Designing a Simple Tone or pulse based Intercom system 2

[89c52]

hello all,
this is my first time on this forum so if i make any mistake in asking the question let me know.

Iam willing to design a simple 8 lines intercom system, no trunck or co. line involved, its a simple intercom system with which normal tone or pulse dailing telephone sets can be used . Now i know that i have to make use of microcontoller design the software using assembly language, DTMF IC, have to design my own SLIC but really i have no idea from where to start i have no books nothing and iam unable to find any information on this topic i guess there are no books,

Sir i really need some one to guide me how to make this project.

guide me some steps or any web link from where i can get some information about this.

 

[executone]

The old 1A2 phones systems had a device you hood to them to give them intercom capabilities. Sound just like you are trying to design. It has been so long since I have worked on and not sure of who made them. I would research the 1A2 phone sysytems and that should point you in the correct direction. Good Luck!!

 

[daronwilson]

I once thought this would be fun too, but then things got so inexpensive I gave up the interest. The 1A2 example is a good one, that was simply a logic based system, no microcontroller.

If you don't know telephony, this will be some work for you. The microprocessor side is pretty easy, as it has been done with logic gates.

For books I guess I'm not sure where to send you. Get schematics of the old 1A2, get some theory of telephone operation type book, and then I guess data sheets for the various devices. I doubt you will find a book that is "how to build an microcontroller based 8 station intercom". You might also look in back issues of popular electronics, there were many telephone projects in there, maybe something similar will pop up.

Good Luck!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[89c52]

thankyou both of you for giving my question so much time but i don't understand what is 1A2...
can any one please explain

 

[pansophic]

1A2 was a simple electro-mechanical Key Service Unit (KSU) that used a mechanical interrupter to provide flashing lights (ringing and on hold).

It takes 6 wires for every single line on each telephone. You had a Tip, Ring, A, A1, Lamp and Lamp ground. The phones could actually get by with only a single A (or was it A1) lead, so you could stuff 9 lines on a single 25 pair cable. That also gave you a pair for an intercom ringer and a pair for a ringer.

Here is a link to a book about the 1A2.

http://www.trynci.com/cat/ref4.htm

If you are really still interested, I might be able to dig up a manual from the old days.

pansophic

 

[daronwilson]

I'm pretty sure I tossed all my 1A2 stuff, that link to the books is great. I think I have some of those somewhere, I sure wish a similar set was available with more current information, they were a great series in their time.
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[pansophic]

I just realized, that I never answered the core question here. I think that the point that everyone was trying to make to 89c52 is that this has been done before. You can buy one at just about any telecom supply house, and lots of secondary market shops.

Do a web search on "KSU-less" AND "intercom" and you will see many sites that sell essentially what you are trying to build. So unless you are doing it as a self-improvement project, there is really no reason to do it.

pansophic

 

[executone]

Valco makes some good intercom units

http://www.valcom.com/intercoms.htm

Viking Electronics also has neat telephony equipment

http://www.vikingelectronics.com/techsupport/

 

[89c52]

thankyou all of you for helping me so much. but i think i never mADe my queStion cleaR..
i want to design a simple PABX in which there are 2 trunck lines facility and 8 extensions means a 2+8 PABX and i want to design its SLIC by my self...
so i thought the first step is to make a 8 lines intercom first..
that's why iam looking for some one who has made such kind of project , like designing SLIC , writing assembly language codes for microcontroller...
I want to know how should i start my design for the above PABX like what should i do first make the hardware design or the software i have lots of sample hardware circuits with me but no software guidance...

 

[jeffmoss26]

I did a new install in an office where they had a 1A2 system. Wow, how things have changed! We reused the 25 pair cable for our digital phones, but we still have a ton of 25 pair cables in the phone room. Those phones were big and bulky and you couldnt really do anything with them. The customer is lucky that they got a brand new system! jeff moss
jeffmoss26@adelphia.net

 

[daronwilson]

I dunno what you want us to do. You say you want to design it yourself..but you keep asking where to start. OK, first make the hardware that will take care of each port. That hardware would include a line seizure device which detects when the phone goes off hook and when that happens, your dial tone generator sends a dial tone to the phone that went off hook. Then you switch to listening, you provide a DTMF decoder that listens detects and decodes the digits. Of course you need to deal with the audio portion of all this, bandpass filtering, probably an isolation transformer for the audio, of course a 24-48vdc supply, ring generator, etc. So now, you have hardware together, you need to program your micro to recognize line seizure, enable the tone generator and the DTMF receiver, take data from the DTMF receiver so you can route the call.

SO I would think if you want to do this with a micro, your micro needs to sense line seizure, turn on dial tone generator, get DTMF, turn off dial tone generator, decide where to route call, put ring voltage on port to call set, detect line seizure (answering), turn off ring generator, connect talk path.

Tho, for the life of me, I dont understand why you want to make it when you can buy it and mess with one already built, but hey, i've built stuff that i should have bought, took 10 times longer, but had fun.

Enjoy!
It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[89c52]

sir iam really greatful to you mr. daron for provding me such information...
the main point is that i want to design the system my self a small PABX for 2 truncks and 8 extensions.

Now can you please guide me how should i make the software for this using assmebly or any recommended language.
and how to learn about the micrcontroller ports.

 

[pansophic]

There is no be all, end all language for programming telephone switches. In the systems that I have worked on, the primary language is nearly always a high-level language, like C or CHILL. Unfortunately, due to VERY tight timing constraints in the switching environment, some functions must be programmed in Assembly.

Plus, everyone runs a Real-Time OS (RTOS) because of the critical timing. You need to pick your microprocessor and decide what languages it supports. From there you can move up to the RTOS for application level stuff and user interface.

I have worked on one telephone system based on Windows 3.11, but it was a poor design at best. I'm not sure if they were using an RTOS for interfacing to the telco devices, and Windows for the Application layer stuff, but it was difficult to believe that it would have survived in the public network. Only one government client ever bought it to my knowledge.

pansophic

 

[jeffmoss26]

the Inter-Tel AXXESS system which is digital uses C++ programming. It can have a lot of CTI technology like softphone, pc phone, chat, database programming, unified messaging, etc jeff moss
jeffmoss26@adelphia.net

 

[jerryreeve]

If you take a look at Circuit Cellar Magazine they had a couple of articles in issue 48 and 67 about a home pbx. check out

http://www.dtweed.com/circuitcellar/index.htm

there are links to the articles there. JerryReeve
Communications Systems Int'l
com-sys.com

 

[89c52]

thanks a lot all of you, i am trying to learn the theory first ... so if any one gets any type of info on this intercom system please share your suggestions, iam also putting up another question related to intercom so kindly suggest some solution there also.

 

[DrPbx]

I would go out, buy a Partner ACS proc & move on with my life.

 

[Bobg1]

I have a system boxed up in storage that would do this.
I think it only does 6 phones though