Why ADC is needed in Embedded C - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an ADC input pin.

Embedded C

int adc_pin = [1];

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

A13

BLED_BUILTIN

CD13

DA0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a digital pin number instead of an analog pin label.

The ADC input pin is usually labeled as A0, A1, etc. Here, A0 is the correct analog input pin.

2fill in blank

medium

Complete the code to read the analog value from the ADC pin.

Embedded C

int sensor_value = [1](adc_pin);

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

AdigitalRead

BanalogRead

CreadADC

DgetAnalog

Attempts:

3 left

💡 Hint

Common Mistakes

Using digitalRead() instead of analogRead().

analogRead() is the function used to read the analog value from an ADC pin.

3fill in blank

hard

Fix the error in the code to convert the ADC value to voltage.

Embedded C

float voltage = sensor_value [1] 1023.0 * 5.0;

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

A/

B*

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using multiplication instead of division for scaling.

To convert ADC value to voltage, divide by 1023.0 then multiply by reference voltage 5.0.

4fill in blank

hard

Fill both blanks to create a dictionary of ADC values above threshold.

Embedded C

adc_values = {pin: value [1] value for pin, value in readings.items() if value [2] 500}

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

A*

B>

C<

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '*' instead of '+' for addition.

Using '<' instead of '>' for filtering.

The dictionary comprehension adds value to itself and filters values greater than 500.

5fill in blank

hard

Fill all three blanks to calculate average voltage from ADC readings.

Embedded C

average_voltage = sum([1]) [2] len(adc_readings) [3] 5.0 / 1023.0

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

Aadc_readings

B/

C*

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '*' for voltage scaling.

Dividing by voltage instead of multiplying.

Sum the ADC readings, divide by count to get average ADC value, then multiply by 5.0/1023.0 to get voltage.

Practice

1. Why do microcontrollers need an ADC (Analog to Digital Converter)?

easy

A. To increase the speed of the microcontroller

B. To convert analog signals from sensors into digital values they can process

C. To store data in memory

D. To power the microcontroller

Solution

1. Step 1: Understand what analog signals are

   Analog signals are continuous signals from the real world, like temperature or light intensity.

2. Step 2: Understand microcontroller input requirements

   Microcontrollers work with digital numbers, so they need to convert analog signals into digital form.

3. Final Answer:

   To convert analog signals from sensors into digital values they can process -> Option B

4. Quick Check:

   ADC converts analog to digital [OK]

Hint: ADC changes real signals to digital numbers [OK]

Common Mistakes:

• Thinking ADC increases speed
• Confusing ADC with memory storage
• Believing ADC powers the microcontroller

2. Which of the following is the correct way to declare an ADC input pin in embedded C?

easy

A. char adc_pin = 'A';

B. float adc_pin = 5.0;

C. int adc_pin = 5;

D. void adc_pin = 5;

Solution

1. Step 1: Identify the correct data type for pin numbers

   Pin numbers are integers, so int is appropriate.

2. Step 2: Check each option's syntax

   int adc_pin = 5; uses int with a valid integer value. Others use wrong types or invalid syntax.

3. Final Answer:

   int adc_pin = 5; -> Option C

4. Quick Check:

   Pin numbers use int type [OK]

Hint: Pin numbers are integers, use int type [OK]

Common Mistakes:

• Using float for pin numbers
• Using void as a variable type
• Assigning characters to pin numbers

3. Given this code snippet reading an ADC value:

int adc_value = read_adc(3);
printf("ADC Value: %d\n", adc_value);

What will be the output if the analog input at pin 3 is 2.5V and the ADC reference voltage is 5V with 10-bit resolution?

medium

A. ADC Value: 1023

B. ADC Value: 0

C. ADC Value: 256

D. ADC Value: 512

Solution

1. Step 1: Understand ADC resolution and voltage mapping

   10-bit ADC means values from 0 to 1023 represent 0V to 5V.

2. Step 2: Calculate digital value for 2.5V input

   Value = (2.5 / 5.0) * 1023 = 511.5, rounded to 512.

3. Final Answer:

   ADC Value: 512 -> Option D

4. Quick Check:

   Half voltage gives half max ADC value [OK]

Hint: Half voltage equals half max ADC count [OK]

Common Mistakes:

• Using max ADC value for half voltage
• Confusing resolution bits with max value
• Ignoring voltage reference

4. This code tries to read an ADC value but always prints zero:

int adc_value;
adc_value = read_adc();
printf("Value: %d\n", adc_value);

What is the likely error?

medium

A. read_adc() needs a pin number argument

B. printf format specifier is wrong

C. adc_value should be float

D. Missing semicolon after read_adc()

Solution

1. Step 1: Check function usage

   read_adc() usually requires the ADC channel or pin number as argument.

2. Step 2: Identify missing argument

   Code calls read_adc() without pin, so it cannot read correct value, returns zero.

3. Final Answer:

   read_adc() needs a pin number argument -> Option A

4. Quick Check:

   Missing pin argument causes zero reading [OK]

Hint: Always pass pin/channel to ADC read function [OK]

Common Mistakes:

• Assuming default pin if none given
• Thinking printf format causes zero
• Using float instead of int for adc_value

5. You want to measure temperature using an analog sensor connected to ADC channel 1. The sensor outputs 0V at 0°C and 3.3V at 100°C. The ADC reference voltage is 3.3V with 12-bit resolution. How do you calculate the temperature from the ADC reading in embedded C?

hard

A. temperature = (adc_value * 100.0) / 4095.0;

B. temperature = (adc_value * 3.3) / 100.0;

C. temperature = (adc_value * 4095.0) / 100.0;

D. temperature = (adc_value * 100.0) / 3.3;

Solution

1. Step 1: Understand ADC resolution and voltage range

   12-bit ADC max value is 4095, voltage range is 0 to 3.3V.

2. Step 2: Map ADC value to voltage then to temperature

   Voltage = (adc_value / 4095) * 3.3V; Temperature = (Voltage / 3.3V) * 100°C.

3. Step 3: Simplify formula combining steps

   Temperature = (adc_value / 4095) * 100 = (adc_value * 100.0) / 4095.0;

4. Final Answer:

   temperature = (adc_value * 100.0) / 4095.0; -> Option A

5. Quick Check:

   Scale ADC value to 0-100°C range [OK]

Hint: Scale ADC reading by max count to get temperature [OK]

Common Mistakes:

• Dividing by voltage instead of max ADC value
• Multiplying by max ADC value incorrectly
• Ignoring sensor voltage range