In order to get a handle on my DigiKey SMT part cruft without counting parts one by one I built this simple tool to count parts in SMT reels. It's a simple 3D-printed sensor block with a break-beam sensor that I can easily slide the SMT part tape through which is hooked up to a simple Arduino shield with two buttons and a 3 digit 7-seg display for displaying the parts count. The right button resets the count and the left button sets the number of parts per 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.