Flush Detector

Quite often, residents of apartment buildings need to fix a picture, a hanger, a shelf, or some other piece of furniture on the wall of an apartment. To do this, you should mark a point on the wall and drill a small hole with a perforator. However, there is always the possibility of getting into the wiring hidden in the wall under the wallpaper - in this case a small renovation of the interior can result in an inevitable electricians call. To prevent this from happening, you can assemble a simple hidden wiring detector that will show exactly where the wires go and where they are not.


Detector for hidden wiring
The KP103 field-effect transistor is the sensitive element of the circuit, to the gate of which the antenna is connected. You can use the transistor in any package and with any letter index. The device reacts to wires with a voltage of 220 V 50 Hz, regardless of whether the current flows through them, or not. Also in the circuit is used the chip K561LA7, which is 4 logic elements 2I-NOT.It can be replaced by an import analogue, a CD4011 chip. The LED on the circuit lights up when the antenna is in the immediate vicinity of the live wire. As an antenna, you can use a piece of ordinary thin wire, 5-10 cm long. The longer its length, the greater the sensitivity of the device. The circuit consumes about 10-15 mA, powered by a voltage of 9 volts. An ordinary Krone battery is suitable for power supply. If necessary, you can connect any piezoceramic emitter, for example, ZP-3, to the 10th output of the microcircuit, then the sound will be heard when a wire is detected. You can download the fee here:
Detector for hidden wiring

Detector assembly

The circuit is assembled on a miniature printed circuit board with dimensions of 40 x 30 mm, which can be done using the LUT method. The printed circuit board is completely ready for printing, you do not need to mirror it. After etching, it is advisable to tin the tracks, this will simplify the soldering of parts, and copper will not oxidize.
Detector hidden wiring
After the manufacture of the printed circuit board, you can solder the details.You should be careful when handling the microcircuit - it is sensitive to static and can be easily damaged. Therefore, we solder the socket to the board under the microcircuit and place the microchip into it only after the assembly is completed. You also need to be careful when soldering the transistor - if it is in a plastic case, then only two legs are soldered onto the board - the drain and the source, and the antenna is soldered directly to the gate. If the case is metal, all three legs are soldered to the board along with the antenna. It is important not to confuse the cap, otherwise the device will not work. Power wires, for convenience, you can immediately solder to the connector for the Crown, as I did. After the soldering is completed, it is imperative to wash the flux residues from the board, otherwise the sensitivity may suffer. It is also advisable to check the correctness of the installation and the adjacent tracks to the closure.
Detector for hidden wiring
Flush Detector Detector

Detector Tests

After the assembly is completed, you can begin the tests. We take the crown and connect it to the board, putting an ammeter in the gap of one of the wires. Consumption of the circuit should be 10-15 mA.If the current is normal, you can bring the detector's antenna to any network wire and observe how the LED will light up and squeak when the piezo emitter is installed. The detection range of the wiring is approximately 3-5 cm, depending on the length of the antenna. In this case, do not touch the antenna, this significantly decreases the sensitivity. The device does not require any configuration and begins to work immediately after the power supply. In addition to network wires, it also reacts to twisted pair cable. Successful assembly.

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