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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING High humidity alarm. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers If you forget about the dishes with water put on the hot stove for a long time, several liters of water evaporated and the dishes spoiled will not please you. To prevent this from happening, you can assemble a simple device that, when placed, for example, in the kitchen, will notify you with sound signals about high humidity in the room. The diagram of the signaling device for high air humidity is shown in fig. 1. In combination, he can also signal a puddle formed on the floor, which will reduce trouble in case of damage to plumbing or heating equipment or overflow of the sink when the tap is left open for a long time and the drain hole is clogged.
Gas resistor B1 is used as a sensitive element in the signaling device. These were used in video cassette recorders and video cameras to block the operation of the tape drive mechanism at high humidity inside the device. Logical elements DD1.1 and DD1.2 form a pulse generator, following about 15 times per minute. This frequency is set by resistors R13, R15, R16 and capacitor C9. Thanks to the VD7 diode, the pulses are much (about 10 times) shorter than the pauses between them. When the gas resistor is dry, its resistance does not exceed 1 ... 3 kOhm and the voltage at the connection point of the resistors R4, R5, R7 is not enough to open the transistor VT1. The transistor VT2 is also closed. The logical voltage level at the lower (according to the circuit) input of the DD1.1 element is low, which prohibits the operation of the pulse generator on the elements DD1.1 and DD1.2, and the output of the DD1.2 element is set to a low level, which in turn prohibits the operation of the pulse generator audio frequency on the elements DD1.3 and DD1.4. If the humidity of the air surrounding the gas resistor increases (to check, it is enough to make two or three exhalations to the gas resistor from a distance of 5 ... 10 cm), then the resistance of the gas resistor will increase to 10 ... 20 MΩ. The increased voltage at the base of the transistor VT1 will open, and the transistor VT2 will open along with it. At the lower (according to the scheme) input of the DD1.1 element, a high logic voltage level will be set. Both pulse generators will work. The piezo sound emitter HA1 will emit sound signals every 4 s with a duration of about 0,5 s. Feedback through resistor R7 accelerates the opening and closing of transistors VT1, VT2 and creates a small hysteresis in their switching characteristics. This provides a clear, without "bounce" operation of the signaling device when the humidity slowly approaches the threshold. The response threshold is set by a trimming resistor R3. The device will also give a signal if the transistor VT1 remains closed, and the transistor VT2 opens as a result of contact E1 and E2 being closed by spilled water. Resistors R6 and R8 not only limit the base current of the transistor VT2, but also reduce the risk of electric shock to a person who has touched the contacts. Mains voltage can get on them as a result of water penetration into the detector or insulation failure between the windings of the transformer T1. So that the signaling device does not annoy with sound signals while the reasons for its operation are eliminated, by pressing the SB1 button, you can block the operation of the generators for approximately 18 minutes. So much time the capacitor C8, discharged by pressing the button, will be charged through the resistor R17. Resistor R22 limits the discharge current of the capacitor, protecting the button contacts from burning. It should be noted that the recovery of the low resistance of gas resistor B1 after exposure to high humidity is very slow. Therefore, to get rid of annoying signals, you may need to press the SB1 button several times. The piezo sound emitter HA1 is connected to the outputs of the elements DD1.3, DD1.4 through emitter followers on transistors VT5, VT6 and VT7, VT8. This increases the load capacity of the generator and makes it possible to connect several sound emitters to it in parallel, placing them, for example, in different rooms. The HL1 LED signals the inclusion of the signaling device in the network, and the HL2 LED turns on at the moments of sound signals, as well as when the generators are blocked by a low voltage level on the capacitor C8. Capacitors C1 and C2 prevent false alarms caused by noise. The mains voltage of 220 V is supplied to the primary winding of the step-down transformer T1 through protective resistors R1 and R2. Varistor RU1 protects the transformer from power surges. A voltage of about 17 V from the secondary winding of the transformer rectifies the diode bridge VD2-VD5. All stabilizer nodes are powered by a voltage of +9,2 V, obtained from a stabilizer rectified using transistors VT3 and VT4. Its value depends on the stabilization voltage of the Zener diode VD6. Since a low-power step-down transformer from a Xerox copier is used as T1 in the design, designed for a load current of about 10 mA, the current through the zener diode is chosen very small - less than 1 mA. The low power of the transformer also determined the choice of the nature of the sound signal - a short tone pulse and a long pause. You can also use a more powerful transformer, for example, TPK-2-12V, designed for a load current of up to 0,21 A. For self-production of a transformer, an W-shaped magnetic circuit with a cross-sectional area of \u2b\uXNUMXbthe central rod of XNUMX cm is suitable2. The primary winding should consist of 5900 turns of winding wire with a diameter of 0,06 mm. The secondary winding, containing 500 turns, is wound with a wire with a diameter of about 0,2 mm. The plates of the magnetic circuit are assembled in an overlap. The finished transformer can be coated with an epoxy compound. Most parts of the device are located on a 75x45 mm circuit board, shown in fig. 2. Resistors R6, R8 and resistors R1, R2 with varistor RU1 are mounted on small separate boards.
A ready-made board from a network adapter was also used, on which diodes VD2-VD5 and a capacitor C3 are installed. After manufacturing, all these boards are covered on the mounting side with a moisture-proof varnish, for example XB-784. Together with the T1 transformer, they are housed in a plastic case measuring 160x110x32 mm from the RR-701R intrusion alarm receiver. Gas resistor B1, removed from the Funai VCR, is fixed on a massive metal plate and together with it is placed in a plastic case measuring 46x42x15 mm (Fig. 3) with holes for air access. Its sensitivity is much higher than that of the domestic GZR-2B gas resistor used in the design described in the article "Light and sound signaling device for boiling water" ("Radio", 2004, No. 12, pp. 42, 43). Nevertheless, GZR-2B and other similar gas resistors can also work in the described signaling device.
The device can be used fixed resistors of any type (MLT, C1-4, C1-14, C2-23). It is desirable that the resistors R1 and R2 are non-flammable. Trimmer resistor R3 - miniature in a housing that protects it from external influences. It is highly undesirable to use open trimming resistors (for example, SP3-38) because of their low reliability. Varistor RU1 - HEL14D471K or other disk varistor with a classification voltage of 470 V. Oxide capacitors - K50-68, K53-19, K53-30 and their imported counterparts. Capacitor C8 must be low leakage current. The copy used by the author has a leakage current of less than 10 nA at a voltage of 18 V. The remaining capacitors are ceramic K10-17, K10-50, KM-5 or their analogues. Capacitor C4 must be rated for at least 35 V. Instead of diodes 1 N4002, any of 1N4001-1 N4007, UF4001 -UF4007, as well as the KD208, KD209, KD243 series, are suitable. Diodes 1N4148 can be replaced with 1SS244, 1N914, KD510A, KD521A, KD521B, KD522A, KD522B. The Zener diode BZV55C-10 is replaced by TZMC-10, KS210Ts, KS210Ts1, 2S210K1, 2S210K, 2S210Ts, transistors 2SC1685 and 2SC2058 - by 2SC1815, 2SC1845, SS9014, as well as series KT3102, KT6111, and transistor 2SA1015 - on SS9012, SS9015, 2SA733 or series KT3107, KT6112. Replacing transistors 2SC2331 - 2SC2383, SS8050, BD136, BD138, KT646A, KT683A. Instead of transistors 2SA1273 and 2SA1270, SS8550, 2SB564, BD231, KT639A, KT644A, KT684A are suitable. It should be borne in mind that transistors offered as replacements may have differences in package type and pinout. The K561LA7 chip will be replaced by domestic KR1561LA7, N564LA7, 564LA7 (the last two in other cases) or imported CD4011A. Inductor L1 - small-sized industrial production with an inductance of at least 100 μH and a winding resistance of 3 ... 30 Ohm. Button SB1 - PKN-125. The sound emitter HA1 is a piezoelectric call device of a telephone set. Its own capacitance is 0,03 uF. Other piezo emitters are also suitable, even with a larger capacity, rated for a voltage of at least 20 V. Several of these emitters can be connected in parallel. Instead of a piezo emitter, an electromagnetic telephone capsule or a dynamic head with a winding resistance of at least 32 ohms, for example, PQAS57P3ZA-DZ, can be connected to the output of the device through a non-polar coupling capacitor. A water leakage sensor can be made, for example, from a plate of fiberglass laminated on one side. The foil is divided along a broken line by a gap into two isolated parts, one of which serves as the E1 electrode, and the second as the E2 electrode. The greater the length of the gap, the higher the probability that the very first drops of water falling on the plate will fall on it and close the electrodes. Several such sensors, by connecting them in parallel, can be placed in the most dangerous places from the point of view of water leakage, for example, under heating radiators, a washing machine, water pipe joints. A box with a gas resistor is placed in the place of the room most prone to fogging at high humidity, but not on the window. Trimmer resistor R3 sets the alarm threshold. If the "dry resistance" of gas resistor B1 is restored after a decrease in humidity for too long, resistors R4 and R5 can be installed in the alarm device with three times less resistance. You can increase the sensitivity of the leaking water sensor by increasing the resistance of the resistor R9 to 100 kOhm. By selecting the resistance of the resistor R20, you can set the desired tone of the audio signals. For the convenience of checking the performance and setting up the signaling device, the capacitor C8 can be temporarily disconnected. Author: A. Butov
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