Design of fully automatic dishwasher based on STC89C52

The dishwasher is a kind of kitchen equipment that automatically cleans tableware. Its appearance reduces the labor intensity of cooks and household "cooks" and improves the corresponding work efficiency. At present, dishwashers have been widely used in ordinary households in Europe and the United States. According to statistics, in major European and American countries, the penetration rate of dishwashers has reached more than 70%, and it is almost a must-have kitchen appliance for every household. Due to the short development time of dishwashers in China, the household penetration rate is very low. With the advancement of technology and the times, people's pursuit of convenience in life is also increasing, and dishwashers are bound to be pursued by contemporary youth.

1. System design

This design is based on a single-chip microcomputer to realize the function of an automatic dishwasher and realize the entire process of one-button operation. The main processes of the dishwasher designed include the functions of automatic water inlet, cycle dishwashing, and automatic water discharge, and can display the current remaining time in real time; in addition, in order to better realize the convenience of life, the system is also designed Performs functions such as UV disinfection and air drying of dishes, chopsticks, etc. In order to realize the functions of each part, this design mainly uses the timer/counter function of the microcontroller to control the time variable. By comparing the time variables, the dishwasher is controlled to execute the sequence of automatic water inlet, automatic cycle stirring, automatic water outlet, air drying, and disinfection, thereby realizing a simple operation process of starting the dishwasher with one click. The overall design block diagram of the dishwasher is shown in Figure 1.

Figure 1 Overall design block diagram of the dishwasher

2. Hardware design

2.1. Microcontroller small system design

This design uses STC89C52 microcontroller as the core processor. STC89C52 is a low-power, high-performance CMOS 8-bit microprocessor with 8K system programmable Flash memory. It is an enhanced 8051 microcontroller. The instruction code is fully compatible with the traditional 8051 microcontroller. The user-applicable program space is 8K bytes. It integrates 512 bytes of RAM on the chip and has an EEPROM function and a watchdog function. In addition, there are three 16-bit timers/counters. In terms of programming, its ISP/IAP does not require a dedicated programmer or dedicated emulator, and the program can be downloaded directly through the serial port line. The clock circuit of a microcontroller usually uses an internal clock circuit, using a parallel resonant circuit composed of a quartz crystal and a capacitor. Crystal load capacitance

Cd and Cg in the formula are the capacitors connected to the two pins of the crystal oscillator and to ground respectively, and the empirical value of Cic+c is 3-5pf. The size of the capacitor can play a role in frequency fine-tuning. Usually when the crystal oscillator is at 11.592MHZ, the matching capacitor is 22p. The reset circuit enables the microcontroller to return the value of a register to its initial state after an error occurs. After the clock circuit works, the reset operation can be completed by a high level on the reset pin for 2 machine cycles. In order to facilitate operation, the switch reset mode is usually used. When the button is pressed, the capacitor C is short-circuited and RST appears at a high level. If the time exceeds the reset time, the reset operation can be completed. When the button pops up, due to the action of the capacitor (blocking direct traffic), the RESET pin appears low, which allows the microcontroller to resume normal operation. The size of the resistor R and capacitor C can be selected as long as the value of its time constant τ = RC is greater than 2 machine cycles. The EA/VPP pin of STC89C52 controls where the program accesses. When EA=1, the CPU reads instructions from the on-chip ROM; when EA=0, the CPU reads instructions from the off-chip ROM. Since the on-chip ROM can meet the storage size of this design, the pin of this design is set to high level. The STC89C52 microcontroller can download programs through the IAP mode, that is, it accepts the program code that needs to be burned through the serial port, and then performs "self-programming" to complete the burning. Therefore, the circuit design reserves RXD and TXD interfaces to connect to the RS232 to TTL module to complete the burning function. The circuit diagram of the single-chip small system is shown in Figure 2.

Figure 2 Microcontroller small system circuit diagram

2.2. Digital tube display circuit design

The digital tube used in this design is a two-in-one common anode eight-segment digital tube, whose pins respectively control the bit code of the digital tube and the segment code of the digital tube. By encoding each bit code and segment code using the microcontroller, the numbers 0~9 can be displayed on the corresponding bits. In order to ensure the driving current of the digital tube, a 74HC573 latch is added to its segment code pin for data latch during design, and an 8550 transistor is added to its bit code for signal amplification. The digital tube circuit design diagram is shown in Figure 3.

Figure 3 Digital tube circuit design diagram

3. Software design

This design needs to be able to start the dishwashing process with one button, which includes automatic water inlet, circular flow, automatic water outlet, and can be executed three times in a cycle, and the current remaining time is displayed through a digital tube. The program mainly accomplishes the design purpose through the timer/counter function of the microcontroller. The timer/counter function can achieve precise timing. Each time the interrupt service function is entered, the variable count value increases automatically, and the corresponding numerical increment is controlled multiple times. times, you can complete the timing function at any time. The program compares the value of the current global variable to implement the corresponding functions of automatic water inflow, circular flow, and automatic water outlet in different time periods, and displays the current remaining time in real time. The program flow chart is shown in Figure 4.

Figure 4 Program flow chart

3.1. Timer/counter program control

The program software of this design mainly relies on the timer/counter function of the microcontroller to realize the functional requirements. The microcontroller timer/counter functions as a timer when counting internal machine cycles at a fixed time interval; when counting external events, it functions as a counter. This design uses its function of counting internal machine cycles at a fixed time interval. Timer function. The bit control of the timer/counter mode register TMOD and the control register TCON determines the open timer and the corresponding function settings; the THx and TLx eight-bit counters constitute a sixteen-bit adding counter. When the initial value of the adding counter is set , after changing TMOD and TCON with instructions, it can run automatically in the set way in the next machine cycle. The adding counter only applies for interrupt after it is full and overflows. Therefore, when assigning an initial value to it, the required value cannot be assigned directly. Instead, the difference between the maximum value of the counter count and the required assigned value is used as the initial value of the counter. This design uses the timer counting function of timer T0 working in mode 1. The timer T0 initialization program flow chart is shown in Figure 5.

Figure 5 T0 initialization program flow chart

4 Conclusion

In summary, this design studies the implementation of an automatic dishwasher based on a basic single-chip microcomputer. Researched the hardware circuit design to realize the automatic dishwasher, and the corresponding program development, and designed the circuit interfaces for the exhaust fan and ultraviolet lamp to provide a system for realizing the complete functions of automatic dishwasher such as dishwashing, air drying, and disinfection. Design ideas. This design aims to propose the realization of the function of an automatic dishwasher and provide further research on smart homes.