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[050] Citation: Abstract
Apparatus for multiplexing switch state signals comprises a plurality of
switches and parallel weighted resistors connected in series between circuit
ground and a node at a utlitization device. The resistors are weighted as a
function of a power of the same base, such as the power of the base 2, for
coding the multiplexed switch state signals. A constant current source
connected between the node and circuit ground drives current over a single cable
conductor through the resistor. Each switch may be independently closed to
change the switch state voltage signals multiplexed to the node. An analog-to-
digital converter connected between the node and circuit ground demultiplexes
the switch state signals received as at the node and provides a switch state
signals received at the node and provides a switch state signal at each analog-
to-digital output corresponding to the state of the switches at the moment. A
potentiometer may replace a resistor and bypass switch combination in a position
where the potentionmeter has a maximum value of the lowest power of the base in
order to multiplex a true analog voltage signal while switch state signals are
unambiguously coded and multiplexed. The potentiometer in the least significant
position permits the analog value to be in the range from 0 to a maximum
corresponding to the least significant position of the switch state encoding.
The invention may be used in redundancy systems by duplicating the invention
with corresponding switches in each duplication ganged to open and close
simultaneously upon operation of a pushbutton switch.
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Updated: Tue Aug 19 09:16:07 2008
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