Sistema para medição de distâncias horizontais na água utilizando transdutor ultrassônico

Abstract

This work describes the development of a prototype of a sensor that can be embedded into an amphibious UAV (Unmanned Aerial Vehicle) to detect obstacles that can damage the UAV in case of collision. The system consists on an implementation of an excitation circuit, which sends 40 kHz pulses generated by the FPGA Basys 3 converted from low amplitude to high amplitude voltage, using a transformer with variable inductance for transducer coupling. For the treatment of the echo signal, an acquisition circuit was developed. This circuit is protected against high voltage by an T/R Switch which shown 0,195 dB of attenuation loss. The T/R Switch serves as a coupling between the transducer and the amplifier circuit. The amplification circuit is comprised by two amplification stages. The second stage has a variable gain controlled by the FPGA, allowing a gain range from 22 dB to 37 dB. Between the amplification stages a pass-band RLC filter was implemented with a 3 dB bandwidth of 3,33 kHz, improving the circuit selectivity. The amplified signal pass through a peak detector and then through an analogic comparator, which will indicate to the FPGA if an echo was received or not. The data was transmitted to the computes using a serial communication, and the software developed in Visual Studio calculates the distance using the received value, presenting the results graphically. In laboratory tests, the system presented measurement error of ± 3cm, which is small for a maximum distance of 15 m.