Open Collector
How to wire a sensor with an open collector output?
Open collector means the component you are using has not a "high" or "low" voltage on its output, but instead there's the emitter and collector of a transistor. The output is acting very similar to a switch - but since a transistor is only conducting in one direction (from collector to emitter) the polarity matters. The emitter might also be just labeled as ground - so the "output" is the collector.
