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COnnecting 2 telephone Sets via optical coupler

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waqar

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iam planning to do a simple experiment for designing a simple 8 lines Pbx system which only involves internal communication no link with outisde telephone service line.

if there is any project on this present on your website please do let me know the link or any where other than your website. or may email of some student of your university who is working on such a project.

I only need guidance on the following thing..and swear that will not ask any thing ever just help me on this..

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 .

Thankyou
 

bogdanfirst

New Member
since you only have 2 telephones, isnt it easyer to make a circuit that sounds the other phone when you take the first on off?
 

waqar

New Member
Thanks for reply but one problems

ya its really easy to do this but i want to do this using controller so that i can learn the magic of SLIC and DIAl tone etc...

Iam posting another question on this forum let see if any one can reply that...

as far as i have seen no one has any knowledge about this and there is no books or web tutorial on telephony and controller out there.
 

bogdanfirst

New Member
i think that the problem is that the message is too long and you have too many conditions and operation details...i suggest starting with the most important things and then go to details....
 

binzer

Member
waqar said:
ya its really easy to do this but i want to do this using controller so that i can learn the magic of SLIC and DIAl tone etc...

Iam posting another question on this forum let see if any one can reply that...

as far as i have seen no one has any knowledge about this and there is no books or web tutorial on telephony and controller out there.
Not to sound like a butthead, but do you know the basic principles of telephone??

To get voice between 2 handsets you need dc 'talk' battery (48vdc), offhook is sensed by the load presented by the handset (phone) usually by a 'network' which includes a reed switch.
You can multiplex the voice (Time Division Multiplex) and do quite a few 'lines' useing only 4 wires (2 rx, 2tx), of course you need some type of switching to get the bell/buzzer to operate and to read pulses or tones to 'dial'. Ring Tone is 30hz one second on 3 seconds off (if I remember correctly). I worked for ITT Telecomunications for about a year and got sent to school to learn Time Division Multiplexing to be a tech on one of their systems (about 25 years ago).
Good luck, hope I gave you some ideas and info.
 
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