Summary

I wanted to have an optical filament detector. I bought an optical end stop and adapted.

This is a block that fits most optical switches of this variety. It is designed with 1.75mm filament in mind.

This is the one I bought:
https://www.ebay.com/itm/Optical-Endstop-3D-Printer-Parts-Optical-Switch-Sensor-Photoelectric-Light-Co-CA/283519930668?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I will be designing a mounting bracket that will attach to the top of the frame. I use an overhead feed for my direct drive.

Upon a clean print, any filament might have a hard time passing through. After I was able to get it all the way through, I made a few passes on a short piece of filament. I now have no issues with filament passing through. This will not let knotted or melted filament through.