Design of soybean milk machine based on SH69P42 single chip microcomputer

Aiming at the problem of long pulping time, this paper designs an efficient and time-saving soymilk machine based on SH69P42 single- chip microcomputer. On the basis of maintaining the structure and function of the existing soymilk machine, the soymilk machine installs a simple defoaming device on the main shaft of the grinding motor, adopts the control strategy of heating and grinding in parallel, heating and defoaming at the same time, avoiding the problem of prolonged waiting time caused by the separate heating and grinding of the current soymilk machine and the stop of heating due to overflow during the static boiling stage.

1 Basic structure of soybean milk machine

Figure 1 shows the basic structure of an efficient and time-saving soybean milk machine. This structure does not change the original soybean milk machine structure, but installs a defoaming device above the main shaft of the rotating motor. At this time, the motor has the functions of grinding and defoaming. The grinding stage mainly uses the grinding function, and the defoaming function is auxiliary; in the pulping stage, the defoaming function is mainly used, and the grinding function is auxiliary.

2 Control system circuit and working principle

The control system circuit is shown in Figure 2. The circuit consists of Zhongying's SH69P42 microcontroller, temperature detection circuit, overflow detection circuit, dry burning detection circuit, motor control drive circuit, heater control drive circuit, buzzer alarm drive circuit and power supply circuit.

SinoWise's SH69P42 is an advanced CMOS 4-bit MCU that integrates the SH6610D CPU core, RAM, ROM, timer, I/O port, 2-channel 10-bit PWM, watchdog timer, 4-channel 8-bit ADC, and low voltage reset. It is widely used in home appliances and electric vehicle controllers.

The 220 V AC power supply is stepped down by a transformer and bridge rectified to obtain a +12 V voltage, which is used to power relays K1~K2 and the buzzer. The three-terminal voltage regulator 78L05 outputs a +5 V voltage to power the microcontroller. SH69P42 uses an internal RC oscillator with a frequency of 4 MHz. The PC1 pin of SH69P42 outputs an alarm signal, which is amplified by the Q3 transistor and drives the buzzer to alarm. PC2 outputs a motor drive signal, which is amplified by the transistor Q1 and drives the relay K1 to pull in, controlling the motor to run, and can complete the pulping and defoaming work. PC3 outputs a heating signal, which is amplified by the transistor Q2 and drives the relay K2 to pull in, controlling the heating of the electric heating tube. PB3 is the water shortage detection input terminal, PB2 is the overflow detection input terminal, and PA1 is the temperature detection input terminal. The water shortage detection circuit is composed of R8, C9 and the shell of the temperature measuring electrode. The shell of the heating tube is grounded. When working normally, the PB3 pin inputs a low level; if the water level is lower than the temperature measuring electrode, that is, when there is a lack of water, the PB3 pin inputs a high level, and the heating and motor are automatically powered off, thereby realizing water shortage protection. At the same time, the buzzer emits a rapid alarm sound. The same method can be used to detect whether the soy milk overflows. The anti-overflow electrode is connected to the PB2 pin. Before the soy milk boils, the anti-overflow electrode is far away from the water surface, and the PB2 pin is a high level. When the foam rises and touches the anti-overflow electrode, the PB2 pin is a low level. [page]

3. Soymilk machine workflow and control system software design

Put the soaked soybeans or dry beans and water into the cup as required, plug in the power plug, press the start button and you will hear a buzzer sound, the single chip starts working, the PC3 pin outputs a high level, K2 pulls in the heating tube to start heating; the PA1 pin is connected to the negative temperature coefficient thermistor (NTC), which is installed in the temperature measuring electrode. When the water temperature rises to about 80℃, the PA1 pin is low level, and the PC2 pin is controlled to be high level at this time, K2 pulls in the motor to start working, and the blade installed on the shaft rotates at high speed to break the soaked beans and produce soy milk. When the first overflow occurs, the first stage of heating starts with 750 W heating, and the heating time is 60 s. During this period, if overflow is judged, the heating stops for 2 s and then continues. After entering the second stage, 400 W heating is started, and the heating time is 30 s. During this period, if overflow is judged, the heating stops for 2 s and then continues. At the end of the second stage, the motor stops rotating. After entering the third stage, 350 W heating is started for 210 s. During this period, if overflow is detected, heating will not stop, but the motor will stop after 5 s. At this time, the motor mainly plays a role in defoaming. Until the end, the buzzer emits a uniform beep, indicating that the soy milk is cooked, and the system stops working. Figure 3 is a flow chart of this control system. It can be seen that the entire pulping process takes about 10 minutes, which is about 1 times more efficient than the soy milk machines currently on the market.

4 Conclusion

The single-chip control system has the advantages of strong anti-interference ability, isolation of strong and weak electricity, watchdog in the software, safety and reliability, etc. In particular, it uses high-power heating to shorten the preheating time, and uses defoaming control in the subsequent low-power pulping stage to keep heating, ensuring that the soy milk is fully cooked and has a strong flavor, avoiding soy milk overflow, and shortening the overall pulping time. Based on the SH69P42 single-chip microcomputer efficient and time-saving soy milk machine design, without changing the basic structure and function of the original soy milk machine, a simple defoaming device is installed on the motor spindle, and a control strategy of heating and grinding in parallel, heating and defoaming at the same time is adopted.