Hand dryer program design and development

After washing your hands, stretch your hands near the air outlet of the automatic hand dryer (hand dryer), and there will be (hot) wind blowing out to dry your hands. Once your hands leave during the drying process, the automatic hand dryer will quickly stop working. Once it has been working continuously for a period of time, the automatic hand dryer will stop working, and if you try again later, it will continue to work. Since automatic hand dryers are hygienic and convenient, more and more public places have begun to use automatic hand dryers, and some families have also begun to use automatic hand dryers. According to the blowing speed, automatic hand dryers can be divided into slow and fast; according to the installation method, automatic hand dryers can be divided into two types: wall-mounted and standing.

1. Working principle of automatic hand dryer

The automatic hand dryer works by far-infrared automatic induction. It is composed of an infrared transmitter, a receiver, a monostable delay switch, a solid state relay and a hair dryer, etc., forming a simple self-excited multivibrator, which is sent out by an infrared emitting tube Modulated infrared light with a frequency of about 40kHz. When the human hand reaches under the automatic hand dryer, the emitted infrared light is reflected back by the human hand, and after being received by the photosensitive transistor, it is converted into an electrical signal of the same frequency, and then amplified, shaped, and reshaped by the infrared receiving special preamplifier integrated circuit. After the band-pass comparison, the low-level pulse signal is output, which then triggers the formed monostable circuit to enter the transient state, so that it outputs high-level, emits light, and the AC solid-state relay is turned on, so that the hair dryer can send out hot air when it is energized. When the hand dryer leaves, the infrared pulse signal is lost and the high level is restored, and the monostable circuit is quickly reset. Due to the delay effect, the hair dryer will automatically recover after working for about 10s at most and stop working. In order to adjust and change the action sensitivity of the automatic hand dryer, a series connection network composed of resistors and capacitors can be added to the circuit to improve the frequency characteristics and gain of the preamplifier, and to ensure that the short-term signal disappears such as the shaking of the hand that deviates from the infrared detection range. , The power supply of the circuit will not jump instantly, ensuring that the hair dryer can still work stably and continuously.

Two, the key components of the hand dryer

The "heart" of the automatic hand dryer is mainly a single-phase different motor that drives the fan blades. Considering that the automatic hand dryer is used in a humid environment with a water source, the structure of the motor must adapt to the humid environment so as not to cause early failure. For example, single-phase capacitive induction motors often reduce the operational reliability of capacitive induction motors in humid environments due to capacitor failures. If a single-phase series motor is used, the commutator working in a humid environment is prone to damp and short-circuit, and the insulation performance of the dielectric deteriorates, resulting in the durability and service life of the motor. The motor is noisy and has serious interference to radio waves. During operation, the images of televisions and video recording equipment in and near the room will have multiple horizontal stripes, which affect the clarity, so it is not suitable for use. The single-phase double-ring shaded-pole asynchronous motor is more suitable for the above environment. It eliminates the shortcomings of the above two types of motors. The shaded-pole motor has better durability in humid environments and has a long service life. The motor stator pole is removable, and the excitation winding is a concentrated winding. , Directly wind into the nylon bobbin and put it on the iron core magnetic poles and then press the iron core magnetic poles into the stator yoke with a special fixture. This work is completed on a 49kV press. The electrical strength of the medium of this motor structure is greater than 4000V. 1min does not break down, in line with the GB4706.1-2005 safety technical standard for household appliances, Class II electrical products have electrical strength 3000V. 1min does not break down and does not flashover, generally at the rated voltage A smooth start has a larger safety margin compared with the specified value that the rated voltage should be able to start smoothly.

3. Common quality problems of hand dryers

Due to the low sales volume of automatic hand dryers, large enterprises are unwilling to organize production, so that the current domestic automatic hand dryer manufacturers are generally small enterprises with small production scale, poor technical strength, and backward production equipment, and there are even some hand-crafted workshops. The quality of the products produced by these companies is worrying. In recent years, the pass rate of the automatic hand dryer type test spot check is less than 50%. The main quality problems are as follows:

(1) Incomplete or irregular product marking: The marking should contain important information that guides users to use it correctly. Correctly marking the product's marking is one of the basic measures to ensure the personal and property safety of users. The mark shall be durable and eye-catching, shall not fall off after normal use, and the content shall be legible. Common problems are no manufacturer's name, model number, no waterproof grade mark, no assembly drawing, instruction manual, improper marking of II appliances, improper rated voltage, improper power marking, incomplete marking, etc.

(2) Many electrical safety performance problems: Exaggerate technical indicators, deceive and mislead consumers (mainly focus on one-sided exaggeration of input power); internal wiring disorder, unreliable ground connection, unqualified heat and flame resistance test and unqualified protection against electric shock, These unqualified items are all mandatory items closely related to the user's personal safety and environmental safety. The main reasons for these unqualified products are: the small scale of the manufacturer and the weak technical strength, which caused the manufacturer to make mistakes in the parameter design of the electric heating element, which caused the input power deviation to be too large; the air outlet opening was too large, causing some products to be contacted by the test finger To the charged body. Some internal wiring uses multi-stranded wires and simple soldering connection methods that make the connection unreliable; the selected insulating material does not have inferior materials with heat resistance of 125°C. Some companies lack the necessary testing methods, and a few companies do not strictly control product quality.

Fourth, the design ideas of hand dryers

As a modern sanitary appliance, hand dryers are more suitable than traditional towels and avoid cross-infection of diseases and bacteria. The hand dryer is a multi-directional air outlet device, and an air guide device is set up at the air outlet. There is a wind guide sheet on the device. In the process of rotating the air guide sheet, the hand dryer began to circulate and non-directional air out. Most of the hand dryer products on the market are basically composed of very common digital devices. Regardless of whether it is debugging or installation, the circuit structure is not very convenient and presents a single function. If the internal circuit of the hand dryer fails, the maintenance is inconvenient, and it is relatively difficult to replace it with other circuit components. Using single-chip microcomputer technology in the production of hand dryers, the entire circuit is relatively simple. The single-chip microcomputer is an integrated circuit chip that integrates the central processing unit CPU, read-only memory ROM, random access memory RAM, and a variety of I/0 ports and interrupt systems. It is called a micro computer system with low price and strong transaction processing ability.

The single-chip microcomputer selected for the production of the hand dryer is the 89C52 single-chip product of the MCS-51 series of INTEL. The 89(352 single-chip microcomputer is used as the controller of the entire circuit chip, and its electronic switches are mainly controlled by infrared rays. Generally speaking, ordinary hand dryers are equipped with infrared sensing equipment, which can sense the temperature of the human hand and control the switch. The electric hair dryer is turned on. The temperature of the hand is left, and the switch is controlled to turn off the electric hair dryer. Therefore, the use of single-chip technology is used in the production of hand dryers, and infrared control switches and electric hair dryers must be installed inside. Connect them with wires and use The effect is the same as the automatic hand dryer sold in the market. When the hand dryer is made, you can also play freely, adding lighting effects or sound effects. You can also paste some ornaments on the surface of the hand dryer to enhance the aesthetics. Using single-chip technology Only one integrated block is enough to make a hand dryer, which has the same function as the basic circuit.

5. Technical principle of hand dryer development

After the hand dryer with single-chip technology is completed, connect the power supply. The whole hand dryer has electric current, initialize the i/o port, the main control program starts to mobilize the sound and light system, and the sound and light prompt appears. Program the internal settings so that the single-chip microcomputer outputs a small square wave in a short period of time. 89C52 single-chip microcomputer has the ability of low-level drive, which can drive the transmitter to start emitting infrared rays. When installing the transmitting head and receiving head, pay attention to careful adjustment and keep the best distance. You can use an object to approach the transmitter and receiver, and the infrared light will be emitted to the object and reflected back to be received by the receiver. Once the receiving head receives the infrared light, its high level will change to a low level. Because the external pull-down is low, the P3 port of 89C52 will output current, causing the central processing unit to disconnect. The entire service program is interrupted and closed. The lights, speakers, and relays in the program are all connected to one line, causing the electric hair dryer to blow hot air.

The external interrupter began to become an I/0 port, and the peripheral level was detected irregularly. When the P3 port writes "1", they are internally pulled up to high level, and then returned, the central processing unit is connected, and the system is in standby. Be prepared for a delay during this time. Human hands will keep shaking in the hand dryer. If the receiving head is not prepared for delay, it will continuously send out signals, causing the relay to open and close again, and it will not stop beating. Be prepared for a delay, and also be prepared for reflection. The self-made hand dryer has a delay time of 3 seconds, which basically solves the jitter phenomenon. The method of playing acoustic sound is the oscillation method, which takes a long time and closes the relay suddenly every time it is interrupted. The jumping frequency of the relay is high, thus affecting the service life. If you want to avoid the occurrence of a large bounce frequency and extend the pull-in time of the relay, then a capacitor can be used to store energy. The P2 port in the 89C52 microcontroller is an 8-bit bidirectional I/O port with an internal pull-up resistor, which can limit the amount of current input, reduce the charging response of the capacitor, and avoid damaging the I/0 port.

Six, the power circuit of the hand dryer microcontroller

(1) Power supply circuit: The power supply circuit of the single-chip microcomputer uses the transformer rectifier diode current to obtain direct current, and then obtains 5V direct current through the three-terminal voltage regulator integrated circuit, which can be used by the single-chip microcomputer. The internal hair dryer uses AC 220V.

(2) Infrared detection circuit: infrared detection is composed of infrared emitting components and infrared receiving components. The infrared emitting component is composed of infrared light emitting diode IRLED. The infrared receiving component is a receiving circuit, which mainly includes infrared monitoring diodes, limiters, amplifiers, integrating circuits, band-pass filters, etc., and a receiving head to receive infrared information.

(3) The working circuit of the electric hair dryer: the relay adopts the specifications of 5V voltage and 5A current, and the relay line port is connected in parallel with the IN4007 diode. The coil of the relay is connected in series with a PNP transistor. Resistance should be added to the line port, and the resistance should be connected to the electrode.

7. Installation and debugging procedures of hand dryer (hand dryer)

To apply the SCM technology to the production of hand dryers, it is necessary to debug the self-made hand dryers. Debugging can measure the sensitivity of the received signal. Using an integrated receiving head can fix the sensitivity of the received signal and adjust the transmit frequency. The most sensitive frequency of the receiving head is about 36kHz-40kHz, and the sensing distance is often extended to about 7 meters, which exceeds the pre-sensing distance. Therefore, for infrared diodes, a frequency of 500kHz can be used for debugging. Adjusting the level change in the timer interrupt program can change the transmit frequency. Through debugging, it is found that the sensing distance should be between 15cm-20cm.

to sum up

The hand dryers on the market have a single function, a complex structure, and a relatively high price. The use of single-chip technology in the production of hand dryers has more stable and reliable performance, convenient maintenance, and low price. The circuit of single-chip technology is relatively simple, and the program is simple and flexible, so there are no major circuit problems in the process of making hand dryers. The single-chip microcomputer integrates the central processing unit CPU, read-only memory ROM, random access memory RAM and a variety of I/0 ports and interrupt systems. Because of its obvious advantages in the production of hand dryers, it will be more widely used in future life. in.