resistance_func.cpp

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/**
 * @author Matthew Kennedy, (c) 2019
 */
 
#include "resistance_func.h"
 
void ResistanceFunc::configure(float supplyVoltage, float pullupResistor, bool isPulldown) {
    m_pullupResistor = pullupResistor;
    m_supplyVoltage = supplyVoltage;
    m_isPulldown = isPulldown;
}
 
SensorResult ResistanceFunc::convert(float raw) const {
    // If the voltage is very low, the sensor is a dead short.
    if (raw < 0.05f) {
        return UnexpectedCode::Low;
    }
 
    // If the voltage is very high (98% VCC), the sensor is open circuit.
    if (raw > (m_supplyVoltage * 0.98f)) {
        return UnexpectedCode::High;
    }
 
    if (m_isPulldown) {
        // If the sensor is on the high side (fixed resistor is pulldown),
        // invert the voltage so the math comes out correctly
        raw = m_supplyVoltage - raw;
    }
 
    // Voltage is in a sensible range - convert
    float resistance = m_pullupResistor / (m_supplyVoltage / raw - 1);
 
    return resistance;
}