Three phone locks. Scheme, description

Free technical library

ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
Free library / Schemes of radio-electronic and electrical devices

Three phone locks. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Telephony

Comments on the article

Since we are not threatened with widespread telephone installation in the near future, some of our compatriots have learned to solve their problems at the expense of their neighbors. Having connected to other people's telephone lines, they call wherever they want. Those who have been the victim of such piracy know how frustrating it is to receive unexpectedly increased phone bills. Of course, you can put a caller ID phone with line protection functions from unauthorized access. But such devices are quite expensive, and the telephone exchange requires additional payment for using them.

The most optimal in this situation is the use of special locks-locks. Unlike conventional blockers [1], these devices perform the function of a kind of "barn" lock on the telephone line, making it impossible to dial the number correctly into the line, and the passage of the ringing signal. Such devices do not interfere with the normal operation of telephone exchanges.

The scheme of the simplest lock is shown in fig. 1. In the initial state, the capacitor C2 is not charged, and the transistor VT1 is locked. When an alternating voltage occurs in the telephone line (dialing or calling the PBX), the voltage of the charged capacitor C2 opens the transistor VT1, and the telephone line closes for a short time.

Three phone locks
Fig. 1

The charge of the capacitor C2 stops, and it is discharged through the resistor R2. Transistor VT1 closes. The telephone line remains open until the next pulses. The disadvantage of such a lock is that when it is connected to a telephone line, polarity is required.

The scheme presented in Fig. 2 contains more details, but is spared from the above drawback.

Three phone locks
pic.2

In life, it is not always necessary to "extinguish" the ringing signal from the PBX. More often it is required to "spoil" only dialing. The locks shown in Figs. 1 and 2 do not make such a selection. A more perfect lock is shown in Fig.3. It is powered from the telephone line through the resistor R8 and consumes no more than 0,1 mA from the line in standby mode. Zener diode VD3 - parametric voltage stabilizer. The voltage pulses that occur in the telephone line when dialing a number or when ringing from the PBX, through the cascade on the transistor VT2, are fed to the clock input C (pin 14) of the DD2 microcircuit. After five pulses, a high level appears at pin 1 of the DD2 microcircuit, the transistor VT3 opens, and the telephone line is blocked. At the same time, this high level is applied to the enable account input DD2 (pin 13) and prohibits further counting. Logic level "1" at the input of the element DD1.1 after double inversion causes the output of the element DD1.2 voltage high level. Capacitor C1 begins to slowly charge through resistor R7, and after about 1 s a high level at the input of element DD1.3 causes a single level signal to appear at the input R of the DD2 chip. The counter is reset, the transistor VT3 turns off, the circuit returns to its original state.

(click to enlarge)

The cascade on the transistor VT1 responds only to the ringing signal from the PBX and serves to prohibit the operation of the "lock" from the call signal. The low voltage level taken from the VT1 drain, applied to pin 6 of DD1.4, causes a high level to appear at the R input of the DD2 chip, i.e. the counter is kept in its original state. The user can disable or allow the call signal from the PBX using switch S1. Switch S2 is used to disable the operation of the entire device when the owner of the telephone line himself needs to dial a number.

The only timing circuit R7, C1, VD1 performs two functions:

- determines the line blocking time when the "lock" is turned on;

- in standby mode, forcibly sets the counter DD2 to its original state.

Chip DD1 can be replaced by K561LA7. Transistors VT1, VT2 can be with any letter - A, B, C, but the transistor VT3 - only with the letter A. The light indication of the inclusion of locks can also be supplemented with sound.

Figure 4 shows a sound generator made on a 1554 series chip (similar to 74AC00N). Unlike the 561 series, the microcircuits of the above series are operational at a supply voltage of 2 V.

Three phone locks
pic.4

The piezoelectric BQ1 is connected in a bridge circuit. The generator is powered by the voltage released on the LED, i.e. the outputs "Power" and "Common" DD1 are connected to the anode and cathode of the LED in any of the lock circuits.

Literature

Kizlyuk A. Handbook on the device and repair of telephone sets of foreign and domestic production. - M., 1997.
Yankovsky S. Telephone watchman. - RadioAmator, 1996, No. 7, p.5.

Author: A. Mikhalevich, Minsk; Publication: N. Bolshakov, rf.atnn.ru

See other articles Section Telephony.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Artificial leather for touch emulation 15.04.2024

In a modern technology world where distance is becoming increasingly commonplace, maintaining connection and a sense of closeness is important. Recent developments in artificial skin by German scientists from Saarland University represent a new era in virtual interactions. German researchers from Saarland University have developed ultra-thin films that can transmit the sensation of touch over a distance. This cutting-edge technology provides new opportunities for virtual communication, especially for those who find themselves far from their loved ones. The ultra-thin films developed by the researchers, just 50 micrometers thick, can be integrated into textiles and worn like a second skin. These films act as sensors that recognize tactile signals from mom or dad, and as actuators that transmit these movements to the baby. Parents' touch to the fabric activates sensors that react to pressure and deform the ultra-thin film. This ... >>

Petgugu Global cat litter 15.04.2024

Taking care of pets can often be a challenge, especially when it comes to keeping your home clean. A new interesting solution from the Petgugu Global startup has been presented, which will make life easier for cat owners and help them keep their home perfectly clean and tidy. Startup Petgugu Global has unveiled a unique cat toilet that can automatically flush feces, keeping your home clean and fresh. This innovative device is equipped with various smart sensors that monitor your pet's toilet activity and activate to automatically clean after use. The device connects to the sewer system and ensures efficient waste removal without the need for intervention from the owner. Additionally, the toilet has a large flushable storage capacity, making it ideal for multi-cat households. The Petgugu cat litter bowl is designed for use with water-soluble litters and offers a range of additional ... >>

The attractiveness of caring men 14.04.2024

The stereotype that women prefer "bad boys" has long been widespread. However, recent research conducted by British scientists from Monash University offers a new perspective on this issue. They looked at how women responded to men's emotional responsibility and willingness to help others. The study's findings could change our understanding of what makes men attractive to women. A study conducted by scientists from Monash University leads to new findings about men's attractiveness to women. In the experiment, women were shown photographs of men with brief stories about their behavior in various situations, including their reaction to an encounter with a homeless person. Some of the men ignored the homeless man, while others helped him, such as buying him food. A study found that men who showed empathy and kindness were more attractive to women compared to men who showed empathy and kindness. ... >>

Random news from the Archive

Huawei's fastest smartphone 02.03.2013

Huawei Device Company introduced the world's fastest smartphone, as the manufacturer himself called it.

The Ascend P2 model is equipped with a 4 GHz quad-core processor, a 1,5-inch display with a resolution of 4,7 x 1280 pixels, a 720-megapixel camera, a 13 mAh battery and runs on Android 2420.
Android 4.1 is considered the fastest because it supports LTE Cat4 with data transfer rates up to 150 Mbps. This is the only mobile phone on the market that supports this speed, notes Engadget.

Buy Huawei Ascend P2 in Europe will be available from the II quarter of 2013 at a price of 399 euros.

Other interesting news:

▪ Apex Storage X21 AIC Adapter

▪ Transistors of the MDMESH V family

▪ Music from the machine

▪ Hereditary obesity is not always determined by genes

▪ Wireless BLE sensor STEVAL-BCN002V1B

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the website Audiotechnics. Article selection

▪ article Art starts with a little bit. Popular expression

▪ article Where did the first watermelons appear? Detailed answer

▪ article Technological tank handler. Standard instruction on labor protection

▪ article Lubricant used when cutting screws. Simple recipes and tips

▪ article Pencil and book. physical experiment

Leave your comment on this article:

All languages of this page

Home page | Library | Articles | Website map | Site Reviews