Contingency Plans
Contingency plans are good to have
I've ordered and just got 11 spare photo reflective sensors, as they seem to be prone to breaking out of everything. This at least provides me the option to rebuild a new card reader if the worst should happen. I'll sell them again on ebay if I don't end up using them...
It also lets me set up a little demo on the bench for visitors, to show how it works using a multimeter and a bit of white or black card.