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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Three designs of a rural radio amateur. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur DMM Power Option Small-sized digital multimeters are very popular among radio amateurs. But the relative high cost of good 9-volt batteries forces us to look for alternative power options for these devices. One of them is the use of transformer network units [1]. However, due to leakage currents and capacitive coupling with the network, the probability of damage to the CMOS ADC KR572PV5 of the multimeter or its analogs increases sharply. It was possible to provide almost perfect decoupling from the lighting network using a secondary power source, made according to the scheme shown in fig. 1].
As an energy source for powering the multimeter, photodiodes VD1 - VD24 of the infrared range, connected in series, were used. When the photodiode is illuminated with a sufficiently powerful light source, for example, incandescent lamps EL1 - EL3 for a voltage of 6,3 V and a current of 0,3 A, the photodiode produces a voltage of at least 0,4 V at a load of 200 ohms. Connect the power supply in parallel with the multimeter battery to prolong its life. If instead of a conventional battery ("Korund", "Krona") a rechargeable type "Nika" is used, the power source will recharge it with a small current. It is possible to use a source without a battery at all, but in this case it is necessary to connect a low-power zener diode in parallel with capacitor C1, for example, D814V, KS510A, KS210Zh. The device uses miniature incandescent lamps used in industrial network radio equipment to illuminate the scale. Other similar lamps with a power of 0,5 - 1,5 W are also suitable. The photodiodes indicated in the diagram can be replaced with FD256. Good results are also obtained with frameless photocells from readers from punched tapes from CNC machines. It is desirable to use a capacitor with a low leakage current, for example, K52, K53 series. The details of the power supply device are placed on a board with dimensions of 150x50 mm. Incandescent lamps are inserted into three holes of the appropriate diameter, drilled at a distance of 40 mm from each other. Eight photodiodes are placed around each lamp (Fig. 2).
When setting up the device, the nominal voltage is applied to the lamps, and a 4,3 kΩ resistor and a digital voltmeter are connected to the source output. Photodiodes are oriented relative to the lamps, achieving a maximum voltage at the output of the source. After that, the photodiodes are fixed with a drop of epoxy glue. If necessary, the number of photodiodes can be reduced or increased. Adapter power indicator Only a few parts will be needed to upgrade a small-sized foreign power supply (adapter of the brand "SOVU", "ELECA", "RW" or similar). In such a product, I propose to install an LED in the circuit of the primary winding of the transformer (like other input parts, it is highlighted in Fig. 3 with a thick line), which will allow not only to control the inclusion of the adapter in the network, but also to avoid additional current load on the transformer and rectifier diodes bridge. Zener diodes VD1, VD2 and resistor R2 protect the LED from current surges when the adapter is connected to the network.
Resistor R1 - safety non-flammable, type P1 -25. Based on many years of experience in the operation of adapters in which such a resistor was installed, we can say that its presence prevents the thin copper wire of the primary winding of the transformer from burning out at the moment it is connected to the network. If there is no such resistor, it is permissible to install P1-7 or a conventional metal-film MLT-0,5. Its resistance should be such that at the rated load current, a power of 0,15 ... 0,2 W is dissipated on the resistor. The LED can be any other from the KIPD23 series, its brightness is set by selecting the resistor R2, the resistance of which usually lies in the range of 47 ... 270 Ohms. Instead of those indicated in the diagram, it is permissible to install zener diodes KS139A, KS126V, KS126G. In the case of using an adapter to power radio receivers or transmitters, to reduce background or interference, each of the bridge diodes must be shunted with a ceramic capacitor with a capacity of 0,01 ... 0,047 μF. If the adapter has a "blind" (completely closed) case, it is advisable to drill several dozen holes with a diameter of 2...3 mm in it for better cooling of parts. Electronic turn signal relay The proposed device is designed to replace failed thermal or electronic circuit breakers. It is equipped with light and sound signaling, capable of working with lamps with a total power of up to 90 watts. When installing this design in most domestic cars, minimal changes in wiring will be required. In standby mode, the current drawn by the relay is close to zero. When the standard turn direction switch SA1 (see Fig. 4), located, for example, on the steering column, is set to neutral, capacitor C1 is charged to the supply voltage. The transistor VT1 is closed, so the power supply to the blinking LED HL1 and the piezoceramic emitter BF1 with a built-in generator is not supplied.
As soon as the switch is set to the "Left" or "Right" position, the capacitor C1 will quickly discharge through the VD1 diode and the connected incandescent lamps of the corresponding direction indicator. Transistor VT1 will open, the flashing LED will flash briefly, and the piezoceramic emitter will emit beeps. Lamps EL1 - EL4 or EL5 - EL8 will flash. This is why it happens. When a blinking LED flashes, the voltage across it is at a minimum and the current through it is at a maximum. The voltage that appears on the emitter causes sound signals, and on the gate of the field-effect transistor VT2, it opens it. As a result, a powerful key opens on transistors VT3, VT4, through which a supply voltage is supplied to one of the groups of lamps. They ignite. When the flashing LED goes out, there is practically no voltage on the emitter and gate of the field-effect transistor. The beep stops and the transistor closes. At the same time, a powerful key closes, disconnecting the lamps from the power source. The repetition rate and duty cycle of the flashes depend on the parameters of the applied LED. Instead of those indicated in the diagram, transistors of the KT3107, KT502, KT361 (VT1) series can be used; KP501A, KP501B (VT2); KT814, KT816, KT837 or their foreign counterparts BD234, BD438 with a base current transfer ratio of at least 80 (VT3); KT818, 2T818 with letter indices AM-GM or foreign analogues 2SA1216, 2SA1302, 2SA1494 (VT4). In place of VT4, a composite transistor, say, KT896A, is able to work. In any case, this transistor is mounted on a heat sink with a total surface area of 50...80 cm2. It is permissible to replace the diode with any of the KD209, KD208, KD105 series. The blinking LED is used in red color of luminescence with a light output of 40 mCd with a diameter of 5 mA from the company "KING-BRIGHT". Any other similar one will do, for example, L-796BSRC-B, L-796BGD, L-56BGD. A piezoceramic emitter with a built-in generator is used with a diameter of 24 mm for an operating voltage of 12 V - it consumes a current of about 5 mA. Another emitter of this series with similar parameters will do. Set up the device in the following order. Car lamps with a total current consumption of 5 ... 7 A are connected to the output of the key, the LED leads are closed, and then the supply voltage is applied. Measure the voltage between the collector and emitter of the transistor VT4. If it is more than 1 V, replace it with the same transistor or connect another transistor in parallel. After checking and adjusting the device, it is advisable to cover the installation with a thin layer of epoxy glue, after which it dries, place the board in a metal case (by the way, it can become a radiator for the VT4 transistor). A flashing LED is fixed on the dashboard of the car. This relay has an interesting feature - with a sharp increase in voltage in the on-board network, a short beep will follow, which may indicate poor battery quality or a malfunction of the voltage regulator relay. In the event of a burnout of all the lamps of one of the groups or an open circuit in their circuit, there will be no sound and light signaling of the turn signals on. Literature
Author: A.Butov, village of Kurba, Yaroslavl region
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