Help me doing an internal phone

[arash_micro]

internal phone (help)

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

 

[shafee001]

internal phone (help)

you need switchm you may design it or buy it,
just dtmf decoder and few relays to oprn cerials paths

 

[Code Warrior]

Re: internal phone (help)

Hello,
You can use EPABX for connecting phones. Some time parallel connection does not allowed by telephone exchange.

Bye

 

[arash_micro]

internal phone (help)

What is EPABX

 

[Code Warrior]

internal phone (help)

Hello,
EPABX stands for Electronics Private Automatic Branch Exchange. It is used mostly in firms and those home who have lot of rooms.

Bye

 

[arash_micro]

internal phone (help)

Well can help more than this

 

[artem]

internal phone (help)

your requirement is not clear . What you would like to do ?
To get all phones listen to each other just out electronic gyrator or simple 1 - 2 kOm 2 watt resistor to DC 48 volts and connect phones in parallel with one sode connected to resistor and another to ground . That is simplest and it works . But if you want to improive speech quality (the volume will be decreased ) - you should supply every phone through separate resistor and connect them via capacitor. To get better performance you should preamplify each telefone signal and then sum them.
Novadays conference call devives are done in form of dsp where sum and echo cancelling is done in software .

 

[Code Warrior]

internal phone (help)

Exactly what you want to do with telephone tell us.

 

[eng_ahmed22]

Re: internal phone (help)

hi
this is schematic for DTMF Decoder. you can interface it to any microcontroller to perform a function like EPABX.
hope to be usefull
bye
Ahmed