← ESP32 PLC Flow Measurement with a Pulse Flow Meter

ESP32 PLC Flow Measurement with a Pulse Flow Meter — full example

Measure oil flow in L/min from a magnetic pulse sensor on an ESP32 PLC 38R. Interrupt timing, K-factor math, presence detection and full Arduino code.

Complete, runnable program for the ESP32 PLC 38R (pulse-flow-meter-38r.ino): wiring header, requirements and integration notes included.

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/*
 * COMPLETE EXAMPLE — Flow rate from magnetic/inductive sensor pulses
 *
 * Hardware:  ESP32 PLC 38R (Industrial Shields)
 * Based on:  hydraulic moving floor project, main.cpp (flow measurement)
 *
 * Wiring:
 *   I0_0  Inductive detector of the flow meter (1 pulse per turbine turn)
 *   I0_1  Flow meter presence signal (HIGH = sensor connected)
 *
 * Logic:
 *   - Each detector pulse is timed by interrupt (micros()).
 *   - The period between pulses is converted to L/min using the flow
 *     meter K factor (pulses per liter).
 *   - If no pulses arrive within FLOW_TIMEOUT_MS, flow is considered 0.
 *   - If the presence signal drops, the sensor is flagged as disconnected
 *     (validity flag, same pattern as the 4-20 mA sensors in this catalog).
 *
 * Integration with other catalog modules:
 *   - The flow rate can be notified over BLE in the [F]liters_min frame
 *     (see ejemplos/piso-movil/ble-mobile-app-control-38r.ino).
 *   - The accumulated volume can be persisted in NVS
 *     (see ejemplos/piso-movil/nvs-persistent-counters-38r.ino).
 */

#define PIN_PULSES     I0_0      // inductive detector
#define PIN_PRESENCE   I0_1      // flow meter presence

#define PULSES_PER_LITER   45.0  // flow meter K factor (adjust)
#define FLOW_TIMEOUT_MS    3000  // no pulses in 3 s -> flow 0

// Variables shared with the ISR: always volatile
volatile uint32_t lastPulseUs = 0;   // instant of the last pulse
volatile uint32_t periodUs    = 0;   // period between the 2 last pulses
volatile uint32_t totalPulses = 0;   // accumulated total for volume

float flowLmin   = 0.0;  // computed flow rate in L/min
float volumeL    = 0.0;  // accumulated volume in liters
bool  sensorOk   = false;

// ISR: timing only, no Serial and no heavy float math here
void IRAM_ATTR pulseIsr() {
  uint32_t now = micros();
  if (lastPulseUs != 0) {
    periodUs = now - lastPulseUs;
  }
  lastPulseUs = now;
  totalPulses++;
}

void setup() {
  Serial.begin(115200);

  pinMode(PIN_PULSES, INPUT);
  pinMode(PIN_PRESENCE, INPUT);

  attachInterrupt(digitalPinToInterrupt(PIN_PULSES), pulseIsr, RISING);

  Serial.println("Pulse flow meter ready (ESP32 PLC 38R)");
}

void loop() {
  // 1. Presence: if the signal drops, the flow meter is disconnected
  sensorOk = (digitalRead(PIN_PRESENCE) == HIGH);

  // 2. Atomic copy of the ISR variables
  noInterrupts();
  uint32_t period = periodUs;
  uint32_t last   = lastPulseUs;
  uint32_t pulses = totalPulses;
  interrupts();

  // 3. Flow rate: if too much time has passed since the last pulse, flow is 0
  bool hasFlow = (last != 0) &&
                 (micros() - last) < (FLOW_TIMEOUT_MS * 1000UL);

  if (sensorOk && hasFlow && period > 0) {
    // pulses/s = 1e6 / periodUs ; L/min = (pulses/s / K) * 60
    float pulsesPerSecond = 1000000.0 / (float)period;
    flowLmin = (pulsesPerSecond / PULSES_PER_LITER) * 60.0;
  } else {
    flowLmin = 0.0;
  }

  // 4. Accumulated volume from the total pulse count
  volumeL = (float)pulses / PULSES_PER_LITER;

  // 5. Report every second (in the real project this travels over BLE: [F]value)
  static uint32_t tLast = 0;
  if (millis() - tLast > 1000) {
    tLast = millis();
    if (!sensorOk) {
      Serial.println("[F]ERROR flow meter disconnected");
    } else {
      Serial.print("[F]");
      Serial.print(flowLmin, 1);
      Serial.print(" L/min  volume=");
      Serial.print(volumeL, 2);
      Serial.println(" L");
    }
  }

  delay(20);
}