Automatic thermostat for the backyard. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power regulators, thermometers, heat stabilizers

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When growing seedlings and plants in greenhouses or on heated soil, it is important to constantly maintain the temperature within the specified limits. This function is successfully performed by an automatic thermostat based on an electric contact thermometer with limits of 0-50°.

(click to enlarge)
Rice. 1. Schematic and wiring diagram of a temperature controller based on a contact thermometer
Rice. 2. Schematic and wiring diagram of a thermostat based on a thermistor
Rice. 3. Schematic and wiring diagram of the moisture meter
Rice. 4. Moisture sensor device: 1 - nail, 2 - human hair, 3 - fixed plates, 4 - movable plate, 5 - base
Rice. 5. Principal and wiring diagrams of the attachment of the automatic humidity level controller
Rice. 6. Schematic and wiring diagrams of the first version of the light-dependent regulator
Rice. 7. Schematic and wiring diagram of the second version of the light-dependent regulator
Rice. 8. Principal and wiring diagrams of the watering machine

The principle of operation of the device is simple. When the temperature drops below the set value, the electronic device on the VI transistor (Fig. 1) is activated and the contact system of the K1 MKU-48 relay turns on the heating elements - heating elements with a power of 0,5-1 kW or heaters with mirror reflectors.

The MKU-48 relay should operate at a voltage of 12 V, so its winding must be rewound with a PEV 0,18 wire before the frame is filled. Using resistor R1, the current through the thermometer is set to a value of not more than 15 mA. Any medium power transistor (P1, P4-P213, P215, P217-P601) is suitable as V605.

Instead of a contact thermometer, you can use a thermistor (for example, MMT-1). However, the electronic part of the second version of the thermostat is more complicated. Thermistor R1 (Fig. 2) is included in the shoulder of the bridge, consisting of resistors R2-R5. Potentiometer R5 regulate the operation of the device within + 15-60 ° and calibrate the scale accordingly.

The RES-10 relay (passport RS4.524.314) is used in the automatic device; when adjusting it, the armature springs should be loosened.

It is possible to store seeds and fruits, to grow certain types of plants only at a certain humidity. That is why a humidity meter is needed in a household plot or in a summer cottage. A variant of such a device is made on the basis of a device for determining the values ​​of small capacitances (3-30 pF), but instead of the measured capacitance, a humidity sensor is installed in it (Fig. 3). It consists of two copper (preferably silver-plated) plates with an area of ​​15 cm2 each, fixed at a distance of 6-7 mm from each other on a rigid base with a thickness of at least 2-3 mm, made of insulating material (getinax, fiberglass, plexiglass, plywood). Between these two plates, a third one, made of the same metal, is suspended on a human hair (Fig. 4).

The length of the hair is selected depending on the type of microammeter: the more sensitive the dial indicator, the shorter the hair. For example, for a device with a scale of 25-50 µA, the length of a hair is approximately 40 cm.

The humidity meter is calibrated according to an identical industrial one - the maximum deviation of the arrow corresponds to 100% humidity, the minimum - 10%.

Capacitor C3 serves to test the device and has such a value that when it is connected (without a sensor), the microammeter needle deviates as much as possible.

By modifying the meter, it is easy to turn it into an automatic machine for maintaining a given humidity. To the circuit section marked with the letter A (see Fig. 3), a trigger with an electromagnetic relay is connected (Fig. 5). Variable resistor R1 sets the level of operation of the automatic device at a given percentage of humidity.

As humidity rises, the square wave voltage through diode V1 charges capacitor C1 to a level that opens transistor V2. The trigger is activated, and the contact plates of relay K1 turn on the fan. When the humidity drops to a predetermined level, V2 closes and the trigger turns off the relay K1 RES-10 (passport RS4.524.314). When setting it up, you need to loosen the clamping springs.

Seedlings and early vegetables require a certain amount of light for normal development. It will be provided by a light-dependent regulator (Fig. 6). With the onset of twilight, the resistance of the photoresistor R2 increases, and the transistor V1 gradually closes, and V2 opens. The lamp H1 glows depending on the current flowing through the semiconductor triode V2. Accordingly, the resistance of the photoresistor R4 in the control electrode circuit of the trinistor V3 changes, thereby adjusting the intensity of illumination. The total power of H2 lamps depends on the type of triode thyristor.

The device is assembled on two separate boards, installed next to each other in such a way that the lamp H1 and the photoresistor R4 form an optocoupler pair, they are covered with an opaque cap.

If we need to set a certain level of illumination, assemble an automatic device with a manual lamp intensity control. It is made on a variable resistor R3 (Fig. 7). The control voltage is supplied from a divider, consisting of a photoresistor R1 and resistors R2, R3, to a triode thyristor V5. When R1 is darkened, its resistance increases, and the voltage drop across it increases. As a result, the V5 trinistor opens more strongly, the H1 lamp burns brighter. Capacitor C1 smooths out the ripple of the rectified voltage. The photoresistor SF-2 can be replaced with a similar one of any type (for example, FSK-1, FSK-2).

Moisture-loving plants require that the soil is always sufficiently moist, but not excessive. Automation will also help here. Consisting of two transistors V1, V2 (Fig. 8), an electronic device - a soil humidifier - is connected to a sensor stuck into the ground - two stainless steel plates 20-25 mm wide. Their length depends on the depth of soil moisture, and the distance between the plates is selected experimentally - it largely depends on the type of soil. The places where the wires are connected to the sensor must be covered with waterproof paint.

The level of operation of the automatic device is set by a variable resistor R1, which, using the contact plates of the relay K1, turns on the solenoid connected to the valve that controls the water supply.

The level of operation of the device is limited (in order to prevent waterlogging of the soil) by shunting the sensor with a variable resistor (shown in the diagram by a dotted line).

Transistors MP139-MP 12 (V1) can be used in the device, and any semiconductor triode of medium power (P2, P4-P213, P215, P217 - P601) is suitable as V605. K1 - RSM-2 relay (passport 1017.181.02).

See other articles Section Power regulators, thermometers, heat stabilizers.

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