Teleconferencing please help

[shaiqbashir]

Hi Guys!

well! i have seen this circuit over some site.



this circuit will enable one person to talk to two different persons on different telephones simultaneously. I can explain it like this

suppose that "A" calls "B", B recieves the call and puts it on hold and then dials C on another telephone and puts it on hold too and then he just closed switch 1 and 2 and then they can talk simultaneously.

Now as you can see in the diagram, it is given the left side will be connected to TIP and RING and the right side is also connected to TIP and RING. I want to know how to connect this.

in a telephone wire i know

there are four wires actually

TIP
RING

TIP
RING

are they talking about them. How i have to connect the circuit to it.,

Thanks a lot in advance

[audioguru]

Hi Shaiq,
Most telephones have only a single phone line. They can't put one call on hold then call someone else. They use only two wires.

Then the transistor isn't necessary. Just connect phone #1 with its own phone line to one switch, and a second phone with its own phone line to the switch on the other side of the circuit.
Phone #1 calls person #1. If both switches are closed then phone #2 hears dial-tone plus the other 2 people. Everyone hears each other and the dial-tone.

If Phone #1 calls person #1 and phone #2 calls person #2 and the switches are closed, then all 4 people are in a conference.
There is usually a big loss in volume between one side to the other because the lines have an impedance that is too low due to the coupling. If the calls are long-distance then an echo might occur due to the mismatch in impedance.

I worked for a tele-conferencing company. Our equipment properly terminated each line then coupled together hundreds of phone-calls. Because the background noise all added, voice-switching allowed only the loudest two people to talk, or our operator could switch a single phone or two to have priority. ;D

Then we got into video conferencing! Lots of fun. ;D