CN109270580B - Chargeable, sensitivity-adjustable and high-sensitivity handheld metal detector - Google Patents

Chargeable, sensitivity-adjustable and high-sensitivity handheld metal detector Download PDF

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CN109270580B
CN109270580B CN201811373218.6A CN201811373218A CN109270580B CN 109270580 B CN109270580 B CN 109270580B CN 201811373218 A CN201811373218 A CN 201811373218A CN 109270580 B CN109270580 B CN 109270580B
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CN109270580A (en
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雷鸣
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Yongzhou Nuofangzhou Electronic Technology Co ltd
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    • G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
    • G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
    • G01V3/10—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils
    • G01V3/101—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices using induction coils by measuring the impedance of the search coil; by measuring features of a resonant circuit comprising the search coil

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Abstract

The invention discloses a rechargeable, sensitivity-adjustable and high-sensitivity handheld metal detector which comprises a miller oscillation module, a voltage doubling and rectifying filter module, a sensitivity adjusting and direct current comparator module and a lithium battery, wherein the miller oscillation module outputs a detection signal to the voltage doubling and rectifying filter module, the voltage doubling and rectifying filter module outputs a rectified and filtered signal to the sensitivity adjusting and direct current comparator module, and the lithium battery is used for supplying power. The invention adopts special circuit design, so that the user can easily adjust the sensitivity in a large range, and the invention is suitable for various use scenes. Where high sensitivity is required, it is also straightforward to adjust directly to the maximum sensitivity of the instrument (no false triggering). By adopting the lithium battery and carrying out low-power-consumption design, the built-in lithium battery can be fully charged within two hours, and can be continuously used for more than 60 hours after being fully charged.

Description

Chargeable, sensitivity-adjustable and high-sensitivity handheld metal detector
Technical Field
The invention discloses a handheld metal detector, in particular to a rechargeable, adjustable-sensitivity and high-sensitivity handheld metal detector, and belongs to the technical field of metal detection equipment.
Background
Hand-held metal detectors are widely used in various fields, such as: security protection in stations, airports, examination rooms and other places; detecting the shallow layer in the wall and the underground and the metal water supply and drainage pipeline during building construction; detecting metal impurities of raw materials and products in processing factories of wood, food and the like.
The required detection sensitivity varies from field of use to field of use. The conventional handheld metal detector is inconvenient to operate on sensitivity adjustment, and particularly in some application occasions requiring high detection sensitivity, the over-high sensitivity easily causes false alarm and the over-low sensitivity is difficult to meet the requirement. In addition, the existing handheld metal detector mostly uses 9V batteries for power supply, the cruising ability is generally low, the charging is inconvenient, the charging speed is slow, and the 9V rechargeable battery and the non-rechargeable battery are easy to be confused, if a user cannot distinguish, the non-rechargeable battery in the machine is charged, and the potential safety hazard is very large.
Disclosure of Invention
Aiming at the defect that the sensitivity of the handheld metal detector in the prior art is inconvenient to adjust, the invention provides the rechargeable high-sensitivity adjustable handheld metal detector, which adopts a Zeller oscillating circuit and a voltage doubling rectifying filter circuit to match with a sensitivity adjusting and voltage comparator circuit, and can realize the characteristics of high sensitivity, adjustable sensitivity, easy adjustment, quick charging and long endurance time of the detector.
The technical scheme adopted by the invention for solving the technical problems is as follows: a rechargeable, sensitivity-adjustable and high-sensitivity handheld metal detector comprises a Ocer oscillation module, a voltage doubling rectifying filter module, a sensitivity adjusting and direct current comparator module and a lithium battery, wherein the Ocer oscillation module outputs a detection signal to the voltage doubling rectifying filter module, the voltage doubling rectifying filter module outputs a rectified and filtered signal to the sensitivity adjusting and direct current comparator module, and the lithium battery is used for supplying power.
The technical scheme adopted by the invention for solving the technical problem further comprises the following steps:
the miller oscillation module comprises an inductor L51, a capacitor C51, a resistor R54, a resistor R59, a capacitor C58, a triode Q50, a resistor R60, a capacitor C54 and a capacitor C59, wherein the inductor L51 is an induction coil, the inductor L51 is connected with the capacitor C51 in parallel, one end of the inductor L51 is connected with a +5V power supply, the other end of the inductor L51 is connected with a collector of the triode Q51, an emitter of the triode Q51 is grounded through the resistor R51 connected in series, the resistor R51 is connected between the collector and a base of the triode Q51, the resistor R51 is connected between the base of the triode Q51 and the ground, the capacitor C51 is connected with the resistor R51 in parallel, the capacitor C51 is connected with the capacitor C51 in series, one end of the capacitor C51 is connected with the inductor L51, the other end of the capacitor C51 is connected with one end.
The inductor L51 adopts a self-adhesive coil with inductance of 1 mH.
The voltage-doubling rectifying filter module comprises a capacitor C52, a resistor R52, a resistor R55, a diode D51, a diode D53, a resistor R56 and a capacitor C57, wherein the capacitor C52 is connected in series with the output end of the Sieler oscillation module, the resistor R55 is connected between the output end of the Sieler oscillation module and the ground, the resistor R55 is arranged at the rear end of the capacitor C52, the diode D53 is connected in parallel with the resistor R55, the anode of the diode D53 is grounded, the cathode of the diode D53 is connected with the capacitor C52, the resistor R52 is connected in series with the output end of the Sieler oscillation module, the resistor R52 is connected with the rear end of the capacitor C52, the diode D51 is connected in parallel with the resistor R52, the anode of the diode D51 is connected with the capacitor C51, the cathode of the diode D51 is the output end of the voltage-doubling rectifying filter module, and the resistor R51 and the capacitor C.
The sensitivity adjusting and direct current comparator module comprises an amplifier U51A and an amplifier U51B, wherein the amplifier U51A and the amplifier U51B form a direct current comparator with low-pass filtering together with peripheral elements.
The non-inverting input end of the amplifier U51A is grounded through a resistor R57, the inverting input end of the amplifier U51A is connected with the output end of the voltage-doubled rectifying filter module through a capacitor C53 and a resistor R51 which are connected in series, a diode D50 is connected between the output end and the inverting input end of the amplifier U51A, the anode of the diode D50 is connected with the inverting input end of the amplifier U51A, the cathode of the diode D50 is connected with the output end of the amplifier U51A, a capacitor C50 is connected in parallel with the diode D50, a +5V power supply S5V is connected with the inverting input end of the amplifier U51A through a resistor R61, a potentiometer RS1B and a resistor R50 which are sequentially connected in series, the potentiometer RS1B is connected between the resistor R61 and a signal ground SGND, and the middle connection point of the potentiometer RS1B is connected with the resistor.
The non-inverting input terminal of the amplifier U51B is connected with the signal ground through a resistor R58, the inverting input terminal of the amplifier U51B is connected with the output terminal of the amplifier U51A through a resistor R53, the inverting input terminal of the amplifier U51B is connected with a diode D52 in parallel with a capacitor C55 through a capacitor C55, the anode of a diode D52 is connected with the inverting input terminal of the amplifier U51B, the cathode of a diode D52 is connected with the signal ground, and a capacitor C56 is connected between the non-inverting input terminal and the output terminal of the amplifier U51B.
The output end of the sensitivity adjusting and direct current comparator module is connected with an alarm circuit, and the alarm circuit adopts one or more of a light indication module, a sound indication module and a vibration indication module.
The light indicating module comprises a control chip U20, an LED indicating lamp and a control switch, a TRIG pin of a control chip U20 is in short circuit with a Thre pin, a capacitor C20 is connected in series between the Thre pin of the control chip U20 and the ground, a resistor R23 is connected in series between the TRIG pin of the control chip U20 and the DC pin, a resistor R22 is connected in series between the TRIG pin of the control chip U20 and the VCC pin, the VCC pin of the control chip U20 is connected with a positive power supply, the RST pin of the control chip U20 is connected with the positive power supply through a resistor R21, an MOS tube Q21 is connected between the RST pin of the control chip U20 and the ground, a zener diode ZD20 and a resistor R25 are connected in series between the power output end and the ground, the grid of the MOS tube Q21 is connected with the common ends of the zener diode 20 and the resistor R25, the LED indicating lamp comprises a red LED indicating lamp and a green LED indicating lamp, the red LED indicating lamp are respectively connected with the positive power, the green LED indicator lamp is connected with an OUT pin of the control chip U20 through an MOS tube Q20, the red LED indicator lamp is grounded through an MOS tube Q22, the grid electrode of the MOS tube Q20 is connected to the common end of the red LED indicator lamp and the MOS tube Q22, and the grid electrode of the MOS tube Q22 is connected with the output end of the sensitivity adjusting and direct current comparator module.
The lithium battery is charged through the power management module, a cathode power line of the lithium battery is connected with an MOS tube Q10 in series, a grid electrode of the MOS tube Q10 is connected to an anode of the lithium battery, a positive power line of the lithium battery is connected with a power switch RS1A in series, the lithium battery is connected to a DC/DC boost converter U11, an inductor L10 is connected between a VIN pin and a SW pin of the DC/DC boost converter U11, a VIN pin, an NC pin and an EN pin of the DC/DC boost converter U11 are all connected with a cathode of the lithium battery, a GND pin of the DC/DC boost converter U11 is grounded, a diode D12, a resistor R12 and a resistor R13 are sequentially connected between the SW pin and the GND pin of the DC/DC boost converter U11 in series, the FB pin of the DC/DC boost converter U11 is connected with the common end of the resistor R12 and the resistor R13, the output end of the DC/DC boost converter U11 is connected with the input end of the voltage stabilizing chip U10.
The invention has the beneficial effects that: the invention adopts special circuit design, so that the user can easily adjust the sensitivity in a large range, and the invention is suitable for various use scenes. Where high sensitivity is required, it is also straightforward to adjust directly to the maximum sensitivity of the instrument (no false triggering). By adopting the lithium battery and carrying out low-power-consumption design, the built-in lithium battery can be fully charged within two hours, and can be continuously used for more than 60 hours after being fully charged.
The invention will be further described with reference to the accompanying drawings and specific embodiments.
Drawings
FIG. 1 is a block diagram of the circuit of the present invention.
Fig. 2 is a schematic circuit diagram of a part of the lithium battery charging circuit in the invention.
FIG. 3 is a schematic diagram of a battery and power supply circuit according to the present invention.
Fig. 4 is a schematic diagram of a circuit of a portion of the miller oscillator circuit of the present invention.
FIG. 5 is a schematic diagram of a portion of the double voltage rectifying filter circuit according to the present invention.
FIG. 6 is a schematic diagram of a circuit portion of the sensitivity adjustment and DC comparator circuit of the present invention.
FIG. 7 is a schematic circuit diagram of a portion of the light indicating circuit of the present invention.
FIG. 8 is a schematic diagram of a circuit of a buzzer and a vibration motor according to the present invention.
Detailed Description
The present embodiment is a preferred embodiment of the present invention, and other principles and basic structures that are the same as or similar to the present embodiment are within the scope of the present invention.
Referring to fig. 1 to 8, the present invention mainly includes a miller oscillation module, a voltage doubling rectifying filter module, a sensitivity adjusting and dc comparator module, and a lithium battery, wherein the miller oscillation module outputs a detection signal to the voltage doubling rectifying filter module, the voltage doubling rectifying filter module outputs a rectified and filtered signal to the sensitivity adjusting and dc comparator module, and the lithium battery is used for supplying power.
In this embodiment, the miller oscillation module adopts an improved three-point capacitive oscillation circuit, which mainly includes an inductor L51, a capacitor C51, a resistor R54, and a resistor R59, capacitor C58, transistor Q50, resistor R60, capacitor C54 and capacitor C59, and inductor L51 is an induction coil, in this embodiment, inductor L51 uses a self-adhesive coil with inductance of 1mH, inductor L51 and capacitor C51 are connected in parallel, one end of inductor L51 is connected to a +5V power supply, the other end is connected to the collector of transistor Q50, the emitter of transistor Q50 is grounded through series-connected resistor R60, resistor R54 is connected between the collector and the base of transistor Q50, resistor R59 is connected between the base of transistor Q50 and ground, capacitor C58 is connected in parallel to resistor R59, capacitor C54 and capacitor C59 are connected in series, one end of capacitor C54 is connected to inductor L51, the other end of capacitor C54 is connected to one end of capacitor C59, and the other end of capacitor C59 is grounded. In this embodiment, the current consumption of the miller oscillation module is about 0.4mA, and a voltage difference of about 0.4V is generated between SGND and GND through the resistor R14.
The oscillation frequency of the miller oscillation module is jointly determined by the inductor L51, the capacitor C51, the capacitor C54 and the capacitor C59, and the formula is as follows:
Figure BDA0001870104640000061
wherein, L is L51, C is C54 and C59 are connected in series and then connected in parallel with C51, and the formula is as follows:
L＝L51
Figure BDA0001870104640000062
in this example, L51 is 1mH, C51 is 22nF, C54 is 10nF, and C59 is 100 nF.
The oscillation frequency can be obtained to be 28.5KHz according to the formula.
When the miller oscillation module works normally and no other metal is near the inductor L51, a sine wave with an amplitude of about ± 4.5V is generated on the sine; when metal is present near the inductor L51, the alternating magnetic field generated by the inductor L51 induces eddy currents in the metal and dissipates energy, reducing the amplitude of the oscillating circuit.
In this embodiment, the voltage-doubling rectifying filter module includes a capacitor C52, a resistor R52, a resistor R55, a diode D51, a diode D53, a resistor R56, and a capacitor C57, the capacitor C52 is connected in series to an output end of the miller oscillation module (i.e., a signal line SINE), the resistor R55 is connected between the output end of the miller oscillation module and ground, the resistor R55 is disposed at a rear end of the capacitor C52, the diode D53 is connected in parallel to the resistor R55, an anode of the diode D53 is grounded, a cathode of the diode D53 is connected to the capacitor C52, the resistor R52 is connected in series to the output end of the miller oscillation module (i.e., the signal line SINE), the resistor R52 is connected to a rear end of the capacitor C52, the diode D51 is connected in parallel to the resistor R52, an anode of the diode D51 is connected to the capacitor C51, and a cathode of the diode D51 is connected to an output end of the voltage-doubling rectifying filter module (i.e., a signal line signal _ level). In this embodiment, the voltage doubling rectifying and filtering module rectifies and filters a sine wave of ± 4.5V to a dc voltage of about 8V, and outputs the dc voltage to the signal _ level network. In this embodiment, the voltage-doubling rectifying filter module further includes a low-pass filter composed of a resistor R52 and a capacitor C57, the amplitude of the sine wave is ± 4.5V, and the maximum ripple of the signal _ level after the low-pass filtering is 5.4 mV.
In this embodiment, the sensitivity adjusting and dc comparator module includes an amplifier U51A and an amplifier U51B, the amplifier U51A and the amplifier U51B and peripheral components form a dc comparator with low-pass filtering, in this embodiment, the amplifier U51A and the amplifier U51B adopt a dual operational amplifier with a model LM358, and the amplifier U51A and the amplifier U51B are integrated into one device. The non-inverting input terminal of the amplifier U51A is grounded (SGND) through a resistor R57, the directional input terminal of the amplifier U51A is connected to the output terminal of the voltage-doubled rectifying and filtering module (i.e., signal _ level) through a capacitor C53 and a resistor R51 connected in series, a diode D50 is connected between the output terminal and the inverting input terminal of the amplifier U51A, the anode of the diode D50 is connected to the inverting input terminal of the amplifier U51A, the cathode of the diode D50 is connected to the output terminal of the amplifier U51A, a capacitor C50 is connected in parallel to the diode D50, a +5V power source S5V is connected to the inverting input terminal of the amplifier U51A through a resistor R61, a potentiometer RS1B and a resistor R50 connected in series in sequence, a potentiometer RS1B is connected between the resistor R9 and a signal ground SGND, an intermediate connection point of the potentiometer RS1B is connected to the resistor R50, and in this embodiment, a capacitor C60 is connected between the +5V power.
Since the input bias current of LM358 is 50nA, the maximum input offset current is 50nA, and the non-inverting input terminal voltage of amplifier U51A (hereinafter denoted as V)U51A_in+) The maximum voltage of (50nA +50nA/2) × 1K × 1.05 ═ 78.75 uV.
When V isU51A_in-Higher than VU51A_in+At this time, the output amp _ out of the amplifier U51A outputs low.
When V isU51A_in-Below VU51A_in+At this time, the output terminal amp _ out of the amplifier U51A outputs high.
The static bias point V of the inverting input of the amplifier U51A is due to the capacitor C53 acting as a cross-over DC blocking capacitorU51A_IN-Depends on the resistor R61 and the voltage reference generated by the potentiometer RS1B and the input bias current of the amplifier U51A. When the potentiometer RS1B is turned to the highest sensitivity, one end of the resistor R50 is shorted to the signal ground SGND, and V is set to the highest sensitivityU51A_IN-＝(50nA-50nA/2)*1M*0.95＝23.75mV。
Maximum input offset voltage of 9mV, V combined with AC ripple 5.4mV coupled from capacitor C53 and LM358U51A_IN--5.4 mV-9 mV-9.35 mV, still greater than VU51A_in+78.75uV and a safety margin of about 9mV, the system can not be triggered by mistake.
When the inductor L51 approaches the metal, which causes the amplitude of the Siler oscillation module to decrease, the voltage of the signal _ level will also decrease, and the voltage change will be coupled to V through the capacitor C53U51A_IN-If the amplitude reduction is greater than 10mV, V will be reducedU51A_IN-<VU51A_in+The comparator outputs high level to drive the rear stage acousto-optic alarm circuit to alarm.
By adjusting the potentiometer RS1B, the static state V can be setU51A_IN-–VU51A_in+The sensitivity of the sensor can be adjusted to the highest sensitivity easily (only the knob is screwed to the bottom) and the false triggering caused by over sensitivity can be avoided.
When the instrument is close to the metal and then fixed, the capacitor C53 will discharge through the resistor R51 and the resistor R50 to make VU51A_IN-Gradually stabilizing to the original set potential, and the later stage recovers low level output. The discharge time of the capacitor C53 determines the duration of the alarm, if the detected metal object is small and the voltage variation is largeIf the discharge time is short, and the instrument only sends out a transient alarm signal; if the detected metal object is large and the voltage variation is large, the discharge time is long, and the alarm signal of the instrument lasts for a long time.
In this embodiment, the non-inverting input terminal of the amplifier U51B is connected to the Signal Ground (SGND) through the resistor R58, the inverting input terminal of the amplifier U51B is connected to the output terminal of the amplifier U51A through the resistor R53, the inverting input terminal of the amplifier U51B is connected to the diode D52 in parallel with the capacitor C55 through the capacitor C55, the anode of the diode D52 is connected to the inverting input terminal of the amplifier U51B, the cathode of the diode D52 is connected to the Signal Ground (SGND), and the capacitor C56 is connected between the non-inverting input terminal and the output terminal of the amplifier U51B.
In this embodiment, an alarm circuit is connected to an output terminal of the sensitivity adjustment and dc comparator module, and the alarm circuit may be one or more of a light indication module, a sound indication module, and a vibration indication module.
The light indicating module comprises a control chip U20, an LED indicator lamp and a control switch, the control chip U20 adopts an NE555D chip, a TRIG pin of the control chip U20 is in short circuit with a Thre pin, a capacitor C20 is connected in series between the Thre pin of the control chip U20 and the ground, a resistor R23 is connected in series between the TRIG pin of the control chip U20 and the DC pin, a resistor R22 is connected in series between the TRIG pin of the control chip U20 and the VCC pin, the VCC pin of the control chip U20 is connected with a positive power supply, a RST pin of the control chip U20 is connected with the positive power supply through a resistor R21, a MOS tube Q21 is connected between the RST pin of the control chip U20 and the ground, a zener diode ZD20 and a resistor R25 are connected in series between the power output end and the ground, a gate of the MOS tube Q21 is connected with a common end of the zener diode ZD20 and the positive power supply R25, in this embodiment, the LED indicator lamp comprises a red indicator lamp and a green indicator lamp, and a current-limiting, the green LED indicator lamp is connected with an OUT pin of the control chip U20 through an MOS tube Q20, the red LED indicator lamp is grounded through an MOS tube Q22, the grid electrode of the MOS tube Q20 is connected to the common end of the red LED indicator lamp and the MOS tube Q22, and the grid electrode of the MOS tube Q22 is connected with the output end of the sensitivity adjusting and direct current comparator module.
When metal is detected, the output end amp _ out of the sensitivity adjusting and direct current comparator module is at a high level, the red LED is lightened, and the green LED is not lightened;
when the battery is charged, the RED is pulled low, the RED LED is lit, and the green LED is not lit.
When RED is high, the MOS transistor Q20 is turned on, allowing the green LED to light up.
The control chip U20 is NE555D, and through adjusting the peripheral resistance capacitance, can stabilize the square wave of output duty ratio 55%, frequency 3.3 Hz.
When the battery voltage (BAT) is higher than 3.6V, the MOS transistor Q21 is turned on, the control chip U20 is placed in Reset state, the OUT terminal of the control chip U20 continuously outputs low level, and the green LED is normally on, which represents that the instrument works normally.
When the battery voltage (BAT) is lower than 3.0V, the MOS tube Q21 is cut off, the control chip U20 works normally, and the green LED flickers at the frequency of 3.3Hz, which indicates that the battery power is low.
The diode D1 and the diode D13 are power isolation diodes that provide power to the light circuit during charging and normal operation of the instrument.
The sound indication module and the vibration indication module are either modules, the sound indication module adopts a buzzer BELL, the vibration indication module adopts a vibration MOTOR MOTOR, the buzzer BELL and the vibration MOTOR MOTOR are respectively connected to one pin of a single-pole double-throw SWITCH, a common pin of the single-pole double-throw SWITCH is grounded through an MOS (metal oxide semiconductor) tube Q3, and a grid electrode of the MOS tube Q3 is connected with an output end of the sensitivity adjustment and direct current comparator module.
In this embodiment, power module adopts the lithium cell, gives other module power supplies through the lithium cell, and the lithium cell charges through power management module, and power management module adopts the model to be LTC 4054's power management chip, can provide the charging current of the highest 800mA, just can fill to full electric quantity about only needing two hours to 1400mA lithium polymer battery that this product used. During charging, the CHAR pin of LTC4054 will output a low level, which will pull RED (i.e. the gate of the MOS transistor Q20) low, and light a RED light, indicating that the battery is being charged.
In this embodiment, a negative power line of the lithium battery (BAT adopts a 3.7V lithium battery) is connected in series with the MOS transistor Q10, a gate of the MOS transistor Q10 is connected to a positive electrode of the lithium battery, and the MOS transistor Q10 adopts an N-channel MOS transistor with a model number of SI2302, which plays a role in preventing reverse connection of the power supply. A power switch RS1A is connected in series with an anode power line of the lithium battery, the lithium battery is connected with a DC/DC boost converter U11, an inductor L10 is connected between a VIN pin and a SW pin of the DC/DC boost converter U11, the VIN pin, an NC pin and an EN pin of the DC/DC boost converter U11 are all connected with the anode of the lithium battery, a GND pin of the DC/DC boost converter U11 is grounded, a diode D12, a resistor R12 and a resistor R13 are sequentially connected in series between the SW pin and the GND pin of the DC/DC boost converter U11, an FB pin of the DC/DC boost converter U11 is connected with a common end of the resistor R12 and the resistor R13, and 3.7V voltage of the lithium battery is converted into 6V power by the DC/DC boost converter U11 and is supplied to a rear-stage circuit. In this embodiment, a filter capacitor C0 is connected between the positive and negative power lines at the front stage of the DC/DC boost converter U11, and a filter capacitor C1 is connected between the positive and negative power lines at the rear stage of the DC/DC boost converter U11. The output end of the DC/DC boost converter U11 is connected to the input end of a voltage stabilizing chip U10, a 6V power supply generated by the DC/DC converter U11 obtains a relatively clean 5V power supply through the voltage stabilizing chip U10 and supplies the power supply to the Sieler oscillation circuit, in the embodiment, the model of the voltage stabilizing chip U10 is XC6206P502, and the element is selected to be focused on ultra-low power consumption.
When the metal detector is used, when metal is detected, the output end amp _ out of the sensitivity adjusting and direct current comparator module is at a high level, the red LED is lightened, and meanwhile, the buzzer or the vibrating motor works.
The invention adopts special circuit design, so that the user can easily adjust the sensitivity in a large range, and the invention is suitable for various use scenes. Where high sensitivity is required, it is also straightforward to adjust directly to the maximum sensitivity of the instrument (no false triggering). By adopting the lithium battery and carrying out low-power-consumption design, the built-in lithium battery can be fully charged within two hours, and can be continuously used for more than 60 hours after being fully charged.

Claims (8)

1. A chargeable, sensitivity-adjustable and high-sensitivity handheld metal detector is characterized in that: the metal detector comprises a Miller oscillation module, a voltage doubling rectifying filter module, a sensitivity adjusting and direct current comparator module and a lithium battery, wherein the Miller oscillation module outputs a detection signal to the voltage doubling rectifying filter module, the voltage doubling rectifying filter module outputs a rectified and filtered signal to the sensitivity adjusting and direct current comparator module, the lithium battery is used for supplying power, the sensitivity adjusting and direct current comparator module comprises an amplifier U51A and an amplifier U51B, the amplifier U51A and the amplifier U51B form a direct current comparator with low-pass filtering with peripheral elements, the non-inverting input end of the amplifier U51A is grounded through a resistor R57, the inverting input end of the amplifier U51A is connected with the output end of the voltage doubling rectifying filter module through a capacitor C53 and a resistor R51 which are connected in series, a diode D50 is connected between the output end and the inverting input end of the amplifier U51A, the anode of the diode D50 is connected with the inverting input end of the amplifier U51A, the negative electrode of the diode D50 is connected to the output terminal of the amplifier U51A, the capacitor C50 is connected in parallel with the diode D50, the +5V power source S5V is connected to the inverting input terminal of the amplifier U51A through the resistor R61, the potentiometer RS1B and the resistor R50 which are connected in series in this order, the potentiometer RS1B is connected between the resistor R61 and the signal ground SGND, and the intermediate connection point of the potentiometer RS1B is connected to the resistor R50.
2. The rechargeable, sensitivity-adjustable, high-sensitivity hand-held metal detector of claim 1, wherein: the miller oscillation module comprises an inductor L51, a capacitor C51, a resistor R54, a resistor R59, a capacitor C58, a triode Q50, a resistor R60, a capacitor C54 and a capacitor C59, wherein the inductor L51 is an induction coil, the inductor L51 is connected with the capacitor C51 in parallel, one end of the inductor L51 is connected with a +5V power supply, the other end of the inductor L51 is connected with a collector of the triode Q51, an emitter of the triode Q51 is grounded through the resistor R51 connected in series, the resistor R51 is connected between the collector and a base of the triode Q51, the resistor R51 is connected between the base of the triode Q51 and the ground, the capacitor C51 is connected with the resistor R51 in parallel, the capacitor C51 is connected with the capacitor C51 in series, one end of the capacitor C51 is connected with the inductor L51, the other end of the capacitor C51 is connected with one end.
3. The rechargeable, sensitivity adjustable, high sensitivity hand-held metal detector of claim 2, wherein: the inductor L51 adopts a self-adhesive coil with inductance of 1 mH.
4. The rechargeable, sensitivity-adjustable, high-sensitivity hand-held metal detector of claim 1, wherein: the voltage-doubling rectifying filter module comprises a capacitor C52, a resistor R52, a resistor R55, a diode D51, a diode D53, a resistor R56 and a capacitor C57, wherein the capacitor C52 is connected in series with the output end of the Sieler oscillation module, the resistor R55 is connected between the output end of the Sieler oscillation module and the ground, the resistor R55 is arranged at the rear end of the capacitor C52, the diode D53 is connected in parallel with the resistor R55, the anode of the diode D53 is grounded, the cathode of the diode D53 is connected with the capacitor C52, the resistor R52 is connected in series with the output end of the Sieler oscillation module, the resistor R52 is connected with the rear end of the capacitor C52, the diode D51 is connected in parallel with the resistor R52, the anode of the diode D51 is connected with the capacitor C51, the cathode of the diode D51 is the output end of the voltage-doubling rectifying filter module, and the resistor R51 and the capacitor C.
5. The rechargeable, sensitivity-adjustable, high-sensitivity hand-held metal detector of claim 1, wherein: the non-inverting input terminal of the amplifier U51B is connected with the signal ground through a resistor R58, the inverting input terminal of the amplifier U51B is connected with the output terminal of the amplifier U51A through a resistor R53, the inverting input terminal of the amplifier U51B is connected with a diode D52 in parallel with a capacitor C55 through a capacitor C55, the anode of a diode D52 is connected with the inverting input terminal of the amplifier U51B, the cathode of a diode D52 is connected with the signal ground, and a capacitor C56 is connected between the non-inverting input terminal and the output terminal of the amplifier U51B.
6. The rechargeable, sensitivity-adjustable, high-sensitivity hand-held metal detector of claim 1, wherein: the output end of the sensitivity adjusting and direct current comparator module is connected with an alarm circuit, and the alarm circuit adopts one or more of a light indication module, a sound indication module and a vibration indication module.
7. The rechargeable, sensitivity adjustable, high sensitivity hand-held metal detector of claim 6, wherein: the light indicating module comprises a control chip U20, an LED indicating lamp and a control switch, a TRIG pin of a control chip U20 is in short circuit with a Thre pin, a capacitor C20 is connected in series between the Thre pin of the control chip U20 and the ground, a resistor R23 is connected in series between the TRIG pin of the control chip U20 and the DC pin, a resistor R22 is connected in series between the TRIG pin of the control chip U20 and the VCC pin, the VCC pin of the control chip U20 is connected with a positive power supply, the RST pin of the control chip U20 is connected with the positive power supply through a resistor R21, an MOS tube Q21 is connected between the RST pin of the control chip U20 and the ground, a zener diode ZD20 and a resistor R25 are connected in series between the power output end and the ground, the grid of the MOS tube Q21 is connected with the common ends of the zener diode 20 and the resistor R25, the LED indicating lamp comprises a red LED indicating lamp and a green LED indicating lamp, the red LED indicating lamp are respectively connected with the positive power, the green LED indicator lamp is connected with an OUT pin of the control chip U20 through an MOS tube Q20, the red LED indicator lamp is grounded through an MOS tube Q22, the grid electrode of the MOS tube Q20 is connected to the common end of the red LED indicator lamp and the MOS tube Q22, and the grid electrode of the MOS tube Q22 is connected with the output end of the sensitivity adjusting and direct current comparator module.
8. The rechargeable, sensitivity-adjustable, high-sensitivity hand-held metal detector of claim 1, wherein: the lithium battery is charged through the power management module, a cathode power line of the lithium battery is connected with an MOS tube Q10 in series, a grid electrode of the MOS tube Q10 is connected with an anode of the lithium battery, a cathode power line of the lithium battery is connected with a power switch RS1A in series, the lithium battery is connected with a DC/DC boost converter U11, an inductor L10 is connected between a VIN pin and a SW pin of the DC/DC boost converter U11, a VIN pin, an NC pin and an EN pin of the DC/DC boost converter U11 are all connected with the anode of the lithium battery, a GND pin of the DC/DC boost converter U11 is grounded, a diode D12 is sequentially connected between the SW pin and the GND pin of the DC/DC boost converter U11 in series, the resistor R12 and the resistor R13, the FB pin of the DC/DC boost converter U11 is connected with the common end of the resistor R12 and the resistor R13, and the output end of the DC/DC boost converter U11 is connected with the input end of the voltage stabilizing chip U10.
CN201811373218.6A 2018-11-19 2018-11-19 Chargeable, sensitivity-adjustable and high-sensitivity handheld metal detector Active CN109270580B (en)

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