Re: Physically Protecting The Local Loop Metwork?

I think I remember once seeing a little circuit board that did nothing

> except guarantee Part 68 compliance. (It even had its own Ringer > Equivalence Number, a whole 0.0B.) It was designed for people who > wanted to attach their own homebrew projects to the phone line but not > worry about causing problems. I don't remember where I saw it, sorry, > but you could probably find something like it wherever you buy other > bare electronic circuit thingies.

A long time ago, when they first started allowing other people to connect modems to a phone line, but NOT directly, there was the DAA ("Data Access Arrangement", I think). I worked with these in the late

1970's. You rented it from the phone company. It had a defined interface so you could pass voice through it, take the phone off the hook, pulse dial, detect ringing, etc. For tone dialing you'd just take the phone off hook and send tones. For pulse dialing you'd do the equivalent of rapidly jiggling switch-hook. Most of it was providing isolation between the phone line and your side so if lightning hit your gadget, it wouldn't get through to the phone line (much). It was also supposed to protect the other way. Typically there was transformer isolation for the voice signal and maybe relay or optical isolation for the ringing signal and switch-hook.

Eventually they built these into modems, but I can still see a use for these as interfaces to one-off projects that aren't worth going through FCC certification for.

Gordon L. Burditt

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Gordon Burditt
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