internal phone (help)

[arash]

Hi all
I want to make an internal phone but i have a problem .I can't connect 3 or more phone together.
How can i do this.Canyou help me?

[metal]

Hi

Do you need to make a conversataion between many people at the same time, or just a converstaion between two people at a time.

I have a circuit that uses two lines to make some kind of virtual full duplex if you like, it uses two opamps.

You can also use ordinary swithches, or if you are familiar with microcontroller, you can make it switch channels uing relays and push buttons.

Let me know what exactly you need to do, I might be able to help you further.

[arash]

I need to make a conversataion between many people at the same time

[parallaxis]

I need to make a conversataion between many people at the same time

You need something like PBX - it means some relays, some DTMF decoders and processor (or microcontroller) to controll all of them. Not so easy...

[metal]

Hi

Now, suppose you have 4 terminals. making them talk to each other at the same time seems to be out of my cabability to help. But I can help you if you need to make terminal 1 talk to terminal 2, and terminal 3 talk to 4 at the same time. Or terminal 2 talks to terminal 3, and terminal 4 talks to termianl 1 at the same time, etc.... I mean two terminals talk to each other at the same time, the fact that there are many terminals is not a problem, as long as we follow this rule.

As a start, you need a mic pre-amplifier circuit for each terminal, and a small power amplifier for the speakers, also for each terminal. Then, the way channels connected can be controlled using an analog multiplexer, say MPC series from texas instrumnets would be a good choice. If you are planning to connect people with far distances, then you will need a speech filter, 300Hz-->3Khz, and the mic pre-amplifier be two stages at least.

Then, you canplace the central unit that contain the controller, multiplecers, and an interface, say to your PC.

[arash]

Hi metal.
Thanks for your help.There is some notes.
 
  -I need to make "terminal 1 talk to terminal 2, and terminal 3 talk to 4 at the same time" ,etc...
  -I'm using phone device insted of mic pre-amplifier or other amplifire.

My problem is swiching betwin users.

[parallaxis]

 -I need to make "terminal 1 talk to terminal 2, and terminal 3 talk to 4 at the same time" ,etc...
My problem is swiching betwin users.

Look at Maxim web or Analog Devices web, they makes ICs called "analog multiplexers", "analog switches", "crosspoints" etc.

You must make something like "4x4 switch array" - e.g. 2x MAX4052 (http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1352/ln/), which contains dual 4:1 analog multiplexer.

Pay attention to "common telephone device", because they use 48volts as ring signal...

[max]

Hi,

You can use the AS2540 telephone ic to make the simultaneous conversation
b/w multiple lines. data sheet can be downloaded from following link

http://www.austriamicrosystems.com/03products/products_detail/AS2540/download/AS2540_datasheet.pdf