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[on:]

Hello friends
I'd like to connect the entry phone of the office I'm working to a PC to let everybody hear who is ringing, reply and open the door without moving from the desk.
The buzzer/door relay part is controlled by Arduino of course, using optocouplers.
The big question is, how to connect the audio lines to the PC sound card without frying it?
I know the buzzer works at 12V AC, but don't know if it's the same on the audio signal. What kind of measurement should I make? Screaming to the phone and take the highest voltage?  

[Reply #1 on:]

Very boring idea, I know... but wouldn't it be as good, and not risk your PC, to connect the entry phone to a simple set of PC-type externam speakers, one of the speaker sets with a built in amplifier?

If not as good, than I haven't understood your question.

[Reply #2 on:]

Thank you Tkbyd for the reply
It's the first idea I've come up with... but it works only if the office it's an open space. Unfortunately there are a few rooms you couldn't hear the speakers, plus you have the problem to connect them to a relay with a timer otherwise you hear street noise all the time.

My idea is to send an alarm to all the clients when the Arduino senses the buzzer, and broadcast the audio via software (Windows Media Server I think) digitalized by the server audio card. But I don't want to fry the audio card or, worse, the server!  

[Reply #3 on:]

Hello,
Did you make any progress on that project ?
I want to do more or less the same.
Another solution to get the audio to the computer could be to connect the entry phone to a PBX like Asterisk. In my case i must deal with an old entry phone so it will need some work, but VoIP entry phones exists.
Also, PBX opens new possibilities ...

[Reply #4 on:]

I might be wrong but I thought PC sound cards are only +-1V AC max. You'll damage your PC if you pass 12V AC. Maybe you can easily get away with a voltage divider. Say you have a 10K and 10K potentiometer in series between the speaker lines, turn the pot to 0 and hook it to pc and have someone scream and watch the audio level while you turn up the pot. Turn it up till the volume on your PC is about max and set it there. Tape it down so curious cats won't be able to change it with their paws.