In general construction, once a building is completed, various infrastructures are typically in place. Among these, power lines are often embedded within the walls. When it comes to secondary renovation or the installation of weak current lines, it's crucial to avoid 220V power wires. Most of these secondary tasks are handled by experienced workers who rely on their expertise. Additionally, when old wiring fails, detecting the location of wires inside the wall becomes necessary. Based on these needs, 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 test was successful, the device was cumbersome. In the same year, TI released the first LDC series of inductive-to-digital converters, which significantly improved the accuracy of wall wire detection. The measuring system is controlled by an STM32F107 microcontroller, with the LDC1000 serving as the sensor for detecting wire positions.
The wall wire measuring instrument consists of three main components: the STM32F107 microcontroller for data acquisition and processing, the LDC1000 inductive digital sensor circuit, and the LCD12864 display unit. The STM32F107, based on the Cortex-M3 architecture, is compact, low-power, and operates over a wide temperature range, making it ideal for such applications. It communicates with the LDC1000 via SPI, allowing for precise distance and position measurements.
The LDC1000 is capable of detecting metal objects without direct contact, using an external PCB coil. Unlike traditional Q meters that measure inductance, the LDC1000 detects the presence and position of metal objects in its vicinity. This makes it highly suitable for identifying the location of wires hidden behind walls.
The hardware design focuses on the integration of the LDC1000 with the STM32F107. Power is supplied through a lithium battery, with +5V and +3.3V regulators ensuring stable operation. The SPI interface facilitates communication between the microcontroller and the sensor, while interrupts and clock signals help manage the measurement process.
The PCB coil used in the system has specific dimensions—15mm diameter, 25 turns, and 4 mils width. The coil is connected to the LDC1000, and when an alternating current is applied, it generates an electromagnetic field. If a metal object enters this field, eddy currents are induced, altering the inductance and enabling the detection of the object’s position.
To improve efficiency, a capacitor is connected in parallel with the coil, reducing energy loss through resonance. The equivalent circuit illustrates how the resistance changes with the distance of the metal object, allowing for accurate positioning.
On the software side, the RpMAX and RpMIN registers of the LDC1000 are calibrated to ensure accurate readings. By testing the maximum and minimum resistance values under different conditions, the system can reliably detect the position of the wire.
The user interface includes a 4x4 button array, allowing users to start the device, initiate measurements, and record results. The LCD12864 display provides real-time feedback, indicating whether the wire is horizontal or vertical.
Testing confirmed that the device achieves 100% accuracy in detecting wire positions. The final prototype features a compact design with intuitive controls and clear visual indicators, making it easy to use in real-world scenarios.
In conclusion, this paper introduces a new method for detecting wall wires using an inductive digital sensor. Through detailed hardware and software design, the system effectively identifies the exact location of hidden cables, offering a reliable solution for construction and maintenance tasks.
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