|
Parallel
Telephones with Secrecy
|
|
Often
a need arises for connection of two telephone instruments
in parallel to one line. But it creates quite a few
problems in their proper performance, such as overloading
and overhearing of the conversation by an undesired
person. In order to eliminate all such problems and
get a clear reception, a simple scheme is presented
here (Fig. 1).
|
|
This
system will enable the incoming ring to be heard at
both the ends. The DPDT switch, installed with each
of the parallel telephones, connects you to the line
in one position of the switch and disconnects you in
the other position of the switch. At any one time, only
one telephone is connected to the line. To receive a
call at an end where the instrument is not connected
to the line, you just have to flip the toggle switch
at your end to receive the call, and act as usual to
have a conversation. As soon as the position of the
toggle switch is changed, the line gets transferred
to the other telephone instrument.
|
| Mount
one DPDT toggle switch, one telephone ringer, and one
telephone terminal box on two wooden electrical switchboards,
as shown in
Fig. 3. Interconnect the boards using a 4-pair telephone
cable as
per Fig. 1. The system is ready to use. Ensure that the
two lower leads of switch S2 are connected to switch S1
after reversal, as shown in the figure. |
| Lab.
Note: The external ringer for the project, as shown
in Fig. 2, was designed/fabricated at EFY Lab. |
|
|
Click on the Image for its larger version
|
