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.
Last
Updated : February 15, 2002 
