Compute ADC Voltage Scale

Question

Problem: Compute ADC Voltage Scale. Solve this hands-on electronics task on EWskills.

Accepted Answer

#include 
#include 

using namespace std;

// Compile-time ADC scale computation using integer truncation
constexpr int32_t computeScale(int32_t maxAdc, int32_t maxVoltage_mV) {
    // Convert millivolts to microvolts, then divide by ADC resolution
    // (3300 * 1000) / 4095 = 805.86... -> truncated to 805
    return (maxVoltage_mV * 1000) / maxAdc;
}

// Compile-time microvolts-per-count scale factor
constexpr int32_t SCALE_UV = computeScale(4095, 3300);

int main() {
    int32_t x;
    if (!(cin >> x)) return 0;

    // Runtime ADC-to-voltage conversion
    // Max result: 4095 * 805 = 3,296,475 (fits in int32_t)
    int32_t voltage_uv = x * SCALE_UV;

    cout << voltage_uv;
    return 0;
}

Explanation & Logic Summary

Compile-time optimization:
The constexpr function ensures the scale factor is computed at compile time, eliminating division at runtime.
Fixed-point scaling:
Microvolts are used instead of volts to preserve precision while using integer arithmetic, which is preferred on MCUs without FPUs.
Deterministic truncation:
Integer division truncates toward zero, matching the behavior expected in embedded fixed-point math.
Portability:
Using int32_t guarantees consistent behavior across 8-bit, 16-bit, and 32-bit embedded targets.

Firmware Relevance & Real Embedded Meaning

In real embedded systems (e.g., STM32, AVR, MSP430), ADC peripherals produce raw digital counts. Converting these counts into meaningful physical units is a fundamental firmware task.

Using constexpr for scale factors is a best practice in modern Embedded C++:

Eliminates runtime overhead
Improves determinism
Enables zero-cost abstractions
Keeps code readable and maintainable without sacrificing performance

This pattern is commonly used in HAL drivers, sensor pipelines, battery monitors, and analog measurement subsystems.

63. Compute ADC Voltage Scale