Using sensor libraries in Arduino - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to include the sensor library.

Arduino

#include [1]

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

A<DHT.h>

B"DHT.h"

C<Wire.h>

D"Servo.h"

Attempts:

3 left

💡 Hint

Common Mistakes

Using quotes instead of angle brackets for installed sensor libraries.

Including the wrong library like Servo.h.

The sensor library DHT.h is included using angle brackets because it is an installed Arduino library.

2fill in blank

medium

Complete the code to create a sensor object named 'sensor'.

Arduino

DHT [1](2, DHT22);

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

AmySensor

BDHT

CtempSensor

Dsensor

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class name 'DHT' as the object name.

Using unrelated names like 'tempSensor' without context.

The sensor object is named 'sensor' to match the example.

3fill in blank

hard

Fix the error in the setup function to start the sensor.

Arduino

void setup() {
  Serial.begin(9600);
  [1].begin();
}

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

Adht

BSensor

Csensor

DDHT

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect capitalization like 'Sensor' or 'DHT'.

Calling begin() on the class name instead of the object.

The sensor object is named 'sensor' and must be called with .begin() to initialize.

4fill in blank

hard

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

Arduino

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

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

Asensor

BtempSensor

CSensor

Ddht

Attempts:

3 left

💡 Hint

Common Mistakes

Using different or incorrect object names for humidity and temperature.

Using capitalized names that do not match the object.

The sensor object named 'sensor' is used to call both readHumidity() and readTemperature() methods.

5fill in blank

hard

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

Arduino

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

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

Ahumidity

Btemperature

CDHT

Dsensor

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong variable names in isnan checks.

Mentioning the object name instead of the class name in the message.

We check if humidity or temperature is NaN and print an error message mentioning the DHT sensor.

Practice

1. What is the first step when using a sensor library in an Arduino sketch?

easy

A. Include the sensor library at the top of the sketch

B. Read sensor values in the loop() function

C. Create a sensor object inside the loop()

D. Start the sensor in the loop() function

Solution

1. Step 1: Understand the library usage

   Before using a sensor, you must include its library so Arduino knows how to communicate with it.

2. Step 2: Identify correct placement

   Including the library is done at the top of the sketch, before setup() and loop().

3. Final Answer:

   Include the sensor library at the top of the sketch -> Option A

4. Quick Check:

   Include library first = A [OK]

Hint: Always include libraries before setup() [OK]

Common Mistakes:

• Trying to create sensor object before including library
• Starting sensor in loop() instead of setup()
• Reading sensor before initializing it

2. Which of the following is the correct way to create a sensor object for a DHT sensor using its library?

easy

A. DHT sensor = DHT(2);

B. DHT sensor = new DHT(2, DHT11);

C. DHT sensor(2, DHT11);

D. DHT sensor = DHT11(2);

Solution

1. Step 1: Recall object creation syntax in Arduino C++

   Objects are created by calling the constructor directly, like ClassName objectName(parameters); without '=' or 'new' keyword.

2. Step 2: Match correct syntax for DHT library

   The DHT library uses: DHT sensor(pin, type); so DHT sensor(2, DHT11); matches this exactly.

3. Final Answer:

   DHT sensor(2, DHT11); -> Option C

4. Quick Check:

   Object creation = ClassName object(params); [OK]

Hint: Create objects without '=' or 'new' in Arduino [OK]

Common Mistakes:

• Using '=' sign when creating objects
• Using 'new' keyword which is not typical in Arduino sketches
• Confusing sensor type and pin order

3. Given the code below, what will be printed if the sensor reading fails?

#include <DHT.h>
#define DHTPIN 2
#define DHTTYPE DHT11
DHT dht(DHTPIN, DHTTYPE);

void setup() {
  Serial.begin(9600);
  dht.begin();
}

void loop() {
  float h = dht.readHumidity();
  if (isnan(h)) {
    Serial.println("Failed to read humidity!");
  } else {
    Serial.print("Humidity: ");
    Serial.println(h);
  }
  delay(2000);
}

medium

A. Failed to read humidity!

B. Humidity: 0.00

C. Humidity: NaN

D. No output

Solution

1. Step 1: Understand the isnan() check

   The code checks if the humidity reading is 'NaN' (not a number), which means the sensor failed to read.

2. Step 2: Determine output when reading fails

   If isnan(h) is true, the code prints "Failed to read humidity!" to Serial.

3. Final Answer:

   Failed to read humidity! -> Option A

4. Quick Check:

   isnan true prints error message [OK]

Hint: Check isnan() to detect sensor read failure [OK]

Common Mistakes:

• Assuming sensor returns 0 on failure
• Printing raw value without checking for NaN
• Not calling dht.begin() in setup()

4. Identify the error in this Arduino sketch snippet using a sensor library:

#include <DHT.h>
DHT dht(2, DHT11);

void setup() {
  Serial.begin(9600);
}

void loop() {
  dht.begin();
  float t = dht.readTemperature();
  Serial.println(t);
  delay(1000);
}

medium

A. readTemperature() returns int, not float

B. dht.begin() should be called in setup(), not loop()

C. Missing #define for sensor pin

D. Serial.begin() should be called in loop()

Solution

1. Step 1: Locate sensor initialization

   dht.begin() initializes the sensor and should be called once in setup() to avoid repeated initialization.

2. Step 2: Identify why calling dht.begin() in loop() is wrong

   Calling dht.begin() repeatedly in loop() can cause sensor communication issues and slow down the program.

3. Final Answer:

   dht.begin() should be called in setup(), not loop() -> Option B

4. Quick Check:

   Initialize sensor once in setup() [OK]

Hint: Initialize sensors once in setup() [OK]

Common Mistakes:

• Calling sensor start functions repeatedly in loop()
• Confusing Serial.begin() placement
• Assuming readTemperature() returns int

5. You want to read temperature and humidity from a DHT11 sensor and turn on an LED if humidity is above 70%. Which code snippet correctly uses the sensor library and controls the LED?

hard

A. #include <DHT.h>
#define DHTPIN 2
#define DHTTYPE DHT11
#define LEDPIN 13
DHT dht(DHTPIN, DHTTYPE);

void setup() {
Serial.begin(9600);
dht.begin();
pinMode(LEDPIN, OUTPUT);
}

void loop() {
float h = dht.readHumidity();
if (!isnan(h) || h > 70) {
digitalWrite(LEDPIN, HIGH);
} else {
digitalWrite(LEDPIN, LOW);
}
delay(2000);
}

B. #include <DHT.h>
#define DHTPIN 2
#define DHTTYPE DHT11
#define LEDPIN 13
DHT dht(DHTPIN, DHTTYPE);

void setup() {
Serial.begin(9600);
pinMode(LEDPIN, OUTPUT);
}

void loop() {
float h = dht.readHumidity();
if (h > 70) {
digitalWrite(LEDPIN, HIGH);
} else {
digitalWrite(LEDPIN, LOW);
}
delay(2000);
}

C. #include <DHT.h>
#define DHTPIN 2
#define DHTTYPE DHT11
#define LEDPIN 13
DHT dht(DHTPIN, DHTTYPE);

void setup() {
Serial.begin(9600);
dht.begin();
pinMode(LEDPIN, OUTPUT);
}

void loop() {
float h = dht.readHumidity();
if (h < 70) {
digitalWrite(LEDPIN, HIGH);
} else {
digitalWrite(LEDPIN, LOW);
}
delay(2000);
}

D. #include <DHT.h>
#define DHTPIN 2
#define DHTTYPE DHT11
#define LEDPIN 13
DHT dht(DHTPIN, DHTTYPE);

void setup() {
Serial.begin(9600);
dht.begin();
pinMode(LEDPIN, OUTPUT);
}

void loop() {
float h = dht.readHumidity();
if (!isnan(h) && h > 70) {
digitalWrite(LEDPIN, HIGH);
} else {
digitalWrite(LEDPIN, LOW);
}
delay(2000);
}

Solution

1. Step 1: Check sensor initialization and pin setup

   #include <DHT.h>
   #define DHTPIN 2
   #define DHTTYPE DHT11
   #define LEDPIN 13
   DHT dht(DHTPIN, DHTTYPE);
   
   void setup() {
     Serial.begin(9600);
     dht.begin();
     pinMode(LEDPIN, OUTPUT);
   }
   
   void loop() {
     float h = dht.readHumidity();
     if (!isnan(h) && h > 70) {
       digitalWrite(LEDPIN, HIGH);
     } else {
       digitalWrite(LEDPIN, LOW);
     }
     delay(2000);
   }
   

   correctly calls dht.begin() in setup() and sets LED pin as output.

2. Step 2: Verify humidity check and LED control logic

   #include <DHT.h>
   #define DHTPIN 2
   #define DHTTYPE DHT11
   #define LEDPIN 13
   DHT dht(DHTPIN, DHTTYPE);
   
   void setup() {
     Serial.begin(9600);
     dht.begin();
     pinMode(LEDPIN, OUTPUT);
   }
   
   void loop() {
     float h = dht.readHumidity();
     if (!isnan(h) && h > 70) {
       digitalWrite(LEDPIN, HIGH);
     } else {
       digitalWrite(LEDPIN, LOW);
     }
     delay(2000);
   }
   

   checks if humidity is not NaN and greater than 70 before turning LED on, which prevents errors from failed reads.

3. Final Answer:

   The code snippet with !isnan(h) check and && h > 70 -> Option D

4. Quick Check:

   Initialize sensor + check isnan + control LED = A [OK]

Hint: Always check isnan() before using sensor values [OK]

Common Mistakes:

• Not calling dht.begin() in setup()
• Missing isnan() check causing wrong LED behavior
• Using || instead of && in humidity condition