Design and implementation of a fully automatic rice cooker system based on SIM900A

Today's electric rice cookers are developing in the direction of integrating rice cooking, soup making and heat preservation. Although current rice cookers have the function of scheduled cooking, the taste of rice is affected by the long scheduled time. The fully automatic rice cooker designed in this paper integrates embedded technology and wireless communication technology, which not only realizes the remote intelligent control of rice cooking, but also ensures the good taste of the cooked rice.

1 Working principle of fully automatic rice cooker

The designed rice cooker is in standby state when not working. When the SIM900A module receives the text message or GPRS control command from the user's mobile phone, it sends the command to the STM32F103 microcontroller, which parses the command and then controls the entire process of the rice cooker to automatically drain, wash and cook rice. The temperature sensor is used to detect the working temperature of the rice cooker in real time. At the same time, it can intelligently alarm according to the working status of the rice cooker, ensuring the reliable and stable operation of the rice cooker. The overall design of the system is shown in Figure 1.

2 Mechanical structure design

This system makes a new mechanical structure improvement on the ordinary rice cooker, and is designed from three aspects: rice storage, rice washing mechanism, and rice cooker, as shown in Figure 2.

The top of the device is a rice storage device, which can store up to 5 kg of rice at a time. The pressure sensor can accurately measure the amount of rice required for cooking. The solenoid valve controls the in and out of rice and water. The rice washing mechanism is driven by the stepper motor to wash the rice. After washing, the rice and the appropriate amount of water are sent to the rice cooker, and then the conveyor belt transports the rice cooker from the idle position to the designated working position for cooking. At the same time, the robot automatically places the rice cooker lid on the rice cooker driven by the motor. The device is automatically completed under the control of the single-chip microcomputer.

3 Hardware Circuit Design

The hardware circuit of the device consists of a main control circuit, a SIM900A wireless communication circuit, a sensor circuit, a relay circuit, a motor drive circuit, a power supply circuit, an alarm circuit, etc. The hardware circuit is shown in Figure 3.

The main control circuit chip should have the characteristics of high performance, low cost, low power consumption, fast storage speed, etc. This circuit uses the 32-bit MCU STM32F103 with ARM core as the control core, which has a wide operating temperature range, 7 timers and 9 communication interfaces; it has a 7-channel DMA controller and built-in 2 12-bit A/D converters.

The working frequency band of SIM900A wireless data communication circuit is EGSM900 and DSC1800, and the working temperature range is -30～+80℃. It has the characteristics of power saving, fast transmission rate, support for packet broadcast control channel, support for real-time clock, support for software control of RTS/CTS hardware flow control, etc. SIM900A in this design is used to receive text messages or GPRS control commands from mobile phones, and then transmit the commands to the STM32F103 chip, thereby realizing the remote control of the rice cooker. The connection between SIM900A and the controller is shown in Figure 4.

The relay is mainly used to control the disconnection and conduction of the solenoid valve and the shutoff of the main power supply of the rice cooker. Its working principle is shown in Figure 5.

4 Software Design

4.1 Main program software

The software control process of the system is as follows: after the SIM900A wireless communication module receives an external text message or CPRS command, it sends the command to the STM32F103 main control chip, then starts the rice cooker system and monitors the working temperature in real time. At the same time, the system intelligently alarms according to the working status, and the STM32F103 controls the rice cooker to realize automatic rice draining, rice washing, and rice cooking. The main program flow is shown in Figure 6.

4.2 Software Design of Rice Leaking Device

STM32F103 receives the command from SIM900A wireless communication module: suppose the amount of rice required for n people to eat is m1; at this time, the program of the rice leaker is started and initialized, and the amount of rice in the initialized rice storage is measured to be m2; then the data is sent to the control core for calculation to obtain the difference in rice amount m3=m2-m1, and then the rice leaker continues to leak rice and detects the weight m4 of the rice in the rice storage through the pressure sensor, and when m3=m4, the rice storage switch is turned off, the values ​​of m2 and m4 in the subroutine are returned, and the program ends. The process of the rice leaker is shown in Figure 7.

4.3 Software Design of Rice Washer

After the rice-leaking device completes the rice-leaking action, the rice-washing device starts working and is initialized. To reduce the error, the values ​​of m2 and m4 returned to the main program are sent to the control center to obtain the actual amount of rice leaked m=m4-m2, and the amount of water for washing rice in the program is called according to the value of m, and the solenoid valve is controlled according to the timer in STM32F103. The solenoid valve controls the amount of water entering the rice washing, and at the same time, the amount of water for cooking rice is controlled in this way. After the rice-washing device completes the rice-washing action, the solenoid valve is opened to discharge the rice-washing water. The water discharge time is determined according to the delay program of STM32F103. A water filter membrane is installed on the solenoid valve at the water outlet to prevent the rice from leaking with the water or the water from clogging the solenoid valve. The process of the rice-washing device is shown in Figure 8.

5 System Testing

After the system design is completed, the whole machine testing phase begins. The control instructions of the rice cooker are sent remotely to the rice cooker. After receiving the text message, the rice cooker analyzes the instructions and sets the working mode according to the control instructions to automatically complete operations such as taking rice, washing rice, and cooking. At the same time, the working status of the rice cooker is monitored. When the rice cooker finishes cooking or a working failure occurs, a prompt text message is sent to the user's mobile phone.

The system was tested in two working modes: automatic rice cooking and automatic porridge cooking. The rice cooker sets the working mode according to the SMS control command. In this working mode, the required amount of rice and water added are automatically calculated according to the set number of people eating, and the cooking time is accurately controlled. The test program sets the amount of rice required for one person's rice cooking mode to be 100 g, the increment interval is 100 g, and the amount of water added is twice the amount of rice. The amount of rice required for the porridge cooking mode is 50 g, the increment interval is 50 g, and the amount of water added is 4 times the amount of rice. The amount of rice and water added are deduced according to the number of people. The rice cooking and porridge cooking tests were conducted 5 times, each experiment was repeated 3 times, and the test results are shown in Tables 1 and 2. It can be seen from the table that the actual test value of the system is close to the set value, the measurement error is small, and the taste of cooking rice and porridge is good. The system runs stably and reliably.

6 Conclusion

Based on the SIM900A module, the system realizes remote control of the rice cooker's intelligent rice adding, intelligent rice washing, intelligent rice cooking, temperature detection and alarm functions. At the same time, it uses mechanical structures such as belt conveyors and manipulators to assist in the automation of the rice cooker. It has the advantages of easy parts assembly, cheap overall equipment, stable system operation and simple control.