The software uses this distance as a zero point and check if there are negative or positive variations from it. The height of the user is processed just one time at the start of the system, this measure able us to fix the parameter of that the system read the variations caused by the obstacles detection. Instead, in the void loop, the variations from zero are recorded continuously and, when the processor records a variation from zero, over the noise band (as explained in the following), it sends the output signals to the vibrating motors.