For about 4 years I have been developing a robot for mapping environment, it could be a labyrinth, finding a predetermined exit or point.
One of the modules is the obstacle sensor. Ultrasonic Ultrasonic Sensor Sensor HC-SR04 moved by a Micro Servo Motor SG90.
To communicate the robot with my cell phone, I used the RS232 Bluetooth Module - HC-06.
I developed an Arduino Sketch to move the radar and read the sensor. This Outline communicates with an App, developed in App Inventor 2.