datasheet, Supply 7 to 36 V; 0/4-20 mA in; 0-3.3 / 5 / 10 V out set by zero and span trimmers

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