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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Designs by A.Partin. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur Intercom (Fig. 1)
The basis of the device is an audio frequency amplifier, made on two transistors connected according to a common emitter circuit. In order to more accurately establish the optimal mode of their operation, variable resistors (R1 and R4) are included in the transistor base circuit. The intercom is equipped with two capsules from TON-2 headphones - BF1 and BF2. The first of them can be located near the amplifier, the second, together with the SB2 pushbutton switch, is removed to the desired distance and connected to the amplifier with three wires. In the position shown in the diagram of the moving contacts of the pushbutton switches SB1 and SB2, the capsules are set to receive messages. If a subscriber with a BF1 capsule presses the SB1 switch button, the BF1 capsule will be connected to the amplifier input and the conversation will be heard by the owner of the BF2 capsule. In a similar way, the second subscriber will be able to send a message to the first if he presses the button SB2 (button SB1 must be released). The easiest way to set up an amplifier is cascading, starting with a cascade on a VT2 transistor. To do this, the output of the capacitor C2, left according to the scheme, is disconnected from the collector of the transistor VT1 and the BF1 capsule is connected between this output and the common wire. Having asked someone to say a few phrases in front of the BF1 capsule, listen to the sound in the BF2 capsule. By moving the slider of the resistor R4, they achieve the highest sound volume and the least distortion. Similarly, the operating mode of the transistor VT1 is set with a variable resistor R1 by connecting the BF1 capsule to the left terminal of the capacitor C1 according to the diagram or by pressing the SB1 button (the connection of the capacitor C2 to the collector of the transistor VT1 must, of course, be restored). You can also adjust the device using a DC voltmeter connected to the collector and emitter terminals of the transistors. The corresponding variable resistor sets the collector voltage to about 6 V. Audio frequency generator (Fig. 2)
It is assembled on just one transistor. Headphone TON-2 (BF1), the capsules of which are desirable to be connected in series, and capacitors C1, C2 form an oscillatory circuit. In order for generation to occur, the "tap" of the circuit is connected to the emitter of the transistor stage - this is a positive feedback circuit. The frequency of the generated oscillations depends on the values of the circuit capacitors and the input resistance of the variable resistor R1. Listening to the sound in phones, make sure that its tone changes when the resistor slider is moved. If it is possible to change the supply voltage (reduce it to 3 V), it is easy to notice its effect on the generator frequency. Multivibrator - "flasher" (Fig. 3)
If two amplifying stages, for example, shown in Fig. 1, interconnected so that the output signal of each goes to the input of the other, we get a pulse generator called a multivibrator. Our experimental multivibrator is equipped with BF1 headphones, which are used to listen to the sound. Its tone can be changed by variable resistors R2 and R4. Moreover, it will be perceived as clicks of different repetition rates - depending on the position of the variable resistor sliders. To make the operation of the multivibrator more clearly visible, it is supplemented with a light signaling device made on the VT3 transistor. The HL1 LED is included in its emitter circuit. Now clicks in phones will be accompanied by LED flashes. Their brightness is set by resistor R7. From the flashes of the LED, it can be seen that the resistor R4 affects not only the pulse frequency, but also the duration of the flashes, and R2 - the duration of the pauses. By moving the sliders of variable resistors, you can achieve the same duration of LED flashes and pauses between them. Siren (Fig. 4)
The design is made on two multivibrators. One of them (on transistors VT3, VT4) is designed to receive a sound with a frequency of about 1000 Hz, the pulses of the other (on transistors VT1, VT2) follow at a frequency of 0,5 ... 1 Hz. Since the output of the low-frequency generator is connected to the frequency control input of the higher-frequency one, a signal of varying frequency is heard in the headphones - from 500 to 1000 Hz. These changes are spasmodic - with the open transistor VT2, a sound of one tone is heard, and with the closed one - another. A smoother frequency change can be achieved by installing a larger resistor R5. To make the siren sound louder, the TON-2 headphone capsules should be connected in parallel. Bicycle direction indicator (Fig. 5)
The basis of this device is a pulse generator made on transistors VT1 and VT2. The pulse repetition rate depends mainly on the capacitance of the capacitor C1 and the resistance of the resistors R4 - R6. While the movable contact of switch SA1 is in the position shown in the diagram, the generator does not work, since the supply voltage is not supplied to it. It is worth moving the moving contact to the left according to the scheme, as the emitter circuits of the transistors will be connected to a common wire (minus the supply voltage). At the same time, the signal LEDs HL1, HL2 will be switched on in the emitter circuit and will start blinking. When the movable contact of the switch is moved to the right according to the scheme, the voltage will be supplied to the generator through the diode VD2, and the LEDs HL3, HL4 will blink. If you want to install this design on your bike, the LEDs should be attached to the wheel guards: HL1 and HL2 to the left of the wheels (respectively on the front and rear guards), and HL3 and HL4 to the right. Acoustic relay (fig. 6)
This is the name of a device that "triggers" on a sound signal (loud voice, clap, etc.) and turns on the load, for example, a lighting lamp. The acoustic relay consists of a BM1 microphone (its role is played by the TON-2 headphone capsule), a sensitive audio frequency amplifier based on VT1-VT3 transistors, a VD1, VD2 diode detector, an electronic key based on a VT4 transistor and an electromagnetic relay K1. The contacts of the relay K1.1 are included in the circuit of the light indicator of the operation of the device - the HL1 LED. The operating mode of the amplifier is set by a variable resistor R4. While there is no sound signal, transistor VT4 is closed, the relay is de-energized. It is enough to say, say, a loud "A" near the microphone, as an audio signal is sent to the amplifier. From the output of the amplifier, it will be fed to the detector. The signal that appeared on the load of the detector (resistor R6) in the form of long-duration unipolar pulses will open the transistor VT4. The relay will work and with its contacts will supply power to the LED. Its brightness is limited by resistor R7. After the sound signal stops, the relay will be held for some time by the charging current of capacitor C4, after which it will be released. The LED will turn off. Relay - reed switch RES55A, passport RS4.569.600-10. Its resistance is 377 ohms with a spread of ± 56,5 ohms, the response voltage is 5,9 V, the operating voltage is 10 V. The establishment of the relay begins with a check of the output stage - an electronic key. When a 10 kΩ resistor is connected between the plus of the power source and the base of the transistor VT4, relay K1 should work and the LED should light up. Then they say some sounds or phrases near the microphone and again observe the ignition of the LED. By moving the slider of the variable resistor R4, the greatest sensitivity is achieved so that the acoustic relay reacts to the voice from the greatest possible distance from the microphone. Time relay (Fig. 7)
It is known that when a discharged capacitor is connected to a power source, a charging current begins to flow through it. As the capacitor charges, this current decreases and stops when the capacitor is fully charged. The duration of charging depends on the capacitance of the capacitor and the resistance of the circuit to which it is connected. On this principle, our relay is built, which allows you to count the specified time. As in the previous device, it uses an electronic key on the VT2 transistor, as well as a light signaling on the HL1 LED. The cascade on the transistor VT1 is a current amplifier. As soon as a power source is connected to the device, the charging of capacitor C1 will begin. Both transistors will immediately open, the electromagnetic relay K1 will work and the contacts K1.1 will turn on the LED. As the capacitor charges, the current through the transistor VT1 will begin to decrease, and the voltage across the resistor R4 and, therefore, at the base of the transistor VT2 will fall. After a certain time, which depends on the capacitance of the capacitor and the resistance of the resistor R1, there will come a moment when both transistors close, relay K1 releases, the LED goes out. For the subsequent start of the time relay, it is enough to briefly press the SB1 button to discharge the capacitor. Relay K1 is the same as in the previous design. The time relay can be used, for example, in a burglar alarm. It will turn on at the moment of entry into the protected premises or exit from it by officials. Touch switch (Fig. 8)
This is the name of a proximity switch that works when a special sensitive (touch) pad, or simply a sensor, is touched with a finger. The switch has two "channels", each of which consists of a composite transistor assembled from two bipolar ones, a trinistor (VS1 in one "channel" and VS2 in the other) and an LED indicator. The trinistor has three electrodes - an anode, a cathode, a control electrode - and has an interesting property: if a positive voltage is applied to the control electrode for a short time, in other words, a current is passed through the control electrode - cathode circuit, the trinistor will open and remain in this state until until the anode voltage is removed from it or the anode and cathode terminals are closed. When the sensor E1, i.e., the base of the composite transistor, is touched with a finger, it opens. The current flowing through it and the control electrode of the trinistor VS1 leads to the opening of the trinistor. The HL1 LED lights up, and HL2 remains off. Capacitor C1 is charged in such a way that on its right output, according to the output circuit, there is a plus voltage, and on the left - a minus. If you now touch the sensor E2, the composite transistor VT4 VT3 will open, and after it, the trinistor VS2. The capacitor will be connected between the anode and cathode of the trinistor VS1 in reverse polarity, i.e. minus to the anode, which is equivalent to shorting these electrodes. LED HL1 will go out, and HL2 will light up. Some instances of trinistors are not kept open due to insufficient anode current. Then you will have to increase this current by connecting a constant resistor in parallel with the indication circuit. For example, in our case - between the lower output of the resistor R1 according to the circuit and the plus of the power source, if the trinistor VS1 is not held. Combination lock (Fig. 9)
Such a lock can be found, say, on the doors of residential buildings, apartments, laboratories and in other places where access to unauthorized persons must be restricted. The automatic lock works only when several buttons located on the remote control are pressed in a certain sequence. If successful, the lock will work and open the front door. The proposed layout of the lock contains three "correct" buttons (SB1-SB3) and the same number of "fake" ones (SB4-SB6). In the initial state, the transistor VT1 is open, the trinistors VS1-VS3 are closed. The "program" of the lock is designed so that you first need to press the SB3 button. The trinistor VS3 will open and remain in this state, since there is a load (resistor R3) in its anode circuit that provides the desired holding current. Next, you need to press the SB2 button to trigger the trinistor VS2 (its load is resistor R2). The last button is pressed SB1. The trinistor VS1 opens, the HL1 LED lights up, signaling the correct operation of the automation. Usually, this place is occupied by an actuator - a solenoid that extends the bolt of the lock, or an electromagnetic relay that supplies voltage to the solenoid. If these buttons are pressed in a different order, the lock will not open. If at least one button from SB4-SB6 is accidentally pressed, the transistor VT1 will close and remove power from the trinistors - the one that has already opened will close. The more buttons "correct" and "fake", the greater the secrecy of the lock, the more difficult it is to unravel the code and open the door. It may happen that the VS1 trinistor will not hold after opening. Then you should use the recommendations for the previous design and increase the anode current by connecting a 300 Ohm resistor between the LED cathode and the plus of the power source. Author: A.Partin
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