@_thegeoff do you have experience or ideas on how to mask off infrared leakage from an emitter to a detector that are next to each other (the intent is to detect reflections/diffuse reflections)?

I currently have 5mm IR LEDs and a photodiode next to each other, in black heat shrink that extends down to the slight ridge in the base, but don't overlap it. I still get significant signal when there's nothing in front and adding more layers of heat shrink doesn't help. My best guess is that I am seeing emission going backwards and scattering off the pcb into the photodiode, but am somewhat unsure how to deal with that given that I need something ir-opaque, nonconductive, and able to withstand the heat of soldering.