Sensor reading through ADC (temperature, light) in Embedded C - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this ADC temperature reading code?

Consider this embedded C code snippet that reads a temperature sensor value through ADC and converts it to Celsius. What will be printed?

Embedded C

#include <stdio.h>
#define ADC_MAX 1023
#define V_REF 5.0

int read_adc() {
    return 512; // Simulated ADC value
}

int main() {
    int adc_value = read_adc();
    float voltage = (adc_value * V_REF) / ADC_MAX;
    float temperature_c = (voltage - 0.5) * 100;
    printf("Temperature: %.1f C\n", temperature_c);
    return 0;
}

A Temperature: 200.2 C

B Temperature: 50.0 C

C Temperature: 0.0 C

D Temperature: 100.0 C

💡 Hint

Calculate voltage first, then apply the formula for temperature.

The ADC value 512 corresponds to voltage = (512 * 5.0) / 1023 ≈ 2.502 V. Then temperature = (2.502 - 0.5) * 100 ≈ 200.2 C, which is printed as 'Temperature: 200.2 C'.

❓ Predict Output

intermediate

What is the light intensity output from this ADC reading?

This code reads a light sensor value from ADC and converts it to a percentage of light intensity. What will be printed?

Embedded C

#include <stdio.h>
#define ADC_MAX 1023

int read_adc() {
    return 256; // Simulated ADC value
}

int main() {
    int adc_value = read_adc();
    float light_percent = (adc_value * 100.0) / ADC_MAX;
    printf("Light Intensity: %.1f%%\n", light_percent);
    return 0;
}

A Light Intensity: 100.0%

B Light Intensity: 50.0%

C Light Intensity: 25.0%

D Light Intensity: 75.0%

💡 Hint

Calculate the percentage by dividing ADC value by max ADC value.

256 / 1023 ≈ 0.25, so light intensity is about 25%.

🔧 Debug

advanced

What error does this ADC temperature conversion code produce?

Examine this code snippet that attempts to convert ADC reading to temperature. What error will it cause?

Embedded C

#include <stdio.h>
#define ADC_MAX 1023
#define V_REF 5.0

int main() {
    int adc_value = 600;
    float voltage = adc_value / ADC_MAX * V_REF;
    float temperature_c = (voltage - 0.5) * 100;
    printf("Temperature: %.1f C\n", temperature_c);
    return 0;
}

A Temperature: 2.4 C

B Temperature: -50.0 C

C Temperature: 0.0 C

D Temperature: 294.0 C

💡 Hint

Check the order of operations and data types in the voltage calculation.

Integer division adc_value / ADC_MAX = 600 / 1023 = 0 (since both ints). Then voltage = 0 * 5.0 = 0. temperature_c = (0 - 0.5) * 100 = -50.0. Prints 'Temperature: -50.0 C'.

📝 Syntax

advanced

Which option causes a syntax error in ADC reading code?

Identify which code snippet will cause a syntax error when compiling.

A float voltage = (adc_value * 5.0) / 1023;

B float voltage = adc_value * 5.0 / 1023;

C int adc_value = read_adc(); float voltage = (adc_value * 5.0) / 1023;

D int adc_value = read_adc() float voltage = (adc_value * 5.0) / 1023;

💡 Hint

Look for missing semicolons or punctuation.

Option D misses a semicolon after read_adc() call, causing a syntax error.

🚀 Application

expert

How many distinct temperature values are possible from this 10-bit ADC?

A 10-bit ADC reads a temperature sensor. How many distinct temperature values can the system represent if the ADC output is directly converted to temperature using a linear scale?

A 1024

B 512

C 2048

D 1000

💡 Hint

Recall how many values a 10-bit number can represent.

A 10-bit ADC can represent 2^10 = 1024 distinct values, so 1024 temperature values are possible.