Legacy System Modernization: Remote Monitoring for a 1972 Diesel Engine

// ── Gateway → Node: command packet ─────────────────────────────
// One JSON object per virtual pin trigger (Blynk BLYNK_WRITE)
{ "V1": 1 }   // Start engine (Relay 1 pulse)
{ "V2": 1 }   // Stop engine  (Relay 2 → cooldown sequence)
{ "V5": 1 }   // Throttle  (linear actuator, 1-second pulse)
{ "V6": 1 }   // Brake     (linear actuator, 1-second pulse)
{ "V24": 5 }  // RPM target (slider 0–10, mapped to 1000–75000)

// ── Node → Gateway: telemetry array ────────────────────────────
// Sent every 60 s and after any relay state change
[
  12.8,   // [0] Battery voltage (V)  — avgVoltage1
  14.1,   // [1] Alternator voltage (V) — avgVoltage2
  3.2,    // [2] Oil pressure (bar)   — avgPresion1
  0,      // [3] Electrovalve state   — LedRelay_7
  1,      // [4] Engine OFF indicator — LedRelay_3
  0,      // [5] Engine ON indicator  — LedRelay_4
  1,      // [6] Fuel level (digital) — StateLevel
  1850,   // [7] Engine RPM           — totalRPM
  5       // [8] RPM slider position  — RPM_Slider
]

// LoRaSender() — Diesel_Motor_Lora_Node/functions_rpm.h
void LoRaSender() {
  const size_t CAPACITY = JSON_ARRAY_SIZE(9);
  StaticJsonDocument<CAPACITY> doc;
  JsonArray array = doc.to<JsonArray>();

  array.add(avgVoltage1);   // battery voltage
  array.add(avgVoltage2);   // alternator voltage
  array.add(avgPresion1);   // oil pressure
  array.add(LedRelay_7);    // electrovalve state
  array.add(LedRelay_3);    // motor-off indicator
  array.add(LedRelay_4);    // motor-on indicator
  array.add(StateLevel);    // fuel level (digital)
  array.add(totalRPM);      // engine RPM
  array.add(RPM_Slider);    // RPM target slider

  char output[200];
  serializeJson(doc, output, sizeof(output));

  LoRa.beginPacket();
  LoRa.write(destination);   // 0xFF — gateway
  LoRa.write(localAddress);  // 0xBB — this node
  LoRa.write(msgCount);
  LoRa.write(sizeof(output));
  LoRa.print(output);
  LoRa.endPacket();
  msgCount++;

  onReceive(LoRa.parsePacket());  // immediately poll for reply
}

// Voltage averaging — VoltageFunction1() in functions_rpm.h
void VoltageFunction1() {
  sumVoltage1 = 0;
  for (int i = 0; i <= 100; i++) {
    int raw = analogRead(VoltageSensor);
    // Vin = (raw × 5V × (R1+R2)) / (R2 × 1023)  R1=22kΩ  R2=4.7kΩ
    float v = raw * 5.0 * (22.0 + 4.7) / (1023.0 * 4.7);
    sumVoltage1 += v;
  }
  avgVoltage1 = sumVoltage1 / 100;
}

// RPM measurement — interrupt-based, 1-second window
void ISRCountPulse3() { pulseCount3++; }

void loop_rpm() {
  if ((millis() - lastmillis) >= 1000) {
    detachInterrupt(digitalPinToInterrupt(RPM_PIN));
    unsigned long interval = millis() - lastmillis;
    // 1 pulse per rotation; multiply by 60 to convert Hz → RPM
    totalRPM = 60.0 * (pulseCount3 / (interval / 1000.0));
    lastmillis = millis();
    pulseCount3 = 0;
    attachInterrupt(digitalPinToInterrupt(RPM_PIN), ISRCountPulse3, RISING);
  }
}

// Start/stop state machine — loop_funtions() in functions_rpm.h
void loop_funtions() {
  started  = EEPROM.get(addr,  started);   // restore from EEPROM
  executed = EEPROM.get(addr1, executed);

  VoltageFunction1();
  VoltageFunction2();
  PressionFunction1();

  StateLevel = (!digitalRead(FuelLevel));

  // Guard: only start if not already running
  if (StateRelay_1 == 1 && started == 0) Start();

  // Guard: only stop if currently running
  if (StateRelay_2 == 1 && started == 1) OffMotor();
}

// Start() — 500 ms key pulse + EEPROM persistence
void Start() {
  digitalWrite(Relay_1, LOW);    // energise starter relay
  digitalWrite(Relay_4, LOW);    // oil pump ON
  started = 1;
  EEPROM.update(addr, started);  // persist across power cycles
  timer.setTimeout(500, turnRelay1Off);  // release after 500 ms
}

// Stop sequence: stop pulse → 5 s → 3 s cooldown
void OffMotor() {
  digitalWrite(Relay_2, LOW);
  started = 0;
  EEPROM.update(addr, started);
  timer.setTimeout(550, turnRelay2Off);   // release stop relay
  // turnRelay2Off() → setTimeout(5000, turnRelay3ON)
  // turnRelay3ON()  → setTimeout(3000, turnRelay3OFF)
}