Star Tech Journal

CD
November 1994
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SWITCH MATRIX
STAR* TECH Journal
0PTO SWITCH
Your Source For:
OPERATION
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Wayne Glover
State Sales & Service
Baltimore, Maryland
SUBJECT
Let's examine one of the playfield switches used
in the switch matrix, the opto switch.
OPERATION
The opto switch is a two part device. One part
being the L.E.D., (emitter or opto transmitter)
and the other being the opto receiver or photo
detector (the switch).
The switch is open when light from the L.E.D.
shines on the receiver and closed when light is
blocked.
TEST
To check for proper operation of the opto switch,
the L.E.D. should always have approximately 1.4
volts across it. The receiver should have between
0.1 and 0.7 volts when the opto is blocked. Un-
blocked it should be 11 to 13 volts.
IN CIRCUIT
The output of the opto switch is wired to the in-
put of a comparator circuit which is located on an
opto PC board. The positive input of the compara-
tor has a constant voltage, in this case + 5 volts.
The negative input is from the opto switch itself.
When the negative input of the comparator has a
high signal, the output is high. When the input
signal goes low, the output goes low. This in turn,
puts a low on the return line of the switch matrix
and the C.P.U. recognizes this as a switch closure.
- ee your switch matrix schematics to follow this
description. Simple, eh?
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