Version 2

Full Code :

#include <WiFi.h>
#include "ThingSpeak.h"

#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>

// ================= WIFI =================
char ssid[] = "A";
char pass[] = "12345678";

WiFiClient client;

unsigned long myChannelNumber = 3209793;
const char * myWriteAPIKey = "9PC614ZGGO6X53YY";

// ================= OLED =================
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 32
Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);

// ================= BUTTONS =================
#define BTN_PAGE 32
#define BTN_HOME 33

// ================= BUZZER =================
#define BUZZER_PIN 25
#define BUZZER_DURATION 60000UL

// ================= PARAMETERS =================
int engineTemp = 3000;
int pumpRPM    = 22000;
bool fuelFlowStable = true;
int vibration = 0;

// ================= STATE =================
int currentPage = 0; // 0=Home,1=Status,2=Advisory
bool buzzerActive = false;
unsigned long buzzerStartTime = 0;

// ================= TIMING =================
unsigned long lastUpdate = 0;
unsigned long lastThingSpeakUpdate = 0;

const unsigned long updateInterval = 3000;
const unsigned long thingSpeakInterval = 20000;

// =====================================================

void setup() {
  Serial.begin(115200);
  randomSeed(analogRead(34));

  pinMode(BUZZER_PIN, OUTPUT);
  digitalWrite(BUZZER_PIN, LOW);

  pinMode(BTN_PAGE, INPUT_PULLUP);
  pinMode(BTN_HOME, INPUT_PULLUP);

  // OLED
  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("OLED failed");
    while (1);
  }

  display.clearDisplay();
  display.display();

  // WiFi
  WiFi.mode(WIFI_STA);
  ThingSpeak.begin(client);

  showHome();
}

// =====================================================

void loop() {

  // -------- SENSOR UPDATE --------
  if (millis() - lastUpdate >= updateInterval) {
    lastUpdate = millis();
    updateParameters();

    if (currentPage == 1) showStatus();
    else if (currentPage == 2) showAdvisory();
  }

  // -------- THINGSPEAK --------
  if (millis() - lastThingSpeakUpdate >= thingSpeakInterval) {
    lastThingSpeakUpdate = millis();
    sendToThingSpeak();
  }

  // -------- BUZZER TIMER --------
  if (buzzerActive && millis() - buzzerStartTime >= BUZZER_DURATION) {
    digitalWrite(BUZZER_PIN, LOW);
    buzzerActive = false;
  }

  // -------- BUTTONS --------
  if (digitalRead(BTN_PAGE) == LOW) {
    currentPage++;
    if (currentPage > 2) currentPage = 1;
    delay(300);
  }

  if (digitalRead(BTN_HOME) == LOW) {
    currentPage = 0;
    showHome();
    delay(300);
  }
}

// =====================================================

void updateParameters() {

  engineTemp = random(2800, 3401);
  pumpRPM    = random(20000, 26001);
  vibration  = random(0, 101);

  fuelFlowStable = !(engineTemp > 3200 || pumpRPM > 24000);

  Serial.print("TEMP: "); Serial.print(engineTemp);
  Serial.print(" | RPM: "); Serial.print(pumpRPM);
  Serial.print(" | FUEL: "); Serial.print(fuelFlowStable);
  Serial.print(" | VIB: "); Serial.println(vibration);

  checkCritical();
}

// =====================================================

void checkCritical() {

  bool tempCritical = (engineTemp >= 3273);
  bool rpmCritical  = (pumpRPM >= 25000);
  bool fuelCritical = (!fuelFlowStable);

  if (tempCritical || rpmCritical || fuelCritical) {
    if (!buzzerActive) {
      digitalWrite(BUZZER_PIN, HIGH);
      buzzerActive = true;
      buzzerStartTime = millis();
    }
  } else {
    digitalWrite(BUZZER_PIN, LOW);
    buzzerActive = false;
  }
}

// =====================================================

void sendToThingSpeak() {

  if (WiFi.status() != WL_CONNECTED) {
    WiFi.begin(ssid, pass);
    Serial.println("Connecting WiFi...");
    return;
  }

  ThingSpeak.setField(1, engineTemp);
  ThingSpeak.setField(2, pumpRPM);
  ThingSpeak.setField(3, fuelFlowStable ? 1 : 0);
  ThingSpeak.setField(4, vibration);

  int x = ThingSpeak.writeFields(myChannelNumber, myWriteAPIKey);

  if (x == 200)
    Serial.println("ThingSpeak Updated");
  else
    Serial.println("ThingSpeak Error: " + String(x));
}

// =====================================================
// OLED PAGES

void showHome() {
  display.clearDisplay();
  display.setTextSize(2);
  display.setCursor(0, 8);
  display.println("BUILD CLUB");
  display.display();
}

void showStatus() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setCursor(0, 0);

  display.println("ENGINE STATUS");
  display.print("TEMP: "); display.println(engineTemp);
  display.print("RPM : "); display.println(pumpRPM);
  display.print("FUEL: ");
  display.println(fuelFlowStable ? "STABLE" : "UNSTABLE");

  display.display();
}

void showAdvisory() {
  display.clearDisplay();
  display.setTextSize(1);
  display.setCursor(0, 0);

  display.println("CREW ADVISORY");

  if (fuelFlowStable) {
    display.println("STATUS: NORMAL");
    display.println("- Monitor systems");
  } else {
    display.println("STATUS: CRITICAL");
    display.println("- Reduce load");
    display.println("- Check fuel");
  }

  display.display();
}