Telephone Call Recorder

Today cellphone has turn out to be a vital part of our are livings. It is the most broadly used communication device in the world. Owing to its large popularity & popular use, there come ups a necessity for name recording units, which find software in call cent-res, inventory broking companies, police, administrative centers, homes, and so forth. Here they are describing a name recorder that makes use of only some sections. But in an effort to keep in mind its working, should first have the elemental information of usual cellphone wiring in addition to a stereo plug.

In India, land-line rings primarily use RJ11 wiring, which has wires-tip and ring. While tip is the positive wire, ring is the poor. And collectively they full the phone circuit. In a cellphone line, voltage between tip and ring is round 48V DC when handset is on the cradle(idle line). In order to ring the phone for an incoming name, a 20Hz AC current of round 90V is superimposed over the DC voltage already current within the idle line. The bad wire from the cellphone line goes to IN1, whereas the certain wire goes to IN2. Further, the negative wire from OUT1 and the certain wire from OUT2 are linked to the phone. All the resistors used are zero.25W carbon film resistors and the entire capacitors used are rated for 250V or more.

Read More..

Telephone Conversation recorder

This circuit enables  automatic switching-on  of  the  tape  recorder  when  the  handset  is  lifted.  The tape recorder gets switched off when the handset is replaced. The signals are suit-ably  attenuated  to  a  level  at  which  they can be recorded using the MICIN socket of the tape recorder. Points X and Y in the circuit are connected to the telephone lines. Resistors R1 and R2 act as a voltage divider.

The voltage appearing across R2 is fed to the MIC-IN socket of the tape recorder. The values of R1 and R2 may be changed depending on the input impedance of the tape recorders MIC-IN  terminals.  Capacitor C1 is used for blocking the flow of DC. The second part of the circuit controls relay RL1, which is used to switch on/off the tape recorder.A  voltage  of  48  volts  appears across  the  telephone  lines  in on-hook  condition. This  voltage drops  to  about  9  volts  when  the handset  is  lifted.  Diodes  D1 through  D4  constitute  a  bridge rectifier/polarity  guard. 

Telephone Conversation recorder Circuit Diagram

This ensures that transistor T1 gets voltage of proper polarity, irrespective of the polarity of the telephone lines.During on-hook condition, the output from the bridge (48V DC) passes through 12V zener D5 and is applied to the base of transistor T1 via the voltage divider comprising resistors R3 and R4. This switches on transistor T1 and its collector is pulled low. This, in turn, causes transistor T2 to cut off and relay RL1 is not energised. When the telephone handset is lifted, the voltage across points X and Y falls below 12 volts and so zener diode D5 does not conduct.

As a result, base of transistor  T1  is  pulled  to  ground  potential  via resistor R4 and thus is cut off. Thus, base of  transistor  T2  gets  forward  biased  via resistor R5, which results in the energisation  of  relay  RL1. The  tape  recorder  is switched on and recording begins. The tape recorder should be kept loaded with a cassette and the record button of the tape recorder should remain pressed to enable it to record  the conversation as soon as the handset is lifted. Capacitor  C2  ensures  that  the  re-lay is not switched on-and-off repeatedly when a number is being dialled in pulse dialling mode

Read More..