Telephone adapters for auto-recording of information. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Telephone adapters for auto-recording of information. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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Adapters are designed for automatic recording of signals from a telephone line and work in conjunction with tape recorders. The adapters include a node for matching the polarity and level of the input signal and a threshold-switching device. The node for matching the polarity and level of the input signal (Fig.1...3) is made on the basis of a diode-bridge circuit and a resistive voltage divider.

(click to enlarge)

Using this node allows you to connect adapters to a telephone line without observing polarity. The threshold-switching device (PKU) provides load control when the level of the input control signal (line voltage) changes. The following can be used as a load: an electric motor of a tape recorder, a relay, an LED of an optocoupler, an incandescent lamp, etc. This device operates in binary mode, if the input of the device is logical '1'", i.e. the phone is on-hook, the voltage in the telephone line is nominal (60 V) - the load is de-energized. As soon as the logical "0" appears at the PKU input ( the tube is removed, the voltage on the line is about 12 V), the load is turned on, and information is automatically recorded. In the first PKU circuit (Fig. 1), a composite transistor VT1, VT2 is used. divider R1, R1, through the diode VD2 is fed to the power bus.A blocking voltage (+5 V) is set at the control junction of the transistor VT1, and the load is turned off. , the load turns on. The load current is determined by the type of transistor VT0,7 (0 ... 1 mA). Another version of the PKU (Fig. 2) is based on a comparator (IC DA30 K100SAZ), the threshold of which is set by resistor R2.

(click to enlarge)

The load current of the device can reach 150...200 mA. Another PKU circuit (Fig. 3) is assembled on a CMOS switch (microcircuit DA1 K176KT1). Unused switch keys are connected in parallel with those involved.

(click to enlarge)

The output transistor load current can be hundreds of milliamps. The signal "to record" is connected to the input of the tape recorder. The tape recorder must be in record mode. As a recording device, it is desirable to use a tape recorder that has automatic recording level control and a reliable tape drive mechanism that prevents jamming of the tape. To protect the input circuits of the adapters from random surges such as lightning discharges at the input of the device, it is advisable to install arresters for a voltage of about 200 V.

Author: M. Shustov, Tomsk; Publication: N. Bolshakov, rf.atnn.ru

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