* spend less time in interrupt handler.
* avoid pointer usage to prevent the inclination adjusted reading being
replaced by the interrupt handler's calculation.
* only calculate the actual distance based on the measurement when
required.
series development board.
These boards can be picked up for less than $11, coupled with a 10DOF
sensor board they make a great development platform or cheap expandable
FC.
Pretty much all pins are available to be used, unlike on the less
capable and more expensive OLIMEXINO.
This allows sonar to be used at the same time as parallel PWM for the receiver. If the RX_PARALLEL_PWM feature is enabled, then the sonar system uses motor ports 5 and 6, otherwise it uses receiver pins 7 and 8.
