1. Working Principle

1. Water flows in from the inlet, driving the turbine impeller to rotate

2. The magnet on the impeller rotates with the wheel, causing periodic magnetic field changes

3. The Hall sensor detects magnetic field changes and outputs square wave pulses (HIGH/LOW)

4. Pulse frequency is proportional to flow rate; total pulse count is proportional to water volume

5. Microcontroller (e.g., Arduino) reads pulses to calculate flow rate and volume

2. Selection Guide

• Interface Size: G1/2 (4分)

• Flow Range: 1-30L/min

• Voltage: DC 5V, compatible with Arduino/microcontrollers

• Media: Clean cold/warm water, avoid debris

• Accuracy: Typical ±3%, suitable for consumer and DIY projects

3. Installation Steps

4. Hardware Wiring

3-wire sensor (Red/Black/Yellow), simple wiring, no extra components needed

Note: Signal pin must connect to interrupt pin to avoid missing pulses

5. Code Implementation

Function: Output instantaneous flow (L/min) and cumulative volume (L) every second

// Define pins and parameters
#define sensorPin 2          // Signal pin connected to D2
#define pulsePerLiter 600    // USN-HS21TA: 600 pulses/L
volatile unsigned long pulseCount = 0;
unsigned long oldTime = 0;
float flowRate = 0;
float totalVolume = 0;

void setup() {
  pinMode(sensorPin, INPUT);
  Serial.begin(9600);
  attachInterrupt(digitalPinToInterrupt(sensorPin), pulseCounter, FALLING);
}

void loop() {
  if (millis() - oldTime > 1000) {
    detachInterrupt(digitalPinToInterrupt(sensorPin));

    flowRate = ((float)pulseCount / pulsePerLiter) * 60.0;
    totalVolume += (float)pulseCount / pulsePerLiter;

    Serial.print("Flow: ");
    Serial.print(flowRate, 2);
    Serial.print(" L/min | Volume: ");
    Serial.print(totalVolume, 2);
    Serial.println(" L");

    pulseCount = 0;
    oldTime = millis();
    attachInterrupt(digitalPinToInterrupt(sensorPin), pulseCounter, FALLING);
  }
}

void pulseCounter() {
  pulseCount++;
}

6. Calibration & Troubleshooting

7. Applications