Humidity and temperature (DHT11/DHT22) in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to include the DHT sensor library.

Arduino

#include [1]

Drag options to blanks, or click blank then click option'

A<Wire.h>

B<DHT.h>

C<SPI.h>

D<Servo.h>

Attempts:

3 left

💡 Hint

Common Mistakes

Including the wrong library like Wire.h or SPI.h which are for other sensors.

Forgetting the angle brackets <> around the library name.

The DHT sensor library is included with #include to use the DHT11 or DHT22 sensors.

2fill in blank

medium

Complete the code to define the DHT sensor type as DHT22.

Arduino

#define DHTTYPE [1]

Drag options to blanks, or click blank then click option'

ADHT11

BDHT12

CDHT22

DDHT33

Attempts:

3 left

💡 Hint

Common Mistakes

Using DHT11 when the sensor is actually DHT22.

Using undefined sensor types like DHT33.

Defining DHTTYPE as DHT22 tells the code which sensor model is used.

3fill in blank

hard

Fix the error in initializing the DHT sensor object on pin 2.

Arduino

DHT dht([1], DHTTYPE);

Drag options to blanks, or click blank then click option'

A2

BDHTTYPE

C3

DDHT

Attempts:

3 left

💡 Hint

Common Mistakes

Using the sensor type or class name instead of the pin number.

Using a pin number that does not match the hardware connection.

The first argument is the pin number where the sensor data line is connected, here pin 2.

4fill in blank

hard

Fill both blanks to read humidity and temperature values from the sensor.

Arduino

float humidity = dht.[1]();
float temperature = dht.[2]();

Drag options to blanks, or click blank then click option'

AreadHumidity

BreadTemperature

CreadTemp

DgetHumidity

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect function names like readTemp or getHumidity which do not exist.

Mixing up humidity and temperature function calls.

Use readHumidity() to get humidity and readTemperature() to get temperature from the sensor.

5fill in blank

hard

Fill all three blanks to check if readings are valid and print them to the serial monitor.

Arduino

if (isnan([1]) || isnan([2])) {
  Serial.println("Failed to read from DHT sensor!");
  return;
}
Serial.print("Humidity: ");
Serial.print([3]);
Serial.println(" %");

Drag options to blanks, or click blank then click option'

Atemperature

Bhumidity

Dtemp

Attempts:

3 left

💡 Hint

Common Mistakes

Checking variables that do not exist or are misspelled.

Printing temperature instead of humidity in the last print statement.

We check if humidity or temperature is NaN (not a number) to detect errors. Then we print humidity value.

Practice

1. What does the DHT11 sensor measure in an Arduino project?

easy

A. Humidity and temperature

B. Light intensity

C. Sound levels

D. Distance

Solution

1. Step 1: Understand sensor purpose

   The DHT11 sensor is designed to measure environmental conditions.

2. Step 2: Identify measured values

   It specifically measures humidity and temperature, not light, sound, or distance.

3. Final Answer:

   Humidity and temperature -> Option A

4. Quick Check:

   DHT11 measures humidity and temperature [OK]

Hint: Remember DHT sensors measure air humidity and temperature [OK]

Common Mistakes:

• Confusing DHT11 with light or sound sensors
• Thinking it measures distance
• Assuming it measures pressure

2. Which of the following is the correct way to include the DHT library in an Arduino sketch?

easy

A. #include "dht11.h"

B. #include

C. #include <dht_sensor>

D. #include

Solution

1. Step 1: Recall library inclusion syntax

   Arduino libraries are included with #include and angle brackets for installed libraries.

2. Step 2: Identify correct library name

   The standard DHT library is included as #include <DHT.h>.

3. Final Answer:

   #include <DHT.h> -> Option D

4. Quick Check:

   Use #include <DHT.h> to include DHT library [OK]

Hint: Use angle brackets and correct case for library names [OK]

Common Mistakes:

• Using wrong file names
• Using quotes instead of angle brackets
• Incorrect capitalization

3. What will be the output of this Arduino code snippet if the sensor reading is successful?

float h = dht.readHumidity();
float t = dht.readTemperature();
Serial.print("Humidity: ");
Serial.print(h);
Serial.print(" %\t");
Serial.print("Temperature: ");
Serial.print(t);
Serial.println(" *C");

medium

A. Error reading sensor

B. Humidity: % Temperature: *C

C. Humidity: 45.00 % Temperature: 23.00 *C

D. Humidity: NaN % Temperature: NaN *C

Solution

1. Step 1: Understand sensor reading functions

   The functions readHumidity() and readTemperature() return float values if successful.

2. Step 2: Analyze Serial output

   The code prints humidity and temperature values with labels and units, separated by tab.

3. Final Answer:

   Humidity: 45.00 % Temperature: 23.00 *C -> Option C

4. Quick Check:

   Successful read prints values with labels [OK]

Hint: Successful reads print numbers, errors show NaN or messages [OK]

Common Mistakes:

• Expecting error message on success
• Ignoring units in output
• Confusing NaN with valid numbers

4. Identify the error in this Arduino code snippet for reading DHT sensor data:

float humidity = dht.readHumidity();
float temperature = dht.readTemperature();
if (humidity == NULL || temperature == NULL) {
  Serial.println("Failed to read from DHT sensor!");
}

medium

A. Using NULL to check float values is incorrect

B. Missing semicolon after readTemperature()

C. Serial.println syntax is wrong

D. Variables humidity and temperature should be int

Solution

1. Step 1: Understand data types and checks

   readHumidity() and readTemperature() return float, not pointers, so NULL is invalid.

2. Step 2: Correct way to check errors

   Use isnan() function to check if readings failed (NaN means not a number).

3. Final Answer:

   Using NULL to check float values is incorrect -> Option A

4. Quick Check:

   Check floats with isnan(), not NULL [OK]

Hint: Use isnan() to check float errors, not NULL [OK]

Common Mistakes:

• Checking floats against NULL
• Assuming int type for sensor data
• Syntax errors in Serial print

5. You want to display temperature in Fahrenheit using DHT22 sensor readings in Arduino. Which code snippet correctly converts Celsius to Fahrenheit after reading temperature?

float tempC = dht.readTemperature();
float tempF = ?;
Serial.print("Temperature: ");
Serial.print(tempF);
Serial.println(" *F");

hard

A. tempF = tempC * 5 / 9 + 32;

B. tempF = tempC * 9 / 5 + 32;

C. tempF = tempC / 9 * 5 + 32;

D. tempF = (tempC + 32) * 9 / 5;

Solution

1. Step 1: Recall Celsius to Fahrenheit formula

   The correct formula is Fahrenheit = Celsius * 9/5 + 32.

2. Step 2: Apply formula in code

   Assign tempF = tempC * 9 / 5 + 32; to convert temperature correctly.

3. Final Answer:

   tempF = tempC * 9 / 5 + 32; -> Option B

4. Quick Check:

   Celsius to Fahrenheit = C * 9/5 + 32 [OK]

Hint: Use C * 9/5 + 32 to convert Celsius to Fahrenheit [OK]

Common Mistakes:

• Mixing multiplication and division order
• Adding 32 before multiplying
• Using wrong formula