Dual phone line auto recorder

Many times exists the need recording some conversations from a telephone line and this it's relatively easy. If we want however to have the possibility recording from two telephone lines simultaneously in a tape recorder, we needed a circuit as what appears in the Fig.1. The circuit stimulates when earphone from a telephone unit is raised, beginning simultaneously and the recording, from the one or from two telephone lines. At the same time it gives the voltage that needs the tape recorder it work also him it stops as we lower also the two earphones. If somebody of the earphones is raised, then recording is continued regularly. The power supply of circuit can become from external power pack, that will have the possibility to give at least + 16V DC in his output.
Dual phone line auto recorder - schematic

The IC4 supply the circuit and relay with + 12V and the IC5 with the TR1 can be regulated so as to it gives in the exit his essential voltage that the tape recorder needs to works, usually + 3V DC. The IC4 should be placed on heatsink. The two resistors R17-18 are essential so that they throw the voltage in the input of IC5 in lower levels, so that it's produced as long as the possible least heat than the IC5. Their value can change so that it matching in your data. The input and output for the telephone lines becomes from the connectors J1-2, follows two switches S1-2 with which we have the possibility is isolated the circuit from the lines, so that we do not have excitation of circuit each time where we will raise the earphone of telephone unit. It can they are suppressed if it's judged that them you don't need. The circuit round the optical optocoupler IC1-3 ensures the isolation of lines from the remainder circuit and in collaboration with the IC2 drive the two relay RL1-2, which the contacts give the supply voltage command in the tape recorder, of also recording. If the supply of tape recorder becomes from batteries and exist input ''Remote in'', then we can modify the circuit as appear in the Fig.2. Capacitors C1-6 prevents the circuit stimulate when in the line they exist the ringing pulses. The diodes led D4-9 give an optical clue if and who line has turn on. The sound of telephones from the telephone isolation...

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