Encyclopedia of radio electronics and electrical engineering / Civil radio communications

 Comments on the article

Ease of use of radio equipment is one of its indispensable quality indicators. This article describes a simple improvement that will allow you to more rationally use the capabilities of the radio.

Most small-sized radios have power switches combined with a volume control. This solution simplifies the design, but is inconvenient in practice. In order to turn off the receiver, you have to turn the volume control knob, violating the previously set volume level control and spend some time to set the same level when turned on. It should be noted that a few decades ago, a similar switch, combined with one of the adjustments, was widely used in household radio equipment, but today it is clearly outdated. Modern equipment is controlled differently - by convenient quasi-touch switches, when the impulse from the short-stroke button is processed by the microprocessor. Of course, in simple receivers there is no microprocessor control, nevertheless, a power switch controlled by a slight push of a button can be built into it by assembling a simple device according to one of the options below.

Pocket-type radios are powered primarily by two limited-capacity AA-type AA cells. This imposes rather stringent requirements on the device being developed in terms of efficiency, the absence of voltage losses in the switching circuit. In addition, the dimensions of the switch block must be minimal in order to be able to embed it in the body of a miniature receiver.

A possible circuit of a quasi-sensor switch that satisfies such requirements is shown in fig. 1. It is based on a counting trigger, made on one of the two D-flip-flops of the K564TM2 chip. The trigger is obtained by connecting the inverted output to the information input D, which turns the clock input C into a counting one. The trigger output signal is applied to the base of the transistor switch VT1 through the HL1 LED, which acts as a power indicator. Switch SA1 - the mentioned standard switch of the radio receiver, combined with the volume control (not shown in the diagram). The SB1 button controls the quasi-sensor switch - its closing contact connects the "plus" of the power supply to the input C of the DD1 trigger, forming a counting pulse. The initial zero potential at this input determines the R1C1 circuit, which, in addition, prevents possible interference and contact bounce.

The operation of the device is based on the logic of the trigger - its output state will be changed each time to the opposite when a positive voltage drop of the pulse arrives at input C. Suppose that the initial state of the trigger is such that its direct output is log. 1. Then the base-emitter voltage of the transistor VT1 is zero, the transistor is closed, the radio is turned off. When you press the SB1 button, the front of the pulse at the input C switches the trigger to the log 0 state. At the same time, the output. 1 chip voltage is close to the supply voltage. The HL1 LED circuit - the B-E junction of the transistor begins to flow a current sufficient to ignite the LED and open the VT1 transistor - the load (receiver) through the low resistance of the E-K will be connected to the power source. At the same time, the HL1 LED indicates the inclusion of the radio. The next press of the SB 1 button returns the trigger to its original state, the transistor VT1 closes, the HL1 LED goes out - the receiver is turned off. In this state, it can be indefinitely, until the next press of the SB1 button.

The power consumed by the DD1 chip (CMOS structure) in static mode is negligible. As a result, in the "off" state, the device practically does not consume current. In the "on" state with the open transistor VT1, the total current consumption increases by no more than 1 mA, but the power indicator LED also works - a feature that deserves attention. Low costs, and therefore high efficiency, are obtained through the use of the KT208V transistor, which has a low saturation voltage - the normalized value at a current of 300 mA is 0,3 V, and the measured value at a current of 25 mA did not exceed 0,05 V.

Even higher efficiency has a switch, the diagram of which is shown in Fig. 2. Here, a special field-effect transistor KP505A with a low threshold voltage and an open channel resistance of the order of tenths of an ohm is used as a switching element. Its insulated gate control circuit has an infinitely large input impedance and therefore draws no current. Due to this, as well as the characteristics of the microcircuit, properties are provided that are close to those of a mechanical switch - "zero" power consumption in both modes, no losses in the closed state of the "contact".

In accordance with its structure, the field-effect transistor VT1 is included in the break of the "negative" power wire. It is open when on the pin. 1 chip high level, and closed - in the opposite state. Otherwise, the operation of the device does not differ from the operation of the previous one.

Although the normalized lower voltage limit for CMOS logic chips is 3 V, the trigger works stably when the supply voltage drops to 1,5 V, and some deterioration in performance (speed and others) does not matter in this case. If you select a transistor VT1 for the device according to the circuit in Fig. 1 with the parameter h21e>200, and for the device according to fig. 2 - with a minimum threshold voltage (-1,6 V), then the switch according to the circuit in fig. 1 is operational when the supply voltage drops to 1,8 V, and according to fig. 2 - up to 1,6 V. Without the selection of transistors, both devices work well in the range of 2 ... 3 V. A slightly higher allowable voltage in the switch according to the circuit in fig. 1 can be explained by the presence of the HL1 LED, but there is also an advantage - the LED acts as an indicator for turning on the receiver and discharging the battery: the batteries should be changed when it goes out.

The microcircuit can be replaced with a similar one from the 561 series, however, this will increase the dimensions and require reworking the printed circuit board. The KT208 transistor is applicable with the letter index E. The best replacement for it is KT529A. Button SB1 - short-stroke non-fixed, from imported radio equipment, dimensions 6x6x3 mm with a stem with a diameter of 3 mm. It is convenient in that it can have a stem of different lengths. Of course, you can use other buttons, including those of domestic production (for example, the MP7 microswitch). LED HL1 should have a maximum brightness at a current of 1 mA. Good results here are given by imported red LEDs. It is undesirable to use emitters of a different color, since they have a larger forward voltage drop and lower brightness. Resistor - MLT-0,125, capacitor - any miniature ceramic.

The device according to fig. 2 is assembled on a single-sided printed circuit board by surface mounting (Fig. 3).

The printed circuit board is connected by flexible wires to the battery and the plus and minus terminals to the receiver board. The regular power switch SA1 is left in the circuit (it is permanently closed), it does not interfere with the operation of the quasi-sensor, and sometimes it can be useful, for example, during long-term storage of the receiver, transportation, etc. A prerequisite for connecting the device is to disconnect one of the receiver's power buses directly at the battery compartment: positive - for the device according to the scheme of fig. 1 and negative - for the device according to the scheme of fig. 2.

Switches do not require settings. Embedding in a radio receiver consists in installing a finished board (for example, on brackets) in any free place so that the rod protrudes 1,5 ... 2 mm above the surface of the housing, in which a hole with a diameter of 3,5 mm should be pre-drilled. The said button does not require any special pushers, although, if desired, they can, of course, be made for decorative purposes.

The reliability of the developed devices is very high: for the entire period of operation, there were no false positives and other failures in the transistor radio. The scope of use of devices is much wider than small-sized receivers. They can also work normally with a supply voltage of 9 ... 12 V, for this it is enough only in the circuit according to fig. 1 connect a limiting resistor between the cathode of the HL1 LED and the base of the transistor VT1 until the current in this circuit is 1 mA. With a supply voltage of 9 V, it may be necessary to select the capacitor C1 for a clear operation. The power of the switched equipment depends on the allowable current through the VT1 transistor, which is 150 mA or 1 A with the KT529A transistor (see Fig. 1) and 1,4 A (see Fig. 2), respectively.

Author: A.Pakhomov, Zernograd, Rostov region

See other articles Section Civil radio communications.

Read and write useful comments on this article.

<< Back

<< Back

Latest news of science and technology, new electronics:

The world's tallest astronomical observatory opened 04.05.2024

Exploring space and its mysteries is a task that attracts the attention of astronomers from all over the world. In the fresh air of the high mountains, far from city light pollution, the stars and planets reveal their secrets with greater clarity. A new page is opening in the history of astronomy with the opening of the world's highest astronomical observatory - the Atacama Observatory of the University of Tokyo. The Atacama Observatory, located at an altitude of 5640 meters above sea level, opens up new opportunities for astronomers in the study of space. This site has become the highest location for a ground-based telescope, providing researchers with a unique tool for studying infrared waves in the Universe. Although the high altitude location provides clearer skies and less interference from the atmosphere, building an observatory on a high mountain poses enormous difficulties and challenges. However, despite the difficulties, the new observatory opens up broad research prospects for astronomers. ... >>

Controlling objects using air currents 04.05.2024

The development of robotics continues to open up new prospects for us in the field of automation and control of various objects. Recently, Finnish scientists presented an innovative approach to controlling humanoid robots using air currents. This method promises to revolutionize the way objects are manipulated and open new horizons in the field of robotics. The idea of ​​controlling objects using air currents is not new, but until recently, implementing such concepts remained a challenge. Finnish researchers have developed an innovative method that allows robots to manipulate objects using special air jets as "air fingers". The air flow control algorithm, developed by a team of specialists, is based on a thorough study of the movement of objects in the air flow. The air jet control system, carried out using special motors, allows you to direct objects without resorting to physical ... >>

Purebred dogs get sick no more often than purebred dogs 03.05.2024

Caring for the health of our pets is an important aspect of the life of every dog ​​owner. However, there is a common assumption that purebred dogs are more susceptible to diseases compared to mixed dogs. New research led by researchers at the Texas School of Veterinary Medicine and Biomedical Sciences brings new perspective to this question. A study conducted by the Dog Aging Project (DAP) of more than 27 companion dogs found that purebred and mixed dogs were generally equally likely to experience various diseases. Although some breeds may be more susceptible to certain diseases, the overall diagnosis rate is virtually the same between both groups. The Dog Aging Project's chief veterinarian, Dr. Keith Creevy, notes that there are several well-known diseases that are more common in certain breeds of dogs, which supports the notion that purebred dogs are more susceptible to disease. ... >>

Random news from the Archive Europe is warming faster than other continents 23.04.2024 Europe is facing dramatic climate change, and the consequences are becoming more and more acute. Data from two leading climate monitoring organizations suggests the continent is warming significantly faster than the global average. A joint report by the UN World Meteorological Organization and EU climate agency Copernicus on the state of the climate in Europe over the past year has revealed that the continent is experiencing a rise in temperatures double the global average. An increase in average temperatures of 2,3 degrees Celsius above pre-industrial levels puts Europe in a difficult position. This rise in temperature is 1,3 degrees Celsius above the global average and is no longer just a statistic, but a fact that is having a major impact on people's lives. Heat-related deaths are increasing across the continent, highlighting the importance of adapting to new climate conditions. The dire consequences of extreme weather conditions such as storms, floods and wildfires are becoming increasingly visible and require greater efforts to prevent their devastating impact. However, despite all the challenges, there is an opportunity for Europe to develop strategies to accelerate the transition to renewable energy sources. Successful measures in the field of renewable energy are already showing their effectiveness, and further development in this direction can help mitigate the negative impacts of climate change. Europe faces real challenges from climate change and it is important to take effective action to mitigate its negative impacts. Despite the challenges, the opportunity to transition to renewable energy offers the continent a chance to move forward and build a more sustainable future.

Other interesting news:

▪ skin neuron

▪ Furnace for radio lovers

▪ Hydrogen in nanopetals

▪ The moon may have been responsible for the sinking of the Titanic

▪ Chip TDA15600 to control the LCD TV screen

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ site section Voltage converters, rectifiers, inverters. Article selection

▪ article Soul high impulses. Popular expression

▪ article What is the difference between timpani and drum? Detailed answer

▪ article Machinist of dust pumps. Standard instruction on labor protection

▪ article Remote control of household equipment based on TC9148-9150 chips. Encyclopedia of radio electronics and electrical engineering

▪ article Linear stabilizers with high efficiency. Encyclopedia of radio electronics and electrical engineering

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

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

www.diagram.com.ua
2000-2024