| The 21st century is the biological science and the agricultural engineering technology century. Making the engineering technology and the biological technology to close coordination, providing the high level facility equipment as far as possible, establishing the consummation cultivation control system and cultivating the improved seed are the keys to develop the facility agriculture. According to the crops' characteristic, establishing high automation control system, complete set advanced transportation nutrient liquid system and necessary series equipment have become facility agricultural development direction.The modern agriculture tends to select the method of soilless culture. The soilless culture does not use the natural soil, but is the nutrients which the plant growth must to need to be dissolved in the water mixing the nutrient liquid and providing the nutrition by the nutrient liquid to cultivate crops. The widely uses of soilless culture technology is now the major characteristic of the world installation horticulture production. It changed the traditional ideas of survivaling on land and the way of cultivating soil.And the soilless culture is the main form of the crops factorization production and the new way of developing effective agricultural.As the modern agricultural production way, soilless culture has the very big superiority and the the huge productive forces. Mainly displays in such several aspects:⑴Enhances the crops output, improves product quality.⑵Reduces the production cost, enhances the working efficiency.⑶The production is the true non-environmental damage and the non-pollution organic foods.⑷Adapts the region to be widespread, is advantageous in the realization factorization production.⑸Avoids the soil continuous cropping barrier. Our country's soilless culture technology still was at the initial stage, but the nutrient liquid mixed is the foundation of soilless culture technology and one of the modern facility agriculture key technologies. The supply of the nutrient liquid has the direct influence on the crops' growth condition and the state of health which could affect the output and the quality of the production. Therefore, in order to enhance working efficiency better and to improve the control device of the nutrienr liquid mixs and supplies, this article develops a set of circulating control system of soilless culture nutrient liquid according to the characteristic of soilless culture carring on the examination and the control to the nutrient liquid. This control system takes the potential of hydrogen and the density of the nutrient liquid as the primary control parameter. Its realization to enhances the benefit of the facility agriculture has the extremely vital role.After analyzing the present situation and the characteristic of our country's soilless culture nutrient liquid, the system regards single-chip microcomputer as the core. Main research work is as follows:⑴After detailing analyzed the ways of soilless culture in domestic and international, we consider that the system regards single-chip microcomputer as the core of automatic control system.⑵After comparing all kinds of single-chip microcomputers, we choose AT89C51 of the company of ATMEL. It can simplify the electric circuit greatly.⑶The part of data acquisition uses the PH sensor and the EC sensor gathering data, and then passes to the monolithic integrated circuit through the amplifier the signal the I/O mouth, so that it could achieve controls effectively.⑷Using the ADC0809CCN chip, gathers various sensors the simulated signal to transform into the digital signal and transmits carry on processing to the monolithic integrated circuit.⑸Using the HD74LS164P chip to actuate eight light emitting diodes monitors and using for to demonstrate examines PH value and EC value. There is only two serial interface lines that the HD74LS164 connected with the the single-chip microcomputer, comparing with other chips, simplified the electric circuit board and reduced the system cost. ⑹Using the weak electricity to control the strong electricity principle, the control section lets the relay circular telegram. And then controls each solenoid valve opening that could realize the function of crops nutrient liquid automatic configuration.⑺Writing the procedure of the software with assembly language.⑻Draws up the circuit diagram with Protel, welds panel the electric circuit according to various part of circuit design the circuit element. Uniting the hardware and the software carry on the debugging.This design carries on the design according to the total design project of system, selecting all chips first: single-chip microcomputer AT89C51, and the chip HD74LS164, and A/D switch, and the chip ADC0809 and so on, completed the design of each parts of electric circuit, including: repositions the electric circuit, Oscillating circuit, the examination electric circuit, shows electric circuit, control circuit and so on. After completing the electric circuit design, weld the electric circuit component according to the design of the electric circuit board, and does the electric circuits test. At the same time, write the procedure of assembly language for the system. The soft hardware consociation adjusts to try, completing the creation of the system.
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