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====== Proximity Hall sensor - NJK-5002C ======
<WRAP center round alert 60%>
It is powered with the voltage from 6 V to 36 V. Type: NPN.
</WRAP>

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===== ARDUINO PINS =====
  * PIN2
  * GND
  * 5V

===== ARDUINO CODE =====
<code>
// Hall sensor wheel speed calculator (auto-zero)
// Arduino MKR NB 1500 + NJK-5002C
// 7 cm radius, 4 magnets = 0.10996 m per pulse

const int sensorPin = 2;
const int ledPin = LED_BUILTIN;

const float pulseDistance = 0.10996;  // meters per magnet pulse
unsigned long lastDetectTime = 0;
unsigned long lastPrint = 0;
float speed_kmh = 0.0;
int lastState = HIGH;

void setup() {
  Serial.begin(9600);
  pinMode(sensorPin, INPUT_PULLUP);
  pinMode(ledPin, OUTPUT);
  Serial.println("Wheel speed calculation running...");
}

void loop() {
  int state = digitalRead(sensorPin);

// detect magnet arrival edge (HIGH → LOW)
  if (lastState == HIGH && state == LOW) {
    unsigned long now = millis();

if (lastDetectTime > 0) {
      unsigned long delta = now - lastDetectTime; // time between pulses (ms)
      float delta_s = delta / 1000.0;             // convert to seconds

float speed_mps = pulseDistance / delta_s;  // m/s
      speed_kmh = speed_mps * 3.6;                // km/h
    }

lastDetectTime = now;
    digitalWrite(ledPin, HIGH); // blink LED when detected
  }

// turn LED off shortly after detection
  if (digitalRead(ledPin) == HIGH && (millis() - lastDetectTime > 50)) {
    digitalWrite(ledPin, LOW);
  }

// auto-zero speed if no pulse for 1 second
  if (millis() - lastDetectTime > 1000) {
    speed_kmh = 0.0;
  }

// print speed every 0.5 s
  if (millis() - lastPrint > 500) {
    lastPrint = millis();

Serial.print("Speed: ");
    Serial.print(speed_kmh, 2);
    Serial.println(" km/h");
  }

lastState = state;
}

</code>

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