Smart Classroom Welcome Monitor

#include <Arduino.h>
#include <DHT.h>
#include <MD_Parola.h>
#include <MD_MAX72xx.h>
#include <SPI.h>

// ── Pin definitions ───────────────────────────────────────────────
#define DHT_PIN         2
#define LED_PIN         3
#define MATRIX_DIN_PIN  11
#define MATRIX_CLK_PIN  13
#define MATRIX_CS_PIN   8

// ── Config ────────────────────────────────────────────────────────
#define DHTTYPE         DHT11
#define MAX_DEVICES     1          // Change to 2, 3 … for more panels
#define SCROLL_SPEED    120        // Lower = faster scroll (ms per step)
#define HOT_THRESHOLD   27.0f      // °C — red LED turns on above this
#define SENSOR_INTERVAL 3000UL     // ms between sensor reads

// ── Objects ───────────────────────────────────────────────────────

// Forward declarations
void readSensor();

DHT dht(DHT_PIN, DHTTYPE);
MD_Parola matrix = MD_Parola(MD_MAX72XX::FC16_HW, MATRIX_CS_PIN, MAX_DEVICES);

// ── State ─────────────────────────────────────────────────────────
char displayBuf[32];
float lastTemp = 0.0f;
float lastHum  = 0.0f;
unsigned long lastSensorRead = 0;

// ── Helpers ───────────────────────────────────────────────────────
void readSensor() {
    float t = dht.readTemperature();
    float h = dht.readHumidity();
    if (!isnan(t)) lastTemp = t;
    if (!isnan(h)) lastHum  = h;

    // Red LED
    digitalWrite(LED_PIN, lastTemp > HOT_THRESHOLD ? HIGH : LOW);

    // Build display string  e.g.  "Temp:24C  Hum:55%"
    snprintf(displayBuf, sizeof(displayBuf),
             "Temp:%dC  Hum:%d%%",
             (int)round(lastTemp), (int)round(lastHum));
}

void setup() {
    Serial.begin(9600);
    pinMode(LED_PIN, OUTPUT);
    digitalWrite(LED_PIN, LOW);

    dht.begin();

    matrix.begin();
    matrix.setIntensity(4);          // 0 (dim) – 15 (bright)
    matrix.setTextAlignment(PA_LEFT);

    // First sensor read
    delay(2000);                     // DHT11 warm-up
    readSensor();

    // Kick off first scroll
    matrix.displayScroll(displayBuf, PA_LEFT, PA_SCROLL_LEFT, SCROLL_SPEED);

    Serial.println(F("Smart Classroom ready."));
}

void loop() {
    // Update display on each scroll completion
    if (matrix.displayAnimate()) {

        // Time to refresh sensor?
        unsigned long now = millis();
        if (now - lastSensorRead >= SENSOR_INTERVAL) {
            lastSensorRead = now;
            readSensor();
            Serial.print(F("Temp: ")); Serial.print(lastTemp);
            Serial.print(F(" C  Hum: ")); Serial.print(lastHum);
            Serial.println(F(" %"));
        }

        // Restart the scroll with the (possibly updated) buffer
        matrix.displayScroll(displayBuf, PA_LEFT, PA_SCROLL_LEFT, SCROLL_SPEED);
    }
}