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Automatic Phone Recorder
by
Atomic Punk
May 1, 1989
This device will allow any standard cassette tape recorder the
ability to automatically record phone conversations. The device
will start the tape recorder when the phone handset is lifted and
stop the recorder when the handset is returned to the cradle.
The device is a DC switch that is normally on via the forward
biasing of Q1 via R3. Q1 now clamps Q2 into a forward state by
biasing its complement well into a saturated state via R4. The
DC switch is turned off via a negative voltage above that of the
Zener (D1). This voltage is usually about 48 volts and is the on
hook value of the phone line. This negative voltage over rides
the effect of R3 and keeps the circuit off. When the phone is
off the hook, the 48 volts drops to 10 volts, which is below the
[more] zener voltage of D1, and R3 now turns the circuit on. Audio
signal is via attenuator resistor R1 and DC isolating capacitors
C1 and C2.
This device is really only a high impedance switch that isolates
the recording controlled device from the phone line via some
simple electronic circuitry. It requires no battery and obtains
power for operating from the remote jack that in most recorders
is a source of 6 volts. When the remote jack is grounded,
recorder operation starts, and when the grounding condition is
removed, recorder operation stops.
Parts list: Here's all you need:
Name Qty Description
R4 1 220 ohm 1/4 watt resistor
R3 1 39k ohm 1/4 watt resistor
R1 & R2 2 100k ohm 1/4 watt resistor
C1 & C2 2 0.01 mfd/ 50V disc cap.
Q2 1 PN2222 NPN Silicon
Q1 1 PN2907 NPN Silicon
[more] Z1 1 15 volt Zener diode
P1 1 Sub-mini plug 2.5mm dia.
CL1 & CL2 2 Alligator clips
P2 1 Mini-Plug 3.5mm dia.
Enclosure 1 Suitable enclosure for device
PB1 1 1.25x1.67 perfboard
WR4 (18") #24 hook-up black wire
WR3 (18") #24 hook-up red wire
Casto Castolite or paraffin wax
[more] Circuit Diagram
Red wire
----------|---------Z1--------|--------------------|--------|----------
| | | |
Green | | | |
-----| | | | |
| | | | |
| | | e |
| | | | |
| | R3 |-----R4---b-Q2 |---P1
| | *No connection* | | | |To remote
| | | c c |of
| *|* | | | |recorder
|--- | ------------------|-----b-Q1 | |
| | | | |
| | e | |
| | |------------|--------|
| |
| | C1
[more] | |----------------------------? ?-----------------|
| |
| |---P2
| C2 |To Aux
|--------------R1-----------------? ?-----------------|on
Recorder