Inside an Otis elevator button (with schematic)

It's always interesting to take a look at elevator components. Especially Otis components because of their iconic history. This is a fairly standard illuminated halo button that may be used by other elevator manufacturers too.

A search on AliExpress for the keyword br27c will find similar buttons, but they may have different connections than this one. Usually 24V because that's a standard control voltage in industrial applications. I've just ordered a couple to look at.

The electrical configuration of this button is odd, because it has a four pin connector, but only three pins are used. A different style of button has the LEDs and switch on four separate connections. It does make sense to use 3 wires though, as the switch signal is also 24V in some applications.

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