Telephone Call Recorder

Posted on Feb 7, 2014

Today phone has become an integral part of our lives. It is the most widely used communication tool in the world. Owing to its immense popularity & widespread use, there arises a necessity for call recording devices, which find application in call cent-res, stock broking firms, police, offices, homes, etc. Here they are describing a call recorder

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that makes use of only a few parts. But in order to understand its working, must first have the basic knowledge of standard phone wiring as well as a stereo plug. In India, land-line rings primarily use RJ11 wiring, which has wireless-tip & ring. While tip is the positive wire, ring is the negative. & together they complete the phone circuit. In a phone line, voltage between tip & ring is around 48V DC when handset is on the cradle(idle line). In order to ring the phone for an incoming call, a 20Hz AC current of around 90V is superimposed over the DC voltage already present in the idle line. The negative wire from the phone line goes to IN1, while the positive wire goes to IN2. Further, the negative wire from OUT1 & the positive wire from OUT2 are connected to the phone. All the resistors used are 0. 25W carbon film resistors & all the capacitors used are rated for 250V. The negative terminal of To AUX IN is connected to pin one of the stereo jack while the positive terminal is connected to pins two and three of the stereo jack. This stereo jack, in turn, is connected to the AUX IN of any recording tool, such as computer, audio cas-setts player, CD player, DVD player, etc. Here they shall be connecting it to a computer. When a call comes in, around 90V AC current at 20Hz is superimposed over the DC voltage already present in the idle line. This current is converted in to DC by the diodes & fed to resistor R1, which reduces...

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