Searching \ for '[EE]:Telephone ring and busy indication?' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/pots/dtmf.htm?key=telephone
Search entire site for: 'Telephone ring and busy indication?'.

Exact match. Not showing close matches.
PICList Thread
'[EE]:Telephone ring and busy indication?'
2002\01\30@115540 by Steve Kasm

flavicon
face
Hello All,



Does anyone know of the simplest way to detect the following 2 condition
on a telephone line?



1.      When it is ringing
2.      When it is busy/off hook.



My output from the above circuit needs to be logic 1 when the conditions
are true and logic 0 when they are false.

The circuit must also conform to the proper specs for interfacing to the
phone line with regards to line isolation.







Regards,

Steve

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email spam_OUTlistservTakeThisOuTspammitvma.mit.edu with SET PICList DIGEST in the body


2002\01\30@174052 by Russell McMahon

picon face
> Does anyone know of the simplest way to detect the following 2 condition
> on a telephone line?
>
>
>
> 1.      When it is ringing
> 2.      When it is busy/off hook.
>
>
>
> My output from the above circuit needs to be logic 1 when the conditions
> are true and logic 0 when they are false.
>
> The circuit must also conform to the proper specs for interfacing to the
> phone line with regards to line isolation.


General guidelines.

When a telephone connected to a normal analog exchange is ringing an AC
signal is imposed on one wire relative to the other.
This causes the polarity to reverse on negative ringing peaks. Detecting
such a reversal will indicate ringing. You could cheat somewhat and simply
detect a non positive signal.

When the phone is off hook the DC voltage across the line will drop to a
substantially lower level than when "on hook" Actual value depends on feed
bridge resistance, line resistance and telephone resistance. (The 1st and
the last may be generated electronically by eg a current source and current
sink  rather than true resistances).

As a first attempt you could have two devices (transistors, gates etc) which
turn off when the applied voltage falls below a preset threshold. The off
hook detector determines when the line voltage falls to a lower level and
the ring detector determines when the voltage falls to zero or below zero
during ringing.



       Russell McMahon

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email .....listservKILLspamspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body


2002\01\30@174751 by David VanHorn

flavicon
face
At 11:21 AM 1/31/02 +1300, Russell McMahon wrote:
{Quote hidden}

Rectified line voltage will jump from a nominal 12/24/48 to much higher
values, depending on the ring voltage. (nominal 90V)

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listservspamKILLspammitvma.mit.edu with SET PICList DIGEST in the body


2002\01\30@190052 by Josh Koffman

flavicon
face
If you will need to pass inspection or certification, I'd go with a
precertified module. They certify the line connection so you don't have
to. For a hobbiest type application, I'd check out
http://www.epanorama.net . He's got tons of stuff there, surely
something will work for you.

Josh

--
A common mistake that people make when trying to design something
completely foolproof is to underestimate the ingenuity of complete
fools.
       -Douglas Adams

Steve Kasm wrote:
{Quote hidden}

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email .....listservKILLspamspam.....mitvma.mit.edu with SET PICList DIGEST in the body


More... (looser matching)
- Last day of these posts
- In 2002 , 2003 only
- Today
- New search...