| Care and assistant for the blind is a symbol of social civilization. A practical, low-cost, portable mobile aid based on Biosonar is a new way to help blind people. After analyzing the disadvantages of the current aid for the blind, a new model of mobile aid based on echolocation of bats is proposed by this thesis. The Biosonar aid can provide the distance, orientation, size, shape, and etc. information about the targets, making the dream of "to see with sound" like bats possible for human beings.The thesis analyzes some basic features of bat sonar, demonstrating and designing the program of the DSP core, dual-channel acquisition, stereo output, producing a prototype of the Biosonar aid, and carrying out some experiments. Firstly, two kinds of chirps, constant frequency (CF) and frequency modulation (FM), were designed to be used in the Biosonar aid through simulating the basic form of bat chirps. Secondly, a new method was proposed by this thesis to convert echo frequency down portationally for hearing, and then, a method of signal reconstruction was developed to solve the problems of frequency concentration and too short audible time, remain the amplitude profile of original echo, and improve the discrimination ability for different targets. Thirdly, the hardware of the Biosonar aid was designed and produced, including chirp transmission and echo receiving module, DSP core control module, audio DAC output module, power module, etc. The software of the Biosonar aid was also developed here, including chirp generation and output, dual-channel acquisition, signal reconstruction, audible signal output, keyboard module, and etc.Tests with this Biosonar aid indicate:the SNR is high, the detection range of the aid is up to 8m, the detection angle is about 34°, the detection size is about 1.5m, and the distant, orientation, shape information about targets can be converted well. The work of this Biosonar aid for the blind may provide the reference for similar devices and biosoanr research. |
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