The AT89C51 microcontroller as the core, the work of the refrigerator to control the process, so that energy-saving refrigerators and humane. Introduces the system structure and hardware circuits, software design, the system has strong functions, performance, and reliable.
In recent years, with the microelectronic technology, sensor technology and computer control technology, the refrigerator control people have become increasingly demanding, which is a higher refrigerator controller requirements, multi-functional, humane and Energy conservation is the development direction. Traditional mechanical and simple electronic control has been difficult to meet the development requirements. Therefore, this article describes the use of AT89C51 microcontroller as the core controller of the refrigerator to control the work process, and the refrigerator with a voice broadcast from some of the work process, so that the control process more humane. ASIC through the MCU control of SA8382 PWM signal generated by PWM signal to control the power module to the compressor frequency control. According to the temperature feedback signal to adjust the detection frequency range, reaching the compressor work best to achieve variable cooling, so as to achieve energy savings.
1 System hardware components
The main task of the controller refrigerator compressor control, defrost heating, fans, etc. to maintain the optimal temperature inside the food, the food preservation purposes, that is to ensure that the food stored chilled or frozen after after to maintain color, flavor, moisture, nutrients remain basically unchanged. LED will be set by temperature or actual temperature is not shown, when the freezer temperature is too high or when you open the door for a long time, but also with the voice prompts. System components shown in Figure 1.
1.1 Frequency Control Refrigerator
Refrigerator variable frequency control to change the past, start and stop control, frequency conversion adjustment with asynchronous motor principle, according to refrigerator temperature and cooling demand, generated by SCM SA8382 SPWM signal, drive the power modules of the inverter circuit, the output of different base wave frequency AC voltage, controlled refrigerator compressor rotation speed, thus changing the speed of the process of refrigeration cycle refrigerator to achieve the variable cooling purposes. Refrigerator frequency control circuit diagram shown in Figure 2.
Control system is to be transferred in accordance with the amount of (collection temperature) to control the deviation. In the system, real-time acquisition of the temperature achieved by the temperature detection circuit, at any time the temperature inside the refrigerator temperature sensor LM134 integrated circuit is passed to the temperature T / V, the temperature value into a corresponding voltage value. Through the A / D conversion by the digital acquisition of temperature, into the 89C51 microcontroller. Temperature will be collected to compare with the temperature set value, set value if the temperature is higher than 20 ?, then the frequency will be in accordance with the step of gradually increasing frequency and speed of 1Hz to 50Hz, so that the refrigerator compressor working at high frequency, acceleration refrigeration system cycle, the temperature inside the refrigerator to follow the rapid temperature setting, if the temperature drops below the set value of 20 ?, then the frequency step size in accordance with the rate gradually reduced frequency of 1Hz to 10Hz, so that the refrigerator compressor In the low frequency condition, so that the temperature rise to the set value allows the range. If the temperature had returned to the set value range (± 0.50 ?), then the frequency will be in accordance with the step of gradually increasing frequency and speed of 1Hz or lower frequency to the normal operating frequency of 20Hz, the compressor runs at low temperature state.
1.2 Defrosting heating wire, fan control circuit
Defrost electric heating wire, fan control circuit is simple. By the I / O port output signal, by 8050 inverting drive circuit to control the relay, then the relay control of the creams or fan-powered electric heating wire.
1.3 off memory
System memory expansion to a AT24C01A working state before the power failure, an incoming call based upon the work set before the power failure. AT24C01A for the I2C bus, using AT89C51 the P1 port P1.0, P1.1 for SCL, SDA signal, shown in Figure 3, where R23, R24 for the pull-up resistor, I2C bus to read and write timing is controlled by software.
1.4 voice prompts and alarm circuit
Each time power on, changing work patterns, over-temperature alarm freezer sweet voice will prompt you to in order to ensure proper operation, voice prompt will start to spread some of your refrigerator to use common sense. Alarm circuit is mainly used for the freezer temperature is too high, the freezing temperature display will be shown with some frequency, and use voice prompts "freezer over-temperature." You should check the refrigerator door is closed (please shut the refrigerator door), is a lot more time into the hot food, refrigerator working for some time, the freezer temperature decreases, the freezing temperature display stops flashing, over-temperature alarm automatically eliminated.
1.5 shows the circuit
8 shows the digital circuit by four tubes, used to display the actual temperature of the refrigerator, set the temperature or failure. Section of code to display the data from the microcontroller AT89C51 serial port output, the 74LS164 in the series - and the conversion and latches. Four 74LS164 respectively, corresponding to the four common anode drive and realization of digital static display to improve display brightness.
1.6 Power off, under-voltage protection circuit
The circuit mainly by the power transformer, rectifier, filter, regulator and test integrated circuits MAX813L composition. When an overvoltage or undervoltage time, MAX813L the RESET pin output sent to MCU and dealt with accordingly high.
2 System software architecture
The system software mainly consists of the main flow, functional subroutines, interrupt service routines. Mainly by the keyboard scan subroutine, key code analysis, temperature measurement, sensor detection, artificial intelligence module, the refrigerator temperature acquisition and control, freezer temperature acquisition and control, display digital computation modules, memory modules and other components operating parameters, such as the main process Figure 4.
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2.1 Function subroutine
Keyboard scanning and key code analysis routines, in the scan to button, according to the current operating status and key to change the operation flag, and start the timer, if the key will be valid for 5 seconds continuously set the corresponding control unit. Artificial intelligence module level by detecting the ambient temperature, automatically determines the temperature of the freezer and refrigerator set, if the environmental temperature is high, the corresponding to refrigerator, freezer temperature is set higher; if the ambient temperature is low, the corresponding to refrigerator, freezer temperature is set lower, so that the compressor is running or not running a long time. Freezer (refrigerator) temperature acquisition and control, through the freezing chamber (refrigerator) freezer temperature sensor acquisition (refrigerator) temperatures, the data into the display buffer, and the measured temperature freezer (freezer) to set the temperature value of the comparison, if the measured temperature is higher than set temperature, the home freezer (freezer) high marks, otherwise.
Down frequency control 2.2 refrigerator
System control program, in order to prevent excessive lifting frequency generated over voltage, over current, taken step by step down the frequency of the control method, through the Interrupt Control Program. Up-down-conversion interrupt control procedures established by the state under the determined words voltage refrigerator compressors in what will eventually run frequency. Program by reading the current frequency refers to the frequency of direct comparison with the final decision is up-or down-or remain at 20Hz, and then rewrite the SA8382 by the power control register in the frequency control word to achieve it. Interrupt control program changes the power frequency control word, is the use of look-up table to achieve. About the power of each frequency 0-50Hz frequency control word corresponding calculated fitted to the table, into the data store. Running, by frequency pointer plus 1 or minus 1, the end of the frequency control word check store address, remove the corresponding data, write SA8381 control register, the output PWM wave fundamental frequency changes, so as to control the work of refrigerator compressors frequency change, to achieve lift-frequency control. Control process shown in Figure .
