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2. The ultrasonic
An ultrasonic sensor is a device that transforms other forms of energies into ultrasonic energy with
desired frequency or transforms the ultrasonic energy into other forms of energy with the same frequency.
The ultrasonic sensors are commonly classified into two categories, the acoustic type and the hydrodynamic
type. Acoustic type mainly has: 1, piezoelectric sensor; 2, magneto strictive sensor sensor; 3, electrostatic
sensor. The hydrodynamic type includes the gas whistle and the liquid whistle. At present most of the
ultrasonic sensors are working using piezoelectric sensors. Distance measurement with the ultrasonic is also
a hot spot.
In the "Hummer-Bot" car, we use HC-SR04 ultrasonic module which has the 2cm-400cm non-contact
distance sensing function, the measurement accuracy can achieve to 3mm; the temperature sensor can
correct the measured results using the GPIO communication mode, the module has a stable and reliable
watchdog. The module includes an ultrasonic transmitter, receiver and control circuit, which can measure
distance and steer like in some projects. The smart car can detect obstacles in front of itself, so that the smart
car can change direction in time, avoid obstacles. A common ultrasonic sensor is shown in Fig.3.2.26.
Figure .3.2.25 Physical Map of Steering Gear
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