MorganS:
Then just use pulseIn() or the NewPing library
Does NewPing support Due? In the bitbucket notes for V1.7 it says:
"Removed support for the Arduino Due and Zero because they're both 3.3 volt boards and are not 5 volt tolerant while the HC-SR04 is a 5 volt sensor. Also, the Due and Zero don't support pin manipulation compatibility via port registers which can be done (see the Teensy 3.2)."