ADC conversion process (sample and hold) in Embedded C - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to start the ADC conversion.

Embedded C

ADC_StartConversion([1]);

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AADC_CHANNEL_0

BADC_CHANNEL_3

CADC_CHANNEL_2

DADC_CHANNEL_1

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong channel number

Forgetting to specify channel

The function ADC_StartConversion requires the channel number to start conversion. Here, channel 1 is used.

2fill in blank

medium

Complete the code to enable the ADC sample and hold feature.

Embedded C

ADC_ControlRegister |= [1];

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AADC_CONVERSION_START

BADC_SAMPLE_ENABLE

CADC_SAMPLE_HOLD_ENABLE

DADC_INTERRUPT_ENABLE

Attempts:

3 left

💡 Hint

Common Mistakes

Enabling wrong bits

Confusing sample enable with sample and hold

To enable sample and hold, the ADC_SAMPLE_HOLD_ENABLE bit must be set in the control register.

3fill in blank

hard

Fix the error in the code to wait until ADC conversion is complete.

Embedded C

while (!(ADC_StatusRegister & [1])) {}

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AADC_CONVERSION_COMPLETE_FLAG

BADC_SAMPLE_HOLD_FLAG

CADC_START_CONVERSION_FLAG

DADC_INTERRUPT_FLAG

Attempts:

3 left

💡 Hint

Common Mistakes

Waiting on wrong flag

Using sample hold flag instead of conversion complete

The loop waits until the conversion complete flag is set in the status register.

4fill in blank

hard

Complete the code to correctly read the ADC result and clear the conversion flag.

Embedded C

uint16_t result = ADC_ResultRegister;
ADC_StatusRegister &= ~[1];

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BADC_CONVERSION_COMPLETE_FLAG

D0xFFFF

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to modify the result value

Not clearing the flag properly

The ADC result is read directly from the result register without modification. The conversion complete flag is cleared by ANDing with its complement.

5fill in blank

hard

Fill all three blanks to configure ADC for sample and hold with 10-bit resolution and start conversion.

Embedded C

ADC_ControlRegister = [1] | [2];
ADC_StartConversion([3]);

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AADC_SAMPLE_HOLD_ENABLE

BADC_RESOLUTION_10BIT

CADC_CHANNEL_2

DADC_CHANNEL_0

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong resolution bits

Starting conversion on wrong channel

The control register is set to enable sample and hold and 10-bit resolution. Then conversion starts on channel 2.

Practice

1.

What is the main purpose of the sample and hold stage in an ADC conversion process?

easy

A. To amplify the analog signal before conversion

B. To convert the analog signal directly to digital bits

C. To capture and hold the analog voltage steady during conversion

D. To reset the ADC hardware before starting conversion

Solution

1. Step 1: Understand the role of sample and hold

   The sample and hold stage captures the analog voltage at a specific moment and holds it steady.

2. Step 2: Differentiate from other ADC stages

   Conversion to digital bits happens after holding; amplification or reset are separate steps.

3. Final Answer:

   To capture and hold the analog voltage steady during conversion -> Option C

4. Quick Check:

   Sample and hold = capture and hold voltage [OK]

Hint: Sample and hold freezes input voltage for accurate conversion [OK]

Common Mistakes:

• Confusing sample and hold with conversion step
• Thinking sample and hold amplifies signal
• Assuming sample and hold resets ADC

2.

Which of the following is the correct way to start ADC sampling in embedded C?

ADC_Start();

easy

A. ADC_Start(); // Starts sampling and conversion immediately

B. ADC_Start; // Missing parentheses causes error

C. ADC_Start[]; // Incorrect syntax for function call

D. Start_ADC(); // Wrong function name

Solution

1. Step 1: Identify correct function call syntax

   Functions in C require parentheses even if no arguments are passed.

2. Step 2: Check each option's syntax

   ADC_Start(); // Starts sampling and conversion immediately uses correct syntax with parentheses; others have syntax errors or wrong names.

3. Final Answer:

   ADC_Start(); // Starts sampling and conversion immediately -> Option A

4. Quick Check:

   Function call needs parentheses () [OK]

Hint: Function calls always need parentheses () in C [OK]

Common Mistakes:

• Omitting parentheses when calling functions
• Using brackets [] instead of parentheses
• Using incorrect function names

3.

Consider the following embedded C code snippet for ADC conversion:

int adc_value = 0;
ADC_Start();
while(!ADC_ConversionComplete()) {}
adc_value = ADC_Read();
printf("%d", adc_value);

What will be the output if the analog input voltage corresponds to digital value 512?

medium

A. 0

B. 512

C. 1023

D. Conversion error

Solution

1. Step 1: Analyze the ADC process in code

   ADC_Start() begins sampling; the while loop waits until conversion is done; ADC_Read() reads the digital value.

2. Step 2: Understand the analog input mapping

   If analog input corresponds to digital 512, ADC_Read() returns 512, which is printed.

3. Final Answer:

   512 -> Option B

4. Quick Check:

   ADC_Read() returns converted digital value [OK]

Hint: Wait for conversion complete before reading ADC value [OK]

Common Mistakes:

• Reading ADC value before conversion completes
• Assuming ADC_Read() returns zero by default
• Confusing max ADC value with current reading

4.

Identify the error in this ADC conversion code snippet:

ADC_Start();
if(ADC_ConversionComplete()) {
    int value = ADC_Read();
    printf("%d", value);
}

What is the problem?

medium

A. Missing semicolon after ADC_Start()

B. No error, code is correct

C. Incorrect function name ADC_Read()

D. Using if instead of while to wait for conversion

Solution

1. Step 1: Check how conversion completion is handled

   The code uses if to check conversion complete, which may be false if conversion not done yet.

2. Step 2: Explain why while loop is needed

   Using while waits until conversion finishes; if may skip reading if conversion incomplete.

3. Final Answer:

   Using if instead of while to wait for conversion -> Option D

4. Quick Check:

   Wait loop needed to ensure conversion done [OK]

Hint: Use while loop to wait for ADC conversion completion [OK]

Common Mistakes:

• Using if instead of while to wait
• Assuming conversion is instant
• Ignoring need to wait before reading

5.

You want to read an analog sensor value using ADC with sample and hold. Which sequence of steps is correct in embedded C?

1. Start sampling
2. Wait for sample and hold to stabilize
3. Start conversion
4. Wait for conversion complete
5. Read digital value

Which option correctly orders these steps?

hard

A. 1, 2, 3, 4, 5

B. 3, 1, 2, 5, 4

C. 1, 3, 2, 4, 5

D. 2, 1, 3, 5, 4

Solution

1. Step 1: Understand sample and hold timing

   First, start sampling to capture the analog signal, then wait for it to stabilize (hold).

2. Step 2: Start conversion after hold stabilizes, then wait for conversion to finish, and finally read value

   This ensures accurate digital reading of the stable analog input.

3. Final Answer:

   1, 2, 3, 4, 5 -> Option A

4. Quick Check:

   Sample, hold, convert, wait, read = 1,2,3,4,5 [OK]

Hint: Sample and hold before conversion, then wait and read [OK]

Common Mistakes:

• Starting conversion before sample stabilizes
• Reading value before conversion completes
• Mixing order of steps