Phone interface. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Telephony
Comments on the article
We propose another one compared to that published in [1]. telephone interface option. It is designed to connect a simplex radio station to a telephone line.
This scheme uses a mixed control algorithm. The radio base station is switched on for transmission when the carrier or CTSS signal disappears, and switched off at the end of the PBX subscriber's phrase (voice control system). Such an algorithm can significantly reduce the loss of information from the subscriber on the part of the PBX, which is characteristic of systems that work only with a voice key with a delay.
This scheme has the following features:
- individual access code;
- saving in the memory of the last dialed number;
- control of presence of speech of the subscriber of automatic telephone exchange;
- provision of a fixed time interval to the subscriber by the PBX (in case of a poor-quality signal in the telephone line, which does not allow the voice presence control system to work);
- protection of the line from "hangup", shutdown in case of "loss" of the radio subscriber;
- work in the modes of pulse and tone dialing TONE/PULSE;
- user programming interface modes; - work with the dispatcher.
(click to enlarge)
The radio subscriber controls the interface using a DTMF keyboard. in its absence, a beeper can be used.
The use of standard DTMF codes made it possible to abandon the mobile part of the interface.
The interface is controlled by the PIC controller D3. The PIC16C84 chip has a non-volatile memory. This memory stores the operating modes of the interface. Programming of modes is carried out from a mobile radio station using DTMF codes.
The user can also change the access code to his interface.
D2 decoder is used to process DTMF codes. The MT3270BE chip can process the signal incoming to it in a wide dynamic range (50 dB).
To control the presence of the voice of a PBX subscriber, it is necessary to analyze the signal in the telephone line. For this, a comparator is assembled on the elements of the D4 chip. It also processes the PBX call signal.
Relay K1 is used to switch the signal coming from the telephone line to the microphone input of the radio station, or from the radio station to the telephone line. The signal from the radio station is fed to an amplifier assembled on a D 1 chip. Galvanic isolation from the telephone line is made on a T1 transformer. Relay K2 is used to seize the line and dial.
You can purchase customized boards or finished products from the authors of the article.
Literature
1. Kotov V. Golovko A. Telephone interface. - Radio amateur, 1997, No. 2, p.18.
Authors: V.Kotov, A.Golovko, Ukraine, Donetsk region, Maryinka; Publication: N. Bolshakov, rf.atnn.ru
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