Hi all,
I know that iam asking the same old telephone connecting with micrcontroller question again and again ...but thing is that iam not getting any answer not even starting thing....so now i am willing to make the most simplest circuit before going further in any other big telephone exchange design...

hope to get some help from you people....

1) I have a Pulse Dialing Telephone Set,

2) This Telephone Set is connected with a off-hook indicator circuit which contains a Optical Coupler.

3) When ever the telephone set goes off hook ,

4) optical coupler circuit sents a logical high signal output.

5) Now this logical high out put is connected to a micrcontroller (AT89c52) input Pin 1.0.

(in controller there is program written in assembly which detects the off hook and then generate DIAL TONE....more details are in my attachment which you can see in MS word. I also have difficult in writing that program but i need much help on connected the out put from the controller to the telephone set)

5) Now when the telephone goes off-hook ,

6) Controller Sents a 1000Hz Square Wave at Pin 2.0 now my question is how to connect this wire with telephone set so that a DIAL TONE can be heared in the Telephone Set...?

please see the attachment rough BLOCK Diagram

if the attachment is not avaiable then please try to imagine this:-

1) A out put from Telephone Set goes in Optical Coupler circuit,

2) from Optical COupler circuit logical high wire goes to Pin1.0 of controller,

3) from Controller out put wire which will supply a DIAL TONE signal goes out from Pin 2.0 , now where on Telephone Set should i connect this or how ?