Circuit Program Design of Hand Dryer Control Board

With the development of electronic technology, more and more electronic products have become necessary supplies in our lives. Nowadays, electronic automation has become a form of enjoyment for people. Many places, such as factories, companies, hotels and high-end places, will use passive pyroelectric infrared induction for human body. It is widely used by users because of its stable performance and long-term stable and reliable work. Welcome, this switch is mainly composed of pyroelectric infrared sensor, signal processing circuit, control and execution circuit, power supply circuit and other parts.

1. Design idea of automatic hand dryer

Now we can also use a single-chip microcomputer to realize this automatic drying function, which is more convenient and reliable. The transmitting and receiving functions of the human pyroelectric infrared sensor are designed by the single-chip microcomputer system. That is, when someone stretches his hand at a fixed position, the signal emitted by the infrared light-emitting diode is reflected to the receiving head through the hand, and then the fan is controlled to run. Until the hand leaves, the fan stops running.

2. Demonstration and comparison of hand dryer solutions

(1) Traditional solution: Most hand dryers are realized by using integrated circuits such as chips and timers. The whole circuit is composed of encoding circuit, decoding circuit, timing circuit, control circuit and alarm circuit.

(2) Design scheme of this paper: This scheme is realized by 89S51 single-chip microcomputer system. The software programming of the single-chip microcomputer is flexible and has a large degree of freedom, and various logic controls can be realized by software programming. It can realize multiple functions such as digital display and keyboard setting.

(3) Scheme comparison: The traditional scheme uses more chips, and the welding between the pins often has false welding and desoldering, which makes the circuit unable to realize its function. In addition, the circuit is too complicated, so there will be welding errors during the welding process, which brings unnecessary troubles when checking the circuit, and it is also difficult to check out the problem during the debugging process.

The chip used in this design scheme is less, and the welding is easier. The single-chip microcomputer control system with 89S51 as the control core is also more convenient in software debugging. Therefore, we adopt the design scheme in this paper.

3. The hardware principle and design of the hand dryer system

3.1 SCM system

The microcontroller system uses the AT89S51 chip. AT89S51 has 4K bytes of FLASH flash memory, 128 bytes of internal RAM, 32 I/O ports, infrared receiver, two data pointers, two 16-bit timers/counters, a 5-vector two-level interrupt structure, A full-duplex serial communication port, on-chip oscillator and clock circuit. At the same time, AT89S51 can drop to 0HZ static logic operation, and supports two software-selectable node working modes. The idle mode stops the work of CPU, but allows RAM, timer/counter, serial communication port and interrupt system to continue to work. The power-down mode saves the content in RAM, but the oscillator stops working and prohibits all other components from working until the next hardware reset.

3.2 Crystal oscillator circuit and reset circuit

An external quartz crystal (or ceramic resonator) and capacitors C1 and C2 are connected to the feedback circuit of the amplifier to form a parallel oscillator circuit. Although there are no very strict requirements on the external capacitors C1 and C2, the size of the capacitors will slightly affect the oscillation frequency, the stability of the oscillator, the difficulty of starting the oscillation, and the temperature stability. If a quartz crystal is used, 30 PF is recommended for capacitors, and 40 PF is recommended for ceramic resonators.

The circuit is equipped with a reset switch, press reset during the drying process or after drying, the system will be cleared and return to the initial state.

3.3 Working principle and characteristics of human body pyroelectric infrared sensor

Ordinary human body emits infrared rays with a specific wavelength of about 10 μm, and the presence or absence of such infrared rays can be detected with a specially designed sensor. When the infrared rays of the human body irradiate the sensor, the charge will be released due to the pyroelectric effect , the follow-up circuit can generate a control signal after detection and processing. This specially designed probe is only sensitive to infrared radiation with a wavelength of about 10 μm, so objects other than the human body will not trigger the probe action.

4.The design of the schematic diagram of the hand dryer

The circuit diagram is drawn by Protel99 SE software. The main features of Protel 99 SE are: ①SCH: provide more than 60,000 components; provide electrical law detection ERC. ②PCB: Automatic layout and routing, or manual; provide design rules to detect DRC. And we only use SCH mapping.

Therefore, choosing Protel99 SE not only reduces the trouble of the line, but also enables us to debug the circuit on the computer to check whether the circuit can realize the required function.

When using Protel99 SE to design and draw schematic diagrams, attention should be paid to the design process of circuit schematic diagrams, the establishment of schematic diagram design documents, the setting of the working environment of the design system, the operation of components and SCH component libraries, the drawing of circuit schematic diagrams, and the editing of circuit schematic diagrams . The common processing technologies that are needed after the schematic drawing is completed include: hierarchical circuit design, electrical rule test (ERC) and generation of common reports.

5. Summary of function debugging of hand dryer

(1) Hardware part: first check whether the circuit is soldered or not, and whether the connection is correct. Then turn on the +5 power supply, reach out to a fixed position, and observe whether the hair dryer is running. Finally, check that the circuit resets by pressing the reset button under any circumstances.

(2) Software part: First, according to the requirements, the overall item can be decomposed into several sub-function modules, and each function module completes a specific function. Then, according to the overall requirements and the decomposed functional modules, determine the relationship between each functional module, and draw a complete program flow chart. Finally, when the program is debugged, the designed program is input, assembled, and syntax errors are eliminated. Connect the wires on the experimental platform according to the designed schematic diagram, and check that it is correct. Transfer the compiled program to the experimental setup. Execute the program, check whether the program meets the design requirements, if not, modify the program until the requirements are met.

Summarize

When designing the software part, there were many mistakes. Grammatical errors often occur, so I read various materials, searched online to obtain more information, and consulted colleagues, and finally corrected many grammatical errors. When designing a program, the first problem is the allocation of the program address space. Because the resources in the 51 single-chip microcomputer are limited, conflicts often occur, and protection is very important at this time. The second is because the assembly readability is poor, and because jump instructions are often used when writing programs, mistakes are often made. To overcome this problem requires a lot of programming experience and a lot of patience. The third is the efficiency of assembly. Although there are only a few instructions, the usage is quite flexible, so you should study harder to write efficient code. During the debugging process, the program often fails to run normally due to symbol errors and grammatical errors, so you should check carefully when you complete the program.

The above is the development example of the hand dryer introduced by Shenzhen Zuchuang Microelectronics Co., Ltd. for you. If you have bluetooth headset solution 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.