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Switch Matrix Circuit
The microprocessor con stantly strobes the colum n side of the switch circu it. When point "A" on
the column circuit toggl es low the column is act ive.
When a switch closes, point "C " on the row circu it drops low, the + input to the LM339 is below +5V so
point "D" is low and the row is active . When corresponding row and column switches are low at
the same time , the switch circu it is active and is registered as closed (made) by the microprocessor.
When the swit ch opens, point "C" on the row circuit is high, the + input to the LM339 is above +5V so
point ".0" is high and the row is inact ive .
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