Remote Vehicle Fuel Load Monitor

#define TINY_GSM_MODEM_SIM7600
#define TINY_GSM_RX_BUFFER 1024

#include <Arduino.h>
#include <Wire.h>
#include <TinyGsmClient.h>
#include <ArduinoHttpClient.h>
#include <Adafruit_ADS1X15.h>

// These pins match the installed SIM7600 and ADS1115 wiring.
static const int MODEM_RX_PIN = 16;
static const int MODEM_TX_PIN = 17;
static const int MODEM_PWRKEY_PIN = 27;
static const int I2C_SDA_PIN = 21;
static const int I2C_SCL_PIN = 22;

// Set these three values for the fleet SIM and the telemetry server before field use.
static const char APN[] = "SET_FLEET_SIM_APN";
static const char APN_USER[] = "";
static const char APN_PASS[] = "";
static const char TELEMETRY_HOST[] = "telemetry.example.invalid";
static const uint16_t TELEMETRY_PORT = 80;
static const char TELEMETRY_PATH[] = "/api/v1/vehicle-telemetry";
static const char VEHICLE_ID[] = "TRUCK-001";

// The signal receiver modules produce 0.6 V at 4 mA and 3.0 V at 20 mA.
static const float LOOP_MIN_V = 0.60f;
static const float LOOP_MAX_V = 3.00f;
static const float SENSOR_MIN_BAR = 0.0f;
static const float SENSOR_MAX_BAR = 10.0f;
static const float FUEL_TANK_LITRES = 400.0f;  // Change to the actual calibrated tank capacity.

// Calibration profiles: replace coefficients after weighing each vehicle empty and loaded.
struct VehicleProfile {
  const char *name;
  float emptyTonnes;
  float frontTonnesPerBar;
  float rearTonnesPerBar;
};
static const VehicleProfile PROFILES[] = {
  {"rigid_light", 5.0f, 0.18f, 0.42f},
  {"rigid_heavy", 8.5f, 0.24f, 0.62f},
  {"tractor_trailer", 13.0f, 0.30f, 0.85f}
};
static const uint8_t ACTIVE_PROFILE = 2;
static const unsigned long REPORT_INTERVAL_MS = 120000UL;

HardwareSerial modemSerial(2);
TinyGsm modem(modemSerial);
TinyGsmClient cellularClient(modem);
Adafruit_ADS1115 ads;

struct Measurement {
  float volts;
  float percent;
  bool valid;
};

float latitude = 0.0f;
float longitude = 0.0f;
bool gpsValid = false;
unsigned long lastReportMs = 0;

Measurement readLoop(uint8_t channel) {
  int16_t raw = ads.readADC_SingleEnded(channel);
  // GAIN_ONE gives 0.125 mV per count. The ADC is powered from the ESP32 3.3 V rail.
  float volts = raw * 0.000125f;
  bool valid = volts >= (LOOP_MIN_V - 0.12f) && volts <= (LOOP_MAX_V + 0.12f);
  float percent = (volts - LOOP_MIN_V) * 100.0f / (LOOP_MAX_V - LOOP_MIN_V);
  percent = constrain(percent, 0.0f, 100.0f);
  return {volts, percent, valid};
}

void powerModemOn() {
  pinMode(MODEM_PWRKEY_PIN, OUTPUT);
  digitalWrite(MODEM_PWRKEY_PIN, LOW);
  delay(100);
  digitalWrite(MODEM_PWRKEY_PIN, HIGH);
  delay(1200);
  digitalWrite(MODEM_PWRKEY_PIN, LOW);
  delay(5000);
}

bool updateGps() {
  float lat = 0.0f;
  float lon = 0.0f;
  // SIM7600 supplies GNSS through AT commands; its external GNSS antenna must be fitted.
  if (modem.enableGPS() && modem.getGPS(&lat, &lon)) {
    latitude = lat;
    longitude = lon;
    gpsValid = true;
    return true;
  }
  gpsValid = false;
  return false;
}

bool telemetryConfigured() {
  return strcmp(APN, "SET_FLEET_SIM_APN") != 0 &&
         strcmp(TELEMETRY_HOST, "telemetry.example.invalid") != 0;
}

bool postTelemetry(const String &json) {
  if (!telemetryConfigured()) {
    Serial.println("Telemetry not sent: set APN and server host first.");
    return false;
  }
  if (!modem.isNetworkConnected() && !modem.waitForNetwork(60000L)) {
    Serial.println("Cellular network unavailable.");
    return false;
  }
  if (!modem.isGprsConnected() && !modem.gprsConnect(APN, APN_USER, APN_PASS)) {
    Serial.println("Cellular data connection failed.");
    return false;
  }
  HttpClient http(cellularClient, TELEMETRY_HOST, TELEMETRY_PORT);
  http.post(TELEMETRY_PATH, "application/json", json);
  int statusCode = http.responseStatusCode();
  String response = http.responseBody();
  Serial.printf("Telemetry HTTP status: %d\n", statusCode);
  if (response.length() > 0) Serial.println(response);
  http.stop();
  return statusCode >= 200 && statusCode < 300;
}

void reportMeasurements() {
  Measurement front = readLoop(0);
  Measurement rear = readLoop(1);
  Measurement fuel = readLoop(2);
  const VehicleProfile &profile = PROFILES[ACTIVE_PROFILE];

  float frontBar = SENSOR_MIN_BAR + (front.percent / 100.0f) * (SENSOR_MAX_BAR - SENSOR_MIN_BAR);
  float rearBar = SENSOR_MIN_BAR + (rear.percent / 100.0f) * (SENSOR_MAX_BAR - SENSOR_MIN_BAR);
  bool loadValid = front.valid && rear.valid;
  float grossTonnes = profile.emptyTonnes + frontBar * profile.frontTonnesPerBar + rearBar * profile.rearTonnesPerBar;
  float cargoTonnes = max(0.0f, grossTonnes - profile.emptyTonnes);
  float fuelLitres = (fuel.percent / 100.0f) * FUEL_TANK_LITRES;

  updateGps();
  String json = "{\"vehicle_id\":\"" + String(VEHICLE_ID) + "\",";
  json += "\"profile\":\"" + String(profile.name) + "\",";
  json += "\"gps_valid\":" + String(gpsValid ? "true" : "false") + ",";
  json += "\"latitude\":" + String(latitude, 6) + ",\"longitude\":" + String(longitude, 6) + ",";
  json += "\"front_pressure_bar\":" + String(frontBar, 2) + ",\"rear_pressure_bar\":" + String(rearBar, 2) + ",";
  json += "\"fuel_percent\":" + String(fuel.percent, 1) + ",\"fuel_litres\":" + String(fuelLitres, 1) + ",";
  json += "\"front_sensor_ok\":" + String(front.valid ? "true" : "false") + ",";
  json += "\"rear_sensor_ok\":" + String(rear.valid ? "true" : "false") + ",";
  json += "\"fuel_sensor_ok\":" + String(fuel.valid ? "true" : "false") + ",";
  json += "\"load_sensor_ok\":" + String(loadValid ? "true" : "false") + ",";
  json += "\"estimated_gross_tonnes\":" + String(grossTonnes, 2) + ",";
  json += "\"estimated_cargo_tonnes\":" + String(cargoTonnes, 2) + "}";

  Serial.println(json);
  postTelemetry(json);
}

void setup() {
  Serial.begin(115200);
  Wire.begin(I2C_SDA_PIN, I2C_SCL_PIN);
  if (!ads.begin()) {
    Serial.println("ADS1115 not found. Check its power and the two I2C wires.");
    while (true) delay(1000);
  }
  ads.setGain(GAIN_ONE);

  modemSerial.begin(115200, SERIAL_8N1, MODEM_RX_PIN, MODEM_TX_PIN);
  powerModemOn();
  if (!modem.restart()) {
    Serial.println("SIM7600 did not answer. Check its 5 V, ground, antenna, and PWRKEY wire.");
  }
  Serial.println("Truck telemetry node started.");
}

void loop() {
  if (millis() - lastReportMs >= REPORT_INTERVAL_MS || lastReportMs == 0) {
    lastReportMs = millis();
    reportMeasurements();
  }
  delay(50);
}