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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Designs by S. Shipovsky. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur "Flasher" - direction indicator (Fig. 1)
The design is based on an asymmetric multivibrator, made on two transistors of different structures. The load of the multivibrator is an incandescent lamp HL1 for a voltage of 3,5 V. The frequency of its flashes depends on the capacitance of the capacitor C1 and the resistance of the resistors R1, R2. Variable resistor R2 smoothly change the frequency of lamp flashes. When moving its slider to the left according to the scheme, it increases, and to the right, it decreases. Instead of a lamp, you can install an AL307A LED, but in series with it, you should turn on a limiting resistor with a resistance of 100 Ohms and install a larger capacitor C1 - 50 microfarads. One of the uses of flashing lights is as a direction indicator for a bicycle. Lamps install C3adi - one to the right of the bicycle wheel, and the other to the left. Instead of the SA1 switch, you need to install a switch with a middle position and two groups of contacts. One group of contacts will turn on the power, and the second will connect the lamp of the right or left turn signal to the collector circuit of the transistor VT2. Moisture indicator (fig. 2)
This is an electronic "nanny". If the multivibrator described above is slightly converted, a moisture indicator will be obtained. A “sensor” is inserted into sockets X1 and X2 - two conductors isolated from each other, for example, pieces of a single-core installation wire in insulation 8 ... 10 cm long connected together. If such a sensor is lowered into a glass of water, then the resistance between the conductors will decrease, and the speaker will beep. It is necessary to take out the conductors - and the sound disappears. The humidity indicator can be used in everyday life, for example, as an electronic "nanny". To do this, it is necessary to make a slightly different sensor, consisting of two thin tinned conductors 1.5 ... 3 cm long, sewn to a piece of fabric at a certain distance from each other. It is placed in baby diapers. As soon as the sensor gets wet, the resistance between its electrodes will decrease sharply. The multivibrator will turn on and the parental alarm will sound. Siren (Fig. 3)
Another option for using an asymmetrical multivibrator is a demo siren. Immediately after the supply voltage is applied by switch SA1, there will be no sound in the dynamic head, since there is no bias voltage based on transistor VT1. The multivibrator is in standby mode. As soon as the SB1 button is pressed, the capacitor C1 begins to charge through the resistor R1. The bias voltage at the base of the transistor VT1 increases, and at a certain value, the transistor opens. In the dynamic head BA1, a sound of a certain tonality is heard. But the bias voltage continues to rise, and the tone of the sound changes smoothly until the capacitor is fully charged. With the values of the capacitor C1 and resistor R1 indicated in the diagram, this process continues for several seconds. It is worth releasing the button - and the capacitor will be discharged through the resistors R2, R3 and the emitter junction of the transistor VT1. The tone of the sound will gradually change, and at a certain bias voltage at the base of the transistor, the sound will disappear. The multivibrator will return to standby mode. The duration of the discharge of the capacitor depends on its capacitance and the resistance of the resistors R2, R3. In standby mode, the siren consumes a small amount of current, so the switch contacts can be closed for a long time. This is necessary, say, when using the device as a house call. When the button contacts are closed, the current consumption increases to several tens of milliamps. "Pass the thread" (Fig. 4)
This is the name of the attraction, in which an asymmetric multivibrator also "participates". On a small wooden stand, a thick sewing needle, conventionally designated as socket X1, is strengthened. What is in fig. 4 is designated as X2 plug - thin (0,2 mm) copper wire in enamel insulation. The task is to thread the "thread" (the end of the wire) into the eye of the needle so that the end does not touch the needle. This is followed by a touch signaling device, made on four transistors. The first two (VT1, VT2) are an electronic key that connects the HL1 incandescent control lamp to the power source of the socket and plug (in other words, when the "thread" touches the eye of the needle). A multivibrator is assembled on the other two transistors - it is connected in parallel with the lamp. As soon as the lamp flashes, voltage will appear on it. The multivibrator will immediately start working, and a sound will be heard from the dynamic head BA1. Its tone depends on the capacitance of the capacitor C2 and the resistance of the resistor R3. Touching the "thread" with the needle can be instantaneous. Will the signaling device feel it, will the lamp flash? In the simplest case, it is unlikely to have time to heat up. But in the signaling device, such a scenario is provided, for which capacitor C1 and resistor R1 are introduced into the signaling device. Voltage is supplied to this chain through a needle and a "thread". Even an instant touch is enough for the capacitor to charge up to the voltage of the GB1 supply battery. And then it starts to discharge through the resistor R1 and a composite transistor made on VT1, VT2. And although the "thread" no longer touches the ear, the lamp is on, and a sound is heard from the dynamic head. It does not last long - less than a second. The dynamic head is 0.5GDSH-2-8, which, despite its small dimensions, has sufficient sound volume. Electronic call (Fig. 5)
By adding to the previous multivibrator an amplifying stage on the transistor VT3. get an email call. Thanks to the use of the BA1 dynamic head, its volume is sufficient for the sound to be heard in the apartment. Button SB1 - bell, installed at the front door. Dynamic head - 0.5GDSH-2-8. Drop sound simulator (Fig. 6)
Drip ... drip ... drip ... - sounds are heard from the street during rain or in spring, when drops of melting snow fall from the roof. These monotonous sounds, like the murmur of a stream, have a calming effect on many people. To make sure of what has been said, a simulator made according to the scheme of a symmetrical multivibrator on two transistors will help. The loads of the multivibrator arms are the dynamic heads VA1 and VA2 (as in the previous design, type 0.5GDSH-2-8). Variable resistor R2 can adjust the frequency of the "drop" over a wide range. Probe for "ringing" installation (Fig. 7)
Before proceeding to check the operation of the assembled structure, you need to "ring" its installation, that is, make sure that all connections are correct in accordance with the circuit diagram. Usually, for these purposes, radio amateurs use an ohmmeter or avometer. operating in resistance measurement mode. Often, such a device will completely replace a compact probe, the task of which is to signal the integrity of a particular circuit. As an example, it is proposed to assemble a probe on three transistors and an LED. A relatively sensitive amplifier is made on transistors, which has a large input resistance (several megaohms), which allows you to "ring out" high-ohm circuits. While the probes X1 and X2 are open, the transistors are closed, the HL1 LED is off. When the probes are closed, or when a working connecting circuit of the installation is "dialed", the transistors open and the LED flashes. The highest brightness of the LED is observed at low resistance of the tested circuit. As this resistance increases, the brightness of the LED decreases. In order to avoid false turning on of the LED during AC pickups on the input circuits of the probe, a blocking capacitor C1 is installed. If you install a crocodile clip instead of the X1 probe, and connect the X2 probe to a bracelet worn on your hand, you can make a "dialing" in a different way. The clip is connected to one end of the connecting circuit, and the other is touched with a finger. With a good circuit, the LED will light up. The probe does not have a power switch because the standby current draw when all transistors are off is negligible. Direct gain radio (fig. 8)
It is designed to receive radio stations in the medium wave (MW) range. Its sensitivity is sufficient to receive signals from local and remote stations. Listen to them on a miniature headphone BF1 (TM-2). The oscillatory circuit of the magnetic antenna WA1 consists of an inductor L1 and a variable capacitor C1 (KP-180). The radio frequency signal isolated by the circuit enters through the coupling coil and capacitor C2 to the radio frequency amplifier, made on the transistor VT1. From the load of the amplifier (resistor R1), the signal is fed to the detector, assembled on diodes VD1. VD2. The radio frequency component of the signal is filtered by capacitor C5. and the audio frequency component (3H signal) is allocated to the variable resistor P.5. This is the volume control. From the variable resistor engine, the signal is fed to a two-stage AF amplifier on VT2 transistors. VT3. Amplifier load - Headphone BF1. The magnetic antenna is made on a round rod made of 400NN or 600NN ferrite. A standard rod used in industrial small size transistor receivers will do. If desired, it can be shortened to 100.. .80 mm. if you need to assemble a "pocket" radio receiver according to this scheme. Coil L1 should contain 65 ... 70 turns of PEV-1 wire with a diameter of 0.1 mm, and L2 - 3 turns of the same wire. Coils are wound coil to coil and placed at a distance of 3 ... 5 mm from each other. If you want to switch to the range of long waves (LW), the number of turns of the coils is tripled. The frequency band overlapped during the restructuring of the variable capacitor C1. set by selecting the number of turns of the contour coil. Author: S.Shipovsky
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