HCSR04.cpp

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#include "HCSR04.hh"

bool
HCSR04::read(uint16_t& distance)
{
  distance = 0;

  // Give the device a trigger pulse
  m_trigger.pulse(10);
  uint16_t timeout = TIMEOUT;

  // Wait for the response
  while (m_echo.is_clear() && timeout--) DELAY(1);
  if (timeout == 0) return (false);

  // Measure the lenght of the return pulse
  uint16_t count = 0;
  synchronized {
    while (m_echo.is_set() && timeout--) count++;
  }
  if (timeout == 0) return (false);

  // And calculate the distance in milli-meters
  distance = (count * 100L) / COUNT_PER_DM;
  return (true);
}

void
HCSR04::on_event(uint8_t type, uint16_t value)
{
  UNUSED(type);
  UNUSED(value);
  uint16_t distance;

  // Read the distance and check if there was a change
  if (!read(distance) || (m_distance == distance)) return;

  // Save the new distance and call the change handler
  m_distance = distance;
  on_change(distance);
}