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Valleylab Force FX-C - Footswitch Board; Footswitch Decode Circuit

Valleylab Force FX-C
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Footswitch
Board
Force
FXTM-C
Service
Manual
Footswitcl7
Board
•
When
COMO
is
selected,
the
power
control
switches
may
be
read.
•
When
COM1
is
selected,
the
Recall
switch
and
the
bipolar
mode
select
svvitches
may
be
read.
•
When
COM2
is
selected,
the
cut
and
coag
mode
select
switches
may
be
read.
To
read
the
switches,
the
main
microcontroller
asserts
the
desired
BANK
select
line
and
reads
the
state
of
the
keyboard
switch
return
lines
KBD
_DO
through
KED _D7.
These
lines
are
read
through
port
A
of
the
1/ 0
expansion
port
(U2)
on
the
Control
board.
Refer
to
Section 9
for
Components
and
the
Schematics
Supplement
for
Board
Dra.vings
and
Schematics.
The
Footswitch
board
is
mounted
inside
the
rear
panel.
It
contains
circuitry
accepting
and
decoding
footswitch
keying
inputs
and
an
audio
circuit for
announcing
generator
keying
and
various
alarm
tones.
The
Footsv\ritch
board
interfaces
with
the
Power
Supply
/RF
board.
Footswitch
Decode
Circuit
Two
monopolar
footswitch
connectors
and
a
bipolar
footswitch
connector
are
mOlmted
on
the
Footsvvitch
board
and
extend
through
the
rear
panel.
The
monopolar
footswitch
connectors
03
and
J2)
accept
monopolar
footsvvitches
and
provide
footswitching
capability
for
the
Monopolar
1/
CEM
and
Monopok'lr 2
Instrument
receptacles
located
on
the
front
panel.
The
bipolar
footswitch
connector
04) accepts a
bipolar
footswitch
and
provides
foots
witching
capability
for
the
Bipolar
Instrument
receptacle
on
the
front
panel.
Capacitors
C39-C46
provide
filtering
that
blocks
high
frequency
noise
from
exiting
the
generator
on
the
footswitch
cables.
As
required
by
the
lEe
the
footswitch
circuit
is
isolated
from
patient
connected
and
ground
referenced
circuits
and
is
able
to
withstand
a
potential
of
500
Vrms
(50/60
Hz).
To
obtain
this
isolation,
the
footswitch
connected
circuitry
is
pmvered
from
an
is01'lted
power
supply
(U2).
The
isolated
power
supply,
an
HPR-I07,
operates
from
the
ground
referenced
+ 12 V
power
supply
and
supplies
an
isolated
12 volts.
Resistors
R18
and
RIg
form
a
voltage
divider
that
yields
a
signal
(Vref2)
of
approximately
6 volts.
This
reference
voltage
is
applied
to
the
noninverting
inputs
of
comparators
U3A, U3B,
U-1A,
U4B,
and
USA.
The
common
terminal
of
each
footswitch
is
connected
to
the
+ 12 V
isolated
power
source.
Footswitch
activation
causes
this
voltage
to
be
applied
to a
resistor
divider.
The
values
of
the
resistors
comprising
the
input
divider
are
selected
to
provide
a
switching
threshold
of
approximately
750
ohms.
The
divided
voltage
is
then
applied
to
the
inverting
input
of
one
of
the
tlve
comparators.
''\Then
the
voltage
at
the
inverting
input
exceeds
the
voltage
at
the
noninverting
input,
the
open
collector
output
of
the
comparator
turns
on,
causing
current
to flow
in
the
LED
of
the
corresponding
optoisolator.
This
current
generates
an
IR
beam
that
causes
4-15

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