***** Moderator's Note *****
> There were a variety of interface devices that were made available
> after the FCC mandated interconnection. I'm most familiar with the
> CDH, which was intended to connect POTS lines to customer provided
> equipment. It did the job, but it was too complicated: not only did it
> have separate supervision leads that were isolated from the talk path,
> but it had separate ringing leads as well. There might have been PBX's
> or other CPE which could access the CDH directly, but ordinary key
> equipment could not: to use it for CPE key equipment, you needed
> _another_ interface to match the CDH interface.
> Ma Bell had too many interfaces and they cost too much to install and
> rent: it was inevitable that the FCC would dictate type-acceptance and
> allow direct connections. I don't remember when that happended, but it's
> been the norm ever since.
Yes Bill, but that doesn't help with stuff that is not type accepted. Isn't the new term of art certified? I'm trying to devise a way to patch the PSTN incoming calls to manual switchboards that predate customer dialing. If you connect the interconnect terminals of some of those boards it will look like an off hook condition to the PSTN.
If you'd said -that- in the first place, you'd have gotten better first-round answers.
Anything 'off the shelf' in the (even semi-) modern world is going to require quite a it of custom 'glue' logic to adapt that cordboard to the weirdness of the CPE side of the adapter box. You may as well just get one of the (many) registered, type-accepted, 'FCC part 68' qualified, 'phone line interface integrated circuits (whew!!), and roll your required custom interfacing logic around -that-. Such chips are only a few dollars (at most), quantity one.
I'm afraid that customizing chip logic is beyond my skill set. I was hoping, vainly it seems, that there existed some box that took in a loop supervised phone line and a supply of some form of power and put out a voice pair, dry closure on ring, and some means to signal the outside lines supervision state.
You are trying to do this today or you are trying to do this in 1970?
There are some old Data Access Arrangement boxes out there, but they are not particularly useful today. Some of them have dialing hardware, some of them do not. Most have four-wire interfaces but some have two. In
1970 they were VERY useful because they provided a political line of demarcation.
If you have an existing switchboard, bringing telco lines into it as a trunk shouldn't be a huge problem, depending on what kind of switchboard it is. Even if it's for a common-battery phone, you should be able to use a repeat coil to get DC isolation between the telco circuit and the phone.