To overcome the challenge of upcycling plastic waste into three-dimensional (3D) printing filament in the distributed recycling and additive manufacturing systems, this study designs, builds, tests, and validates an open-source filament diameter sensor for recycling and winding machines. The modular system for multi-axis optical control of the diameter of the recycled 3D-printer filament makes it possible to scan part of the surface of the processed filament, save the history of measurements along the entire length of the spool, as well as mark defective areas. The sensor is developed as an independent module and integrated into a recyclebot. It was tested on different kinds of polymers (acrylonitrile butadiene styrene (ABS), polylactide (PLA)), different sources of plastic, and different colors including clear plastic. The results were compared with the manual measurements, and the measurements obtained with a one-dimensional digital light caliper. The results found that the developed open-source filament sensing method allows users to obtain significantly more information in comparison with basic one-dimensional light sensors and using the received data not only for more accurate diameter measurements but also for a detailed analysis of the recycled filament surface. This could help to expand the use of plastic recycling technologies in the manufacturing community. The availability of tools for possible texture analysis could also stimulate the growth of composite materials creation. The presented system can greatly enhance the user possibilities and serve as a starting point for a complete recycling control system that will regulate motor parameters to achieve the desired filament diameter with acceptable deviations and even control the extrusion rate on a printer to recover from filament irregularities.