Design of groundwater level monitoring system based on LM3S615

Abstract: This paper introduces the design scheme of a real-time monitoring system for groundwater level. The system mainly includes three parts: signal acquisition, wireless module, data processing and storage. The signal obtained by the pressure sensor is adjusted and amplified, sent to the main controller LM3S615 for A / D conversion and other processing, and then sent to the indoor monitoring room through the wireless communication module PTR8000. After receiving the data, the PTR8000 receiver sends it to the upper computer through the serial port RS232. The human-machine interface is realized by LabVIEW software, which can process, display and store the data. This solution has certain reference value for improving the portability of the monitoring system, reducing costs and energy consumption.

Keywords: groundwater level; LM3S615; PTR8000; LabVIEW

0 Preface

China's groundwater accounts for one-third of the total water resources, and the annual water supply accounts for nearly 20% of the total water supply. It plays an important role in supporting economic and social development. Large-scale groundwater development has caused over-exploitation of groundwater in local areas and induced geological disasters. Such as: ground subsidence, ground fissure disaster, etc.

Nowadays, most of the monitoring points in China are still based on traditional manual timing measurement methods (electric meters, clocks, ropes, etc.), so they are not very good for some sudden groundwater level anomalies. The early warning function also takes up a lot of manpower and there are human errors. Therefore, the automatic monitoring of the key monitoring points of groundwater level is conducive to improving the prediction and prediction of various geological disasters.

Using ARM as the main controller can reduce power consumption and lay the foundation for establishing wireless network communication, making the system more efficient and reliable.

1 Design plan

1.1 Overview of the program

The basic design idea of ​​this system is: the front end uses the differential pressure sensor MPX5100DP to collect the original signal, after conditioning and amplification, it is sent to the main controller LM3S6l5, after internal AD conversion and other processing, sent to the indoor monitoring room through the wireless communication module PTR8000 After receiving the data, the PTR8000 receiver sends it to the upper computer through the serial port RS232 under the control of the controller. The human-machine interface is realized by LabVIEW software, which can process, display and store the data. The system block diagram is shown in Figure 1.

This system mainly includes 8 parts including power module, signal conditioning module, ADC module, LCD module, wireless transmitting module, wireless receiving module, serial communication module and host computer module. The transmitter power supply is powered by a 12V battery because it works in the field; the receiver power supply is powered by USB. The signal conditioning module mainly includes a zero adjustment circuit, a multi-stage amplifier circuit, and a low-pass filter circuit. The ADC and LCD module use the 10-bit AD and LM3S615 built-in LCD on the LM3S615 development board respectively. The wireless transmit and receive module adopts PTR8000 module, half-duplex working mode. The serial communication module has the first controller LM3S101 of the LM3S series to control communication. The host computer interface is written in LabVIEW software.

1.2 Signal acquisition

(1) Pressure sensor

MPX5100DP is an integrated silicon pressure sensor with on-chip signal conditioning function and temperature compensation function, and the output is a high-precision analog voltage signal. The sensor is especially aimed at microcontrollers with built-in A / D. The pressure range is 0 ～ 100kPa, the corresponding water level range is 0 ～ 10m, the full-scale output is 4.7V, and the sensitivity is 45mV / kPa. Figure 2 is the physical diagram of MPX5100DP and the recommended decoupling circuit.

There are two holes in the upper part of MPX5100DP: the Pl hole is a pressure hole, which is in direct contact with water; the P2 hole is a vacuum hole, and air is introduced. The change in voltage is proportional to the change in the difference P between P1 and P2. The MPX series is designed as a positive pressure sensor, ie P1> P2, P = Pl-P2.

(2) Signal conditioning circuit design

When P1 = P2, the sensor has a fixed offset voltage of about 200mV. When designing the circuit, design a subtractor to subtract it. By adjusting the variable resistor before each measurement, when the sensor input is 0, the output voltage is also Is 0. Two gears (& TImes; 1, & TImes; 10) are designed to amplify the output voltage of the sensor. Here, OP27 with low noise and low offset voltage is selected, and precision amplifier resistors 18k and 2k are selected to ensure the accuracy of signal amplification. Before the actual test, adjust the zero adjustment circuit to make the output zero.