This thesis describes the design and implementation of a LED Driving and Sensing Unit, one of the parts of a UV-C LED sterilization machine for the disinfection of plant seeds. The purpose of this part is to drive LEDs which can destroy different structures of pathogens. While doing this, certain parameters like temperature and ozone generation are being measured.
The report covers many design choices such as the choice to put the LEDs in arrays that are a combination of series and parallel circuits, or how SPI addressable variable resistors were used, in order to have full control over the LEDs and the sensing part. Furthermore, through a MATLAB script, it was discovered how the arrays of LEDs must be placed in specific manner to obtain a uniform radiation pattern. From this, it follows that using two arrays with radii of respectively 17 and 41 mm would work best. Furthermore, a literature research was done on UV-C and on what wavelength is theoretically the best for destroying pathogens on seeds. The focus was set on wavelengths of 255 nm and a combination of 275 nm and 285 nm. Also a 395 nm (UV-A) LED was used to investigate whether pathogens can be awakened from a hibernation state with the help of this type of light.
A boost converter capable of controlling the intensity of the LEDs by changing its gain with the aforementioned variable resistors was designed. Finally, the entire unit was tested successfully. The result of the research is a fully working LED driver module that can sense all parameters that need to be measured, completed with the design of a 3D CAD casing, which has all been manufactured and fabricated. This thesis does not include test results of the disinfection of plant seeds. This information will be included in the supplementary seed testing results report.

In this thesis for the Bachelor’s Degree in Electrical Engineering, a Control Unit (PCB and software) is designed for inside the UVC Seed Disinfection Machine of Team UVO. The machine consists of four modules: the Control Unit, the LED Driver, the motor controller and the power supply. The Control Unit allows a user to input the intensity per wavelength (for possible wavelengths: 255 nm, 275 nm, 285 nm and 395 nm), the exposure time and the motor speed.

The design of the machine, including all the modules, is aimed at achieving the optimal wavelength for inactivation and maximum and uniform irradiance, with the ability of changing radiation settings according to the desire of the user.

The Control Unit manages communication with the other modules, data storage, the User Interface, safety checks and system enabling. The thesis covers the design choices regarding the entire design, with an in-depth analysis of the hardware implemented safety checks, the graphical user interface and the design of the communication protocol.

Due to difficulties regarding uploading the code onto the PCB, not every developed functionality could be tested or implemented. However, the functionalities that were tested, did perform as expected. In addition to this, after the thesis has been submitted, more time will be spent on debugging the PCB, implementing and testing its features.

The objective for the graduation project of Team UVO is to provide a proof-of-concept of disinfecting cabbage seeds (Brassica oleracea capitata) from Alternaria using UVC LEDs. This thesis describes design process of the Control Unit module. The results of the decontamination process are provided in
Appendix F.

This thesis presents the design and development of a UV-C LED-based seed treatment machine aimed at enhancing seed quality by the extermination of pathogens. The research covers design choices, including a round irradiation pattern, consisting of two rings with three and nine LEDs for the inner and outer ring respectively, the use of a quartz plate as a holding plate for seeds for its high UV-C light permeability capabilities, the use of a vibration motor underneath the main operational stack for seed movement, and the use of Ethernet ports for power distribution and communication. The thesis discusses a comparative study between square and circular plate configurations, evaluating their performance using simulation results. Safety considerations were prioritized in the design, and appropriate precautions were implemented throughout the design process. The thesis also highlights the iterative design process for the mechanical system, discussing challenges encountered and improvements made to achieve a functional and robust prototype. Results demonstrate successful integration of components and achievement of objectives. The thesis concludes with discussions on the strengths, limitations, and future enhancements of the UV-C LED-based seed treatment machine. The research presented in this thesis provides valuable insights for further advancements in seed treatment technology, contributing to sustainable agricultural practices. Due to time constraints, conclusive results of testing on seed with this machine could not be obtained yet.

For people with hearing impairment, it is important to have good speech intelligibility, while also being able to localise the sound sources. Many beam-forming algorithms for hearing aids have been proposed, that minimise the noise, in combination with spatial scene preservation of the target and the interferers. By constraining the spatial cues, the limited degrees of freedom available for the design of the filter are expended, and this, to some extent degrades the noise reduction performance. Most of these methods try to preserve both the interaural time difference (ITD) and the interaural level difference (ILD) cues of the noise components over the entire frequency spectrum. However not all frequencies rely on both the ITDs and the ILDs for the localisation of sound. More specifically, the ITDs are dominant cues in the frequencies below 1.5 kHz and the ILDs are dominant cues in the frequencies above 1.5 kHz. Based on these facts, in this thesis we try to preserve only the ILD cues of the noise components at frequencies above 1.5 kHz, while keeping the target signal undistorted. We investigate whether doing so saves the degrees of freedom that can be used to improve the noise reduction performance, in contrast to preserving both the cues. The thesis proposes two methods to preserve only the ILD cues of the interferers. The first method preserves the ILD cues perfectly, while the second method achieves a relaxed preservation of the ILD cues. Both methods show similar performance in anechoic and reverberant environments, and show that the noise reduction performance improves only mildly, when only the ILD cues of the noise components in the higher frequencies are preserved.

Public Address systems that include a setup with at least one microphone and speaker can suffer from acoustic feedback. This results in an annoying howling effect which can damage hardware and human hearing. To solve this issue, an adaptive filter that estimates the feedback path and uses this estimate to cancel the feedback can be designed. However, because the adaptive filter receives signals from both the microphone and the feedback, and because sound signals are generally correlated over time, the estimate becomes biased. To reduce this bias, the speaker signal can be decorrelated from the input. In this thesis several options to decorrelate these signals are explored, and they are evaluated based on decorrelation performance and effect on audio quality. Frequency shifting is selected as the best decorrelation method as it provides the most decorrelation while retaining audio quality. Finally it is shown that using Frequency Shifting to decorrelate the microphone and speaker signal indeed improves the estimation of the feedback path.

The most promising method for acoustic feedback control in public address systems is adaptive feedback cancellation (AFC). This approach is based on making an estimation of the room impulse response, which is used to subtract an estimate of the feedback from the microphone signal. A postfilter is often used to improve the performance of such an AFC system by reducing residual feedback or increasing stability. The postfilter implemented in this thesis focuses on the latter. It consists of two modules: howling detection and howling suppression. The final design makes use of the peak to harmonic power ratio criterion (PHPR) and second order digital Butterworth notch filter respectively. Simulation measurements show a successful suppression of howling as long as the loudspeaker signal does not
get saturated.