How to electronically put a telephone line "off-hook"

[Linden]

Hi,

I know how to detect the ring signal and create a logic signal for a
microcontroller, but then how do I "pick-up" the phone line to stop the
ringing and connect with the caller ?

Perhaps with an optocoupler as a relay but what does the relay connect
up to the line to stop the ringing ?

Help appreciated, cheers !

 

[Tom Biasi]

"Linden" <quiksilv@optushome.com.au> wrote in message
news:415299b7$0$23893$afc38c87@news.optusnet.com.au...

Hi,

I know how to detect the ring signal and create a logic signal for a
microcontroller, but then how do I "pick-up" the phone line to stop the
ringing and connect with the caller ?

Perhaps with an optocoupler as a relay but what does the relay connect
up to the line to stop the ringing ?

Help appreciated, cheers !
In the USA putting 600 ohms across the line will produce an off-hook

condition. The audio can be pulled off through a capacitor. Surge
suppressors like MOVs should be used also.
Tom

 

[Linden]

Tom Biasi wrote:

"Linden" <quiksilv@optushome.com.au> wrote in message
news:415299b7$0$23893$afc38c87@news.optusnet.com.au...

Hi,

I know how to detect the ring signal and create a logic signal for a
microcontroller, but then how do I "pick-up" the phone line to stop the
ringing and connect with the caller ?

Perhaps with an optocoupler as a relay but what does the relay connect
up to the line to stop the ringing ?

Help appreciated, cheers !

In the USA putting 600 ohms across the line will produce an off-hook
condition. The audio can be pulled off through a capacitor. Surge
suppressors like MOVs should be used also.
Tom

Oh ok thanks, is that why I see 600 ohm 1:1 transformers in circuits ?
So once the line has 600 ohms across it there is a circuit between me
and the caller and I can then do DTMF or audio ?

To hang up I just remove the 600 ohm resistor ? Cheers!

 

[Dbowey]

Linden posted:

<< I know how to detect the ring signal and create a logic signal for a
microcontroller, but then how do I "pick-up" the phone line to stop the
ringing and connect with the caller ?

Perhaps with an optocoupler as a relay but what does the relay connect
up to the line to stop the ringing ?
What are you going to use as a "telephone?" You indicate that you want your
equipment to auto-answer an incoming call, but then what happens?

A good answer to your question can't be provided without more information.

By the way, your telephone line isn't 600 Ohms impedance, and tripping the ring
with a 600 Ohm resistor is a marginal approach which, depending on how it is
done, can degrade the transmission path.

Don