After a few days of trials and tribulations, the PING sensor finally works with the HC12. The missing piece? the line that clears the IOC flag in the interrupt handler, a mistake second only to the common ground in painfulness. An anti-collision system is now in code that prevents the car from moving in the direction an obstacle is in. Once the circuit for the PING sensors on the front and back of the car is completed, we can give it a spin.