External microphone powered from the communication line. Scheme, description

Free technical library

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

External microphone powered from the communication line. Encyclopedia of radio electronics and electrical engineering

Free technical library

Encyclopedia of radio electronics and electrical engineering / Microphones, radio microphones

Comments on the article

Remote transmission of information is possible using wired communication lines that connect an external sensitive microphone and a final amplifier. Since the output signal taken directly from the microphone has a small amplitude, it is simply impractical to transmit it over the communication line. This is due to the fact that on long connecting wires, various kinds of interference with a significant amplitude are induced. To transmit a signal through these wires, it must be amplified to some extent. To amplify the signal, a sensitive microphone amplifier is used, located in close proximity to the microphone. The power supply of such an amplifier is carried out through the wires of the communication line.

The device uses a dynamic or electromagnetic microphone. The voltage gain of the amplifier is about 3500. Signal transmission can be carried out over tens and hundreds of meters.

(click to enlarge)

The signal from the microphone M1 is fed to an amplifier assembled on transistors VT1, VT2 and VT3. A negative voltage feedback is introduced between the output and input of the amplifier, formed by resistors R1, R2, R3 and capacitor C1. In this case, the initial current flowing through the amplifier along the circuit plus the power supply, resistor R7, is constant and depends on the voltage of the power supply and the resistance of the load resistor R7. The signal amplified by the amplifier causes a change in the output current of the amplifier, which results in a change in voltage across the load. This voltage is supplied to the audio frequency amplifier through capacitor C2. Any audio frequency amplifier can be used. Resistor R6 is needed to match the internal resistance of the microphone amplifier with the resistance of the communication line. The VD1 rectifier bridge of the KTs407 type is necessary to prevent the device from failure due to an erroneous connection of the power source. Transistor VT4, connected according to the "analogue" circuit of the zener diode, prevents voltage surges on the amplifier at the moment the power is connected. In addition, it allows you to get a symmetrical clipping of the output signal when the amplifier is overloaded, which eliminates the appearance of even harmonics, which are especially unpleasant for auditory perception.

The device uses resistors of the MLT-0,125 type (except for R6 and R7). Transistors VT1, VT4 can be of the type KT315, KT312, KT201, KT342, KT3102. Transistor VT2 - KT361, KT345, KT3107. Transistor VT3 - KT608, KT603, KT630, KT626, KT940. The diode bridge VD1 can be replaced by four diodes of the type KD102, KD103.

The setting comes down to setting the required gain by selecting the resistance of the resistor R3. By changing the resistance of the resistor R3 from 0 to 20 kOhm, you can get a gain from 3500 to 10.

The amplifier is powered from a DC source with a voltage of 12 to 60 V. The current flowing through the device should not go beyond 0,5-60 mA. Its value is set by selecting the resistance R7.

If the winding resistance of the electromagnetic or dynamic microphone M1 for direct current is less than 600 ohms, then it is desirable to include it in the emitter circuit of the transistor VT1. A shielded or ordinary wire is used as a communication line. In the latter case, it is desirable to twist the wires together.

Authors: Andrianov V.I., Borodin V.A., Sokolov A.V.

See other articles Section Microphones, radio microphones.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive

New frequency synthesizer chip CDCM7005 27.04.2005

The new CDCM7005 frequency synthesizer IC from TEXAS INSTRUMENTS has a jitter removal system that allows you to get a very clean signal.

Phase noise is only -219 dB/Hz. Synthesizer frequency range up to 2,2 GHz. The microcircuit operates with a supply voltage of 3,3 V in the temperature range from -40 to + 85C. Available in BGA-64 and QFN-48 packages.

Other interesting news:

▪ Panic among mice

▪ 10K TV

▪ Magnetic filling in an empty sandwich

▪ TEKTRONIX TDS6154C - the world's widest bandwidth oscilloscope

▪ New laptops

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Infrared technology. Article selection

▪ Article Bird's milk. Popular expression

▪ article How to determine the optimality (insufficiency, redundancy) of the mass of your weight? Detailed answer

▪ article The functional composition of Elekta TVs. Directory

▪ article IR relay control unit. Encyclopedia of radio electronics and electrical engineering

▪ article Finely compensated volume control on a resistor without taps. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages of this page

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