Unreliable HC-SR04 with Explorer HAT Pro

Note that if you need 3.3V you can use a 'stackable' header on the pHAT, exposing the GPIO for additional purposes as well.

Incidentally, here's the pinout so you can easily see what you've got to play with without risk to overlap the pExplorer's claimed pins:

http://pinout.xyz/pinout/explorer_phat