The adapters are designed for automatic recording of signals from the telephone line and are complete with tape recorders. The composition of the adapters includes a node matching the polarity and level of the input signal and the threshold-switching device. The node matching the polarity and level of the input signal (Fig.1...3) is made on the basis of the diode-bridge circuit and a resistive voltage divider.
Use this node allows you to connect the adapters to a telephone line with the wrong polarity. Threshold-switching device (PKU) provides load control when you change the level of the input control signal (line voltage). The load can be used: the motor of the tape recorder, relay, optocoupler led pairs, incandescent, etc., This device operates in binary mode, if the input device is a logical '1'", i.e. the handset is based on, the voltage on the telephone line nominal (60 In) - the load is de-energized. Once at the entrance of natural grasslands appears logical "0" (off-hook, the voltage on the line 12 In), the load is activated, and automatically record information. In the first scheme of natural grasslands (Fig. 1) used a composite transistor VT1, VT2. When the logic level "1" at the input, the voltage taken from the resistive divider R1, R2, through the diode VD5 is supplied to the power bus. On the control junction of transistor VT1 is set the locking voltage (+0.7 V), and the load is switched off. When the input circuit is supplied to a logical "O", to the base of transistor VT1 is supplied gate trigger voltage, the load is energized. The load current is determined by the type of transistor VT2 (30...100 mA). Another variant PKU (Fig.2) is made on the basis of the comparator (IC DA1 CSS), the threshold of which is set by the resistor R4.
The load current of the device can reach 150...200 mA. Another scheme of natural grasslands (Fig.3) collected on a CMOS switch (micro circuit DA1 CCT). Unused keys switch connected in parallel are involved.
The load current of the output transistor can be hundreds of milliamps. The signal is "on record" is connected to a tape recorder. The tape should work in record mode. As a recording device, it is desirable to use a tape recorder having an automatic adjustment of the recording level and reliable tape drive mechanism, precluding glossing over of the tape. To protect the input circuits of adapters from accidental surge type lightning discharges at the input device, it is desirable to install overvoltage arresters voltage of about 200 V.
Author: M. Shustov, Tomsk; Publication: N. Bolshakov, rf.atnn.ru