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persianboy62

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Hi,
I started a new project and I'm going to make a system as shown bellow. I have a problem in "Sound Generator" unit. In this unit I use "ISD25120" to record and play back the sound. I want to know how can I modulate the output of "ISD25120" and send the output over the phone line.
(Each slave units (Remote Object1 and Remote Object2) is working special tasks such as scale and controlling temprature, Controlling the lights, etc.)
 

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Not sure what you mean by modulate. But try to google pabx trunk schematics.

That should get you to a phone interface circuit that will grab the phone line, the amp to put the sound on the phone line as well as protection from the 90VRMS ring voltage if someone calls your unit, and a DTMF generator to dial the digits.

I assume the unit is to call out?
 
The phone line is current operated, so you just need a DC blocking capacitor and current limiting resistor (and protection from the ring voltage, as mentioned before). I assume you know how to get the phone "off hook"?
 
Here's a site with lots of info about using the phone lines.

**broken link removed**

I wrote this January of 2004. It was meant to mostly discuss using modems, but if you get the isolator circuit mentioned, you can introduce audio devices (speech chips, modems, tape recorders, etc.) as well. It was designed specifically fo rusing a PIC driven circuit, but there are bare essentials in this tohelp in many ways.
Whatever you do, DO NOT just connect a cap and resistor to the phone lines. Besides being dangerous, it's illegal. You'll understand when you get to the part about jail time and stiff fines.

Hope you find this helpful,
kenjj
 
Yes, homebrew circuits to the phone line are illegal in the US. The FCC governs & qualifies what can be connected. Several companies have done this work for you by having their products registered or certified with the FCC. You will pay more for this but it will be legal if you use them.

One such company is here:

**broken link removed**

Look in the catalog for DAA devices. Gives you all the phone control you need, is protected from faults & lightning etc.. and is FCC friendly.
 
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