In the Food program of the USSR much attention is paid to food production in farmlands and suburban areas. A contribution to this important cause made the young Amateurs of RCUT of the Kazakh SSR. They prepared and tested a number of automatic devices that will help to grow agricultural products. The developers sought to create devices that are available for repetition at home. Oki have sufficient accuracy (±5-10%).
When growing seedlings and plants in greenhouses or in heated soil, it is important to maintain the temperature within specified limits. This function successfully executes the automatic temperature controller, made on the basis of electrocontact thermometer with between 0-50°.
The principle of operation is simple. When the temperature drops below the set value triggers the electronic device to the transistor VI (Fig. 1) and the contact system of the relay K1 mku-48 includes heating elements — heating elements with capacity of 0.5—1 kW heaters or with mirrored reflectors.
Relay mku-48 must operate at a voltage of 12 V, so the coil needs rewinding wire PEV 0.18 to fill the frame. With the help of resistor R1 sets the current through the thermometer with the size not more than 15 mA. As V1 you can use any medium power transistor (P4 П213— П215, П217, П601-П605).
Instead of contact thermometer you can use a thermistor (for example, MMT-1). But the electronic part of a second embodiment of a controller more difficult. Thermistor R1 (Fig. 2) included in the shoulder bridge, consisting of resistors R2— R5. R5 potentiometer adjust the operation of the device in the range 15-60°, respectively, graduate scale.
Automatically applied relay RES-10 (RS4 passport.524.314), while establishing it should loosen the spring anchor.
To store seeds and fruits, to grow certain types of plants only at a certain humidity. That’s why in the farm economy or on the country site you need a moisture meter. Version of the device is made on the basis of the device for determining quantities of small containers (3-30 pF), but it is the measured capacitance includes a humidity sensor (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 minimum thickness of 2-3 mm, is made of insulating material (Micarta, fiberglass, plexiglass, plywood). Between these two plates on human hair hanging from the third, made of the same metal (Fig. 4).
The length of the hair is adjusted depending on the type of microammeter: the more sensitive dial gauge, the shorter the hair. For example, for a device with a scale of 25-50 µa hair length is about 40 cm.