Design and development of rice cooker control board

With the development of electronic technology and the increasing demands of the people, various electronic products have entered the public life, among which electric cooker is an extremely widely used electronic product. Traditional electric cooker can basically realize the function of cooking rice, but it is difficult to achieve better cooking effect. With the development of sensor technology and intelligent control technology, the rice cooker based on single-chip microcomputer control can realize the cooking function of fuzzy control according to the cooking process, and achieve better cooking effect. In this paper, the MC68HC08JL3 chip is used as the control chip to realize the software and hardware design of a smart rice cooker, which makes the rice cooker have functions such as LCD display, key reading processing, ADC, and fuzzy control cooking.

1. Design idea of rice cooker control panel

The control circuit of the controller is designed according to Figure 1. The circuit includes seven parts: single-chip microcomputer, power supply and voltage stabilization circuit, keyboard input circuit, buzzer alarm circuit, LED display circuit, temperature detection circuit and power drive circuit. When designing the circuit, the circuit for power processing, external signal drive and reading is made into a PCB board, and the control circuit is made into a PCB board.

In this paper, the 68HC08JL3 chip is used as the control chip to realize the circuit diagram design of the control board. The control board includes an external interface, an LED display, a liquid crystal display, a circuit of a key part, and a working circuit of a single-chip microcomputer.

2. Fuzzy control mechanism of rice cooker

Since the mechanical rice cooker does not have a temperature sensor to detect it, it can only mechanically increase the temperature of the bottom of the pot to about 103 degrees Celsius and then stop heating and enter the heat preservation process. Although the heating process can also go through several process stages, it cannot be done due to lack of time control. It can produce very delicious rice; the fuzzy rice cooker can realize various functions such as water absorption, heating, boiling, stewing rice, and expansion, and these functions can achieve ideal results. In particular, the quality of the rice is determined during the critical heating phase, where the amount of rice needs to be deduced. Rice cookers in the past were difficult to achieve. This article focuses on introducing the practical fuzzy reasoning method which is convenient for single-chip system programming and realization.

2.1 Fuzzy reasoning of the amount of rice in the rice cooker

In the electric cooker with fuzzy control, the heating control and heating time of each stage of the control process are related to the amount of rice. Therefore, the determination of the amount of rice is the first key step, and the subsequent process is controlled accordingly according to the amount of rice. In the water absorption stage of the rice cooker, due to the uncertainty of the initial conditions, the user may use hot water or cold water to cook rice, making it difficult to measure the amount of rice during the water absorption stage, so the determination of the rice amount can only be done is performed during the heating phase.

If the user adds water according to the specified scale, in the heating stage, if the temperature in the pot rises quickly, it can be judged that the amount of rice is less, and if the temperature in the pot rises slowly, it can be judged that the amount of rice is more. There are two thermosensitive lines to read the temperature inside the pot, respectively read the temperature of the bottom of the pot and the temperature of the top of the pot. Since the temperature of the bottom of the pot is equivalent to the temperature of rice, it is difficult for rice and water to form convection when heating. The exchange is poor, so the temperature of the bottom of the pot rises quickly, and it is difficult to reflect the temperature rise of the entire pot body, while the temperature of the pot cover can directly reflect the temperature change in the pot. Therefore, the slope of the pot top temperature-time curve can be used to reflect the amount of rice, the larger the slope, the less rice, and vice versa, the more rice.

In the programming of the single-chip microcomputer, considering the memory limitation and calculation speed of the single-chip microcomputer, the rice amount measurement rules can be set according to the following steps:

(1) Set the low threshold Tmp_Low and high threshold Tmp_High of the pot top temperature, where the value of Tmp_Low cannot be lower than the value of the pot top temperature at the end of the hot water absorption stage when using hot pot hot water, and Tmp_High cannot be higher than the pot top temperature when the water boils Value, these two values need to be determined after the experiment, different types of rice cookers, due to the difference in structure, the determined threshold is also different.

(2) According to the amount of rice between the small amount of rice and the amount of medium rice, and the amount of rice between the amount of medium rice and the amount of rice, the rice is cooked separately, and the time required for the temperature of the top of the pot to rise from Tmp_Low to Tmp_High is calculated. Get Time_Small and Time_Big respectively. Similarly, there are differences in the two quantities for rice cookers with structural differences.

(3) During the cooking process, if the time Time_Det required for the temperature of the top of the pot to rise from Tmp_Low to Tmp_High, if Time_Det<Tmp_Low, it is judged that the current cooking amount is a small amount of rice, and if Time_Det>Tmp_High, then the current cooking amount is judged It is multi-meter quantity. Otherwise, it is the amount of medium rice.

2.2 Working process control of rice cooker

The amount of rice is measured in the heating stage of cooking, and the overall time control of the heating stage and the firepower control of the heating plate in the boiling and stewing stages are determined by the amount of rice.

As mentioned above, the time of the heating stage is controlled at about 10 minutes. It takes 9 minutes to heat until the water boils. It takes a long time when the amount of rice is large, and it takes a short time when the amount of rice is small. In order to basically meet the time requirement of 10 minutes, the heating of the bottom heating plate will be stopped for the remaining 1-3 minutes. At the same time, turn on the top heating plate and heat it until the top temperature is about 100 degrees. On the one hand, it prevents the evaporated water vapor from condensing, and on the other hand, it prepares for the uniform heating of the entire pot body in the next stage. Therefore, in the heating stage, the heating time of the bottom heating plate is different according to the amount of rice.

In the actual program writing process, the heating stage time can also be determined as 10 minutes, and the heating time of the bottom heating plate and the heating stop time are accumulated to 10 minutes.

The boiling and stewing stages should be maintained at about 20 minutes, and the conditions for the end of the stewing stage are determined by the temperature, so the timing of the two processes depends on the firepower of the heating plate. In these two stages, when the amount of rice is relatively large, high-power heating should be used, and when the amount of rice is relatively small, low-fire heating should be used to ensure that the cumulative time of the two stages is about 20 minutes.

2.3 Intelligent cooking program design

According to the technical process of cooking, the rice cooker controlled by a single-chip microcomputer can divide the cooking process into several stages, and the heating methods used in different stages are different.

During the cooking process, the bottom temperature changes with the stages of the cooking process, showing a curve as shown in Figure 3, where the ordinate is the temperature, and the abscissa is the cooking time. In the process of intelligent cooking, almost all the processes that require the heating of the bottom heating plate need to be heated by intermittent heating, because:

(1) The heating power of the bottom heating plate is relatively large. In the case of 220V power supply, it generally reaches more than 850W. Continuous heating can easily make the temperature of the bottom of the pot rise rapidly. (2) When cooking rice, it is a mixture of raw rice and water. The raw rice is close to the bottom of the pot and the water is on top of the rice. If the bottom heating plate is continuously heated, the temperature of the rice will rise rapidly, and the temperature of the water will rise slowly, which will affect the water absorption of the rice, and the whole pot cannot be heated evenly. (3) According to the needs of different cooking functions, the required heating firepower is different. By controlling the heating duty cycle, the firepower of the heating plate can be controlled.

Therefore, when performing intelligent cooking, it is necessary to intermittently control the bottom heating plate, and use a certain duty cycle to control the heating process. In a heating cycle with the same length of time, the longer the bottom heating plate is turned on, the greater the heating firepower, and the shorter the bottom heating plate is turned on, the smaller the heating firepower. Usually, a heating cycle of 20 to 30 seconds is used. If the heating cycle is too short, the relay will often open and close, shortening the service life of the relay.

3. Rice cooker software design

The main program includes an initialization program and a main loop program.

(1) Chip initialization: initialize registers, input and output ports, and variables;

(2) Key reading and key processing: the program sets 2ms to read a key;

(3) Buzzer control: use passive buzzer;

(4) Read AD: The program reads AD once every 250ms, and converts it to the temperature of the pot lid and pot bottom;

(5) Cooking control program: According to the content described in the previous section, corresponding to the control requirements of each stage, complete the fuzzy cooking function, and determine the duty cycle of the bottom heating plate and the heating of the side heating plate and shoulder heating plate according to different execution stages Flag, does not directly deal with input and output ports;

(6) Display data control: complete the setting of LCD display content;

(7) External clock control: provide second platform and minute platform for stage timing and duty cycle timing;

(8) Drive control: Determine whether the bottom heating plate should be turned on according to the duty cycle for the lower layer control program, set the flag bit of the bottom heating plate, and do not directly process the port, and then perform port control according to the flag obtained by the upper layer cooking control program Processing, control whether the heating plate is working or not;

(9) Timer overflow interrupt program: Although it is not drawn in the flow chart, it actually needs to be programmed as a separate function to complete the buzzer sound control, 2ms, 250ms, 1s timing, and process the corresponding flag bits.

Summarize

Through the comparison of the mechanical rice cooker and the fuzzy control rice cooker realized according to the method in this paper, it can be found that compared with the mechanical rice cooker, the rice cooked by the fuzzy control rice cooker has a better taste, and the taste of the rice in each part of the rice cooker is basically the same. Like a mechanical rice cooker, when cooking a lot of rice, the effect of the rice on the upper side of the pot body is far from that of the rice on the lower side of the pot body.

The above is the design and development example of the fuzzy control rice cooker introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have rice cooker program development needs, you can trust us. We represent a variety of single-chip microcomputers, voice chips, dual-mode Bluetooth ICs, and wifi chips. Brands include Songhan MCU, Yingguang MCU, Jerry Bluetooth, Ankai Bluetooth, Allwinner, and Realtek. Our technical services include: PCB design, MCU development, Bluetooth solution, software and hardware custom development, APP development, small program development, WeChat official account development, etc. It can also undertake the design of intelligent electronic products, the development of living appliances, the research and development of beauty equipment, the application of Internet of things platform, the smart home control system, the development of TWS earphones, Bluetooth earphone speakers, the development of children's educational toys, the design of electronic education products, etc.