Ramsey Electronics COM 3 - Power, Control, and Display Systems

5.14 +30 VOLT AND -10 VOLT SUPPLIES
The.+30 V and -10 V supplies within the
Com
3
use
the
16
KHz
which
is
available
throughout
the
Com
3,
as
a
reference
frequency.
Looking
at
the
-10
volt
supply,
the
16
KHz
signal
is
applied
to
transistors
Q18
and
Q19.
Q18
forms
a
simple
inverter
which
drives
transistor
Q17.
Q17's
emitter
is
tied
to
the
collector
of
Q19,
and
at
that
point
forms
a
12
volt
square
wave.
C166,
C167
and
diodes
D41
and_D42
comprise
a
voltage
doubler
which
takes
the
square
wave
and
after
suitable
filtering
and
the
doubling
comes
out
with
a
minus 10 volts supply under load.
The
+30
volt
supply
works
in
a
similiar
manner
in
which
the
16
KHz
wave
is
coupled
to
transistors
Q20
and
Q22
which
again
forms
the
phase
inverter
and
then
to
Q21.
The
emitter
of
Q21
is
tied
to
the
collector
of
Q22
where
once
again
we
get
the
12
volt
square
wave
and
diodes
D43
through
D46
along..with
capacitors
C169
through
C172
form
a
voltage
tripler
which
produce
approximately
--30
volts
under
a
light
loading.
The
-
10
volt
supply
is
somewhat
heavily
loaded
in
that
it
drives
the
op-amp
cemparator
U2,
and
the
PIN
diode
attenuator.
5.15
TRANSMIT
PROTECTION
CIRCUIT
The
Com
3
is
protected
from
transmitter
inputs
up
to
100
watts.
If
a
transmitter
signal
appears
on
the
RF
input
jack
of
the
Com
3,
the
signal
is
detected
by
diodes
D1
and
D2.
The
resultant
DC
output
voltage
is
applied
to
one
section
.of
U1
which
is
configured
as
a
simple
comparator
which
drives
(31.
You'll
note
that
the
relay
K1
is
kept
normally
closed
whenever
the
Com
3
is
in-use.
When
an
Rf
signal
is
present,
it
turns
off
Q1
which
opens
relay
K1.
The
reason
for
this
is
if
the
Com
3
is
not
turned
on,
yet
is
transmitted
into,
.
you
do
not
want
the
RF
power
going
into
the
attenuator,
so
the
unit
is
connected
with
the
normally
closed
contacts
of
the
relay
going
to
the
output
load
jack
on
the
rear
of
the
Com
3.
5.16
DC
SUPPLY
AND
BATTERY
The
power
supply
within
the
Com
3
is
derived
from
a
+12
volt
source.
The
reason
+12
volts
was
chosen
was
that
a
standard
+12
volt
gel
cell
battery
can
be
used,
which
is
internal
to
the
Com
3,
or
an
external
power
Supply.
The
transformer
used
goes
into
a
standard
bridge
rectifier
composed
of
diodes
D32
through
D35
.
which
is
filtered
by
capacitor
C149.
That
output
voltage
which
is
approximately
20
volts
DC
under
load
is
applied
to
a
rear
panel
mounted
5
volt
regulator,
which
produces
5
volts
at
1
amp
which
is
used
through
out
the
circuits
of
the
Com
3.
It
is
also
applied
to
VR1
a
7812
+12
volt
regulator
whose
ground
tab
is
pulled
above
ground
through
a
variable
resistor
R176.
This
causes
the
output
voltage
of
VR1
(7812)
to
be
somewhat
greater
than
+12
volts
,
and
is
adjusted
for
+13.8
volts.
The
+12
V
gel
cell
battery
is
connected
at
this
point.
The
+13.8
V
floats
the
battery
to
maintain
full
charge
at
all
times.
After
passing
through
diode
D37,
and
the
front
panel
switch
we
come
up
with
a
+12
volt
source
which
is
used
throughout
the
Com
3.
A
seperate
5
volt
regulator
VR5
is
used
to
power
the
microprocessor
located
on
the
front
panel
board.
VR5
is
connected.
directly
to
the
+12
volt
gel
cell
battery,
so
it
will
draw
current
all
of
the
time,
although
it
will
be
a
small
amount
of
only
5
ma.
This
5
volt
voltage
is
used
to
power
the
microprocessor
,and
keep
its
memory
alive
in
the
event
AC
power
fails.
In
that
case,
the
battery
will
keep
the
microprocessor
alive
in
a
low
power
mode
to
remember
any
previosly
stored
front
panel
settings.
Series
protection
is
provided
in
diode
D39
in
the
event
that
a
reverse
polarity
power
Supply
is
connected
to
the
Com
3.
5.317
MEMBRANE
SWITCH
The
membrane
switch
is
an
eight
by
four
X-
Y
array.
The
microprocessor
scans
each
column
and
watches
the
rows
for
a
contact
closure.
When
a
key
closure
is
detected,
the
closure
is
timed
for
30
milliseconds
before
it
is
considered
valid.
5.18
MICROPROCESSOR
The
microprocessor
is
a
Hitachi
HD63705VOP
8
bit
unit
with
4k
ROM.
The
microprocessor
does
the
general
housekeeping
functions
of
the
Com
3,
such
as
display
driving,
keyboard
scanning
and
debouncing,
audio
and
RF,
CTS
tone
encoding,
and
synthesizer
loading.