YF-S401 small water flow sensor with ESP32

Supply 5 V Bus GPIO Measures flow

Pins and ESP32 wiring

Pin	Role	ESP32 pin	Notes
VCC	Power	VIN	Red wire. Needs 5 V: use VIN
GND	Ground	GND	Black wire
SIG	Output (the part drives it)	D25	Yellow wire. Pulses at the supply level: use a voltage divider. About 98 pulses per second per L/min

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

This module is sold for 5 V. Its outputs may be 5 V: use a level shifter or a voltage divider on ESP32 inputs.

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

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

YF-S401 seller datasheet, Supply 5 to 24 V; range 0.3 to 6 L/min; about 5880 pulses per litre. Calibrate with a known volume

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