Keywords: metal detection circuit
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Author: 振华
A typical metal detector is composed of a two-oscillator, a mixer, a different frequency enlargement, and the like, and when the detection coil is adjacent to the metal object, the amount of inductance changes, thereby causing changes in the oscillation frequency. Although the metal detector circuit is not too complex, for beginners with limited conditions, the ideal effect is not a matter of easy things. The metal detector described below only one medium wave oscillator, and other functions are replaced by the radio, and the production commissioning is very easy. As shown in the figure, the commonly used co-base capacitor three-point oscillation circuit, the detailed principle is no longer described. First, use the radio to receive a medium wave station as a comparison signal, then adjust C2, so that the oscillation frequency is close to the radio frequency. At this time, the speaker will make a shot, select the appropriate tone, when the inductor coil L is close to metal When the object, the tone changes, and it can be judged whether or not there is a metal object. The inductor coil L is 10% around the 1-in-1 lacquered wire of 0.52 mm in a diameter of 0.52 mm. After the insulating tape is taken back, the diameter of the detection coil can be appropriately changed as needed, and the larger the diameter, the deeper the diameter. However, the detection sensitivity of smaller metal objects is lowered. In addition, when the detection coil L is close to the ground, it is easily affected by the distribution capacitance, and the coil can be shielded by the aluminum foil or a soft metal network. Note that the shield layer cannot form a short circuit ring on the coil, that is, the mask layer in the schematic. It is one-end, otherwise the oscillating circuit will not be able to start. Other components have no special requirements, and can be determined according to their hand conditions.
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As long as the circuit welding is incorrectly turned on, the frequency adjustment range is also wide, and it is easy to succeed. The inductor coil and the circuit board are fixed at the lower end of the insulating rod, and the radio is placed at the upper end. Under normal circumstances, the tone generated by the difference is only determined on the difference between the radio frequency and the oscillation frequency of the circuit, and is not related to the tuning of the radio. The tuning of the radio is accurately affected by the size of the volume, but the radio will be found during the use. Frequency points can receive the speed, and the tone will also change with the tuning of the radio, this phenomenon is particularly obvious in the frequency high side, which is a radio, detecting the oscillation circuit and radio residence. Co-invalidation signals, for using metal detection The circuit is a good thing because the tuning knob that adjusts the radio is more convenient than the variable capacitor of the adjustment oscillation circuit. Second, if the slout is the tuning product of the oscillation signal, the tuning product of the oscillation signal can also increase the sensitivity of the detection.
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