This PhD project introduces a mixed reality passive stylus system designed for smartphones enabling digital ink creation on a surface. Traditional passive stylus systems face challenges in usability and accessibility. This research aims to overcome these limitations through a dual approach that integrates interactive design and robust machine learning, trained on extensive datasets. The research methodology is divided into phases of data collection, design, implementation and evaluation. The project develops an application to deliver an accessible digital tool viable for widespread use, particularly in developing regions.