sensible discussion on "open collector circuit" for sensor
January 6, 2009
Just found this on hackaday:
" ... Why open collector?
An open collector output doesn’t toggle between high and ground, it toggles between ground and unconnected. The unconnected state, also called high impedance, exerts nothing on the output and allows the signal line to float.
Open collector outputs are useful when several sensors need to share the same microcontroller pin. ..." (my emphasis)
More in the article about a sharp IR proximity sensor, with video and this circuit diagram.