Specifications

CONSTRUCTION
a minute, with the remaining two min-
utes reserved for recording other-end
subscriber’s message (i.e. the tape in
the player will run blank for these two
minutes). During these two minutes, if
other-end subscriber is relaying any
message, then the same will be recorded
automatically in the tape recorder that
is already ‘on’.
Whenever the subscriber (owner) in-
tends going out of station, he will have
to rewind the player and press the play
button ‘on’. Similarly, he has to rewind
the recorder for recording the 15 in-
coming messages and also ensure that
the recording button is in ‘on’ (pressed)
condition. Both the recorder and the
player will be automatically switched
‘on’ for the preset duration whenever
three rings are received, as explained
already.
An actual-size PCB for the circuit
in Fig. 2 is shown in Fig. 6 and its
component layout is shown in Fig. 7.
PARTS LIST (Fig. 2)
Semiconductors:
IC1, IC4 - NE555 timer
IC2 - CD4017 decade counter
IC3 - CD40106 inverter
IC5 - 7812 regulator (+12V)
T1 - BC547 npn transistor
D1-D7 - 1N4007 rectifier diode
LED1, LED2 - Red LED
Resistors (all ¼-watt, ±5% carbon, unless
stated otherwise):
R1 - 100-kilo-ohm
R2, R7 - 4.7-kilo-ohm
R3, R4, R8 - 10-kilo-ohm
R5 - 33-kilo-ohm
R6 - 2.2-ohms
R9, R10 - 1-kilo-ohm
VR1 - 1-mega-ohm preset
Capacitors:
C1, C2, C4, C5- 0.1µF, 25V ceramic disk
C3 - 10µF, 25V electrolytic
C6 - 470µF, 16V electrolytic
C7, C8 - 1000µF, 35V electrolytic
Miscellaneous:
X1 - 230V AC primary to
12V-0-12V, 500mA sec.
transformer
RL1-RL3 - 12V, 150-ohm, 2C/o relay
- Tape player with DC supply
source
- Tape recorder
- Telephone instrument
The author is proprietor/technical director of
VEPCO, Madurai.
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