Liquid Flow Controller

Drip irrigation system, which is a sort of high-efficiency irrigation technology, can actively promote the development of agriculture. As one of the most important parts of the drip irrigation system, liquid flow rate controller will contribute to the promotion of drip irrigation system and the effective utilization of water resources for its stable property, simple manipulation and convenient applications.This paper describes the development of the liquid flow rate controller in three parts.In the first part we discuss the communication mode between the host and many slaves and how to achieve the application of each way. Through contrasting their strengths and weakness for the different circumstances, different communication mode may be applied according to the conditions. There are two design schemes for control system. The first one is using PC as the host and AT89c52 monolithic integrated circuits as the controller for slaves. The scheme of communication between the host and the slaves can be realized by means of asynchronous serial communication of information transmitted through the cable. The other one is that both the host and slaves are using AT89C52 monolithic integrated circuits as the controllers. They contact a RF module nRF24l01 severally. The communications between the host and slaves access wireless technology. According to the practical situation of the project, we choose the second scheme. The wireless communication possesses good adaptability, which cannot be influenced by factors of geographical environment and does not involve question of wire arrangement, so the application of wireless communication is more convenience.The second section elaborates the hardware structure of the Liquid flow rate controller. The instrument consisting of two parts, the host and slaves, are both use AT89C52 monolithic integrated circuits as controllers. The hardware circuits include several parts:the signal collecting and enlargement circuit, control circuits, the steering gear control circuit, slaves control circuit, the LED display circuit of slaves, RF module circuit of slaves, the power supply circuits, the LCD display of host, the keyboard of host, the host control circuit for RF module, a host serial communication circuits and so on.In the slaves, the circuit for measuring flow rate consists of opto-coupler and dynatron enlargement circuit. When the dripping drops across through the opto-coupler, the circuit generates pulse signals, and then the signals are enlarged by the circuit of dynatrons. Next, regulate pulse signals are exported and then access into MCU controller. Monolithic integrated circuits calculate the signal period, which is the term of a drip, accordingly calculate the flow rate. The host transmit set a value of the rate through the RF module nRF24l01, we can compare the calculate rate with the setting rate value. Then through a wave of PWM which is generated by the monolithic integrated circuits, we adjust the duty factor of the PWM Pulse to change the rotation angle of the steering gear till the actual rate is equal to the set value. The slaves display the current rate on the LED, so we can transmit work state parameters through RF module nRF24l01 to the host. Sometimes if the communication between the host and slaves is failed, there are four keys on the slaves for the workers to adjust the flow rate manually. The main function of the host is realization of man-machine interactions and displaying the interfaces on the LCD. Staffs can control the cursor position through the host keyboard and choose slave to set value of the import liquid drop rate. The man-machine interface shows work state data of slaves through 12864LCD. The host MCU can be contacted to a computer by RS232 serial ports to download and updated programs.The third section elaborates the software design of the Liquid flow rate controller. The software portion includes the host machine's monitoring program and the slave application software using C language.Host machine's monitoring program realizes the convenient inter operation by man-machine interfaces and displaying pages, including the keyboard control program, the LCD panel display control program, and correspondence between host and slave etc.Slave application software realizes the automatic control of slaves, including monolithic integrated circuits initialization process, the dripping control procedures, the steering gear initialization process, the steering gear adjustment process and led display application, detect keyboard process, keyboard execution process, wireless module initialization process, the value of a wireless module set procedures and interrupt functions, etc.