IoT Room Monitor

Learning Goals 5 min

Cluster B's capstone: a wall-mounted live IoT dashboard for your room. Temperature, humidity, light, with historical charts and phone-app access. The polished combination of everything in L04-07..11. By the end of this lesson you will be able to:

1. Wire 3 sensors (DHT11 for temp + humidity, LDR for light) to a Cloud-capable board.
2. Define a Thing with at least 4 Properties (temperatureC, humidityPct, lightPct, uptime).
3. Build a polished dashboard with gauges, charts, and at-a-glance value cards — ready to share publicly or via per-user invite.

Warm-Up 10 min

Hardware:

• Supported Cloud board (Nano ESP32, MKR WiFi 1010, UNO R4 WiFi).
• DHT11 (cheap, ±5% RH, ±2 °C). Or DHT22 / BME280 for higher precision.
• LDR voltage divider on A0.
• 10 kΩ resistor for the LDR divider.
• USB power supply for permanent install.
• (Optional) An OLED on I²C for local display in addition to the cloud.

Install libraries

If using DHT11 / DHT22: Library Manager → "DHT sensor library" (Adafruit). For DHT22 you may also want "Adafruit Unified Sensor".

New Concept · The polished IoT product 20 min

Architecture review

1. Sensor reads happen at a slow rate (every 10–30 s — DHT11 is slow).
2. Property assignments push to the cloud automatically.
3. Dashboard shows current value (Gauge) + 24h history (Chart).
4. Phone app reads the same dashboard remotely.
5. Optional local OLED + LED for "at home, no internet" reliability.

Properties

Dashboard layout

• Three big Gauges side-by-side: Temp, Humidity, Light.
• One Chart underneath spanning full width — Temperature over 24h.
• One Chart — Humidity over 24h.
• One Slider for tempAlarmThreshold (with the current threshold visible).
• One Value at the bottom-right — uptime.

Worked Example · The full build 30 min

Step 1 — wire

Step 2 — create the Thing

Name: RoomMonitor. Attach device. Add the 5 properties from §3.

Step 3 — the sketch

#include "thingProperties.h"
#include <DHT.h>

#define DHTPIN 2
#define DHTTYPE DHT11
DHT dht(DHTPIN, DHTTYPE);

const int LDR_PIN = A0;
const int LDR_DARK = 100;
const int LDR_BRIGHT = 900;

unsigned long lastSensorAt = 0;
const unsigned long SENSOR_PERIOD_MS = 15000;

void setup() {
  Serial.begin(9600);
  delay(1500);
  initProperties();
  ArduinoCloud.begin(ArduinoIoTPreferredConnection);
  setDebugMessageLevel(2);

  dht.begin();
  tempAlarmThreshold = 28.0;       // default
}

void loop() {
  ArduinoCloud.update();
  unsigned long now = millis();

  if (now - lastSensorAt >= SENSOR_PERIOD_MS) {
    lastSensorAt = now;

    float t = dht.readTemperature();
    float h = dht.readHumidity();
    if (!isnan(t)) temperatureC = t;
    if (!isnan(h)) humidityPct  = h;

    int raw = analogRead(LDR_PIN);
    raw = constrain(raw, LDR_DARK, LDR_BRIGHT);
    lightPct = map(raw, LDR_DARK, LDR_BRIGHT, 0, 100);

    uptime = now / 1000;

    Serial.print("t="); Serial.print(temperatureC);
    Serial.print(" h="); Serial.print(humidityPct);
    Serial.print(" l="); Serial.println(lightPct);

    // Local action on alarm
    if (temperatureC > tempAlarmThreshold) {
      Serial.println("HOT");
      // Could also trigger a webhook here (L03-36 pattern).
    }
  }
}

void onTempAlarmThresholdChange() {
  Serial.print("Threshold changed to ");
  Serial.println(tempAlarmThreshold);
}

Step 4 — dashboard build

Three Gauges + two Charts + Slider + Value, arranged as in §3. Save.

Step 5 — open the phone app

Arduino IoT Remote → RoomMonitor dashboard. Walk around the house. The values track the actual room temperature / humidity / light. Cover the LDR — lightPct drops. Breathe on the DHT11 (or use a hair dryer carefully) — temp + humidity react.

Step 6 — share publicly

Generate a read-only public link. This is your "live room monitor" URL. Bookmark on phone home screen.

Step 7 — leave it running for a day

USB-powered, on a shelf, plugged in. Come back later — the charts have a day's worth of data. Note overnight cooling, daytime warmth, the brightness spike when you turn on lights.

Basic 5 min

Challenge 1 5 min

Challenge 2 5 min

Challenge 3 · Stop the flickering alarm 10 min

A classmate added an alarm LED on D4 to the room monitor. When the room sits near 28 °C, the LED flickers on and off every reading. Some readings also make the temperature jump to nan.

const int ALARM_LED_PIN = 4;

void checkAlarm() {
  float t = dht.readTemperature();
  temperatureC = t;
  if (temperatureC > tempAlarmThreshold) {
    digitalWrite(ALARM_LED_PIN, HIGH);
  } else {
    digitalWrite(ALARM_LED_PIN, LOW);
  }
}

1. Fix the nan problem. A failed read must keep the last good value.
2. Add hysteresis: turn the LED on above the threshold, but only off below the threshold minus 1 °C.
3. Call it from the sensor block of the Worked Example and test with your breath on the DHT11.

It works if the LED turns on above the threshold. It stays on until the room is a full degree below it.

Cluster B done. Cluster C (MQTT + Home Integration) starts in L04-13.

Recap 5 min

IoT Room Monitor combines Cluster B's ideas into a polished product: 3 sensors, 5 properties, gauges + charts + slider, public link + phone app. Code is ~50 lines; the cloud infrastructure carries everything else. This is the IoT pattern that scales — measure, push, visualise, alert. Tomorrow: a heavier-duty cousin called MQTT, which is what every "real" smart-home device uses under the hood.

DHT11 / DHT22

Cheap combined temperature + humidity sensors. DHT11 = ±2 °C, ±5% RH. DHT22 = ±0.5 °C, ±2% RH.

Sensor period

How often you read the sensor. Slow sensors (DHT, BME) have minimum periods.

Calibration constants

Measured values (LDR_DARK, LDR_BRIGHT) used in map() to convert raw ADC readings to friendly units.

Threshold property (READWRITE)

A configurable value (alarm threshold) that the user changes from the dashboard. Survives reboot if persisted; otherwise resets to a default on each boot.

Kiosk mode

Wall-mounted tablet showing dashboard fullscreen. Use a public read-only link.

Once-per-event suppression

Fire alert once on threshold crossing; don't fire again until recovery. From L03-36.

Extra Mission 5 min

Part 1 — Design a monitor for a different place

Pick a place that needs watching — a greenhouse, a pet's room, a garden shed, a fridge. On paper, design a monitor for it.

Your design must include:

• What it measures, and why each reading matters there.
• Every Property, with type, permission and update policy.
• One alarm, with its threshold and its hysteresis.
• A sketch of the dashboard layout.

Part 2 — Make it

Change the IoT Room Monitor to match your design, using the DHT11, LDR and LEDs you have. Leave it running for at least 24 hours.

Bring back next class: the sketch, a screenshot of the 24-hour chart, and a photo of the device in place.