light switches

From:         kinsler@bobcat.ent.ohiou.edu (Mark Kinsler )
Organization: Ohio University, College of Engineerng & Technology
Date:         04 Oct 95 22:52:26 
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A quick question about the reading light switches over the passenger
seats in the Boeing 737.  These switches feel like momentary-contact
pushbutton switches, which would normally not toggle a lamp on and off
like they do.  If these lights use the "intelligent power" chips used in
the rest of the aircraft, they would work as follows:
  When the button is pushed, the "intelligent power" chip on the lamp sends
a request code down the 28 volt power bus to a power processor, which then
sends a turn-on or turn-off code back down to the power chip, which turns
on the light.
  This rather convoluted scheme is used on the zillions of indicator
lights and associated switches in the aircraft to avoid the use of extra
wiring for switching purposes: every device is connected only to the
power bus through a power chip and is controlled by digital signals sent
through the power bus from a central processor.  These signals originate
in chips that connect switches and sensors to this same power bus.
  Are the passenger reading lights controlled in this way?  If so, they'd
be one of the few opportunities that a citizen would have to see an
intelligent power distribution system.

                                           Mark Kinsler