Elenco Electronics MO-1251 Manual de usuario Pagina 43

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C10
180pF
-
2IN\
LDR1
VT 835
i---
02
2N4403
R1
1MEG
TP3
C13
10µF
R18
1MEG
R3
100K
C12
10µF
ICI -b
LM358
fl4
Cl
2.7K
.1
w-
K
R5
1MEG
1M
TPl
C11
001
1
2
3
4
IC2
7555
B
R6
1
100K
^'
BUZZER
TEST
i
V
C16
001
01
1N914
C4
10µF
+
12V
C
+
C
LDR2
VT-635
R20
10MEG
04
BS170
S
C2
C3
.01 .001
R10
100K
D
R8
10MEG
R9
10K
L5
R21
10MEG
116
BS170
D
C17
101,
F
C15
100µf
1
2
3
4
IC3
7555
8
7
6
L4
'otfl
C5
T200pF
R11
20K
R13
1
10K
7'
R12
53.6K
R14
6.2K
R15
33K
04
BS170
FIAT
O
G
S
C6
-
C7
.022
.001
N
05
MPSH11
C8
.001
L1
C9
27pF
XTAL1
R16y
47011
}
05
MPSH
-11
FLAT
B
C
FIG. 3-THE
IR RECEIVER
RF TRANSMITTER receives
the IR beam and transmits an
RF
warning
signal when the
beam is interrupted.
0
-10
z-20
á
30
1-4°
-50
-60
-20 -15
-10
f
48.890
MHz
L__1
/
+5
+10
kHz
+15 +20
FIG. 4 -T1-1E
BANDWIDTH
of the transmit-
ted RF
signal.
voltage
across
C4 and between Q4's
source
and gate
biases
Q4
on
when
it
reaches
approximately
three
volts.
When
pin
3 goes
low
(to
ground),
C4
quickly
discharges
through DI, there-
by biasing Q4 off.
Voltage-
divider R9
and RIO bias
Q4's source
terminal
to approximate-
ly 0.7
volts.
That
voltage,
in conjunc-
tion
with
R8, provide
a delay of
several
seconds
between
when
Q4
turns on and when
it turns off (it
turns
off when
C4 charges
to 3
volts
or
more).
The RC
time -constant
circuit
activates
the RF
transmitter for sev-
eral seconds,
even if pin
3 of lC2 goes
low
for only
a fraction
of a second.
0
ó
o
TP2
(ENO
OF R161
a
ANT
C99r
L3
Transistor Q6
and
its
associated
components function
as an
on -off
switch
that
is
controlled by the inten-
sity of
the ambient
light.
LDR2's re-
sistance is low
when
the device
is
exposed to light,
thereby forcing Q6's
V(,s (gate
-source voltage)
below
the
turn -on
threshold.
Capacitor C17
charges through resistors
R19
-R21
when
LDR2 is not illuminated.
Q6
turns on when
the
voltage
across
Cl7
reaches
approximately 2.5
volts. With
transistor Q6 on,
the negative termi-
nal of
the power supply is
connected
to the circuit ground,
thereby apply-
ing power
to the IR receiver /RF
trans-
mitter.
49
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