When the Prusa i3 MK3 was released in 2017, it was marketed as being “bloody smart” thanks to the impressive number of sensors that had been packed into the printer. The update wasn’t really about ...

Figure 1a shows a slotted optical switch. An LED is mounted in a plastic housing, facing a phototransistor, but separated by a gap. If something moves into the gap, it blocks the light path between ...