SR04.cpp

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#include "SR04.hpp"
#include "../../../../utilities/Utilities.hpp"
namespace
{
const float kTimeToTravelOneCmAndBack   = 29.15F * 2.0F; // In microseconds
const unsigned long kTimeToMeasureOneCm = 120;           // Empirically determined
// We should wait long enough between two consecutive measurements
// so to avoid getting parasitic readings from old returning waves.
const unsigned long kMedianMeasurementDelay = 15; // In milliseconds
} // namespace
 
using namespace smartcarlib::constants::sr04;
using namespace smartcarlib::constants::distanceSensor;
using namespace smartcarlib::utils;
 
SR04::SR04(Runtime& runtime, uint8_t triggerPin, uint8_t echoPin, unsigned int maxDistance)
    : kTriggerPin{ triggerPin }
    , kEchoPin{ echoPin }
    , kMaxDistance{ maxDistance > 0 ? maxDistance : kDefaultMaxDistance }
    , kTimeout{ kMaxDistance * kTimeToMeasureOneCm }
    , mRuntime(runtime)
    , kOutput{ mRuntime.getOutputState() }
    , kInput{ mRuntime.getInputState() }
    , kLow{ mRuntime.getLowState() }
    , kHigh{ mRuntime.getHighState() }
 
{
}
 
void SR04::attach()
{
    if (!mAttached)
    {
        mRuntime.setPinDirection(kTriggerPin, kOutput);
        mRuntime.setPinDirection(kEchoPin, kInput);
        mAttached = true;
    }
}
 
unsigned int SR04::getDistance()
{
    attach();
 
    // Generate the pulse
    mRuntime.setPinState(kTriggerPin, kLow);
    static constexpr auto kSetPinToKnownStateDelay = 5;
    mRuntime.delayMicros(kSetPinToKnownStateDelay);
    mRuntime.setPinState(kTriggerPin, kHigh);
    static constexpr auto kTenMicrosecondPulse = 10;
    mRuntime.delayMicros(kTenMicrosecondPulse); // 10us pulse
    mRuntime.setPinState(kTriggerPin, kLow);
    // Wait for the pulse to arrive and measure its duration
    auto duration = mRuntime.getPulseDuration(kEchoPin, kHigh, kTimeout);
    // Calculate how much far out the object is
    auto calculatedDistance
        = static_cast<unsigned int>(static_cast<float>(duration) / kTimeToTravelOneCmAndBack);
 
    return calculatedDistance <= kMaxDistance ? calculatedDistance : kError;
}
 
unsigned int SR04::getMedianDistance(uint8_t iterations)
{
    if (iterations == 0 || iterations > kMaxMedianMeasurements)
    {
        return kError;
    }
 
    unsigned int measurements[kMaxMedianMeasurements];
    for (auto i = 0; i < iterations; i++)
    {
        measurements[i] = getDistance();
        mRuntime.delayMillis(kMedianMeasurementDelay);
    }
 
    return getMedian(measurements, iterations);
}