Embedded digital filter design and implementation

Sammanfattning: Digital filters have been widely used in signal processing, to reduce or remove unwanted signals of different types, such as noise, and interference, and to enhance or keep desired signals. They are implemented as algorithms on an embedded system (a microcontroller) or a computer. Digital filters are of two different types, finite impulse response (FIR) and infinite impulse response (IIR) filters, each of which can perform different filter functions, such as low-pass (LP), high-pass (HP), band-pass (BP), and band-stop (BS) filtering.The purpose of this thesis project is to develop a filter platform based on an embedded system, which can be used to provide both FIR and IIR filters for LP, HP, BP and BS filtering according to user's needs and specifications. For this purpose, a prototype has been made. It consists of an analog circuit functioning as an anti-aliasing and reconstruction filter, a 32-bit AVR microcontroller with eight analog-to-digital conversions (ADC) channels and two digital-analog conversion (DAC) channels, and a personal computer (PC). On the microcontroller, Digital filters are implemented which can be two or more different filters connected to two inputs (ADCs) and two outputs (DACs). On the PC a user interface is implemented on which the user can specify digital filter types (FIR or IIR), filtering functions (LP, HP, BP and BS) as well as filter order, cutoff frequencies, and the connection of multiple filters in serial or parallel. The prototype has been tested and evaluated. The user interface functions well, sending the user's filter specifications to the microcontroller. The FIR filters for different filtering functions are shown to work satisfactorily. Due to the limited amount of computation, the IIR filter in this case is only of the third order, but the output can still detect the change in signal strength quite clearly. The connections of FIR or IIR filters in series or in parallel through a single channel have been implemented, and they have been shown to work correctly. The combination of FIR and IIR in dual-channel configuration is not successful due to time restriction, and further work for this is needed in the future development.