Re: transmitter...default user
- From: default <default@xxxxxxxxxxxxx>
- Date: Mon, 10 Oct 2005 09:13:41 -0400
On Mon, 10 Oct 2005 19:53:55 +1300, Jasen Betts
<jasen-b@xxxxxxxxxxxxxxxxxx> wrote:
>On 2005-10-09, default <default@xxxxxxxxxxxxx> wrote:
>> On Sun, 09 Oct 2005 03:35:10 -0500,
>> brandondraz@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx (ilox) wrote:
>>
>>>So basically all i need is a relay to have 680 ohms or more of
>>>impedance and it wont make the line appear off hook? these
>>>comparators you speak of i have searched the net but cant seem to
>>>find out much about them. do these things have or act like relays
>>>where they switch the postion of contacts? what do you do exactly or
>>>did you do that you know so much about all this stuff?
>>
>> No. Telephone stuff is not high precision. You want a relay well
>> above 680 (a factor of 10 would be desirable - since some telephones
>> have lights in them that run on the phone power and you'd be adding to
>> that load, if any). Higher resistance is better.
>
>everything I've read says lighted phones are powered from a local
>transformer not the line, but I can't say which fuse it's attached
>to. If you havo one try running your lighted phone on a two conductor
>phone cable.
>
>Bye.
> Jasen
Not entirely true, but I'll agree that most of the stuff is wall wart
powered.
That's probably more true today. It is common practice to add a wall
wart for all the "extra" stuff a phone is asked to do (message
recorder, speaker phone, clock, calculator, and whatever else someone
thinks of including in a telephone).
As the efficiency of some of that stuff increases, you can bet the
manufacturers will dispense with the wall wart power supply as an
added cost. They already have some phones that can record (off hook)
and play messages on hook. Easy now that a tape recorder isn't used.
Likewise there are phones that have LED's in the dials that are phone
line powered.
Back in the darker ages, when AT&T had a monopoly on telephone
service, They didn't allow anyone to connect equipment to phone lines
unless AT&T supplied the equipment. Some of their justification for
that practice was the possibility of a lethal voltage being put on
lines or currents that might damage the line. Remember vacuum toobs
and high voltage power supplies?
The early "princess" touch tone phones had lights in the dials that
were phone line powered. Probably AT&T obeying their own mandate -
later phones had wall warts or small pink/beige potted transformers
that AT&T supplied.
Wall warts and MOV's and semiconductors made the prospect of a high
voltage getting on a phone line very unlikely, so we do things
differently today.
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