Reading digital input pin state in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to read the state of a digital input pin.

Embedded C

int pinState = digitalRead([1]);

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

A13

BOUTPUT

C5

DHIGH

Attempts:

3 left

💡 Hint

Common Mistakes

Using pin mode constants like OUTPUT or HIGH instead of a pin number.

Confusing digitalRead with digitalWrite.

The function digitalRead reads the state of the specified digital pin number. Pin 13 is commonly used for input or output on many boards.

2fill in blank

medium

Complete the code to check if the digital input pin reads HIGH.

Embedded C

if (digitalRead(7) == [1]) {
    // Pin is HIGH
}

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

ALOW

BHIGH

CINPUT

DOUTPUT

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing to pin mode constants like INPUT or OUTPUT.

Using LOW instead of HIGH in the condition.

To check if a pin is HIGH, compare the result of digitalRead to HIGH.

3fill in blank

hard

Fix the error in reading the digital input pin state.

Embedded C

pinMode(8, INPUT);
int state = digitalRead([1]);

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

A8

B9

CINPUT

DHIGH

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different pin number than the one set as input.

Passing mode constants like INPUT or HIGH to digitalRead.

The pin number used in digitalRead must match the pin set as input with pinMode. Here, pin 8 is configured as input, so digitalRead should use 8.

4fill in blank

hard

Fill both blanks to read a digital input pin and check if it is LOW.

Embedded C

pinMode([1], INPUT);
if (digitalRead([2]) == LOW) {
    // Pin is LOW
}

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

A4

BHIGH

D7

Attempts:

3 left

💡 Hint

Common Mistakes

Using different pin numbers in pinMode and digitalRead.

Comparing to HIGH instead of LOW.

Set pin 4 as input and read from pin 4 to check if it is LOW.

5fill in blank

hard

Fill all three blanks to read a digital input pin, store its state, and check if it is HIGH.

Embedded C

pinMode([1], INPUT);
int state = digitalRead([2]);
if (state == [3]) {
    // Pin is HIGH
}

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

A2

CHIGH

D3

Attempts:

3 left

💡 Hint

Common Mistakes

Using different pin numbers in pinMode and digitalRead.

Comparing to LOW instead of HIGH.

The pin number used in pinMode and digitalRead must match. Here, set pin 2 as input, read from pin 2, and check if state is HIGH.

Practice

1. What does the function digitalRead(pin) do in embedded C programming?

easy

A. Configures the pin as an analog input.

B. Sets the digital pin to output mode.

C. Reads the current state (HIGH or LOW) of a digital input pin.

D. Writes a HIGH signal to a digital pin.

Solution

1. Step 1: Understand the purpose of digitalRead

   The function digitalRead(pin) is used to check the current electrical state of a digital input pin, which can be either HIGH (on) or LOW (off).

2. Step 2: Differentiate from other pin functions

   Unlike functions that set pin modes or write signals, digitalRead only reads the pin's state without changing it.

3. Final Answer:

   Reads the current state (HIGH or LOW) of a digital input pin. -> Option C

4. Quick Check:

   digitalRead reads pin state = D [OK]

Hint: digitalRead always reads input pin state, not sets it [OK]

Common Mistakes:

• Confusing digitalRead with pinMode or digitalWrite
• Thinking digitalRead sets pin mode
• Assuming digitalRead writes output signals

2. Which of the following is the correct way to set a pin as input before reading its state?

easy

A. pinMode(pin, OUTPUT);

B. pinMode(pin, INPUT);

C. digitalRead(pin);

D. digitalWrite(pin, HIGH);

Solution

1. Step 1: Identify the function to set pin mode

   pinMode(pin, mode) is used to configure a pin as INPUT or OUTPUT.

2. Step 2: Choose the correct mode for reading input

   To read a digital input pin, it must be set as INPUT using pinMode(pin, INPUT).

3. Final Answer:

   pinMode(pin, INPUT); -> Option B

4. Quick Check:

   Set pin as INPUT before reading = A [OK]

Hint: Use pinMode(pin, INPUT) before digitalRead [OK]

Common Mistakes:

• Setting pin as OUTPUT before reading input
• Calling digitalRead before setting pin mode
• Using digitalWrite to set pin mode

3. What will be the output of the following code snippet if the button connected to pin 7 is pressed (assuming pressed means HIGH)?

pinMode(7, INPUT);
int buttonState = digitalRead(7);
if (buttonState == HIGH) {
    printf("Button is pressed\n");
} else {
    printf("Button is not pressed\n");
}

medium

A. Button is pressed

B. Button is not pressed

C. Compilation error

D. No output

Solution

1. Step 1: Analyze pin mode and reading

   The pin 7 is set as INPUT, so digitalRead(7) correctly reads the pin state.

2. Step 2: Check condition for pressed button

   If the button is pressed, the pin reads HIGH, so the if condition is true and prints "Button is pressed".

3. Final Answer:

   Button is pressed -> Option A

4. Quick Check:

   Pressed button = HIGH = prints pressed [OK]

Hint: Pressed button means digitalRead returns HIGH [OK]

Common Mistakes:

• Forgetting to set pinMode before reading
• Confusing HIGH and LOW states
• Assuming digitalRead returns boolean true/false

4. Identify the error in the following code that reads a digital input pin state:

int pin = 5;
int state;
state = digitalRead();
if(state == HIGH) {
    // do something
}

medium

A. Pin should be set as OUTPUT before reading.

B. The if condition syntax is incorrect.

C. digitalRead returns a float, not int.

D. Missing pin number argument in digitalRead function.

Solution

1. Step 1: Check digitalRead usage

   digitalRead requires the pin number as an argument, but here it is called without any argument.

2. Step 2: Verify other parts of code

   Pin mode setting is missing but not the main error asked; the if condition syntax is correct.

3. Final Answer:

   Missing pin number argument in digitalRead function. -> Option D

4. Quick Check:

   digitalRead needs pin argument = B [OK]

Hint: digitalRead always needs pin number inside parentheses [OK]

Common Mistakes:

• Calling digitalRead without pin argument
• Setting pin as OUTPUT before reading input
• Misunderstanding return type of digitalRead

5. You want to detect if a switch connected to pin 3 is ON and turn on an LED connected to pin 13 accordingly. Which code snippet correctly reads the switch state and controls the LED?

hard

A. pinMode(3, INPUT);
pinMode(13, OUTPUT);
if (digitalRead(3) == HIGH) {
digitalWrite(13, HIGH);
} else {
digitalWrite(13, LOW);
}

B. pinMode(3, OUTPUT);
pinMode(13, INPUT);
if (digitalRead(13) == HIGH) {
digitalWrite(3, HIGH);
}

C. pinMode(3, INPUT);
if (digitalRead(13) == HIGH) {
digitalWrite(3, HIGH);
}

D. pinMode(13, OUTPUT);
digitalWrite(3, HIGH);
if (digitalRead(3) == HIGH) {
digitalWrite(13, HIGH);
}

Solution

1. Step 1: Set correct pin modes

   Pin 3 is input for the switch, so pinMode(3, INPUT). Pin 13 is output for the LED, so pinMode(13, OUTPUT).

2. Step 2: Read switch and control LED

   If digitalRead(3) is HIGH (switch ON), turn LED on with digitalWrite(13, HIGH), else turn it off with digitalWrite(13, LOW).

3. Final Answer:

   pinMode(3, INPUT); pinMode(13, OUTPUT); if (digitalRead(3) == HIGH) { digitalWrite(13, HIGH); } else { digitalWrite(13, LOW); } -> Option A

4. Quick Check:

   Input pin read controls output pin write = A [OK]

Hint: Input pin set INPUT, output pin set OUTPUT, read then write [OK]

Common Mistakes:

• Setting input pin as OUTPUT or vice versa
• Reading wrong pin for switch state
• Not controlling LED pin properly