Abstract: With the popularity of refrigerators in daily life, people have higher and higher requirements for the performance and control functions of electric hail. In order to meet the needs of people in real life, AVR microcontrollers are the core, through hardware and The software designed the control system of the refrigerator. The test results show that the performance indicators and functions of the system have achieved the intended purpose, and have the advantages of complete functions, simple operation and convenient use. The system is at a high level in its class and has high practical value.
For many years, refrigerators have been used as storage and preservation space in the domestic market. People's demand for refrigerators is also the most basic function of freezing and freezing. In recent years, with the popularity of household refrigerators and the rapid rise of the mainstream consumer groups after the 1980s, people have become more and more demanding on the performance of refrigerators, accelerating the transformation and upgrading of the functions and needs of refrigerators, and correspondingly The control function requirements of the refrigerator are also getting higher and higher.
Since the advent of the MCU, the performance has been continuously improved, and the functions have been continuously improved and improved. In addition, it has the characteristics of high integration, strong function, fast speed, small size, low power consumption, convenient use, reliable performance and low price. Therefore, it is widely used in Industrial control, intelligent instrumentation, data acquisition and processing, communication systems, advanced calculators, household appliances, etc., the design of the refrigerator control system based on AVR microcontrollers makes full use of the single-chip technology in the control system of the refrigerator, for modern electricity The development of the refrigerator provides technical support.
1 overall system design
The designed refrigerator control system is based on AVR microcontroller, including hardware design and software design. The entire system has the following features;
1) periodically check the temperature of the freezer compartment and the refrigerating compartment in the refrigerator, manually specify the temperature of the freezer compartment and the refrigerating compartment through the keyboard, and display the set value;
2) Regularly measure the frost thickness and automatically defrost when the frost thickness reaches 3 mm;
3) Regularly check the working voltage, and carry out over-limit alarm and prohibit the compressor from working;
4) Regularly check the status of the door switch and perform the door opening delay for 2 minutes;
5) The single chip determines whether the temperature detected by the freezer compartment and the refrigerating compartment is within the set range, and makes the start and stop operation of the compressor, and the cooling compressor can automatically restart after 3 minutes of stopping after stopping;
6) manually set the continuous cooling time value through the keyboard, and display the set value, the single chip determines whether the quick cooling time is within the set range, and performs the quick cooling operation;
7) Display various states in the system using display circuits.
1.1 Hardware Design
The hardware component block diagram of the refrigerator control system based on AVR is shown in Figure 1. It mainly includes AVR microcontroller, A/D converter, detection circuit, alarm circuit, control circuit, clock and reset circuit, function key and display circuit. .
Figure 1 Hardware block diagram of the control system
AVR microcontroller is a high-speed embedded microcontroller, which is the core component of the entire control system. Because of its high speed, low consumption, confidentiality, low cost, etc., it has been widely used in military, industrial, household appliances, smart toys, portable smart meters and robot production, which greatly enhances product function, accuracy and quality. Low failure rate, high reliability and low cost.
An A/D converter, an analog-to-digital converter, is an electronic component that converts an analog signal into a digital signal. The design uses ADC0809, which is a CMOS process 8-channel, 8-bit successive approximation A/D converter manufactured by National Semiconductor. It has an 8-channel multiplexer inside, which can latch the decoded signal according to the address code and only strobe one of the 8 analog input signals for A/D conversion. It is the most widely used 8-bit universal in China. A/D chip.
The detection circuit mainly completes the temperature detection, frost thickness detection, working voltage detection, and door switch state detection of the freezer compartment and the refrigerating compartment in the refrigerator, and transmits the corresponding information to the single piece for processing. The design of the detection circuit includes the design of circuits such as freezing compartment and refrigerating compartment temperature detection, frost thickness detection, power supply voltage detection, and door opening state detection.
The temperature detecting circuit mainly performs the freezing chamber temperature detection and the refrigerating chamber temperature detection. The frost thickness detecting circuit mainly detects the thickness of the frost so as to automatically defrost when the frost thickness reaches 3 mm. The power supply voltage detection circuit mainly detects the working voltage, and performs an over-limit alarm and prohibits the compressor from working. The alarm circuit mainly sends an alarm signal when the power supply voltage detecting circuit detects that the working voltage exceeds the limit. The control circuit mainly controls the start and stop operations of the refrigeration compressor and the defrosting electric heating wire. Clock and reset circuit clock and reset circuit mainly provide clock and reset signal to the microcontroller to ensure that the microcontroller can work normally. The function keys and display circuit mainly realize setting and quick cooling control settings of the freezer compartment and the refrigerating compartment by the keyboard, and simultaneously displaying the set value and the setting flag and various states of the system.
1.2 Software Design
The software design of the refrigerator control system based on AVR mainly includes the design of main program, subprogram and interrupt program.
1) Main program
The main program is the total control program of the entire refrigerator, such as initialization of the control unit, control interruption, timing, display, startup and repetition of the keyboard program. The main program flow block diagram is shown in Figure 2.
Figure 2 main program flow diagram
2) Subroutine
The subroutine includes a display subroutine, a keyboard scanning subroutine, a corresponding display subroutine according to the flag bit adjustment, a plus and minus one processing subroutine, a read ADC0809 channel conversion number subroutine, a quick cooling processing subroutine, a temperature comparison and processing subroutine, and 8 subroutines such as the defrosting control subroutine.
The display subroutine is to output the data of the display buffer one by one from the RXD terminal to the display to display the data and status. The keyboard scanning subroutine has the function of judging whether there is a key press on the keyboard and a key number for judging the closing.
According to the flag bit, the corresponding display subroutine is to convert the corresponding set number into 7 through the 7-character code according to the content of the flag bit and then send it to the display buffer.
The plus one and minus one processing subroutines are all when the main program judges to add one or subtract one operation, or the corresponding setting number is increased by one or minus one according to the flag bit.
Reading the ADC0809 channel conversion number subroutine starts ADC0809 and reads the converted number into the corresponding buffer.
The rapid cooling control subroutine is to manually set a continuous cooling time, and the single-chip microcomputer performs control to let the continuous working time of the compressor be the set continuous cooling time.
The temperature comparison and processing is to compare the average temperature of the freezer compartment temperature with the actual temperature of the refrigerator compartment temperature and the set temperature, and if it is out of range, it will be processed, otherwise it will return.
The defrosting control subroutine compares the converted value of ADC0809 with the corresponding value when the frost thickness is 3 mm. If it is less than 3 mm, defrosting is not required, otherwise the defrosting heating wire is started for defrosting.
3) Interrupt program
When the central processor is processing internal data, an external emergency has occurred, requiring the CPU to suspend the current work to handle the emergency. After processing, return to the original interrupted address and continue the original work. This process is called interrupt. The part that implements this function is called the interrupt system. The source of the request for the CPU interrupt is called the interrupt source. The program that handles the "quick" is called the interrupt service program, which is a specific program compiled in advance. The T0 and T1 interrupt service procedures are involved in this system.
The T0 interrupt service routine mainly completes the conversion of the ADC0809 channel, the undervoltage of the power supply voltage, the overvoltage processing, and the detection and processing of the parallel gate status.
The T1 interrupt service program mainly completes the 3 min timing and compares, analyzes, and controls the execution of each component based on the detection results. That is, rapid cooling treatment, temperature comparison and processing, frost thickness control and processing are performed.
2 Conclusion
The system has been tested many times after the design. The test data shows that the performance indicators and functions of the system have achieved the expected design goals. It has the advantages of complete functions, simple operation and convenient use. It is in the domestic similar products. High level, with high practical and promotional value.
references:
[1]. ADC0809 datasheet http://
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