Padu wrote:

> Humnn.... not sure wich tag is more appropriate, feel free to change if you think this is not related to [PIC]
> 
> Basically I want to interface a PIC with my digital telephone line. What I envision is a simple device that monitors the digital line and detects when the phone goes on-hook or off-hook. Is there such a thing as a standard between major manufacturers? If not, do they use a common electrical interface at least?  I'd also appreciate if you have any pointers on basic concepts of how digital lines work, preferentially at the electrical level.

It all depends on what kind of digital phone line you have.
If all you want is on/off hook, it may be sufficient that you just
sense load current, assuming that the phone draws more current when
it's off hook and has to power up the analog circuitry.

You could also just look for data streams. An on hook phone will
have a minimal amount of data movement, but when off hook, it still
sends A/D values, even if its all zeros. An simple capacitor coupled
to a leaky peak detector would be sufficient to detect active/not.

Robert


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