I wanted to get a handle on my Digikey SMT part cruft, but didn't want to count the parts by eye. Built a simple 3D-printed sensor block with a break-beam sensor that I can easily slide the SMT part tape through and hooked it up to a simple Arduino shield with two buttons and a 3 digit 7-seg display. The right button resets the count and the left button sets the number of parts/hole on the tape. I was lazy hooking up the 7-segs and put a current-limiting resistor per digit on the low-side, so the brightness changes depending on how many segments are lit up. Still legible and saved me having to add MOSFETs or something to sink the current. Made quick work of my SMT part collection.