Circuit Wiring Solution

 I love the detector , this is actually one of my Hobbys, want to know more you saw the blog Metal Detector, there is lots of interesting information. But when we schema the principle of operation of this detector schema home metal consists of a mixture of two equal frequency causing interference. When one of the oscillators become unstable, the frequency of the interference is modified by changing the tone, so alert the user to the presence of a conductive metal near the coil.

Metal Detector cheap and easy to build



This detector is cheap and easy to build , requires neither a printed schema and can be tested directly over a breadboard . It is constructed using principal components as a transistor and a CMOS integrated schema 4011 .

 The integrated schema 4011

The integrated schema 4011 consists of four NAND gates with two inputs each clock frequency depends on its supply voltage but reaches a maximum 10 MHz It operates in a recommended range of 3 V to 15 V supply range .

The operation of the Metal Detector

The oscillator is built with NAND gate N1 and a ceramic filter intermediate frequency ( IF) of 470kHz is used in this oscillator. The second oscillator was built with NAND gate N3 and an LC schema (coil + capacitor) . The frequency of the second oscillator is adjusted such that it will produce an audible oscillation frequencies of both , hence the name of this type of metal detector BFO ( Beat Frequency Oscillator ) .

The setting of this oscillator is done through the variable capacitor , you should adjust for parelhamento signals from two oscillators let the coil away from metals to prevent feedback . The signal from the second oscillator is amplified in the NAND gate N4 , mixed with the fixed oscillator in NAND gate N2 and amplified by the transistor again before going to the speaker .

If the sensor coil L1 get close to a metal object , this will modify the frequency of oscillation, causing the self - induction coil , unbalancing the frequency and consequently modifying the sound in the output. The metal detector coil L1, is made of 70 turns of enameled wire cover with diam . 0.3 to 0.6 mm and a diameter of 5 cm.

The Metal Detector

A metal detector is an electronic instrument that detects the presence of ferrous or non -ferrous metal nearby. Metal detectors are useful for finding metal objects hidden inside walls or buried in the soil . They usually consist of a portable unit with a sensing coil that can be swept on the ground or other objects .

If the coil approaches a metal piece will sound an alert indicated by a sound , an LED sign, or the oscillation of the galvanometer pointer . Typically, the device gives some indication of the distance when the metal is closest , which is a higher audio tone or higher level pointer.

Another common type of detectors are stationary detector. Metals are used for security screening at access points in prisons, banks, courts detectors, and airports, to detect metal weapons hidden in a persons body.

The first industrial metal detectors were developed in the 1960s and were widely used for mineral exploration and other industrial applications. Uses include de-mining (the detection of land mines), the detection of weapons such as knives and guns, geophysical prospecting, archeology and treasure hunting.

Metal detectors are also used to detect foreign bodies in food, and in the construction industry to detect steel reinforcing bars in concrete, tubes, pipes and wires buried in walls and floors.