detecting that caller is on line or disconnected (Telephone)

[magician]

germany call disconnect tone

Hi everybody
I'm just trying to make an "Answering Machine" that works on telephone line. but i have a problom. I can't detect that the caller is disconnected or is still online. when the caller is disconnected, the answering machine should disconnect from line too and make the line "idle". i don't know how can I do this
can anyboddy help me?
I'll be very thankful

 

[FvM]

line diconnection

Usually, busy tone detection is used to determine call end at the called party side.

 

[magician]

is this line disconnected

Usually, busy tone detection is used to determine call end at the called party side.

thats right
but how can i detect the busy tone? by a special IC or ... ?

 

[umery2k75]

telephone voltage disconnect

Check the voltages when caller is online and when disconnected.

 

[magician]

how to dectect phone disconnect

Check the voltages when caller is online and when disconnected.

I checked the line voltage too, but it hasn't any variation. I should detect busy tone, but how?

 

[FvM]

busy tone ne567 circuit

You need a tone decoder (e.g. NE567) and should check for the periodeical signal.

 

[BABESH]

telephone disconnect tones

try this one xe0055cs2,
i think this gives you an integrated solution to interfacing to uC.

--Babesh.

 

[Audioguru]

phone disconnected tone answer machine

Many telephone exchanges give a short pulse of zero voltage or reversed polarity when the distant end has answered or has terminated a call.

 

[pranam77]

lm567 tone decoder busy tone telephone

I do agree with FvM. The busy tone detection is easiest option. Polarity reversal and the 16Khz tone are sent from the exchange only when a call is matured or in progress. When the called person disconnect the call, a busy tone is heard and it shud be detected.