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.

Try It Yourself 15 min

Mini-Challenge · Ship the monitor 10 min

1. Mount the device in a tidy enclosure with sensors poking through.
2. Set up a wall-mounted tablet showing the dashboard in kiosk mode.
3. Hand the phone-app link to a family member; ask them to add the dashboard to their home screen.
4. Take photos / video of the finished build + the live dashboard.

Ship-ready test:

• Can a non-coder add the public link to their phone's home screen and check the temperature?
• Does the chart show a sensible 24h trend without missing chunks?
• Is the device still alive after 24 hours of continuous operation?

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.

Homework 5 min

1. Install the IoT Room Monitor. Run for at least 24 hours. Screenshot the 24h chart.
2. Share the public link with two people. Ask them to add it to their phone home screen.
3. Read ahead to ARD-L04-13 (MQTT Concepts). Cluster C starts.