Weather Desk

BRIEF A sensor that speaks in sentences

Your photoresistor mumbled a raw number and left you to figure out what it meant. Today's sensor is a different creature. The DHT11 measures temperature and humidity and reports them in real units: degrees Celsius, percent humidity. The same family of sensor lives inside air conditioners, incubators and greenhouses. By the end of this lesson your room will have its own weather report, updating live on your screen.

Time: 45–60 minutes · Difficulty: 3/5 · You need: Lesson 06 done (Serial Monitor habits).

KIT What you need

• R3 board with USB cable
• Breadboard
• The DHT11 module (blue waffle on a small board, three pins)
• Jumper wires

SETUP Install the library, once

1. In the Arduino IDE open Tools → Manage Libraries.
2. Search "DHT sensor library" and install the one by Adafruit.
3. If it offers to install the Adafruit Unified Sensor helper too, say yes, the DHT library needs it.

BUILD Wire it

Unplug the USB. Push the module's three pins into the breadboard and wire from its rows. Check the tiny letters printed next to the pins, most kits mark them S (signal), middle (power), and − (ground), but trust the letters on YOURS over any diagram.

From	To	Why
Module S pin	R3 pin 2	The data line, where the sentences arrive
Module middle pin	R3 5V	Power for the sensor's tiny brain
Module − pin	R3 GND	Loop complete

CODE Program it

// GAMERIFT Beginner Kit, Lesson 09: Weather Desk
// A live weather report for one small room.

#include <DHT.h>                // invite the library in

const int dhtPin = 2;
DHT dht(dhtPin, DHT11);          // our sensor, by name and type

void setup() {
  Serial.begin(9600);
  dht.begin();
  Serial.println("Weather Desk starting...");
}

void loop() {
  float temp = dht.readTemperature();   // degrees C, with decimals
  float hum  = dht.readHumidity();      // percent

  if (isnan(temp) || isnan(hum)) {      // did the sensor not answer?
    Serial.println("Sensor not answering. Check the three wires.");
  } else {
    Serial.print(temp);
    Serial.print(" C   |   ");
    Serial.print(hum);
    Serial.println(" % humidity");
  }

  delay(2000);   // the DHT11 needs 2 seconds between questions
}

1. Upload and open the Serial Monitor (9600 baud).
2. There it is: your room, in degrees and percent, refreshing every two seconds.
3. Compare it with a weather app. Your room is probably warmer than outside, now you can prove it.

BREAK IT Now break it on purpose

1. Breathe on the sensor slowly, like fogging a window. Watch humidity leap 20 points and temperature rise, your breath is warm, wet weather. This is also how you know it is really measuring.
2. Change delay(2000) to delay(200). The DHT11 starts failing or repeating stale readings, it simply cannot think that fast. Some sensors are marathon runners, not sprinters. Respect the datasheet. Put it back.
3. Pull out the S wire. Instead of nonsense numbers, your program calmly says the sensor is not answering, because YOU wrote error handling. Feel slightly heroic. Reconnect.

REMIX Make it yours

• Comfort commentary: add if-statements that print opinions, above 28 "Eish, it is getting hot in here", below 16 "Fetch a jersey". Your first sassy machine.
• Min-max memory: keep two variables for the highest and lowest temperature seen since power-on, and print them alongside. Leave it running overnight, what happened at 3am?
• Heat alarm: bring in Lesson 08's buzzer, three beeps if the temperature crosses your line. You have built a server-room monitor, a real product that companies pay real money for.

LOG IT Show and tell

Screenshot your weather report (bonus: the breath spike) for your lesson log. Stuck? Contact us with a photo of the three wires.