This ultrasonic radar project is from [mircemk] who uses a small ultrasonic distance sensor attached to a rotating platform. A motor rotates it around a 180-degree field-of-view and an Arduino ...

One way to accomplish this involves four HC-SR04 ultrasonic sensor units that transmit data through an Arduino into a Linux computer. The end result is a virtual touchscreen that can be made at home.

Tesla's Autopilot system currently uses eight cameras, 12 ultrasonic sensors, and forward radar to read lane lines and detect nearby cars.