Input devices

YF-S201 flow sensor with ESP32

The YF-S201 counts water with a small turbine and a Hall sensor. Each litre gives about 450 pulses, and the frequency follows F = 7.5 × Q, with Q in litres per minute. Those are nominal figures, and units vary. To do better, run a measured 10 litres through yours, count the pulses and divide by 10. One guide reports this gets you within 2 to 3 percent.

Power it from 5 V. Listed ranges vary a little, starting at 4.5 or 5 V, so 3.3 V is not a safe choice. The signal needs care on an ESP32: one reference describes an open-collector output, and other guides warn of 5 V pulses. Use a divider such as 10 kΩ and 20 kΩ on the signal line, or a level shifter, and check with a meter what your sensor really outputs. If you see no pulses through the divider, the output is probably open collector: remove the divider and use a 10 kΩ pull-up to 3.3 V instead.

Count pulses in an interrupt, and keep that routine to a single line that increments a counter. Do the maths once a second in the main loop. Avoid strapping pins for the input. Keep the wire away from the display cable, because a noisy pulse is counted as water. The sensor sits in the pipe, so check the arrow on the body for the flow direction. Check your version's pressure and temperature limits before fitting it. Very low flow may not turn the rotor at all, and this sensor's listed range starts at about 1 litre per minute.

Power and logic levels

5 V signal: needs a divider or level shifter

Supply	5 V
Signal level	Pulses may be 5 V
On an ESP32	Use a divider, or a pull-up to 3.3 V if the output is open collector.

ESP32 pins, including those on a display board's connectors, work at 3.3 V and are not 5 V tolerant. Modules differ, so if in doubt, measure the signal before you connect it.

const int FLOW_PIN = 5;
const float PULSES_PER_LITRE = 450.0;   // calibrate with a measured volume
volatile uint32_t pulses = 0;
float litres = 0;

void IRAM_ATTR onPulse() { pulses++; }

void setup() {
  Serial.begin(115200);
  pinMode(FLOW_PIN, INPUT);
  attachInterrupt(digitalPinToInterrupt(FLOW_PIN), onPulse, FALLING);
}

void loop() {
  delay(1000);
  noInterrupts();
  uint32_t n = pulses;
  pulses = 0;
  interrupts();
  litres += n / PULSES_PER_LITRE;
  Serial.printf("%.2f L/min  total %.2f L\n", n / 7.5, litres);
}

Use this information at your own risk. It is for general guidance only: the example code compiles, but it has not been tested on every part, and modules differ between sellers. Check the manufacturer's data before you build. Product names belong to their owners, and LCD Ultra Pro is not affiliated with them. See our Terms.