Analog signal generation with Raspberry Pi boards for short-range communications

The aim of this thesis is to realise a low-cost wireless application for short range underwater communications, using ultrasonic frequencies. The project can be described in four main steps. The first one is a detailed study of the serial peripheral interface. It has been carried out in order to understand how to physically and logically connect, through SPI, the hardware involved in this work: a Raspberry Pi 3 model B and the MCP4822 digital to analog converter embedded in the ADC-DAC Pi Zero module. The second phase concerns a Simulink model created in order to reduce the complexity of the problem. It has been useful as a guideline for the development of the software. Then, the implementation step includes the full execution of the code, which processes information data and digital samples of a sine wave and converts them in their respective analog signals. Configurable parameters, as the amplitude and the frequency of the sinusoidal carrier, provide more flexibility to the system. The last testing phase consists in several measurements on the hardware to assess the reliability of the system, varying some parameters and comparing these results with the simulations, run on Simulink. The overall performance respects the low-cost nature of the Raspberry Pi: the analog signals exhibit phase noise due to the not perfect periodicity of the SPI clock but they are still reliable and clear enough for project purposes.