The concept is simple. A scanning HC-SR04 Ultrasonic Sensor does only two things:
If no object is seen, the scanner turns right.
If an object is seen, the scanner turns left.
As shown, the scanner goes left if it sees an object. If it doesn't detect it, the scanner turns right until it does. As a result, the scanner converges on the left edge of the object.
Now the robot always keeps track of the angle of the scanner. So if the scanner is pointing left, the robot turns left. If the scanner is point
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