Design of household heating bathing device based on single chip microcomputer system control

Introduction
A key technology of the household electric hot water circulation heating bath introduced in this article is the nano material far-infrared thin film electric heating tube. More than 20 materials such as tin chloride, silver carbonate, ferric chloride, aluminum oxide, zinc oxide, titanium oxide, silicon dioxide, citric acid, ethanol, polyethylene glycol, xylene, ammonia, ultrafine pure silicon powder, tin powder, etc. are used to chemically configure nano gel with tin dioxide as the main content. High-strength quartz glass tube is selected as the backing, and high-temperature spraying and pulling drying are carried out at high temperature. A film layer with a thickness of about 6μm is instantly formed on the outer wall of the tube to make a nano tin dioxide electric excitation far-infrared thin film liquid heating tube. The tube has a diameter of 20mm, a length of 15cm, and a wall thickness of 2mm. It can withstand high temperatures of 860℃, withstand a water pressure of 0.5MPa, a far-infrared wavelength of 150-250μm, and a power of 800W (220V); multiple heating tubes are connected in parallel in series to form a heating body with a total power of 0.8kW~12kW. Under the excitation of electricity, the electrons inside the atoms of nanomaterials produce violent oscillations, and the energy of the oscillations is radiated in the form of far-infrared rays. Water is a good absorber of far-infrared rays. Under the action of far-infrared rays, the free charges of water molecules and atoms move violently and irregularly. Due to friction, heat is generated, causing the temperature of the water to rise rapidly. Compared with the use of air conditioners and electric heaters for heating, the electric hot water circulation heating bather has small heating temperature fluctuations, small one-time investment, large heating area, and electricity saving; compared with the use of oil burners and gas burners, it is safe, convenient, labor-saving, clean, pollution-free, and does not consume oxygen; compared with collective heating, it has the characteristics of low cost of use, flexibility and convenience. At the same time, the system has the function of bathing with separate pipes for water supply, without the traditional large-capacity water tank, and the heating is fast. After 3-10 seconds, hot water can be used for washing or showering. One machine has multiple uses and avoids repeated investment.
2 Composition of the water circulation system of the heating bather
The composition of the water circulation system of the household electric hot water circulation heating bather is shown in Figure 1. The tap water is controlled within an appropriate range through a pressure reducing valve and enters the heating and bathing systems through independent pipes. In order to make the water circulation system work well, a smaller water distribution tank, water collection tank, and expansion tank are added. The power of the heating body needs to be calculated according to the total area of ​​the heating room, and different types of heating bodies are selected.
3 Composition of the heating bath control system
The composition of the heating bath control system is shown in Figure 2. The entire system is based on the AT89C51 single-chip microcomputer, which performs intelligent detection of parameters such as water temperature, water level, and room temperature. After calculation and comparison, the corresponding actuator is controlled to turn on and off the power, and over-temperature, water shortage, leakage and other protections are performed, and corresponding sound alarms are performed to ensure the reliability of the system.

Figure 1 Block diagram of the water circulation system of a heating bath

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3.1 Data Collection
The DS18B20 chip is used to detect room temperature, heating water temperature, and bathing water temperature signals. DS18B20 is a one-line digital temperature sensor produced by DALLAS, with a 3-pin TO-92 small package; the temperature measurement range is -55℃~+125℃, and it can be programmed to 9-12-bit A/D conversion accuracy, and the temperature measurement resolution can reach 0.0625℃; multiple DS18B20 can be connected in parallel to 3 or 2 lines, and the CPU only needs one port line to communicate with many DS18B20, occupying fewer ports of the microprocessor, which can save a lot of leads and logic circuits, and is more suitable for the system to measure temperature.
For water level detection, three high, medium and low probe points are used in the expansion water tank. The lowest probe point is connected to the working power supply, the middle is the low water level probe point, and the top is the high water level probe point. In order to prevent the probe point from forming scale due to the ionization adsorption of water, in addition to the selection of special materials, its working power supply is powered by AC signals. The detection of the heating and bathing water pressure switch signals uses a switch sensor. When no water flows through the water pressure switch, it outputs a high level; when water flows through the water pressure switch, it outputs a low level signal.
3.2 Actuators
The actuators are all controlled by relays. The execution signal sent by the single-chip microcomputer is amplified by photoelectric isolation and transistor drive to control the current of the relay coil, so that the relay contacts are activated to connect or disconnect the power supply of the circulation pump, solenoid valve and each heating body. The sound alarm circuit consists of a transistor amplifier and a buzzer, which is controlled by the P1 port of the single-chip microcomputer. In order to protect the single-chip microcomputer system and reduce external signal interference, photoelectric couplers are used between each switch sensor, actuator and single-chip microcomputer for signal isolation.
3.3 Keyboard and display circuit The keyboard circuit has two functions, one is to set the heating system, and the other is to select the bathing water temperature. The setting of the heating system includes setting the system time, working mode, and customizing the heating temperature value of each time period. Setting
the system time is mainly to re-call the initialization program of DS12887 to make the system time consistent with the current calendar. The heating system has five working modes: continuous operation at a constant temperature throughout the day, operation at user-defined temperatures for each time period, operation at system default temperatures for each time period, anti-freeze operation when on a business trip, and heating function stop. The choice of bathing water temperature is mainly to set the power of the bathing heater participating in heating through the keyboard to control the outlet water temperature. When taking a shower, you can choose different shower water temperatures according to your personal feelings. The display circuit uses TN-LCD segment liquid crystal, and the display screen is pre-customized. The LCD display can display calendar information, temperature information, working mode information, over-temperature, water shortage, leakage and other fault information. The display module integrates drivers, display RAM, oscillators, etc., uses serial ports for data communication, and is easy to interface with the single-chip microcomputer.
3.4 Other circuits
The time calendar chip uses DS12887/DS12C887 produced by DALLAS. It has complete clock, alarm and calendar functions until 2100, and has 114 bytes of low-power RAM for power-off protection. The chip encapsulates the crystal oscillator, oscillation circuit, charging circuit and rechargeable lithium battery together on the top of the chip to form a thickened integrated circuit module. The DS12887/DS12C887 has a special interface circuit inside, which makes the timing requirements of the external circuit very simple. No peripheral circuit components are required when using it, and the interface with the microcontroller is greatly simplified. In the heating and bathing control system, in addition to providing calendar information and second interrupt signals, the RAM and lithium battery of the DS12887/DS12C887 can well protect the user's custom settings.
4 System control software design
The main software design flow chart of the system is shown in Figures 3 and 4.
The second interrupt of the DS12887 is connected to the external interrupt 0 of the microcontroller, and the main control function of the system is completed in the interrupt service program of INT0. In order to ensure that the user's power load is not too large, the heating and bathing functions are controlled in an interlocking manner, with bathing taking priority. When the system detects that the bathing water pressure switch is turned on, the heating element is turned off and only the original working state of the circulation pump is retained; the water outlet temperature is selected by the panel keyboard, and the maximum water temperature is controlled at 65°C in the bathing function. Only when the bathing water pressure switch is turned off, the bathing heating element is powered off and the heating element can be powered on. When the heating function is working, the water level is first detected. When the water level is too low, the solenoid valve is opened to supply water; after reaching the high water level, the solenoid valve is closed and the circulation pump is turned on. If the heating water pressure switch is not turned on, it means that the water circulation system is faulty. After the water level and water circulation are normal, the water temperature and room temperature are detected. According to the working mode setting and the current clock, the saved heating temperature setting value is read, compared with the measured room temperature value, and the corresponding control signal is given; when the room temperature is 2°C lower than the set temperature, the three groups of heating elements are heated at the same time, until the room temperature is 2°C higher than the set temperature, only one group of heating elements is left for insulation heating; the three groups of heating elements are rotated as insulation heating elements to extend the service life of the heating elements. In the heating function, the maximum heating water temperature is controlled at 85℃. When the temperature exceeds the limit, the heating is stopped and an alarm is sounded.
Innovation of the author of this article
The nanometer material far-infrared thin film electric heating tube is used, which is small in size and high in thermal efficiency. The single chip microcomputer is used to detect parameters such as water temperature, water level, and room temperature. It also has protection against over-temperature, water shortage, and leakage, which improves the reliability and practicality of the system. After debugging and testing, the whole system has the characteristics of low investment, strong functions, and high efficiency, and has broad application prospects.
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