Corrosion-resistant soil moisture sensor, suitable for dacha automation. What types of air humidity sensors are there for a fan? How to choose a temperature and humidity sensor The most interesting videos on Youtube

Water can become a source of great trouble if you do not find out in time about its appearance in places where it is not expected and where it is undesirable, especially in large quantities.

An individual moisture alarm, which can be made very compact, can help a person in such cases and avoid many troubles. The alarm circuit is shown in Fig. 1.

A tone generator is assembled on germanium transistors VT1, VT2, resistors R1, R2, capacitor C1 and a loudspeaker head, which, if the parts are in good working order, begins to sound as soon as the supply voltage is applied to it. Power is supplied to the generator through a key stage using silicon transistors VT3, VT4, resistors R3...R5 and a moisture sensor. Many liquids are electrically conductive and therefore resistant to electric current. Thus, tap water has an ohmic resistance of several kilometers.

Consequently, moisture entering the sensor is equivalent to the appearance of some resistance between the base of transistor VT3 and the “minus” of the power circuit, which makes the electrical potential of the base of transistor VT3 negative with respect to the emitter of this transistor. This switching on for transistor VT3 is opening, and current begins to flow through it, which in turn leads to opening of transistor VT4. Both transistors, having opened, enter saturation mode, the electronic switch closes, and power is supplied to the tone generator through it. The loudspeaker head (0.5 GDSh-2) begins to sound, the tonality and volume of the sound of which can wake up even a sound sleeper. In standby (standby) mode, the alarm consumes a current of significantly less than 1 µA. In alarm mode (when water gets on the sensor), the device consumes a current of no more than 80 mA. Since the device is very economical in standby mode, in the most critical cases installing a power switch in it is not even advisable.

To make sure that the alarm is on and operational, it is enough to close the plates of its sensor with wet fingers or something metal. If it works properly, it will immediately give a “voice”.

The scope of application of the moisture alarm is not limited to security functions. He can follow

filling any containers with liquid, or it can be used as an electronic “nanny”. In the latter case, the sensor(s) are placed under the diaper. As soon as the diapers get wet, the “nanny” will immediately signal about it. To bring the electronic “nanny” into the standby position, simply wipe the sensor with a napkin or rag.

MP11A (MP35...MP38) can be used as VT1, and MP39 (MP16...MP42B) as VT2, i.e. any low-frequency low-power germanium transistors of appropriate conductivity. KT203 was used as VT3, KT814 was used as VT4. A radiator is not needed for VT4. Any power of 0.25...2 W with a nominal electrical resistance of 8 Ohms will be suitable as a loudspeaker head. The device can be mounted either hinged or using a printed circuit board, the dimensions and configuration of which depend on the dimensions of the parts used and the device body.

As a device sensor, you can use a plate of one-sided foil material on which contact strips are etched (Fig. 2). You can cut sensor strips from copper foil and stick them to rubber, leather, etc. The strips should be tinned with solder. Some of the authors advise not to do this, as the appearance becomes artisanal. But if you tin well-cleaned and rosin-rubbed printed conductors with a well-heated, cleaned and tinned tip of a powerful soldering iron, using small amounts of solder (this is a kind of “know-how”), then the quality of the coating is excellent. At the same time, defects in printed conductors due to microcracks are eliminated, and the service life of printed circuit boards is increased, especially those that cannot be coated with a protective varnish due to their application.

The smaller the distance between the sensor strips, the higher the likelihood that the alarm will go off even if a few drops of rain hit the sensor. The length of the conductors connecting the sensor to the device can be from several tens of centimeters to several hundred meters.

S.N. Kovalenko, Zaporozhye

Home plumbing accidents often do not happen suddenly. First it will start to leak, then drip, and then it may burst. And the neighbors above may also start flooding. And it’s better to find out about this early, and not when the rain from the ceiling wakes you up. For my own peace of mind, I decided to play it safe and make an audible humidity alarm. Now I have such a toy next to every radiator, under every sink and in other water-hazardous places. This vigilant guard will warn of danger with the howling of a police siren. The device can also be used to signal high humidity in the room or the formation of condensation.

Specifications:
Supply voltage - 12 volts.
Current consumption at rest - no.
Current consumption in operating mode is 20 mA.

Details:
D1- K561LA7- 1 pc. Analogue - CD4011A.
T1, T2- KP505- 2 pcs. Any n-channel MOSFET with a gate voltage not exceeding 3 volts.
C1- 0.1 µF. Ceramics.
C2, C3- 22 nf. Ceramics.
R2- 1 room - 1 piece. Resistor 0125W.
R4- 3.3 rooms - 1 pc. Resistor 0125W.
R6- 47 rooms - 1 pc. Resistor 0125W.
R1- 68 rooms - 1 pc. Resistor 0125W.
R3- 100 units - 1 pc. Resistor 0125W.
R5- 220 room - 1 pc. Resistor 0125W.
ZP-18- 1 pc. Any piezoceramic emitter.
S1- Any switch.
Bat 12 V - AA battery from the alarm key fob.

Description of work:
As humidity increases, the resistance of the sensor decreases and transistor T2 opens. Both generators of the D1 chip are turned on. The generator based on elements D1-3 and D1-4 operates at a frequency of approximately 1 hertz, the generator based on elements D1-1 and D1-2 operates at the frequency of your emitter (you need to adjust it for maximum volume, in my case about three kilohertz). Transistor T1 with a frequency of 1 hertz connects and disconnects capacitance C3 connected in parallel to capacitance C2, because of this the tone of the second generator changes and an imitation of the sound of a siren is obtained.

Setting:
If assembled correctly, the device does not require configuration.
To reduce the sensitivity of the device, you need to reduce resistor R5; to increase sensitivity, increase it.
With these elements, the alarm is triggered by hand touch.
To increase the volume, you can select the frequency using C2 and C3 to suit your resonator.
Any two conductors located close to each other can be used as a humidity sensor. I cut several adjacent tracks on foil PCB.

There are not many parts and connections, so I decided not to make a printed circuit board.
It's hard to say anything about the price, all the details were at hand. The most expensive element is the battery - 30 rubles.

Many modern imported washing machines are equipped with indicators for water leakage from them. Outdated or cheaper models of washing machines do not have such a service function. Unfortunately, some of their owners already know from their own experience what a “flood” is and “how much it will cost.” In order not to experience this feeling, you can use the materials in the article in advance.

A diagram of the simplest humidity increase alarm is shown in rice. 1. It controls the state of the humidity sensor (sensor), which is connected to the K1 “SENSOR” contacts. The design of the sensor can be very different.

It all depends on the capabilities of its manufacturer. In the simplest case, it is enough to use a “printed” board, on which there are two conductors located at a distance of 0.5...1.5 mm from each other. To increase the operating efficiency of such a sensor while keeping its dimensions to a minimum, the conductors can be made in the form of a spiral. This will increase the “interaction zone” of the conductors without significantly increasing the dimensions of the sensor.

A monostable pulse generator is made on the integrated timer chip IC1 type NE555. The natural frequency of the generator is determined by the values ​​of resistors R1, R2 and capacitor C1.

Any electromagnetic or dynamic emitter is connected to the output of the circuit (short circuit "OUT-REPRO"). To avoid overloading the microcircuit's output, it is necessary that its resistance at a microcircuit supply voltage of 9 V be more than 50 Ohms. You can also use a small-sized piezo emitter. In this case, it will need to be shunted with a resistor with a resistance of 2...20 kOhm. In this case, it will be enough to use a non-polar ceramic capacitor with a capacity of up to 0.22...0.68 µF as capacitor C2 or even replace capacitor C2... with a jumper. Feel free to experiment!

When the humidity sensor is dry, transistor T1 will be in a non-conducting state, the supply voltage is not supplied to the IC1 chip and it is de-energized. If the humidity at the location of the "SENSOR" sensor increases, then transistor T1 will receive a bias in the base junction and will be unlocked. IC1 will receive power and begin to generate electrical signals in the audio frequency range. The emitter will “sound”, signaling a water leak at the location where the sensor is installed.

To increase the sensitivity of the circuit, it is advisable to use transistors with a high gain as T1, for example, BC549S or domestic KT3102E.

Scheme rice. 1 very simple and typical. It would seem, what else can be improved in it? Indeed, beginning radio amateurs can repeat it. Actually, it was designed for them. More curious readers may question the rationality of what is proposed in the diagram rice. 1 a method for turning on/off the generation of a 555 series electronic timer microcircuit. From the operating algorithm of these microcircuits it is known that, depending on the voltage at pin 4, the timer can be in an operating or passive (inhibited) state. So, if a voltage of less than 0.4 V is applied to pin 4, then the output of the timer (regardless of the signals at its other inputs) is set to a low voltage. This mode is called passive.

If the voltage at pin 4 exceeds 1 V, the timer operation blocking circuit is automatically turned off and does not affect subsequent operation of the timer. This is active mode. The microcircuit can work as a monostable oscillator in this case. The microcircuit control current at pin 4 is very small and does not exceed 0.2 mA. This allows you to change the control scheme for its operation. The fact is that with increasing humidity in the area of ​​the "SENSOR" sensor, the resistance of the sensor itself does not change abruptly, but gradually. The resistance of the emitter-collector junction of transistor T1 will gradually decrease in approximately the same way. The supply voltage of microcircuit IC1 increases. At about 3...4 V it starts to generate, but the sound volume in the "REPRO" speaker will be very weak. As the humidity in the sensor area increases, the volume increases.

It is more expedient to try to give the humidity alarm relay properties - the alarm signal should be strong enough even at the minimum permissible level of the controlled parameter (humidity). To do this, it is probably enough to connect pin 8 (+Vcc) of IC1 and resistor R1 directly to the output of power switch S1. Pin 4 of this microcircuit is connected to the emitter of transistor T1 and an additional resistor R3. The second end of this resistor must be connected to the negative power supply of the microcircuit - rice. 2.

As before, while the humidity sensor is dry, transistor T1 is in a non-conducting state. There is no transistor emitter current and no voltage drop across resistor R3. The timer is “inhibited” at pin 4.

When humidity increases, transistor T1 is unlocked, the emitter (collector) current creates a voltage drop across resistor R3. As soon as there is more than 0.4...1 V on this resistor, the timer is unlocked and begins to generate pulses. The relay mode for controlling the operation of the low-frequency generator with a linear change in the resistance of the humidity sensor has been achieved.

In conclusion, I would like to make assumptions in choosing the type of transistor T1 and the value of resistor R3. Since the 555 timer current at pin 4 can be very small (less than 0.5 mA), we will set the collector current of this transistor, for example, 2 mA. This means that with a circuit supply voltage of 9 V, the resistance of R3 can be 4.3 kOhm.

Receiving such a small current through transistor T1 is probably possible even if its gain is not so large. And this allows the use of any types of low-power transistors as T1 without selecting them. It may be advisable to perform the emitter load of transistor T1 in the form of a chain of two resistors (R3 and R4) - rice. 3. This will further facilitate the setup of the circuit.

Literature:
1. Poplachove cidlo vlhoctf // Amaterske RADIO. 2009. No. 12. S.3.
2. B.H. Veniaminov, O.H. Lebedev, A.I. Miroshnichenko. Microcircuits and their application // M.: Publishing house "Radio and Communication". 1989. P.81 -82.

One winter evening I was walking around the Internet looking for a diagram of a soil moisture sensor, and I saw this diagram and I liked it because of its simplicity.

I modified it a little and this is what happened

I routed the tracks to " ", etched the board, soldered the parts and connected the power. I tried to touch contacts D1 D2, the relay clicked, turning the variable made sure that the sensitivity was changing. It seemed like everything needed to calm down, but I remembered that I once took apart a VCR and found what I thought were two resistances (I was not mistaken). Having dug up these resistors in a pile of radio components, I tried to connect one of them and see what happens. By rotating the variable, I made the circuit react to the steam coming from the mouth. You breathe on the sensor and the relay is activated, thus creating an air humidity sensor.

The circuit is very simple with available parts (except for the humidity resistance from the VCR). The device can be used to turn on ventilation in the bathroom, open a window in a greenhouse or greenhouse, and if you replace the resistance with two electrodes, you can automatically turn on watering of plants.

The following parts are used during assembly:

Variable resistor 100 kOhm type R3296; Capacitors 0.022 µF ceramic or film, 220 µF x 16V electrolyte, 470 µF x 25V electrolyte; Resistance 10 kOhm 0.125 W; Transistor KT315 with any letter indexor any analogue of it, for example BC847 ; Diode 1N4007 or any other similar diode; Voltage stabilizer LM7809 (9B) or any other similar; Relay LEG-12 or any other at 12V and the same pin arrangement; Microcircuit K176LA7 or K561LA7 or CD4011 or any of its analogues, the difference between the microcircuits is in the supply voltage;

When using K561LA7 and CD4011 microcircuits instead LM7809 need to install jumper and 12V relay.

If a microcircuit will be used K176LA7, then instead of a jumper (you can see the red jumper between the electrolytes in the photo), you need to solder a stabilizer according to the circuit, since the power supply for this microcircuit is a maximum of 9V. You also need to install a 9V relay instead of a 12V relay.

This is what happened to me

The circuit is adjusted by rotating the variable resistance R1 100 kOhm.

List of radioelements

If you forget for a long time about the dishes with water placed on a hot stove, several liters of water evaporated and the dishes are damaged will not make you happy. 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 circuit diagram of the high air humidity alarm is shown in Fig. 1. At the same time, it can also signal a puddle that has formed on the floor, which will reduce troubles in the event of damage to plumbing or heating equipment or the sink overflowing when the tap is left open for a long time and the drain hole is clogged.

Rice. 1. Diagram of a high air humidity alarm

Gas resistor B1 is used as a sensitive element in the alarm device. These were used in video cassette recorders and video cameras to block the operation of the tape mechanism when the air humidity inside the device was high. Logic elements DD1.1 and DD1.2 form a pulse generator that follows approximately 15 times per minute. This frequency is set by resistors R13, R15, R16 and capacitor C9. Thanks to the VD7 diode, the pulses are significantly (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 resistors R4, R5, R7 is not enough to open transistor VT1. Transistor VT2 is also closed. The logical voltage level at the lower (according to the circuit) input of element DD1.1 is low, which prohibits the operation of the pulse generator on elements DD1.1 and DD1.2, and the output of element DD1.2 is set to a low level, which in turn prohibits the operation of the pulse generator audio frequency on elements DD1.3 and DD1.4.

If the humidity of the air surrounding the gas resistor increases (to check, it is enough to exhale two or three times onto the gas resistor from a distance of 5...10 cm), then the resistance of the gas resistor will increase to 10...20 MOhm. With the increased voltage at the base, transistor VT1 will open, and transistor VT2 will open along with it. A high logical voltage level will be set at the lower (according to the diagram) input of element DD1.1. Both pulse generators will work. The piezo sound emitter HA1 will emit sound signals every 4 seconds, lasting about 0.5 seconds.

Feedback through resistor R7 accelerates the opening and closing of transistors VT1, VT2 and creates a slight hysteresis in their switching characteristics. This ensures clear, rattling-free operation of the alarm when the humidity slowly approaches the threshold. The response threshold is set using trimming resistor R3.

The device will also give a signal if transistor VT1 remains closed and transistor VT2 opens as a result of contacts E1 and E2 being closed by spilled water. Resistors R6 and R8 not only limit the base current of transistor VT2, but also reduce the risk of electric shock to a person who touches the contacts. Mains voltage can reach them as a result of water penetration inside the alarm device or failure of the insulation between the windings of transformer T1.

To prevent the alarm from annoying you 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. For this amount of time, capacitor C8, discharged by pressing the button, will be charged through resistor R17. Resistor R22 limits the discharge current of the capacitor, protecting the button contacts from burning. It should be noted that the restoration 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 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 that the alarm device is connected to the network, and the HL2 LED turns on when sound signals are given, as well as when the generators are blocked by a low voltage level on capacitor C8. Capacitors C1 and C2 prevent false alarms caused by interference.

The 220 V mains voltage is supplied to the primary winding of the step-down transformer T1 through protective resistors R1 and R2. Varistor RU1 protects the transformer from network voltage surges. A voltage of about 17 V from the secondary winding of the transformer rectifies the diode bridge VD2-VD5. All components of the stabilizer are powered by a voltage of +9.2 V, obtained from a voltage rectified using transistors VT3 and VT4 using a stabilizer. Its value depends on the stabilization voltage of the zener diode VD6.

Since the design uses a low-power step-down transformer from a Xerox copy machine as T1, designed for a load current of about 10 mA, the current through the zener diode is chosen to be very small - less than 1 mA. The small 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-manufacturing of a transformer, an W-shaped magnetic core with a cross-sectional area of ​​the central rod of 2 cm 2 is suitable. 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 wire with a diameter of about 0.2 mm. The magnetic circuit plates are assembled across the roof. The finished transformer can be coated with epoxy compound.

Most of the device parts are placed on a circuit board measuring 75x45 mm, shown in Fig. 2. Resistors R6, R8 and resistors R1, R2 with varistor RU1 are mounted on small separate boards.

Rice. 2. Placement of device parts on a circuit board measuring 75x45 mm

A ready-made board from the network adapter was also used, on which diodes VD2-VD5 and capacitor C3 were installed. After manufacturing, all these boards are coated on the installation side with a moisture-proof varnish, for example XB-784. Together with the T1 transformer, they are placed in a plastic case with dimensions of 160x110x32 mm from the RR-701R security alarm receiver.

Gas resistor B1, removed from a Funai VCR, is mounted on a massive metal plate and, together with it, placed in a plastic case measuring 46x42x15 mm (Fig. 3) with holes for air access. Its sensitivity is significantly higher than that of the domestic gas resistor GZR-2B, used in the design described in the article “Light and sound alarm 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 alarm device.

Rice. 3. Gas resistor B1 on a metal plate

The device can use fixed resistors of any type (MLT, S1-4, S1-14, S2-23). It is desirable that resistors R1 and R2 are non-flammable. Trimmer resistor R3 is miniature in a housing that protects it from external influences. It is highly undesirable to use open trimming resistors (for example, SP3-38) due to their low reliability. Varistor RU1 - HEL14D471K or another disk type with a classification voltage of 470 V.

Oxide capacitors - K50-68, K53-19, K53-30 and their imported analogues. Capacitor C8 should have 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 designed for a voltage of at least 35 V.

Instead of diodes 1 N4002, any of the 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. Zener diode BZV55C-10 is replaced by TZMC-10, KS210Ts, KS210Ts1, 2S210K1, 2S210K, 2S210Ts, transistors 2SC1685 and 2SC2058 - with 2SC1815, 2SC1845, SS9014, as well as KT3102, KT6111 series, 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. Please be aware that replacement transistors may differ in case type and pin layout.

The K561LA7 chip will be replaced by the domestic KR1561LA7, N564LA7, 564LA7 (the last two in different packages) or the imported CD4011A.

Choke L1 is a small-sized industrial-made inductance of at least 100 μH and a winding resistance of 3...30 Ohms. Button SB1 - PKN-125.

Sound emitter HA1 is a piezoelectric ringing device for a telephone set. Its own capacitance is 0.03 µF. Other piezo emitters are also suitable, even larger ones, designed for a voltage of at least 20 V. Several such 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 foil on one side. The foil is divided along a broken line by a gap into two insulated parts, one of which serves as electrode E1, and the second as electrode E2. The longer the gap, the higher the probability that the first drops of water falling on the plate will fall on it and short-circuit the electrodes.

Several of these sensors, connected in parallel, can be placed in the most dangerous places from the point of view of water leakage, for example, under heating radiators, washing machines, and water pipe joints. The box with the gas resistor is placed in the place of the room most susceptible 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 takes too long to recover after a decrease in humidity, resistors R4 and R5 with three times less resistance can be installed in the alarm. You can increase the sensitivity of the leaked water sensor by increasing the resistance of resistor R9 to 100 kOhm. By selecting the resistance of resistor R20, you can set the desired tone of the sound signals. To make it easier to check the functionality and set up the alarm, capacitor C8 can be temporarily disabled.

Publication date: 13.09.2015

Readers' opinions

• Ivan / 04/05/2016 - 09:28
  Is there a block diagram, a description of the microcircuits and a printed circuit board?