Clothing Comfort Detection System Based on ARM9 Processor Chip S3C2440

　　Generally speaking, when the temperature and humidity of human skin are in a state of thermal and humidity comfort, people's intelligence, physical strength (manual) or sensory performance are all at a high level. In addition, thermal and humidity comfort is a necessary condition for people to be in the best health state. By measuring the pressure, temperature and humidity of clothing in different parts of the human body under different conditions, the distribution of pressure, temperature and humidity in different parts of the human body after dressing can be obtained. Analysis of the measurement results can provide quantitative indicators for the objective evaluation of clothing pressure and thermal and humidity comfort, and provide a scientific basis for the style and structure design of clothing. In recent years, more and more researchers have carried out research on clothing function testing and have made a lot of progress, but the research and development of related clothing function testing instruments lags far behind the needs of the times. This paper designs a portable clothing pressure, temperature and humidity measurement system based on ARM technology.

　　1 Composition of clothing comfort testing system

　　The clothing comfort detection system consists of a data acquisition module, a control module for data acquisition and storage, and a data analysis module. The structure is shown in Figure 1. The front end of the data acquisition module is composed of multiple FlexiForce pressure sensors, pressure-voltage signal conversion circuits, and DHT90 temperature and humidity digital sensors. These sensors are used to obtain the pressure and temperature and humidity signals of the measured parts, and convert the measured pressure into voltage signals through signal conditioning circuits (signal conversion circuits, filter circuits, etc.). The control module for data acquisition and storage is the core of this system and is mainly responsible for data acquisition and storage control. This module uses the ARM9 processor chip S3C2440 with a built-in 10 b analog-to-digital converter (ADC). The ADC can convert analog voltage signals into digital signals with a resolution of 10 b at a sampling rate of 500 KSPS and use its GPIO interface to realize the acquisition of temperature and humidity digital signals. In addition, this module uses SD cards as storage media to realize offline storage of pressure, temperature and humidity data. The data analysis module is mainly responsible for reading the measurement result data stored in the SD card. This module uses the convenient and realistic instrument panel developed by LabVIEW language to save the measurement results and display them in an intuitive form.

　　2. Hardware Design of Clothing Comfort Detection System

　　The hardware design of the clothing comfort detection system is mainly about the connection design of the system hardware instruments and their devices, mainly referring to the selection of sensors for the data acquisition module and the hardware design of the data acquisition and storage control module. The hardware part of the clothing comfort detection system realizes the instrument control and data acquisition of the clothing comfort detection system. It is the main part of the clothing comfort detection system and is directly related to the performance of the entire system.

　　2.1 Data Acquisition Module Hardware Design

　　The hardware design of the data acquisition module mainly includes the selection of temperature and humidity sensors, the selection of pressure sensors, and the pressure-voltage signal conversion and amplification circuit.

　　2.1.1 Selection of sensors

　　The sensor is at the forefront of the test system and is the window for sensing temperature, humidity and pressure signals. The accuracy of the information obtained and converted is directly related to the performance of the entire test system. This system uses the DHT90 digital temperature and humidity sensor and the FlexiForce pressure sensor from Teksean, USA.

　　The DHT90 digital temperature and humidity sensor can measure humidity, temperature and dew point at the same time. It can directly output calibrated digital signals of relative humidity, temperature and dew point without peripheral components, which can effectively solve the shortcomings of traditional temperature and humidity sensors. It integrates humidity sensitive elements and temperature sensitive elements, amplifiers, a 14b A/D converter, calibration data storage, digital bus interface and voltage stabilization circuit. Since the temperature sensor and humidity sensor are close together on the silicon chip, the dew point can be accurately measured without introducing errors due to the temperature difference between the two; the calibration coefficient is directly stored in the OTP memory on the chip, and the output is a calibrated digital signal. The DHT90 digital temperature and humidity sensor has excellent performance, good stability, low cost and easy use, so this system uses it as a temperature and humidity measurement.

　　The FlexiForce pressure sensor is used for pressure testing. Compared with the sensors used in traditional clothing pressure testing systems, FlexiForce has excellent performance in linearity, hysteresis, drift, temperature and sensitivity. According to the clothing pressure value to be tested, the FlexiForceA201 sensor with a pressure range of 0 to 1 lb (4.4 N) is selected, which is fully capable of clothing pressure testing. Since ARM cannot collect non-electrical physical signals, and the pressure sensor outputs non-electrical pressure signals, the pressure signal needs to be converted into a voltage signal through a pressure-voltage conversion amplifier circuit. Then, the required clothing pressure value is obtained from the corresponding relationship between the calibrated pressure and voltage.

　　2.1.2 Pressure-voltage signal conversion amplifier circuit and pressure-voltage calibration

　　After the sensor passes through the pressure-voltage signal conversion amplifier circuit, the output voltage value Vout. The corresponding relationship between the sensor input signal and the voltage is Vout=-VD*(RF/R), RF=R1+RF 1, where: Vout is the output voltage; RF is the feedback resistor in the amplifier circuit; R is the corresponding resistance of the sensor, and its resistance change corresponds to the change of the pressure acting on the sensor, and RF/R is the amplification factor in the amplifier circuit. The static characteristic pressure-voltage calibration curve of FlexiForce pressure sensor is shown in Figure 2.

　　2.2 Hardware Design of Data Acquisition and Storage Control

　　The data acquisition and storage control module is the core of this system. The performance of this module directly affects the measurement accuracy and running speed of the entire clothing measurement system. The structural block diagram of the data control and storage module is shown in Figure 3. The core part of the data acquisition and storage control module is the high-performance S3C2410 microprocessor produced by Samsung. The processor is a 16/32-bit RISC embedded microprocessor based on the ARM920T core. It mainly integrates 117 general I/O interfaces, 24 external interrupt sources, 4 timers with PWM function and 1 internal clock, 8-channel 10-bit ADC, 3-channel UART, 4-channel SDRAM controller, 1 LCD controller, RTC (real-time clock) with calendar function, SD card interface, etc. At the same time, S3C2410 also provides a complete set of system peripherals, mainly MAX232, buttons, LEDs, SD memory cards, SDRAM, SRAM, etc.

　　The S3C2410 microprocessor uses the built-in 10b analog/digital converter (ADC) to convert the analog voltage signal converted from the pressure signal value into a digital signal with a 10b resolution at a sampling rate of 500 KSPS; the S3C2410 microprocessor uses its GPIO interface to collect digital signals of temperature and humidity. In addition, the processor controls the selection of sampling channels and the sampling rate through buttons; the SD card is used as the storage medium to save the collected data offline. This chip is mainly aimed at handheld devices, as well as cost-effective and low-power applications, and can meet the needs of data acquisition and storage control module control. [page]

　　3. Implementation of clothing comfort testing system software

　　The software implementation of the clothing comfort detection system refers to the software implementation of the data acquisition and storage control hardware module and the software implementation of the data analysis module.

　　3.1 Software implementation of data acquisition and control and data processing hardware modules

　　The software part of the system acquisition and storage module is programmed in C language under the ADS 1.2 environment and implemented for the corresponding hardware functions. The flow chart is shown in Figure 4. The software implementation of the data acquisition, control and data processing hardware modules first initializes the system. The system initialization mainly refers to the initialization of interrupts, memory systems, stacks, and hardware such as keyboards, LEDs, and SD memory cards; then the sampling channel and sampling rate are set through the keyboard; then the A/D conversion is started to convert the collected analog pressure-voltage signal into a digital signal; finally, at the end of sampling, the collected pressure, temperature and humidity signals are imported into the SD memory card to realize the storage operation of the collected signals.

　　3.2 Software Implementation of Data Analysis Module

　　The data analysis module only involves software implementation. The module uses LabVIEW 7.1 software to realize the output of collected data, real-time display of graphics, and generation and saving of Excel test reports. The program diagram is shown in Figure 5. The software implementation of the data analysis module first opens the file of temperature, humidity and pressure signals saved offline in the SD memory card; secondly, enters the While loop to continuously read the signals in the file by setting the control buttons, and shunts its data to realize the graphical display of pressure, temperature and humidity signals of each channel; finally, saves the Excel test report and closes the file.

　　The panel of the designed data analysis module is shown in Figure 6. This module is flexible and concise, and can monitor the pressure, temperature and humidity signals for a long time and continuously, vividly simulating the appearance of traditional instruments. When operating the panel, first point the Boolean switch to "Start", open the text file of the temperature, humidity and pressure signal stored offline in the SD memory card (such as j:\\1.txt) to read the data, that is, read the data continuously at regular intervals, and then the user sets the required reading points and channel selection through the "Read Data Points" and "Read Position" controls on the panel, and points the Boolean switch to "Stop" to end the display of the signal; finally, click the Excel button to save the test report in the form of a spreadsheet. The panel realizes the data display function of 8-channel signals, which is convenient for monitoring the changes of pressure, temperature and humidity signals in multiple parts at the same time. At the same time, the Excel test report realizes the function of long-term storage of test information.

　　4 Test Experiments

　　The curves shown in Figure 6 are the results of the clothing comfort detection system testing the temperature and humidity of the back and armpits and the pressure of the shoulders and abdomen under normal working conditions. Since the pressure and temperature and humidity values ​​of the same part of the human body do not change much over time when the human body is in normal working condition, the test results shown in Figure 6 are consistent with the actual changes in pressure and humidity of different parts of the human body under normal clothing conditions.

　　5 Conclusion

　　A portable clothing pressure, temperature and humidity measurement system based on embedded ARM processor is designed. The system realizes the continuous acquisition and storage of clothing pressure, temperature and humidity of human body under normal working conditions on a single chip, and realizes real-time data analysis based on LabVIEW. The system has the characteristics of small size, low power consumption, fast speed, accurate test and reliable operation. This portable system can provide a basis and foundation for the objective evaluation of clothing comfort and provide a new idea for the development of clothing function measurement system.