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Yashica FX-3 - Page 17

Yashica FX-3
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Composition
of
Circuits
The
circuit
composition
consists
of
4
components
as
shown
in
the
left
figure.
(1)
Information
(2)
Adjustment
(Quantity
of
light)
(3)
Output
(4)
1C
(Control)
Calculate
and
adjust
information
by
1C;
by
using
the
result
of
which
as
output,
LED
is
driven.
EC
switch
information
[light-SPD
~j
jpilm
speed
setting
—
I
j
ASA
variable
resistor
j
j
Aperture
setting
—
Aperturej
!
Variable
Resistor
(AVR)/''
•
✓
/
/
T-"
,
1C
Input
Output
1
LED
I
I
1
_
OVER
I
under]
Adjustment
j"
Semi-fixed
"j
I
resistor
[
■
L
_J
Role
of
Each
Circuit
(1/2)
_
_
A1:
Logarithmic-compress
the
photoelectric
current,
calculate
it
with
V^sA-
^he
result
of
which
is,
as
V2,
sent
to
A2.
Vreg:.
A
constant
voltage
of
1.25±0.15V
is
generated
independent
of
variation
of
a
voltage
(Vcc)
from
the
battery.
Ra2:
Adjust
the
voltage
per
EV
of
Rp
and
Rasa-
The
adjustment
should
be
made
to
hold
as
follows.
Vreg-VI
=226mV
A2:
Calculate
V2,
the
output
of
A1,
Vp,
the
input
of
apperture,
and
Vadj,
the
input
of
light
adjustment,
the
result
(V3)
of
which
is
sent
to
A/D
.
V3
indicates
a
change
of
approximately
30mV
per
EV.
Co:
Amplifier
for
the
battery
checker;
when
Vcc
becomes
lower
than
24V,
a
signal
is
sent
to
A/D
to
turn
off
the
current
of
LED
with
the
result
that
the
LED
is
not
lit.
A/D:
A
circuit
to
determine,
depending
on
the
voltage
of
V3
sent
from
A2,
whether
OVER,
APPRO¬
PRIATE
or
UNDER
of
LED
should
be
lit.
This
is
generally
called
A/D
conversion.
8

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