Greenhouse irrigation control. Scheme, description

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Greenhouse irrigation control. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Home, household, hobby

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The relative humidity of the air in the greenhouse is controlled using a sensor installed in it, according to the readings of which the water supply actuator (pump or solenoid valve) is turned on and off. According to the principle of operation, humidity sensors are capacitive and resistive. The former have an almost linear moisture-capacity relationship and are more accurate. The latter are characterized by a logarithmic dependence of electrical resistance on humidity.

If the relative humidity of the air varies over a wide range from 0 to 100%, it is preferable to measure it using a capacitive sensor. Its sensitive element is a multilayer structure formed by flat platinum plates and a thermosetting polymer filling the space between them [1, 2].

Greenhouse irrigation control
Fig. 1

An 808H5V6 sensor [3] with a conversion factor of about 30 mV per percentage of relative humidity was selected for use in the instrument. A typical dependence of the output voltage (between pins 2 and 1 of the sensor) on the relative humidity of the ambient air at a supply voltage of 3,3 V (between pins 3 and 1) is shown in fig. 1 blue line. In the same place, a thin red line shows an ideal directly proportional dependence for comparison.

Rice. 2 (click to enlarge)

The scheme of the automatic irrigation control is shown in fig. 2. The output voltage of the humidity sensor B1 is fed to the input of the K1003PP1 (DA3) microcircuit, a description of which can be found in [4]. It is a simple analog-to-digital converter containing a resistive divider of the reference voltage (potential difference between the UH and UL inputs) into 12 equal parts and 12 comparators that compare the voltage applied to the IN input with the corresponding share of the reference voltage. The number of triggered comparators and outputs of the microcircuit, which are set to a low voltage level, sequentially increases as the input voltage changes from the lower limit UL to the upper limit Un.

The outputs of the DA3 chip are made according to the open collector circuit and are designed for connecting LEDs that form a linear voltage scale. In the described design, these outputs, united by a chain of normally closed switches SA2-SA12 connected in series into a "mounting" logic element OR, control a powerful triac VS1 through the triac optocoupler U1.

The lower limit of the input voltage of the DA3 microcircuit (0 V) is set by connecting its UL input to a common wire, and the upper limit (3 V) is its UH input through a resistive voltage divider R1R2 with the output of the DA2 microcircuit, which stabilizes the supply voltage of the B1 sensor (3,3 V) . According to the graph in Fig. 1, this corresponds to the range of relative humidity measured by the sensor 0...100%.

The level at which the relative humidity stabilizes is set using switches SA2-SA11. For example, if switch SA7 is open and the others are closed, the greenhouse irrigation system will turn off when it reaches approximately 56% RH and turn on when the humidity drops below the specified value. The power of the triac VS1 must be sufficient to control the pump or solenoid valve of the irrigation system.

The DA1 chip is a standard linear voltage regulator. It is used to power the entire device with a voltage of 12 V.

After assembling the device, it is necessary, first of all, to check the sensor B1 by placing it in an environment with a relative humidity of about 100%, for example, wrapping it in a damp cloth. The output voltage of the sensor under these conditions should be about 3 V. Then, by selecting the resistor R1, the exact same voltage is set at pin 3 (input UH) of the DA3 chip. This completes the setup.

Literature

Berliner M. A. Moisture measurements. - M.: Energy, 1973.
Vigleb G. Sensors: Per. with him. - M.: Mir, 1989.
808H5V6 Humidity Transmitter. - sensorelement.com/humidity/808H5V6.pdf
Novachenko IV et al. Microcircuits for household radio equipment. Directory. - M.: Radio and communication, 1989.

Author: A. Kornev

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