Device for checking telephone sets. Scheme, description

Free technical library

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

Device for checking telephone sets. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Telephony

Comments on the article

If the operability of the telephone set is in doubt, you can, of course, "dig into" it without disconnecting it from the subscriber line and using the signals supplied by the automatic telephone exchange to check the nodes of the device. But this raises a number of problems. Many modern PBXs block the line if dialing is not started within a minute after picking up the handset, and the frequent repetition of this situation may cause claims from the technical services of the station. And with the introduction of time-based payment for calls, it can be very expensive to occupy a line for a long time to check and repair the device. The proposed device will help to find and troubleshoot the telephone without connecting it to the oval line.

The device imitates the signals supplied by the PBX to the subscriber line, with the exception of those generated by the subscriber number identification equipment. The only significant difference is the ringing frequency of 50 Hz instead of the standard 25 Hz, but, as practice shows, this does not matter for the ringing devices of the vast majority of telephone sets. The sound only becomes sharper.

The scheme of the main unit of the device is shown in fig. 1. To power the device under test A1, the rectified voltage of the winding III.2 of the transformer T1 is used. It is stabilized by a 56 V zener diode (VD7). The voltage enters the circuit of the apparatus through the inductor L1, which can be used as a coil of any relay with a resistance of 500 ... 700 Ohms. If the inductor winding has a lower resistance, a resistor of the appropriate rating and power must be connected in series with it.

Device for checking telephone sets
Fig. 1

When you pick up the handset, the direct current flowing through the device A1 (about 35 mA) will create a voltage drop across the resistor R4 sufficient to open the transistor VT2. The current value can be controlled according to the readings of the PA1 milliammeter, the scale of which must be calibrated accordingly. Diode VD1 protects the milliammeter and the base circuit of the transistor VT2 from a negative polarity voltage that appears on the resistor R4 when a ringing signal is applied to the phone.

Approximately 1 s after the transistor VT2 opens (the delay is provided by the R10C8 circuit), the signal generator with a frequency of 425 Hz is allowed to operate on the elements DD1.3 and DD1.4. If switch SA2 is in the lower (according to the scheme) position, this signal, amplified by transistors VT3 and VT4, goes to device A1 and should be heard in its tube.

To check the microphone and related components of the telephone set, switch SA2 to the upper (according to the diagram) position. Everything that is said into the phone should be heard in the dynamic head BA1. The volume is regulated by a variable resistor R9.

Since the voltage level at the output of the DD1.2 element is low when the handset is off, the transistor VT1 is closed and the open contacts of the relay K1 do not make it possible, by pressing the SB1 button, to send a ringing signal to the telephone set from winding III of the transformer T1. This possibility appears only when the tube lies on the place of the device intended for it, when its DC circuit is open and the transistor VT2 is closed.

The power supply unit of the device consists of a bridge voltage rectifier of the winding II of the transformer T3 assembled on diodes VD6-VD1 and an integral stabilizer DA1.

KT315B transistors can be replaced by others of the same series or KT201, KT3102 series and other low-power np-p structures. A replacement for the KT940A transistor should be selected from among the high-voltage ones, since the voltage between its collector and base reaches 180 V when the ringing signal is given. Suitable, for example, transistors KT504A-KT504V, KT969A, as well as imported MPSA-42.

The K157UD1 operational amplifier can be replaced by any 34 power amplifier chip capable of delivering 9 ... 0,5 W to the load at a supply voltage of 1 V. It must be enabled according to the standard scheme. Dynamic head VA1 - GD-0,5 with a resistance of 8 ohms.

Relay K1 - RES-15, passport RS4.591.003. It can be replaced by another small-sized one that reliably operates at a voltage of 9 V, for example, RES-60, version RS4.569.435-02. Instead of a RA1 milliammeter with a total deviation current of 1 mA, a more sensitive device, a microammeter, is also suitable. You just need to choose the right resistor R2.

If necessary, you can supplement the device with nodes that allow you to check the correct operation of the dialer of the telephone set. To check the pulse dialer, you need a node according to the diagram shown in fig. 2. It is connected to the points B, C and D shown in the main unit diagram (Fig. 1).

The counter DD1 (Fig. 2) receives pulses that occur at point B during dialing. With a working dialer, the number on the HG1 indicator at the end of the corresponding series of pulses should become equal to the dialed one. Do not forget only, before dialing the next digit, set the counter to its original state by pressing the SB1 button. This state corresponds to zero on the indicator HG1.

Device for checking telephone sets
Fig. 2

It should be borne in mind that the load capacity of the outputs of the K176IE4 (DD1) microcircuit is small. To connect to it a less sensitive LED indicator than AL304G, additional amplifiers may be required.

Device for checking telephone sets
Fig. 3

The scheme of the tone dialer test node connected to points A, C and D of the main unit is shown in fig. 3. It is built on a specialized microcircuit KR1008VZH18 (DA1) included according to the standard scheme - a receiver-decoder of the DTMF format signal generated by such a dialer. The code of the dialed digit appears in binary form at the outputs Q1-Q4 of this chip and, after conversion by the DD1 chip, is displayed on the seven-element LED indicator HG1. During signal reception, the HL1 LED is on. The output current of the KR514ID1 code converter is limited by its internal circuits to 5 mA. Therefore, the ALS314A indicator indicated in the diagram can only be replaced by such a seven-element LED with a common cathode, for which this current is sufficient.

A 3,58 MHz quartz resonator is available on touch-tone telephones and NTSC color televisions.

Author: R. Ershov, pos. Krasnolesny, Voronezh region; Publication: radioradar.net

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

Dual core processors 23.03.2005

Intel Corporation announced the beginning of the era of dual-core processors. The first processors of this series are Intel Pentium Processor Extreme Edition 840 with a frequency of 3,2 GHz and Intel 955X Express Chipset.

This platform benefits users in the areas of high-definition television, high-quality sound and XNUMXD visualization. Two (or more) processor cores work simultaneously, which dramatically increases work efficiency.

Other interesting news:

▪ Where there are more computers and the Internet

▪ Scientists Prove Nietzsche Right

▪ Habits change the brain

▪ Electromagnetic generator operating without fuel

▪ Three-layer graphene improves superconductivity at room temperature

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Indicators, sensors, detectors. Article selection

▪ article Single-row mechanical seeder. Drawing, description

▪ Article What does hair dryer mean? Detailed answer

▪ article Selector of reference and informational material. Job description

▪ article Call indicator. Encyclopedia of radio electronics and electrical engineering

▪ article Inscription on metal. Chemical experience

Leave your comment on this article:

All languages of this page

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