atcomsystems.ca/forum Forums General General Telephone & Systems Information POTS: What placed between tip/ring will simulate "off hook" condition?

I am trying to electronically simulate an "off hook" condition.

Long story (which I won't bore you with since its not really relevant) but I want to automatically answer a ringing phone, then automatically disconnect.

I'm good with the circuitry to detect a ringing condition, no problem there.

But once that "triggers" I need to know what to place between tip/ring to "answer" or simulate an "off hook" condition. I'm guessing this would be a resistor of some value, but am not sure. I'd like to do this in a TelCo friendly manner (as opposed to just connecting tip/ring together!!).

Thanks!

P.S. If anyone knows of a pre-existing off-the-shelf "answer and hang-up" unit, that would be great. From scratch, I can build this for about $40 in parts so I'm looking for a pretty cheap solution.

just a plain old short will do it

Is that TelCo friendly? I recall doing stuff like that a million years ago when I was a kid which "dropped a card" at the CO, which then prompted a visit to my house by Ma Bell, not pleasing my parents.

I was kinda looking for some resistance value (if that is what is needed) which would act like a real phone.

With phone unpowered, ohm meter between tip and ring with a set off hook, that will give you the value you are looking for.

Thanks for the reply, but unfortunately, I don't own an ohm meter.........

Most phone company POTS test are done with a 600 ohm termination, which is what the old phones put on the line. Todays phones put about a 1200 ohm temination on the line some of the cheap ones are even higher in resistance. You should be fine with 1200 ohms.

Was gonna say the same thing. 600 to 1.2K will work just fine. I believe the old 400E 1A2 cards use 600 ohms for the hold bridge.

I want to automatically answer a ringing phone, then automatically disconnect.

Read some of the threads here by people who wanted to know why they have a ring-trip situation and you will find that it's because they used a protector with a low clamping voltage (lower than the 90V ring). A 75V protector on the line will do what you want all by itself. Ring/click/disconnect.

-Hal

Captain - go back to your old TAPs and look up the "Answeroo" - it does exactly what you are describing. I'll look it up this evening, and PM you.

TTT -- Hey, anyone who remembers TAP is AOK with me! Mine were all lost several moves ago.

The problem with the Answeroo is that the phone doesn't ring at all. I need it to actually ring once for this application.

hbiss -- that's exactly what I am trying to do. Maybe I should have named the thread: "ring/click/disconnect!"

I did a search as you suggested and found some theads discussing clamping and line protection, but no real source for a 75V protector. Can you be a bit more specific because I think you have hit the nail on the head. Thanks.

What is TAP?