Automatic watering the garden. Encyclopedia of radio electronics and electrical engineering

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The proposed machine will free the owner of a summer cottage from worrying about timely watering the garden. It will not only supply the irrigation system with the amount of water necessary for sufficient soil moisture, but will also replenish its stock in the storage tank in time. The parts needed to assemble the machine are easy to find even in areas remote from industrial centers.

The problem of "automation" of the garden on the pages of the magazine "Radio" paid a lot of attention. A variety of options for its solution were proposed [1-7], each with its own characteristics. After their analysis, it was decided to develop their own version of the machine, combining the advantages of the considered ones and, if possible, devoid of their shortcomings.

To control the watering of plants, first of all, you need a sensor that reacts to soil moisture. As shown in fig. 1, it is made of two single-sided foiled fiberglass plates 1 with dimensions of 150x25x2 mm. Each drilled 70-80 holes with a diameter of 1,5 mm, distributed evenly over the entire surface.

(click to enlarge)

Plates 1 with connecting wires soldered to the foil are fixed parallel to each other with the foil inside using screws 2 and insulating bushings 4. In two places between the plates there are foam inserts 3 (workpiece dimensions 25x20x12 mm). The assembled sensor is wrapped around the perimeter with adhesive tape, which protects against ingress of soil particles.

The sensor is buried in the ground to a shallow depth. The foam rubber absorbs water penetrating through the holes in the plates, as a result, the electrical resistance of the sensor (1 ... 2 MΩ in a dry state) decreases to 40 ... 200 Ohms when fully saturated with moisture.

The second sensor - the water level in the storage tank - is made of a piece of power cable AVVG 4x4 mm2, inserted into the tank from above. The ends of the four aluminum wires are approximately 200 mm stripped of insulation. Two wires connected together form a common sensor electrode. Their ends are fixed horizontally at the very bottom of the tank. The end of the third wire is similarly placed 150 mm higher.

This is the "Little" electrode. The end of the fourth wire (electrode "Many") is located in the upper part of the tank at a sufficient distance from its cutoff to prevent overflow.

The scheme of the automaton is shown in fig. 2. The watering control unit is assembled on transistors VT1 -VT3 and relay K1. As long as the soil moisture is satisfactory and the resistance of the sensor is low, the transistor VT1 is closed, and the transistor VT2 that forms the Schmitt trigger with it is open. The voltage supplied through the emitter follower on the transistor VT3 to the winding of relay K1 is not enough to operate the latter.

As the soil dries out, the resistance of the sensor and the voltage at the base of the VT1 transistor increase. At a certain point, the voltage will become sufficient to switch the trigger. The voltage on the winding of relay K1 will increase abruptly. When activated, it closes the power circuit of the solenoid valve, which opens the access of water from the storage tank to the irrigation system or the pump that supplies water to it. A blinking green LED HL3 will indicate that watering is in progress.

With soil moisture, the sensor resistance will drop, the voltage at the base of transistor VT1 will become less than the trigger switching threshold, which will lead to the device returning to its original state. Watering completed.

The operation of relay K1 at the desired humidity is achieved by adjusting the tuned resistor R3. Sometimes you have to change the value of the resistor R2.

Diodes in the emitter circuit of transistors VT1, VT2 - from different semiconductor materials (VD4 - germanium, VD5 - silicon). This improves the temperature stability of the instrument's response threshold.

Capacitor C7, increasing the response and release time of the relay, eliminates the "bounce", often preceding switching. It also reduces the amplitude of voltage surges on the relay winding to a safe value. Diodes VD1 and VD2, together with capacitor C4, serve to eliminate the harmful effects of pickups, inevitable at high the length of the wires connecting the machine to the humidity sensor.

Relay K1 - RMU passport RS4.523.330 (winding resistance - 430 Ohm). You can also use others, designed for switching AC circuits with a frequency of 50 Hz, a voltage of 250 V at a current of up to 5 A. For example, the PE-36 series with a 24 V DC coil.

The control device for water supply to the storage tank consists of two almost identical units that respond to its minimum and maximum levels. When the tank is empty, the resistors R1 and R5 support the log level at the inputs of the elements DD1.1 and DD1.2. 1. The R6C2 and R7C6 circuits serve as filters that suppress interference and impulse noise.

The level at the outputs of the above elements in this state is log. 0, and at the outputs of the elements DD1.3 and DD1.4 - log. 1. LED HL1 (flashing red) is on and indicates that the tank is empty. LED HL2 (green glow) off. Transistors VT4-VT7 are open.

The activated relay K2 closes the winding circuit of the short circuit relay, as a result of which it also works, and the HL4 LED (yellow glow) turns on. KZ.2 contacts close the power circuit of the pump that supplies water to the tank.

Water reaching the "Little" electrode will drastically reduce the resistance between it and the common electrode. log level. 1 at the input of the element DD1. 1 will change to log. 0. As a result, the HL1 LED will go out and the composite transistor VT4VT6 will be closed. However, due to the closed contacts K3.1, this will not lead to a change in the state of the relay K2 and short circuit and the pump will continue to work.

When the tank is filled to the "Many" electrode, the state of the elements DD1.2 and DD1.4 will change, the HL2 LED will turn on and the composite transistor VT5VT7 will be closed. The HL4 LED will go out, the short circuit relay, followed by K2, will release the anchors. The supply of water to the tank will be stopped and will not resume until its level drops below the "Low" electrode, after which the above process will be automatically repeated.

Relay K2 - RES22, passport RF4.500.131 or RES9, passport RS4.524.200. Short circuit relay similar to K1. If the pump electric motor has a power of more than 1 kW, an electromagnetic starter of the appropriate power is required to turn it on, for example, the PME-100 or PME-111 series. In such a case, contacts K3.1 must switch the starter winding circuit.

The supply voltage of the machine (24 V), even in "field" conditions with high humidity, does not pose a danger to humans. However, against its accidental contact with a voltage of 220 V, for example, if the insulation between the primary and secondary windings of the power transformer is damaged, all measures must be taken. It is best to use a transformer whose windings are in different sections of the frame. The possibility of quick automatic or manual emergency disconnection of both outputs of the primary winding from the network should be provided.

The common wire of the device should be reliably grounded, and all work should be carried out in compliance with the "Rules for the Design and Operation of Consumer Electrical Installations" and fire safety measures.

Literature

1. Akhmetzhanov N. Pump control unit. - Radio, 1989, No. 2, p. 25.
2. Belenky V. Automatic for a greenhouse. - Radio, 1990, No. 11, p. 34-36; No. 12, p. 36-39.
3. Kalashnik V. Automatic pumping station. - Radio, 1991, No. 6, p. 32, 33.
4. Vaganov A. With a floatless sensor. - Radio, 1992, No. 1, p. 23, 24.
5. Agarkov A. With a float-reed sensor. - Radio, 1992, No. 1, p. 24, 25.
6. Nechaev I. Automatic pump control. - Radio, 1995, No. 3, p. 38, 39.
7. Tatarko B. Automatic water pump control. - Radio, 2003, No. 8, p. 46.

Author: A.Markov, Tuloma, Murmansk region

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