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When
Q6
is
conducting,
current flows
through
resistor
R19,
Calibrate control
R20,
and
the
meter. Themeterwill
deflect
and
indicate
the
average
current
for
the
onandoff
time
of
transistor
Q6. As the
light
intensity variations
increase
in
frequency
at
:he
photo
resistor,
the average
current
increases.
The increase
:n
the average
current
will
increase
the
meter
reading.
CIRCUIT
BOARD
X.RAY
VIEW
(vlEwED
FROM FOrL
StDE)
t-Rl
Rl9
Zener diode ZD1
holds
constant
level
keeping
battery
becomes weaker
the
supply voltage
to
Q5 and Q6
at
a
the
Tachometer
in
calibration as
the
with
use.
VOLTAGE CHART
(VIEWED FROM
FOIL
SIDE}
-R3-R7-R9-RI1-
T???*]
rt"
g.I-.rfe6
Rit,:
?r{
'ffi*,
@r'6
*"
Rla
PHOTO
RESISTOR
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