Application of SPMC65P2408A single chip microcomputer in refrigerator

1 Introduction
At present, household refrigerators can be divided into two types according to the cooling method inside the box: indirect cooling type and direct cooling type. Indirect cooling type refrigerators are commonly known as frost-free refrigerators, and direct cooling type refrigerators are commonly known as frost-free refrigerators. According to different classifications, refrigerators can be divided into the following types:

Since 2000, the sales volume of household steam compression refrigerators has been increasing day by day. According to Internet news, in 2001, a total of 13.49 million refrigerators were produced in China, an increase of 5.63% over 2000, of which more than 3 million were exported, increasing year by year. The domestic digestion capacity is only 9 to 10 million units. Haier, Kelon, Xinfei, Meiling and other four companies occupy the leading position in the market, and their sales in 2001 exceeded 1 million units.
In a public opinion survey of urban households, the penetration rate of refrigerators has reached 85.4%, of which 3.6% of households own two refrigerators. At present, the volume of refrigerators owned by urban households is relatively scattered, among which 160-200 liters is the most owned volume segment. From the perspective of the time when urban households purchased refrigerators, refrigerators purchased before 1994 dominated the market, reaching 51%, of which refrigerators purchased before 1990 accounted for 23.4%. Based on the service life of refrigerators of 10-15 years, these refrigerators will enter the renewal period one after another, thus constituting the main body of the urban refrigerator market consumption demand in the next five years. The survey results show that urban households are basically satisfied with the refrigeration function of the refrigerators they use, but are less satisfied with the operating noise and power consumption of the refrigerators. This will indicate that refrigerator products with "quiet", "safe" and "energy saving" as the entry point will have a wide demand space in the market in the future.

2 Refrigerator functions
◆ Artificial intelligence, automatic temperature adjustment: In the state of artificial intelligence, the refrigerator can automatically adjust the temperature setting as the ambient temperature changes. Without manual adjustment, it can achieve the best refrigeration effect, making you more worry-free and labor-saving.
◆ LED display, digital temperature control: Using LED display technology, the operation of the refrigerator is dynamically displayed. The temperature of the refrigerator and the freezer can be set and displayed separately, which is clear at a glance, allowing you to understand the operation of the refrigerator in time and use it more conveniently.
◆ Refrigeration and freezing temperature adjustment: The refrigeration temperature can be set between 2℃ and 10℃; the freezing temperature can be set between -16℃ and -26℃ or -7℃.
◆ Multi-temperature preservation function: The freezing temperature can be set at -7℃ to enter the multi-temperature preservation function. By controlling the temperature of the refrigerator, there are multiple temperature zones in the refrigerator. Different areas are suitable for storing different types of food and deadlines.
Quick freezing function: Using cell preservation technology, with super-strong refrigeration capacity, the food quickly passes through the maximum ice crystal formation zone without destroying the cell structure, maintaining cell vitality, and preventing the loss of nutrients, with a good preservation effect.
◆ Refrigeration on/off function: The refrigerator can be forced to close (the refrigerator is not refrigerated), and the refrigerator temperature display goes out at the same time.
◆ Automatic defrosting function: During the operation of the refrigerator, the accumulated running time of the compressor is continuously detected, the number of door openings and the time and ambient temperature are recorded, and the defrosting conditions are determined. When the defrosting conditions are met, the defrosting heating wire is connected, and the compressor and the fan are disconnected at the same time, and the air door is closed. After 30 minutes, the defrosting heating wire is disconnected, and the compressor is connected. After another 15 minutes, the fan is connected to enter the normal control cycle.
◆ Compressor power-off delay protection function: Each time the refrigerator is turned on and powered on, it checks whether the compressor shutdown time has been delayed for 5 minutes. If the compressor has been delayed for 5 minutes, the compressor can be started immediately; if the compressor delay is less than 5 minutes, it will continue to delay for 5 minutes before the compressor can be started.

3 Introduction to the overall system plan
The hardware block diagram is shown in 3-1. It mainly consists of two parts: the main control board and the power board. The main control board is mainly composed of a single-chip microcomputer, a sensor group, a compressor control circuit, a solenoid valve control circuit, a display circuit, a buzzer output, a defrost control circuit, an electric heating wire control circuit, and a fan control circuit. The power board mainly provides 5V power for the main control board and provides power for the compressor, fan motor, etc.

Figure 3-1 Control system block diagram

4 System Hardware Design
The entire hardware system consists of two parts: the power board and the main control board. The main control board mainly consists of the display part, the button part, the sensor part, the power-off memory part, and the crystal oscillator clock part, as shown in Figure 4-1.

Figure 4-1 Refrigerator hardware schematic

4.1 Power supply part
The power supply part mainly converts 220V into relay control power supply and system 5V power supply. The voltage in front of 7805 is used for relay control power supply. The 5V voltage generated after 7805 enters the control board after passing through a 0 ohm resistor to supply power to the entire system. The principle is shown in Figure 4-2

Figure 4-2 Schematic diagram of power supply

4.2 Keyboard input circuit
The keyboard input circuit is shown in Figure 4-3. When a key is pressed, the corresponding IO port is pulled to a high level and the CPU performs corresponding processing.

Figure 4-3 Keyboard input circuit

4.3 Sensor input circuit
The sensor is mainly composed of temperature sensors such as freezer, refrigerator, freezer evaporator coil, refrigerator evaporator coil quick freezing chamber, and ambient temperature detection. The temperature sensor uses a thermistor with a negative temperature coefficient. Its control principle is shown in Figure 4-4.

Figure 4-4 Display circuit

4.4 Display Circuit
The display circuit consists of four 8-segment digital tubes. The interface circuit is shown in Figure 4-5 and is driven by dynamic display.

Figure 4-5 Display circuit

4.5 Control drive circuit
The working principle of the compressor is to output signals from the I/O port, control the relay through the Q1-Q4 drive circuit, and then control the start and stop of the compressor by the relay. The start and stop of the compressor is determined by the temperature of the relevant room. Before each startup, it is necessary to detect whether the delay protection conditions are met before making a startup decision. The control circuit is shown in Figure 4-6.

Figure 4-6 Control drive circuit

4.6 Power-off memory circuit
The system expands an AT24C01A to memorize the working status before power failure, and it still works according to the settings before power failure after power is restored. AT24C01A is an I2C bus, and the IO port of SPMC65P2408A is used to simulate IIC communication. PC4 and PC5 are used as SCL and SDA signal lines respectively, as shown in Figure 4-7, where R8 and R9 are pull-up resistors, and the read and write timing of the I2C bus is controlled by software.

Figure 4-7 Power-off memory circuit

5 Introduction to Chip Features
SPMC65P2408A is an 8-bit industrial control microcontroller designed and developed by Lingyang Company. It adopts Lingyang SPMC65 core and supports bit operation instructions. It has powerful timer/counter, rich external interrupt sources, ADC, PWM, standard communication interface UART, SPI and other functions. It is suitable for general industrial control occasions, computer peripheral control and home appliances. SPMC65P2408A has two packages: 28-pin and 32-pin. The 32-pin package has an additional UART function. This design uses a 32-pin package, as shown in Figure 5.1.
The specific characteristics of the 32-pin packaged chip are as follows:
Operating voltage: 3.0V~5.5V
Operating speed: 8MHz
Operating temperature: -40℃~85℃
Super strong anti-interference, anti-static ESD protection capabilities
8K byte OTP ROM, 256 byte RAM
27 general input and output ports, all of which can be set to pull-up, pull-down and suspension mode
Powerful timing counters: 2 8-bit, 2 16-bit with CaptureComparePWM function
1 1Hz~62.5KHz time base
8-channel 10-bit precision ADC (with external reference voltage)
4 external interrupts, 11 internal interrupts
SPI, UART and other serial communication interfaces
2 power saving modes: Halt, Stop
Buzzer output function
4.0V/2.5V optional low voltage reset function
Programmable watchdog function

Figure 5.1 SPMC65P2408A*32P package

6 System software design
The entire system input includes 5 temperature sensors and 3 buttons; the output includes 4-digit seven-segment digital tubes, compressors, fans, solenoid valves, defrost heating wires, etc., and 1 memory AT24C01A.
6.1 Main program flow chart
According to the control function, the program is designed into several main modules, the flow is shown in Figure 6-1:

Figure 6-1 Main program flow chart

6.2 Introduction to each functional subroutine flow
After the program is reset, it is initialized first, including three parts: system initialization, diagnostic program and initialization interrupt.
◆ System initialization
◆ Diagnostic program
◆ Interrupt initialization
◆ Keyboard scanning
◆ Self-test program
◆ Normal mode key code analysis
◆ Temperature acquisition
◆ Sensor detection program Artificial intelligence
◆ Artificial intelligence
◆ Refrigerator temperature control
◆ Freezer temperature control
◆ Compressor protection and control
◆ Drive control
◆ LED display program

7 Conclusion
With the continuous development of science and technology, household appliances are also constantly updating and developing, moving towards a more intelligent direction. Future refrigerators have strict requirements in all aspects, such as environmental protection, quietness, energy saving, etc. While considering performance, users are more concerned about safety.