A wire sector detector

It is often able at each one of us to have to plant a nail to pose a hook or to have to make a hole in a partition to pose ankle. In the majority of the cases we arrive at the end of this operation without any problem. Alas, it arrives from time to time which one of the unfortunate workers of Sunday that we are, manages to center its hole with a millimetre-length precision into full in wire with electrical installation, thus causing serious damage. To save a few meters of invaluable (and expensive) copper in electrical installations, the wire are embedded in the walls while following courses as unforeseeable as tortuous. It happens sometimes that while planting a nail or while making a hole with a drilling machine, just on the level of a hidden wire, one can run the risk to cause a short-circuit and, in certain extreme cases, to receive a dangerous electrical shock. It that your ankle, is intended there for the installation of the framing of the back grandmother, returns to you at an exorbitant price! If the court T-circuit did not electrocute you, it will be necessary nevertheless to repair. What wants to say, withdraw wire or to cut out the partition to repair. Small do-it-yourself which was to take two minutes transforms into nightmare! This point, two solutions only to avoid this vision of apocalypse! Never not to plant a nail… or to have the apparatus that we propose to you in this article. Indeed, to avoid all the risks which we have just described, it is enough to have a circuit able to indicate in a reliable way the course of the electric wires dissimulated in the partitions.

Electric diagram

Figure 1 : By approaching the small detecting plate of an electric wire traversed by the sector 220 V, this one collects the 50 Hz of the alternating voltage. This weak signal is amplified by operational amplifier IC1/A (see figure 3) and is applied to the pin of entry of second operational amplifier IC1/B used like comparator of tension.

Figure 2 : The C5 condenser and diodes DS1 and DS2 make it possible to take, of the exit of IC1/A, an alternating signal which, of 0 volt, reached a maximum of approximately 8 volts. This signal, applied to pin 5 of IC1/B, is then compared with the positive tension that the R8 potentiometer applies to the opposed pin, the inverseuse pin 6.

Figure 3 : Electric diagram of the wire sector detector. All the resistances used in this project are a model of 1/4 of Watt. This circuit is fed by a traditional pile of 9 volts.

Figure 4 : If, through the R8 potentiometer, you apply a weak positive tension to pin 6 of IC1/B, the circuit will be very sensitive, thus, you will be able to locate wire embedded with an important depth.

Figure 5 : If, through the R8 potentiometer, you apply the positive maximum tension to pin 6 of IC1/B, the circuit will be less sensitive. Thus, you will be able to locate wire embedded with a low depth.

As you can see it on figure 3, to produce this detector, we used an integrated circuit TS27M2/CN containing two operational amplifiers CMOS characterized by an impedance of high entry. The non-inverseuse entry 3 of IC1/A is directly connected to a small detecting plate directly engraved on the printed circuit. If we approach the plate of detection of a wall in which are embedded electric wires, this one will collect the 50 Hz of the electric tension and the operational amplifier will amplify it approximately 84 times. Thus, on its exit, we will find a sinusoidal signal which will be able to reach a maximum value of 8 volts. This alternating voltage, passes through the condenser C5 and joined two diodes DS1 and DS2. As opposed to what we could think, these two diodes do not rectify the sinusoid, because, on the sor tie of diode DS2, there is no electrolytique capacitor. So on the sor tie of diode DS2, we find the same sinusoid as that applied to the entry, the only difference is that it starts from 0 volt and reaches a maximum value of 8 volts, as that is represented on figure 2. This tension is applied to the non-inverseuse entry 5 of IC1/B used like comparator of tension having for threshold of reference the positive tension applied to the opposite inverseuse entry (6) via the R8 potentiometer. This potentiometer is used to regulate the sensitivity of the detector. If we adjust the potentiometer so as to apply to pin 6 of IC1/B a minimal tension, we for rons to detect wire embedded with a certain depth (see figure 4). On the other hand if we regulate it so as to apply the maximum tension to this pin, we can detect only wire embedded little deeply (see figure 5). While turning this potentiometer on the maximum sensitivity, it is possible to locate a surface much larger than that where the electric wire passes. On the other hand while turning it on the sensitivity minimum, it is possible to locate, with an approximation of a few centimetres the tube in which passes this electric wire. Diode LED green, located on the exit of IC1/B, ignites with a high luminosity when the collected signal reached its maximum amplitude and with a weaker luminosity if the collected signal remains below the minimum level. According to the luminosity of this diode LED, we manage to establish with which depth can be embedded the wire of electrical installation. The pushbutton P1, inserted in the circuit, makes it possible to feed the integrated circuit IC1 only during the time used for the research of wire.

Practical realization
On the printed circuit, whose copper side comprises also engraved the plate of detection, it is necessary to assemble the few visible components on figure 6. To start, assemble the support for the integrated circuit IC1, continue with all resistances and finally with two diodes DS1 and DS2, by directing their rings towards the left. After these components, you can insert the ceramic condenser C2, all the condensers polyester and the electrolytique capacitor C7, by respecting the polarity + its legs (long leg with positive). Before placing the R8 potentiometer and diode LED on the printed circuit, you must bore the lid of the plastic box with a drill of 3 mm to make leave the head diode LED and with a drill of 8 mm to make leave the axis the potentiometer. To help you in this operation, we defer on figure 11 a drawing comprising all the dimensions. This operation of simple drilling finished, press the body of the potentiometer on the printed circuit, then connect with three pieces of wire court ts and rigid its three pins to the holes present on the printed circuit. To hold blocked the potentiometer on the printed circuit, we advise you to also weld a piece of wire rigid onto its case, as that is represented on figure 6. Before welding the legs of diode LED onto the printed circuit, turn the longest leg towards the integrated circuit IC1 and control with which distance you must position his body so that the head of diode LED exceeds by the hole carried out on the lid. It will also be necessary to carry out a hole of 8 mm on the side of the box to install the pushbutton P1. The finished assembly, insert the integrated circuit in its support, by directing its reference mark-locating pin in form of " U" towards C5. Close then the box, the assembly is ready to detect the electric wires embedded in the walls.

Use
Apply box in point unspecified of wall or of partition, then support to pushbutton P1 and if you note that diode LED ignites, reduce the sensitivity. With extinct diode LED, start to entirely explore the surface of the wall and immediately you will realize that by approaching you a point under which a wire traversed by the tension passes 220 volts of the sector, diode LED ignites. If diode LED remains lit compared to a too important surface, it is necessary to reduce the sensitivity while operating the R8 potentiometer and, in this configuration, you will note that diode LED will ignite only if you are exactly with the top wire of the electric line. Note: if you are too distant from an electric line, you will note that while supporting on P1, diode LED emits a flash of light which informs you that the circuit is operational. And it is only when you approach it an electric wire connected to the tension of the sector 220 volts which you will see diode LED remaining lit permanently. It is necessary for us to announce that this circuit detects only wire traversed by the tension 220 volts, thus, do not seek wire traversed by low tension (of the 12 volts or the 20 volts) because it will not detect them.

Figure 6 : Diagram of establishment of the components.
To block the R8 potentiometer, visible in bottom of the drawing, we advise you to weld a piece of wire rigid onto its case and to weld it onto the copper track of the printed circuit.

Figure 7 : Drawing of the printed circuit on scale 1.

Figure 8 : For fixing the potentiometer, it is necessary to shorten its axis with approximately 15 Misters.

Figure 9 : The circuit is installed inside a small plastic case comprising a housing for the pile of 9 volts of food. On figure 11, you will find all the dimensions of drilling.

Figure 10 : Stitching of the integrated circuit TS27M2 seen of top with its reference mark in form of " U" directed towards the left. The longest leg of diode LED is always the anode.

Figure 11 : Plan of drilling of the lid of the plastic case. There a third hole will have to be practised on the side of the case to be able to install the pushbutton P1.

Component List
R1 = 4.7 MΩ
R2 = 10 kW
R3 = 10 kilohms
R4 = 12 kΩ
R5 = 1 MΩ
R6 = 82 kΩ
R7 = 220 Ω
R8 = 10 kW pot. flax.
R9 = 220 Ω
R10 = 470 Ω
C1 = 100 nF polyester
C2 = 150 pF ceramic
C3 = 100 nF polyester
C4 = 1.5 nF polyester
C5 = 1 uF polyester
C6 = 100 nF polyester
C7 = 47 uF electrolytic
DS1 = Diode 1N4148
DS2 = Diode 1N4148
DL1 = Diode LED
IC1 = Integrated TS27M2.CN
P1 = Pusher