Basic HTML Version
SWITCH MATRIX
RIGHT UPIDOWN J208-13
RAMP BANK UP
ENTER
LOWER RIGHT
FUPPER E.O.S.
F1
FUPPER
GROUNDED
SWITCHES
62
RIGHT
RAMP
LOCK
72
RIGHT
LOOP
LOW
SWITCH MATRIX CIRCUIT
r--------------------------------------,
: Column (example)+12V
:
~~C!l!::-I--77~"-+ -
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O~
:
J206:
ON
:
A :
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x~~--~
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:
I470Pf
:
ROW
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()
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""'S:O::W'::::IT""CH;-;--;:O""P-:=:EN,.,---1I-*--+*+---+-O-FF-
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Row
example
~
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SWITCH CLOSED
~
~
ON
The microprocessor is constantly strobing the column side of the switch. When point "A" on the column
circuit toggles low, the column side is active. When a switch closes, the row side of the circuit activates.
The "+" input to the LM339 drops below +5V, therefore, its output is low. Corresponding row and column
switches must be low at the same time for the switch to be considered closed by the microprocessor.
When the switch opens, the "+" input to the LM339 is above +5V, its output is high and the row is inactive.
3-2