I created this interposer to allow mounting my indirect filament sensor mod to the stock extruder. This simple mod fixes the laser filament sensor so it will work with all filament colors, even clear. It does this by using a simple proxy (small bearing) that travels with the filament. The laser sensor is actually designed to read stainless steel using its infrared laser, so this mod works reliably. I have been using this mod for months and printing tons of clear and other filaments without issue.
You can get the parts from my Skelestruder project or reverse Bowden. Grab the I-lid (or PI-lid if using MMU2) and the spring. You will need to purchase a single 673 (aka MR63) bearing.
Picture shows it mounted to R3 extruder, but will work with R2 as well.
Why an interposer? I decided not to make a custom version for stock because it would be a maintenance nightmare to keep it in sync with any improvements I make going forward. So I made this interposer to translate the mount to mine. See instructions below.
Recommend printing I-lid with 0.15 layer, turn off thin-wall detection if you have than on. I don't think color choice matters because the bearing fills most of the FOV. But can choose a dark color to be safe if you want.
To assemble: remove filament sensor from extruder and insert into I-lid. Use same screw to hold sensor in place from underneath I-lid. Make sure you see the sensor through the window on the bottom, including dot at the top which is the laser illuminator. Replace your filament cover with the interposer using the same two M3x10mm screws. Slide the bearing onto the spring and lay in the channel of the interposer (see assembly instructions at Skelestruder for pics).
Then place the I-lid over the spring/bearing on the interposer. There is an alignment pin in the back left that fits in a hole on the lid. Then screw down the back right with an M3x10mm. Read this closely: the front screw does not go into the lid, it goes just in front in the interposer (see photo) and the screw head catches the edge. Use a M3x10mm and screw snug but do not over tighten.
Firmware: a very small simple edit is required. You need to flip a sign in the pat9125.c file and recompile firmware using the Arduino IDE. See Instructions to get started. Change the '-=' to '+=' for the Y value (see example). It is very simple after you have done it once. Re-flash the printer.
pat9125_y += iDY; //negative number, because direction switching does not work
You can test everything is working by going into the ‘Support’ menu, ‘Extruder info’. There is an X and Y listed. If you insert filament slowly, you should see the Y value increase and if you pull out the filament it will decrease. If it is opposite, your firmware edit did not take.