Development and design of hair dryer control board
Development and design of hair dryer control board
In the past, fires caused by improper use of hair dryers occurred from time to time, which seriously damaged collective and individual lives and property. Departments at all levels and schools attach great importance to the use of hair dryers in student dormitories, and most schools prohibit students from using hair dryers in dormitories. According to relevant statistics, the fire caused by the hair dryer is mainly that the user does not turn off the hair dryer in time when leaving.
1、 Overall scheme design of hair dryer
The hair dryer designed in this paper includes human body induction module, signal acquisition module, signal processing module, execution module, main circuit, switch, shell and power line; The human body induction module and the signal acquisition module are connected through the detection resistance, the output end of the signal acquisition module is connected with the input end of the signal processing module, the output end of the signal processing module is connected with the power end of the execution module, the contact of the execution module is connected in series with the main circuit of the hair dryer, and the main electric circuit is composed of motor, thermal resistance wire, switch and other elements.
2、 Design of induction module of hair dryer
The human body induction module is composed of high resistance resistance, detection resistance, metal body, human body, fuse, signal line and earth; The high resistance resistance, detection resistance, fuse and signal circuit are built in the hair dryer. After the high resistance resistance, detection resistance and fuse are connected in series through the signal circuit, one end is connected to the power line and the other end is connected to the metal body; The metal body is a metal sheet with good conductivity and embedded in the groove on the handle of the fan, and the depth of the groove shall be consistent with the thickness of the metal body; When the user holds the hair dryer, the palm will be in good contact with the metal body, so that the human body and the earth become a part of the induction circuit; If the power line is connected to the power supply, the current will flow through the power line, high resistance resistance, detection resistance, metal body, human body and fuse into the earth to form a loop. Because the resistance value of high resistance is very high (generally 2-3 megohm), even if the conduction loop is formed, the line resistance is very high, which makes the current very weak and has little impact on the human body, Although the current in the circuit is weak, it can output electrical signals, and the signal acquisition module can collect weak electrical signals, indicating that the hair dryer is in the hands of the user; In order to prevent the resistance from aging and reducing, a fuse is added in the induction circuit, and its fusing value is very small. Once the current exceeds the set value, the fuse will fuse immediately to cut off the circuit and protect the user.
3、 Design of signal acquisition module for hair dryer
The signal acquisition module is built in the hair dryer and is composed of detection resistance and sampling circuit; The detection resistance is a common part of the acquisition module and the human body induction module. Its function is to change the current signal in the human body induction module into a voltage signal; The sampling circuit converts the collected voltage signal into a voltage signal of appropriate size and sends it to STM32 processor; If there is current flowing through the human body induction circuit, the current will produce a voltage difference at both ends of the detection resistance (although the current is very weak, according to Ohm's law, increasing the resistance value can increase the voltage value). The detection voltage is transmitted to STM32 after being amplified and stabilized by the sampling circuit. At this time, STM32 receives an open electrical signal.
4、 Design of signal processing module of hair dryer
The signal processing module is composed of STM processor and rectifier filter circuit. The two parts are built in the handle of the hair dryer. The function of the rectifier filter circuit is to provide power to STM32. The rectifier filter circuit is a circuit board, and the STM32 processor can be embedded in the circuit board, which makes the volume of the signal processing module very small and can be placed in the narrow and long handle of the hair dryer; When the signal acquisition circuit sends a signal voltage to STM32, STM32 will control the relay to be energized.
5、 Design of executive module of hair dryer
The execution module is a small relay with four pins. The two pins are the relay power port. One end of the power port is connected with STM32 pin and one end is connected with zero line. It is powered on or off under the control of STM32. The other two pins are relay contacts, which are connected in series with the main circuit of hair dryer; When the relay is powered on and its contact is closed, press the switch at this time to make the hair dryer work. When the relay is powered off, its contact is disconnected and the hair dryer stops working. If the relay cannot be powered on and its contact is disconnected, the hair dryer will not work no matter how to control the switch.
6、 Main circuit design of hair dryer
The main electric circuit of the hair dryer is composed of motor, thermal resistance wire, fuse, switch and line. The motor and thermal resistance wire are connected in parallel. Each branch is equipped with a switch. Different combinations of switch states can realize various working states. Relay contacts are connected in series on the main circuit to realize that the relay can directly cut off the line, The set fuse can prevent the failure caused by aging of the main circuit or other reasons. Once the current is too large, the fuse will be disconnected immediately.
7、 Work flow of hair dryer
When the user uses the hair dryer, the palm will contact the metal body. At this time, a current will flow through the human body and lead to the earth. When the current flows through the resistance, a voltage will be generated at both ends of the resistance. The signal acquisition module can receive the voltage signal at both ends of the resistance. If there is no user or the user does not contact the metal body, there is no current, No voltage will be detected at both ends of the resistance; After the voltage signal is collected, the signal acquisition module amplifies and stabilizes the voltage signal, and finally outputs the appropriate voltage signal. The voltage signal is sent to the signal processing module. The signal processing module sends a signal to the execution module, the relay acts, and the relay contact connected in series in the main circuit is closed to meet the prerequisite for the operation of the hair dryer. On the basis of meeting this condition, press the switch, The hair dryer will work. When the user does not touch the metal body, if the signal collector does not receive the voltage signal, it will stop transmitting the signal to STM32, and STM32 will immediately send a disconnection signal to the relay to realize power off.