ADC conversion process (sample and hold) in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this ADC sample and hold simulation code?

Consider this embedded C code simulating an ADC sample and hold process. What will be printed?

Embedded C

#include <stdio.h>

int main() {
    int analog_signal = 512; // Simulated analog input (10-bit ADC max 1023)
    int sample_and_hold = 0;
    int digital_value = 0;

    // Sample phase
    sample_and_hold = analog_signal;

    // Hold phase (conversion simulated)
    digital_value = sample_and_hold;

    printf("Digital value: %d\n", digital_value);
    return 0;
}

A Digital value: 512

B Compilation error

C Digital value: 1023

D Digital value: 0

💡 Hint

Think about what the sample and hold phase does to the analog signal before conversion.

The sample and hold phase captures the analog input value (512) and holds it steady for conversion. The digital value printed is the held sample, which is 512.

❓ Predict Output

intermediate

What error occurs in this ADC sample and hold code?

Analyze this code snippet simulating ADC sample and hold. What error will it produce?

Embedded C

#include <stdio.h>

int main() {
    int *sample_and_hold = NULL;
    int analog_signal = 256;

    // Sample phase
    *sample_and_hold = analog_signal; // Attempt to store value

    printf("Value: %d\n", *sample_and_hold);
    return 0;
}

A Undefined behavior but prints 0

B Compilation error: dereferencing NULL pointer not allowed

C Prints: Value: 256

D Segmentation fault (runtime error)

💡 Hint

What happens if you try to write to a NULL pointer?

The pointer sample_and_hold is NULL and dereferencing it causes a segmentation fault at runtime.

🧠 Conceptual

advanced

Which statement correctly describes the sample and hold phase in ADC?

Choose the correct description of the sample and hold phase in an ADC conversion process.

A It captures the analog input voltage and holds it steady during conversion.

B It converts the analog signal directly into a digital value instantly.

C It amplifies the analog signal before conversion.

D It filters out noise from the digital output after conversion.

💡 Hint

Think about why the ADC needs a stable input during conversion.

The sample and hold circuit captures the analog voltage and holds it constant so the ADC can convert it accurately without changes during conversion.

❓ Predict Output

advanced

What is the output of this ADC sample and hold timing simulation?

Given this code simulating ADC sample and hold timing, what will be the output?

Embedded C

#include <stdio.h>
#include <stdbool.h>

int main() {
    int analog_signal = 700;
    int sample_and_hold = 0;
    bool sample_phase = true;

    if (sample_phase) {
        sample_and_hold = analog_signal;
        sample_phase = false;
    }

    // Hold phase
    int digital_value = sample_and_hold;

    printf("Digital value: %d\n", digital_value);
    return 0;
}

A Digital value: 0

B Digital value: 700

C Digital value: 1

D Compilation error

💡 Hint

Check what happens during the sample phase before hold.

The sample phase stores the analog signal (700) into sample_and_hold. The hold phase outputs this value, so the printed digital value is 700.

❓ Predict Output

expert

What is the value of 'digital_value' after this ADC sample and hold code runs?

Analyze this embedded C code simulating an ADC sample and hold with noise. What is the final value of digital_value?

Embedded C

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main() {
    srand(0);
    int analog_signal = 400;
    int sample_and_hold = 0;
    int noise = 0;

    // Sample phase with noise
    noise = rand() % 5 - 2; // Noise between -2 and +2
    sample_and_hold = analog_signal + noise;

    // Hold phase
    int digital_value = sample_and_hold;

    printf("Digital value: %d\n", digital_value);
    return 0;
}

A Digital value: 402

B Digital value: 400

C Digital value: 399

D Digital value: 403

💡 Hint

Check the random noise generated with srand(0) and rand() % 5 - 2.

With srand(0), the first rand() % 5 is 1, so noise = 1 - 2 = -1. The sample_and_hold = 400 + (-1) = 399.