1 Introduction
In the field of industrial control and industrial production, the monitoring of sensors for industrial control and production environments is self-evident. Most of the traditional sensor monitoring systems are controlled by single-chip microcomputers, and the accuracy and real-time performance of monitoring are not satisfactory. This paper finds a practical sensor design solution, which uses temperature and humidity sensor chip, based on PXA310 hardware platform and Linux operating system, can effectively monitor the temperature and humidity changes in the field. When the surrounding environment changes and the work requirements cannot be met, the monitoring data can be obtained and an early warning can be made to improve the reliability and real-time performance of the production and working environment detection.
2, temperature and humidity sensor circuit design
After comparing some sensor application design schemes, the SHT10 chip is selected as the core component of the embedded temperature and humidity sensor. Its peripheral circuit is simple and has its unique advantages compared to other sensor chips (DS18B20).
The SHT10 can perform 3 temperature and humidity measurements per second with a data accuracy of 14 bits and stable operation. The measurement is patented by CMOSens, so the measurement efficiency and accuracy are better than the DS18B20. The DS18B20 uses a single bus control scheme (1-wire), which is measured approximately once per second, with 9 digits of digital temperature data; only temperature measurement is provided. When the production environment is strictly tested, it appears to be insufficient in accuracy and function.
2.1 Introduction to SHT10
The SHT10 is a highly integrated temperature and humidity sensor chip that provides full-scale calibration digital output. The sensor consists of a capacitive polymer moisture sensitive component and a temperature sensitive component made of an energy gap material that is designed on the same chip as a 14-bit A/D converter and a serial interface circuit. The calibration coefficient is stored in the program OTP memory by calibration, and the two-wire serial interface and internal voltage adjustment make the peripheral system integration fast and simple.
2.2 How SHT10 works
SHT10 chip power supply 3.3V. After the sensor is powered on, wait 11ms to complete the "sleep" state. After the communication resets and starts the transfer command, a set of measurement commands are sent ('00000101' indicates relative humidity RH, '00000011' indicates temperature T), and the controller waits for the measurement to end. This process takes approximately 11/55/210ms, corresponding to 8/12/14bit measurements. The SHT10 indicates the end of the measurement by pulling DATA low to LOW. Before the controller triggers the SCK clock, it must wait for this “data ready†signal to correctly read the measurement data.
After the measurement and communication ends, the SHT10 automatically goes into sleep mode. The data transfer uses a two-wire serial interface (not compatible with the I2C interface).
2.3SHT10 circuit schematic
The SHT10 is packaged in an LCC with DATA and SCK pins connected to the PXA310's GPIO78 and GPIO79. The PXA310 controls the peripheral temperature and humidity sensor and data read and write operations in an analog timing mode. Since the SHT10 has high sensitivity to temperature and humidity, it should be kept away from heat sources (such as MCU, LCD, etc.) when the system is integrated. Otherwise, the measurement results will deviate. When wiring the SHT10, the surrounding devices should be reduced as much as possible. interference. The schematic diagram of the SHT10 circuit is shown in Figure 1.
Figure 1 SHT10 circuit schematic
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