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designing a telephony system

designing a telephony system

designing a telephony system

Simple experiment and some help and suggestions needed     

The Objective is only to create communcation between two pulse dialing telephone sets using controller thats all no furture expansion etc...

Suppose you have two Telephone Sets supporting pulse dialing only.

Telephone No.11

Telephone No.22

1) telephone no.11 goes off hook ,
2) a optical coupler detects off hook and,
3) sents signal to At89c51 controller,
4) controller sents a dial tone by generating a 400Hz square wave..
5) The user dial digits "22",
6) signal goes to the controller via the optical coupler,
7) controller counts the incoming pulses using the following rule:

a) 10 pulses per second if digit "0" is pressed,
b) Mark & break Ratio is 60:40,
c) inter-digit space is 800 milli-seconds,

8) after counting the pulses campare it with the digits already stored in its memory registers,

9) If the pulses are not equal to the digits stored in the memory then the controller sents a BUSY DIAL tone to the user using 400Hz square wave with 0.2 seconds ON and 0.2 seconds OFF condition,

10) if the pulses are equal to the digits stored in the memory than the controller do two things which are as follows:-

a) sents a ring back tone using a square wave of 400Hz with 0.5 seconds On and 0.5 seconds off condition and
b) sents signal to the relay connecting 60 volts Ac supply with telephone No.2.

11) Ring occur at the telephone No.2,

12) when the user of telephone No.2 picks up the handset its optical coupler detects off-hook,

13) sents signal to the controller,

14) controller disconnect the relay from ringing signal and bring it to 24 volts Dc supply signal and ,

15) at the same time removes the Ring Back tone from telephone no.1 so that conversation can take place.
the same thing happen if the user of telephone no.2 wants to talk with telephone no1.

Now My question are about :-

1) For these two telephone sets i will be using two optical couplers ,

2) from these couplers two wires ( Logic High) are connected to P1.0 and P1.2 representing telephone no.1 and telephone no.2 respectively.

Question 1:-

This may be silly one but still i have to ask, the above arrangement will sents off-hook detection to the controller but can the same wires will sent data from controller to the telephone sets or not, if not then what should i add in ?
And will the same wire will sent pulse dialing signal to the controller so that controller can count incoming pulses or for that i have to use something else in between telephone sets and controller?

Question 2:-

I am not using any analog switch like Mt8816 or 4066 since i am only using two telephone sets, do i have to use something or not?

Question 3:-

I have made a power supply of 24 Dc volts , 5 Dcvolts and 60 volts Ac using a signal transformer. +ve wire from 5 volts supply (7805 is used) goes to controller VCC, +ve wire from 24 Dc Supply goes to (7824) goes to both telephone sets which are connected with optical coupler.

Now how to connect the Ac supply with telephone sets and controller so that the controller can snet signal to the Ac supply which then turn on the ringing of telephone set when ever desired ? do i have to use dual operational amplifier like KA1458 or please suggest some thing?

since this is not my home work or anything like that so i don't have time limitations , i hope that when ever you feel free you will reply me .


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