Code exit to intercity. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Code exit to intercity. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Telephony

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A circuit based on a MICROCHIP PIC12F629 microcontroller is proposed - a code output device for intercity and mobile digital communications.

The long distance coded exit device is intended for long distance coded exit and mobile digital communication from telephones with pulse dialing, as well as blocking dialing from a telephone that is pirated connected in parallel to a telephone line. The device does not affect the operation of the telephone when dialing a number and conducting urban telephone conversations. The code access device is not designed to work on telephone lines with paired telephones.

The electrical circuit diagram of the device is shown in fig. one.

Code exit to intercity. circuit diagram
Ris.1.

The layout of the elements is shown in fig. 2, and the printed circuit board - in fig. 3.

Code exit to intercity. Layout of elements
Ris.2.

Code exit to intercity. Printed circuit board
Ris.3.

PCB dimensions - 45x23 mm. The printed circuit board of the long distance coded output device is located in the telephone socket housing.

The coded access device is based on the PIC12F629 microcontroller from MICROCHIP with non-volatile memory. The presence of non-volatile memory allows you to save the current access codes and device status, program new codes: - long-distance exit; - disable/enable the code output to long distance; - entering the access code programming mode.

To access the long distance, you need to pick up the handset, sequentially, starting from the highest digit, dial the four-digit access code XXXX and, after 1 ... 1,5 seconds, when a telephone line tone appears, start dialing the long distance number or mobile phone number. This operation must be done every time you try to go through the number "8" to intercity or mobile communications. When attempting to directly dial a long distance or mobile number, the code exit device will block dialing pulses.

There is a code for disabling the function of the code exit to long distance. To do this, pick up the handset and dial another code: YYYY. Exit from the coded access mode to intercity is confirmed by a double beep. After that, the device does not further affect the dialing of long-distance and mobile phone numbers.

To enable the function of the coded exit to long distance, it is necessary to dial the previous code YYYY while lifting the handset. Entry into the mode of code exit to long distance is confirmed by a short beep.

If it becomes necessary to change the access codes, dial another code 7777 with the handset raised and, after a long beep, dial one of the following code combinations:

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хххх 1 - new intercity exit code;

yyyy 5 - a new code for enabling/disabling the coded exit to long distance;

zzzz 9 - a new code for entering the access code programming mode.

Here xxxx, yuuu, zzzz are four-digit access codes. The entry of a new access code is confirmed by a long beep.

If the last dialed digits do not match the above or the handset is on the phone, the device exits the programming mode without changing the access codes and beep.

The initial access codes recorded in the microcontroller memory are as follows:

2111 - exit to intercity;

2115 - enable/disable the coded output to long distance;

2119 - programming access codes.

As for blocking a phone pirated to the telephone line, there are some peculiarities here. Pulse dialing from imported phones and from phones with an electronic dialer is confidently blocked. The situation is somewhat worse if the pirate phone is a domestic telephone with rotary dialing. This is due to the fact that the circuitry of foreign telephones is somewhat different from that adopted in our country. You can read more about this in [1].

When connecting this device to the telephone network, it is necessary to observe the connection polarity indicated in Fig. 1. If the connection to the telephone network is incorrect, the device will not work.

The ratings and types of elements are shown in fig. 1. Instead of the zener diode VD1 KS106A, you can use KS106B. The DD1 PIC12F629 microcontroller is mounted on an 8-pin socket. You can install on such panels and a current stabilizer DA1 KZh101A and a zener diode VD1 KS106A. Quartz ZQ1 at 32768 Hz clock type. Transistors VT1 and VT2 only types KP504A, KP504B.

After mounting the elements on the printed circuit board and checking the work done, the device can be connected through a resistor with a resistance of 470 ... 1000 Ohm with a power of 1 ... 2 W to a voltage source of 50 ... 60 V, and a telephone can be connected to the output of the device. The voltage at the pins of the microcontroller DD1 must be within 2,9 ... 3,5 V, both with the handset on and off.

Next, you need to measure the current consumption of the device from the telephone line with a microammeter, after disconnecting the phone from the coded access device.

If the current value lies within 190 ... 210 μA, then everything is fine. If the current is less than this value, then it is necessary to slightly increase the resistance R1, if the current is greater, reduce the resistance R1 or even short-circuit it.

If there is an oscilloscope, check them for the presence of pulses with a frequency of 32768 Hz at pin 3 of the DD1 microcontroller with the handset up. If they are absent, then you can try to swap the quartz leads. If pulses do not appear, replace the ZQ1 quartz.

In the absence of an oscilloscope, the operability of the code output device with a connected telephone and a lifted handset can be checked by dialing the code to enable / disable the long distance code output. In this case, in the handset, with a working device and with a correct connection to the telephone line, a single or double beep will be heard. This operation can be done periodically to control the operability of the intercity code exit device, not forgetting to return to the previously set state.

On the basis of the program of operation of the intercity coded exit device and the diagram in Fig. 1, devices with other useful functions can be assembled, for example:

periodic monitoring of the telephone line during a telephone conversation for the presence of a pirate telephone with a corresponding sound alarm when the fact of eavesdropping is detected;

limiting the time of talking on the phone with the possibility of programming the duration of the conversation;

blocking access to intercity from departmental telephone exchanges (when accessing the city telephone network through an additional digit);

dialing a city telephone number using a two-four-digit code to protect against radiotelephone pirates (if there is a radiotelephone in the house);

enabling / disabling the specified functions by individual access codes.

For advice on the operation of the coded access device scheme for intercity and with your wishes and suggestions, contact the author of the article.

Literature

Kizlyuk A.I. Handbook on the device and repair of telephone sets of foreign and domestic production.- M .: Biblio, 1995.

Author: N. Kupreev, Minsk; Publication: radioradar.net

See other articles Section Telephony.

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