In general engineering, when a building is constructed, various infrastructures are typically completed. Among these, power lines are often installed. However, during secondary renovation or the installation of weak current lines, it becomes essential to avoid 220V wires embedded in the walls. Traditionally, this process has relied heavily on the experience of skilled workers. Additionally, when old wiring systems fail, detecting the location of hidden wires within the walls is crucial. Based on these requirements, this paper presents a simple and lightweight wall wire detection device.
In 2013, we initially developed a wooden board-based wire detector using a large inductor made from enameled wire. Although the initial test was successful, the device was cumbersome and not practical for daily use. The introduction of the LDC series by Texas Instruments in 2013 marked a significant breakthrough. It allowed for accurate detection of wall wire positions. This system is controlled by an STM32F107 microcontroller, with the LDC1000 serving as the sensing component to detect the location of wires within the wall.
The wall wire measuring instrument consists of three main components: the data acquisition and processing unit based on the STM32F107 microcontroller, the LDC1000 inductive digital sensor circuit, and the LCD12864 display unit. The STM32F107 features a Cortex-M3 core, which ensures minimal code size, low power consumption, and a wide operating temperature range. It communicates with the LDC1000 via an SPI interface, enabling efficient data transfer.
The LDC1000 is capable of detecting both horizontal and vertical distances, angles, displacements, and vibrations. It uses non-contact inductive sensing through an external PCB coil. Unlike traditional Q meters that measure coil inductance, the LDC1000 can detect the presence and position of metal objects in proximity. This makes it ideal for identifying hidden wires in walls.
The third component, the LCD12864 display, is responsible for showing the initialization screen and the measurement results. The overall system architecture is illustrated in Figure 1.
The hardware design focuses on the integration of the LDC1000 with the STM32F107. The system uses a +5V power supply from a lithium battery, with the LDC1000 receiving direct power while the STM32F107 is powered through a TPS78633 voltage regulator. The SPI interface connects the two components, allowing the microcontroller to control the sensor and receive data. Additional connections include the interrupt pin, clock signal, and frequency counting, as shown in Figure 2.
The PCB coil used in the LDC1000 is custom-made with specific dimensions: a diameter of 15 mm, 25 turns, and a line width of 4 mils. The coil's performance is based on electromagnetic induction principles. When an alternating current is applied, an electromagnetic field is generated around the coil. If a metal wire enters this field, eddy currents are induced, which alter the magnetic field and allow the position of the wire to be determined.
To reduce energy loss, a capacitor is connected in parallel with the coil, forming an LC resonance circuit. This minimizes energy dissipation and allows for accurate distance measurements. The equivalent circuit is shown in Figure 5.
The software design involves configuring the LDC1000’s RpMAX and RpMIN registers to ensure accurate measurements. By placing a metal object at different distances from the coil, the maximum and minimum resistance values are recorded. This helps establish a reference curve for detecting the wire's position. The software flowchart is presented in Figure 7, detailing the measurement and recording process.
Experimental testing confirmed the system’s reliability. The device was tested along building walls, and the LCD screen displayed whether the wire was positioned horizontally or vertically. The user interface included 4×4 array buttons for starting the device and recording measurements. The LCD12864 display provided clear feedback, ensuring ease of use.
Finally, the system was fully tested and demonstrated a 100% accuracy rate. This new method offers a reliable and efficient way to locate metal wires in walls, significantly improving safety and efficiency in construction and maintenance tasks.
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