Is it possible to record land line phone calls automatically to sd-card when call starts?
Where do you live? This is illegal in some places.
I think it's okay in the US as long as other parties on the line consent to be recorded.
It will be used only for some calls and both sides clearly know it is recorded.
There is about 40VDC on the phone line when the phone is on-hook and that voltage drops when off-hook so you should be able to detect that voltage change.
You need to protect/isolate your electronics from the 40V and also from the 90VAC ringer voltage. And, be careful when touching the wires because if a call comes-in, the 90V ring voltage can be "unpleasant".
[u]Here[/u] are some devices for tapping-into the audio signals.
You'll probably need a preamp and you might want to try recording some "normal" audio first, such the line-output from a CD/DVD player or the line/headphone output from your computer etc.
DVDdoug:
There is about 40VDC on the phone line when the phone is on-hook and that voltage drops when off-hook so you should be able to detect that voltage change.You need to protect/isolate your electronics from the 40V and also from the 90VAC ringer voltage. And, be careful when touching the wires because if a call comes-in, the 90V ring voltage can be "unpleasant".
[u]Here[/u] are some devices for tapping-into the audio signals.
You'll probably need a preamp and you might want to try recording some "normal" audio first, such the line-output from a CD/DVD player or the line/headphone output from your computer etc.
Thanks. Earlier we used induction coil mic.
Since i'm newbie in electronics and Arduino, i would like to find ready project. I have no idea how to "protect/isolate your electronics from the 40V and 90V" etc. Thanks
Not Arduino related but if your UK based then truecall might be your answer. It can be set to record all phone calls or the option I use is to press a button to record the current call. The nice thing about pressing the button is it does not just start recording from that point but will record the entire phone conversation from the beginning. Handy if something important is said as you can press record and go back later and review the entire call.