Anti-recording transmitting circuit

Abstract

The utility model discloses an anti-recording emission circuit, which comprises an anti-recording interference shielding instrument, a microphone pickup, an audio amplification circuit, a voltage comparison circuit, an analog switch circuit and a power supply module, wherein the microphone pickup is used for collecting external sound signals; the input end of the audio amplification circuit is electrically connected with the output end of the microphone pickup, and the audio amplification circuit is used for amplifying a sound signal collected by the microphone pickup; a plurality of voltage comparison circuits are arranged, the input ends of the plurality of voltage comparison circuits are electrically connected with the output end of the audio amplification circuit, different voltage comparison circuits have different reference voltages, and the voltage comparison circuits are used for comparing the output voltage of the output end of the audio amplification circuit with the reference voltage of the audio amplification circuit. According to the utility model, the magnitude of the output voltage of the power supply can be changed according to the distance between the sound source and the anti-recording interference shielding instrument, so that the transmitting power of the anti-recording interference shielding instrument is changed.

Description

TECHNICAL FIELD

[0001] The utility model belongs to the field of information security technology, especially relates to a kind of anti-recording emission circuit. BACKGROUND

[0002] In commercial meeting and important occasion, sometimes need to utilize anti-recording interference shield instrument to interfere with the recording function of recording equipment (such as mobile phone, recording pen), to prevent important information from leaking out. At present, anti-recording interference shield instrument is mostly with fixed power to emit interference waveform, there are following shortcomings:

[0003] 1, sound source (i.e. the position of the position of the person to emit sound) close to anti-recording interference shield instrument distance does not need too big emission power, always with maximum emission power to emit signal to cause energy waste.

[0004] 2, with fixed emission power, emission signal is big, harmful to human health.

[0005] Therefore, anti-recording interference shield instrument preferably can automatically adjust emission power according to interference distance. INVENTION CONTENT

[0006] The utility model wants to solve technical problem is to provide a kind of anti-recording emission circuit, can change the output voltage size of power supply according to the distance between sound source and anti-recording interference shield instrument, to change the emission power of anti-recording interference shield instrument.

[0007] To solve the above technical problem, the utility model adopts following technical scheme:

[0008] The anti-recording emission circuit comprises an anti-recording interference shielding instrument, and is characterized in that the anti-recording emission circuit further comprises a microphone pickup, an audio amplification circuit, voltage comparison circuits, an analog switch circuit and a power module; the microphone pickup is used for collecting external sound signals; the input end of the audio amplification circuit is electrically connected with the output end of the microphone pickup and is used for amplifying the sound signals collected by the microphone pickup; the voltage comparison circuits are provided in plurality, the input ends of the plurality of voltage comparison circuits are electrically connected with the output end of the audio amplification circuit, different voltage comparison circuits have different reference voltages, the voltage comparison circuits are used for comparing the sizes of the output voltages of the output end of the audio amplification circuit and the reference voltages thereof, when the output voltage is greater than the reference voltage, the voltage output at the output end of the voltage comparison circuit is greater than 0, otherwise, the voltage output at the output end of the voltage comparison circuit is equal to 0; the analog switch circuit comprises a plurality of analog switches, the number of the analog switches is equal to the number of the voltage comparison circuits, one analog switch is connected with one voltage comparison circuit, and the output end of the voltage comparison circuit is electrically connected with the control end of the analog switch; when the output voltage at the output end of the voltage comparison circuit is greater than 0, the corresponding connected analog switch is closed; the power module comprises a DC-DC power chip and proportional resistors; the proportional resistors comprise a plurality of resistors connected in parallel; the voltage feedback pin of the DC-DC power chip is electrically connected with the input ends of the plurality of analog switches, the output end of one analog switch is connected with one end of one resistor in the proportional resistors, and the other ends of the resistors in the proportional resistors are respectively electrically connected with the conversion pin of the DC-DC power chip and the power supply end of the anti-recording interference shielding instrument; the analog switch is used for adjusting the resistance value of the proportional resistors and changing the voltage size of the output end of the DC-DC power chip.

[0009] The anti-recording emission circuit has the advantages that:

[0010] The anti-recording emission circuit is used for being mounted on the anti-recording interference shielding instrument, sound signals emitted by a sound source are collected through the microphone pickup, the collected signals are subjected to signal amplification processing through the audio amplification circuit, the output voltage of the audio amplification circuit is compared with the reference voltages of the plurality of voltage comparison circuits, when the output voltage is greater than the reference voltage, the voltage output at the output end of the voltage comparison circuit is greater than 0, otherwise, the voltage output at the output end of the voltage comparison circuit is equal to 0, the distance of the sound source can be judged according to the voltage sizes at the output ends of the plurality of voltage comparison circuits, the analog switch can be correspondingly controlled to be closed or opened, so as to change the resistance value of the proportional resistors, different resistance voltage division coefficients are provided for the output end of the DC-DC power chip, different output voltage values are generated, the smaller the output voltage is, the lower the emission power of the anti-recording interference shielding instrument is, the greater the output voltage is, the higher the emission power of the anti-recording interference shielding instrument is, and the purpose of changing the emission power of the anti-recording interference shielding instrument is achieved. BRIEF DESCRIPTION OF DRAWINGS

[0011] Fig. 1 is a principle block diagram of the embodiment of the utility model.

[0012] Fig. 2 is the circuit connection diagram of the microphone pickup and the audio amplification circuit of the embodiment of the utility model.

[0013] Fig. 3 is the circuit diagram of the voltage comparison circuit of the embodiment of the utility model.

[0014] Fig. 4 is the circuit connection diagram of the analog switch, DC-DC power supply chip and proportional resistance of the embodiment of the utility model. CONCRETE IMPLEMENTATION

[0015] The utility model is described below in conjunction with the drawings, the concrete implementation described here is only used for explaining and explaining the utility model, and is not used for limiting the utility model, on the premise of not departing from the design spirit of the utility model, the various deformation and improvement of the technical scheme of the utility model made by the ordinary skill in the art of the utility model, all should fall into the protection scope of the utility model.

[0016] As Fig. 1 to Fig. 4 shown, the anti-recording emission circuit of the embodiment is used for installing on the existing anti-recording interference shielding instrument, and it includes microphone pickup, audio amplification circuit, voltage comparison circuit, analog switch circuit and power module.

[0017] The microphone pickup is used to collect external sound signals. The input end of the audio amplification circuit is electrically connected with the output end of the microphone pickup, and is used to amplify the sound signals collected by the microphone pickup. The voltage comparison circuit is provided with a plurality of input ends, and the input ends of the plurality of voltage comparison circuits are electrically connected with the output end of the audio amplification circuit. Different voltage comparison circuits have different reference voltages. The voltage comparison circuit is used to compare the output voltage of the output end of the audio amplification circuit with the reference voltage. When the output voltage is greater than the reference voltage, the voltage output from the output end of the voltage comparison circuit is greater than 0, otherwise, the voltage output from the output end of the voltage comparison circuit is equal to 0. The analog switch circuit includes a plurality of analog switches, the number of analog switches is equal to the number of voltage comparison circuits, one analog switch is connected with one voltage comparison circuit, and the output end of the voltage comparison circuit is electrically connected with the control end of the analog switch. When the output voltage of the output end of the voltage comparison circuit is greater than 0, the corresponding connected analog switch is closed. The power module includes a DC-DC power chip and a proportional resistor. The proportional resistor includes a plurality of resistors connected in parallel. The voltage feedback pin of the DC-DC power chip is electrically connected with the input end of the plurality of analog switches. The output end of one analog switch is connected with one end of one resistor in the proportional resistor. The other end of the resistor in the proportional resistor is respectively electrically connected with the conversion pin of the DC-DC power chip and the power supply end of the anti-recording interference shielding instrument. The analog switch is used to adjust the resistance value of the proportional resistor and change the voltage of the output end of the DC-DC power chip.

[0018] As shown in Fig. 2 The audio amplification circuit of the embodiment includes an audio amplifier, which adopts an LM386 chip. The power module of the embodiment includes a 3V direct current voltage, which is used to provide working voltage for the microphone pickup and the audio amplifier. In the circuit, the microphone pickup is represented by MK1. The microphone pickup and the audio amplifier of the embodiment are provided with a high-frequency filter capacitor C1 and a coupling capacitor C2. The positive output end of the microphone pickup is electrically connected with the 3V direct current voltage, one end of the high-frequency filter capacitor C1 and one end of the coupling capacitor C2. The other end of the high-frequency filter capacitor C1 is electrically connected with the negative output end of the microphone pickup and the GND end. The other end of the coupling capacitor C2 is electrically connected with the input end of the audio amplifier. The high-frequency filter capacitor C1 of the embodiment can filter high-frequency noise and avoid interference on the circuit.

[0019] In addition, the coupling capacitor C2 and the audio amplifier are further provided with a resistor R21 and a resistor R22. One end of the resistor R21 is electrically connected with the coupling capacitor C2, and the other end is electrically connected with the input end of the audio amplifier and one end of the resistor R22. The other end of the resistor R22 is electrically connected with the GND end. The resistors R21 and R22 of the embodiment are connected in series and play a role in voltage division, which can adjust the sensitivity of the microphone pickup.

[0020] The amplification factor of the audio amplifier of the embodiment is a fixed value of 200 times, and the output voltage Audio_o (Uo) of the output end (OUT pin) of the audio amplifier can be calculated by the following formula:

[0021]

[0022] wherein Ui is the output voltage of the microphone, if the distance between the microphone and the sound source is farther, the sound signal collected is weaker, the value of the output voltage Ui of the microphone is smaller, and the value of Uo is also smaller.

[0023] As shown in Fig. 3 The voltage comparison circuit of the embodiment has three, which are a first voltage comparison circuit, a second voltage comparison circuit and a third voltage comparison circuit. The power module of the embodiment further includes a 5V direct current voltage for providing working voltage for the three voltage comparison circuits. The reference voltage of the first voltage comparison circuit is 1.5V, the reference voltage of the second voltage comparison circuit is 3V, and the reference voltage of the third voltage comparison circuit is 4.5V.

[0024] The first voltage comparison circuit of the embodiment includes a first voltage comparator, a resistor R23 and a resistor R25. The non-inverting input end of the first voltage comparator is electrically connected with the output end of the audio amplification circuit, the inverting input end is electrically connected with one end of the resistor R23 and one end of the resistor R25 respectively, the other end of the resistor R23 is electrically connected with the 5V direct current voltage, the other end of the resistor R25 is electrically connected with the negative electrode of the power supply end of the first voltage comparator and the GND end respectively, and the positive electrode of the power supply end of the first voltage comparator is electrically connected with the 5V direct current voltage. The output end of the first voltage comparator is electrically connected with the control end of the analog switch. The resistance value of the resistor R23 of the embodiment is 24KΩ, and the resistance value of the resistor R25 is 10KΩ. The voltage value obtained by the voltage division of the resistor R23 and R25 in series of the inverting input end of the first voltage comparator is about 1.5V, at this time, the reference voltage of the first voltage comparator is 1.5V, if the voltage of the output end Uo of the audio amplification circuit is greater than 1.5V, the voltage of the output end Ctrl1 of the first voltage comparator is 5V, otherwise, the voltage of the output end Ctrl1 of the first voltage comparator is 0V.

[0025] The second voltage comparison circuit comprises a second voltage comparator, a resistor R24 and a resistor R26. The non-inverting input terminal of the second voltage comparator is electrically connected with the output terminal of the audio amplification circuit, and the inverting input terminal is electrically connected with one end of the resistor R24 and one end of the resistor R26 respectively. The other end of the resistor R24 is electrically connected with a 5V direct current voltage, and the other end of the resistor R26 is electrically connected with the negative electrode of the power supply terminal of the second voltage comparator and the GND terminal respectively. The positive electrode of the power supply terminal of the second voltage comparator is electrically connected with the 5V direct current voltage. The output terminal of the second voltage comparator is electrically connected with the control terminal of the analog switch. The resistance value of the resistor R24 in the embodiment is 10KΩ, and the resistance value of the resistor R26 is 15KΩ. The voltage value obtained by the voltage division of the resistor R24 and the resistor R26 in series in the inverting input terminal of the second voltage comparator is 3V. At this time, the reference voltage of the second voltage comparator is 3V. If the voltage of the output terminal Uo of the audio amplification circuit is greater than 3V, the voltage of the output terminal Ctrl1 of the second voltage comparator is 5V, otherwise, the voltage of the output terminal Ctrl1 of the second voltage comparator is 0V.

[0026] The third voltage comparison circuit comprises a third voltage comparator, a resistor R27 and a resistor R28. The non-inverting input terminal of the third voltage comparator is electrically connected with the output terminal of the audio amplification circuit, and the inverting input terminal is electrically connected with one end of the resistor R27 and one end of the resistor R28 respectively. The other end of the resistor R27 is electrically connected with a 5V direct current voltage, and the other end of the resistor R28 is electrically connected with the negative electrode of the power supply terminal of the third voltage comparator and the GND terminal respectively. The positive electrode of the power supply terminal of the third voltage comparator is electrically connected with the 5V direct current voltage. The output terminal of the third voltage comparator is electrically connected with the control terminal of the analog switch. The resistance value of the resistor R27 in the embodiment is 10KΩ, and the resistance value of the resistor R28 is 90KΩ. The voltage value obtained by the voltage division of the resistor R27 and the resistor R28 in series in the inverting input terminal of the third voltage comparator is 4.5V. At this time, the reference voltage of the second voltage comparator is 4.5V. If the voltage of the output terminal Uo of the audio amplification circuit is greater than 4.5V, the voltage of the output terminal Ctrl1 of the third voltage comparator is 5V, otherwise, the voltage of the output terminal Ctrl1 of the third voltage comparator is 0V.

[0027] The first voltage comparator (U2), the second voltage comparator (U3) and the third voltage comparator (U6) in the embodiment all adopt LM393 chips. The distance of the sound source from the anti-recording interference shielding instrument can be judged according to the voltage of Ctrl1, Ctrl2 and Ctrl3, as shown in Table 1.

[0028] Table 1

[0029]

[0030] As Fig. 4As shown, the analog switch circuit of the embodiment adopts CD4066BM96 chip, which includes analog switch K1, analog switch K2 and analog switch K3. The DC-DC power supply chip adopts CN3903 chip. The proportional resistance includes resistors R16, R17, R18 and R19. The power module also includes a 12V DC voltage.

[0031] The control ends of the analog switch K1, the analog switch K2 and the analog switch K3 are electrically connected with the output ends of the first voltage comparison circuit, the second voltage comparison circuit and the third voltage comparison circuit respectively, that is, the control end of the analog switch K1 is electrically connected with the output end of the first voltage comparator, the control end of the analog switch K2 is electrically connected with the output end of the second voltage comparator, and the control end of the analog switch K3 is electrically connected with the output end of the third voltage comparator.

[0032] The input end of the analog switch K1 is electrically connected with the voltage feedback pin (FB pin) of the DC-DC power supply chip, and the output end is electrically connected with one end of the resistor R17. The other end of the resistor R17 is respectively electrically connected with the conversion pin (SW pin) of the DC-DC power supply chip and the power supply end of the anti-recording interference shield instrument.

[0033] The input end of the analog switch K2 is electrically connected with the voltage feedback pin of the DC-DC power supply chip, and the output end is electrically connected with one end of the resistor R18. The other end of the resistor R18 is respectively electrically connected with the conversion pin of the DC-DC power supply chip and the power supply end of the anti-recording interference shield instrument.

[0034] The input end of the analog switch K3 is electrically connected with the voltage feedback pin of the DC-DC power supply chip, and the output end is electrically connected with one end of the resistor R19. The other end of the resistor R19 is respectively electrically connected with the conversion pin of the DC-DC power supply chip and the power supply end of the anti-recording interference shield instrument.

[0035] When the voltage Ctrl1 at the output end of the first voltage comparator is equal to 0V, the analog switch K1 is open. When the voltage Ctrl1 at the output end of the first voltage comparator is greater than 0V (in this embodiment, the voltage Ctrl1 at the output end is equal to 5V), the analog switch K1 is closed. The analog switches K2 and K3 are the same.

[0036] One end of the resistor R16 is electrically connected with the voltage feedback pin of the DC-DC power supply chip, and the other end is respectively electrically connected with the conversion pin of the DC-DC power supply chip and the power supply end of the anti-recording interference shield instrument.

[0037] The power supply end of the DC-DC power supply chip is electrically connected with the 12V DC voltage.

[0038] The internal reference voltage of the DC-DC power chip in the embodiment is 0.925V, the value of the proportional resistor is adjusted by opening and closing of the three analog switches, and different voltage values output by the DC-DC power chip are obtained, for example:

[0039] When the analog switches K1, K2 and K3 in the analog switch circuit are all opened, the resistance R of the proportional resistor is the resistance value 100KΩ of R16, at this time the output voltage of the DC-DC power chip is:

[0040]

[0041] When the analog switch K1 in the analog switch circuit is closed and the analog switches K2 and K3 are opened, the resistance R of the proportional resistor is the parallel resistance of R16 and R17, the value is 67KΩ, at this time the output voltage of the DC-DC power chip is:

[0042]

[0043] Therefore, different output voltages can be obtained by changing the states of the analog switches K1, K2 and K3, and the states of the analog switches K1, K2 and K3 are determined by the output voltages of the three voltage comparators, thus the output voltages of the three voltage comparators can change the size of the power supply voltage of the DC-DC power chip to the anti-recording interference shielding instrument, and further change the transmission power of the anti-recording interference shielding instrument.

[0044] The output voltage of the DC-DC power chip is shown in Table 2:

[0045] Table 2

[0046] Ctrl 1 Ctrl 2 Ctrl 3 Switch state Proportional resistance Output voltage 0V 0V 0V K1, K2, K3 open R16 10V 5V 0V 0V K1 closed, K2, K3 open R16 / / R17 7V 5V 5V 0V K1, K2 closed, K3 open R16 / / R17 / / R18 5.5V 5V 5V 5V K1, K2, K3 closed R16 / / R17 / / R18 / / R19 4V

[0047] In summary, the anti-recording transmission circuit in the embodiment is used to be installed on the anti-recording interference shielding instrument, sound signals emitted by a sound source are collected through a microphone pickup, the collected signals are processed by signal amplification through an audio amplification circuit, the output voltage of the audio amplification circuit is compared with the reference voltages of a plurality of voltage comparison circuits, when the output voltage is greater than the reference voltage, the voltage output at the output end of the voltage comparison circuit is equal to 5V, otherwise the voltage output at the output end of the voltage comparison circuit is 0V, the distance of the sound source can be determined according to the output voltage of the output end of the three voltage comparison circuits, and the analog switches can be controlled to be closed or opened accordingly, so as to change the resistance of the proportional resistor, provide different resistance voltage division coefficients for the output end of the DC-DC power chip, and thus generate different output voltage values, the smaller the output voltage, the lower the transmission power of the anti-recording interference shielding instrument, the greater the output voltage, the higher the transmission power of the anti-recording interference shielding instrument, and thus the purpose of changing the transmission power of the anti-recording interference shielding instrument is achieved.

Claims

1. A sound recording prevention transmitting circuit comprising a sound recording prevention interference shield instrument, characterized in that: Also include microphone pickup, audio amplifier circuit, voltage comparison circuit, analog switch circuit and power module; wherein, The microphone pickup is used for collecting external sound signals; The input end of the audio amplifier circuit is electrically connected with the output end of the microphone pickup, and is used for amplifying the sound signals collected by the microphone pickup; The voltage comparison circuit is provided with a plurality of input ends, and the output end of the audio amplifier circuit is electrically connected with the input end of the voltage comparison circuit, and different voltage comparison circuits have different reference voltages, and the voltage comparison circuit is used for comparing the output voltage of the output end of the audio amplifier circuit with the reference voltage, and when the output voltage is greater than the reference voltage, the voltage output from the output end of the voltage comparison circuit is greater than 0, otherwise, the voltage output from the output end of the voltage comparison circuit is equal to 0; The analog switch circuit includes a plurality of analog switches, the number of analog switches is equal to the number of voltage comparison circuits, one analog switch is connected with one voltage comparison circuit, and the output end of the voltage comparison circuit is electrically connected with the control end of the analog switch; when the output voltage of the output end of the voltage comparison circuit is greater than 0, the corresponding connected analog switch is closed; The power module includes a DC-DC power chip and a proportional resistor; the proportional resistor includes a plurality of resistors connected in parallel; the voltage feedback pin of the DC-DC power chip is electrically connected with the input end of the plurality of analog switches, the output end of one analog switch is connected with one end of one resistor in the proportional resistor, and the other end of the resistor in the proportional resistor is respectively electrically connected with the conversion pin of the DC-DC power chip and the power supply end of the anti-recording interference shielding instrument; the analog switch is used for adjusting the resistance value of the proportional resistor and changing the output voltage of the DC-DC power chip.

2. The anti-recording transmission circuit according to claim 1, characterized in that: The audio amplifier circuit includes an audio amplifier, and the power module includes a 3V direct current voltage; a high-frequency filter capacitor C1 and a coupling capacitor C2 are arranged between the microphone pickup and the audio amplifier, the positive electrode of the output end of the microphone pickup is electrically connected with the 3V direct current voltage, one end of the high-frequency filter capacitor C1 and one end of the coupling capacitor C2 respectively, the other end of the high-frequency filter capacitor C1 is electrically connected with the negative electrode of the output end of the microphone pickup and the GND end respectively; the other end of the coupling capacitor C2 is electrically connected with the input end of the audio amplifier.

3. The anti-recording transmission circuit according to claim 2, characterized in that: The resistance R21 and the resistance R22 are further arranged between the coupling capacitor C2 and the audio amplifier, one end of the resistance R21 is electrically connected with the coupling capacitor C2, the other end is respectively electrically connected with the input end of the audio amplifier and one end of the resistance R22, and the other end of the resistance R22 is electrically connected with the GND end.

4. The anti-recording transmission circuit according to claim 1, characterized in that: The voltage comparison circuit is provided with three, which are first voltage comparison circuit, second voltage comparison circuit and third voltage comparison circuit, wherein the reference voltage of the first voltage comparison circuit is 1.5V, the reference voltage of the second voltage comparison circuit is 3V, and the reference voltage of the third voltage comparison circuit is 4.5V; the power module includes a 5V direct current voltage.

5. The anti-recording transmission circuit according to claim 4, characterized in that: The first voltage comparison circuit comprises a first voltage comparator, a resistor R23 and a resistor R25; the noninverting input terminal of the first voltage comparator is electrically connected with the output terminal of the audio amplification circuit, the inverting input terminal is electrically connected with one end of the resistor R23 and one end of the resistor R25 respectively, the other end of the resistor R23 is electrically connected with a 5V direct current voltage, and the other end of the resistor R25 is electrically connected with the negative electrode of the power supply terminal of the first voltage comparator and the GND terminal respectively; the output terminal of the first voltage comparator is electrically connected with the control terminal of the analog switch; the resistance value of the resistor R23 is 24KΩ, and the resistance value of the resistor R25 is 10KΩ.

6. The anti-recording transmission circuit according to claim 4, characterized in that: The second voltage comparison circuit comprises a second voltage comparator, a resistor R24 and a resistor R26; the noninverting input terminal of the second voltage comparator is electrically connected with the output terminal of the audio amplification circuit, the inverting input terminal is electrically connected with one end of the resistor R24 and one end of the resistor R26 respectively, the other end of the resistor R24 is electrically connected with a 5V direct current voltage, and the other end of the resistor R26 is electrically connected with the negative electrode of the power supply terminal of the second voltage comparator and the GND terminal respectively; the output terminal of the second voltage comparator is electrically connected with the control terminal of the analog switch; the resistance value of the resistor R24 is 10KΩ, and the resistance value of the resistor R26 is 15KΩ.

7. The anti-recording transmission circuit according to claim 4, characterized in that: The third voltage comparison circuit comprises a third voltage comparator, a resistor R27 and a resistor R28; the noninverting input terminal of the third voltage comparator is electrically connected with the output terminal of the audio amplification circuit, the inverting input terminal is electrically connected with one end of the resistor R27 and one end of the resistor R28 respectively, the other end of the resistor R27 is electrically connected with a 5V direct current voltage, and the other end of the resistor R28 is electrically connected with the negative electrode of the power supply terminal of the third voltage comparator and the GND terminal respectively; the output terminal of the third voltage comparator is electrically connected with the control terminal of the analog switch; the resistance value of the resistor R27 is 10KΩ, and the resistance value of the resistor R28 is 90KΩ.

8. The anti-recording transmission circuit according to claim 4, characterized in that: The analog switch circuit adopts a CD4066BM96 chip, which comprises analog switches K1, K2 and K3; the DC-DC power supply chip adopts a CN3903 chip; the proportional resistor comprises resistors R16, R17, R18 and R19; the power supply module comprises a 12V direct current voltage; The control terminals of the analog switches K1, K2 and K3 are electrically connected with the output terminals of the first, second and third voltage comparison circuits respectively; The input terminal of the analog switch K1 is electrically connected with the voltage feedback pin of the DC-DC power supply chip, the output terminal is electrically connected with one end of the resistor R17, and the other end of the resistor R17 is electrically connected with the conversion pin of the DC-DC power supply chip and the power supply terminal of the anti-recording interference shielding instrument respectively; The input terminal of the analog switch K2 is electrically connected with the voltage feedback pin of the DC-DC power supply chip, the output terminal is electrically connected with one end of the resistor R18, and the other end of the resistor R18 is electrically connected with the conversion pin of the DC-DC power supply chip and the power supply terminal of the anti-recording interference shielding instrument respectively; An input end of the analog switch K3 is electrically connected with a voltage feedback pin of the DC-DC power supply chip, an output end is electrically connected with one end of the resistor R19, and the other end of the resistor R19 is respectively electrically connected with a conversion pin of the DC-DC power supply chip and a power supply end of the anti-recording interference shielding instrument; One end of the resistor R16 is electrically connected with the voltage feedback pin of the DC-DC power supply chip, and the other end is respectively electrically connected with the conversion pin of the DC-DC power supply chip and the power supply end and the conversion pin of the anti-recording interference shielding instrument; The power supply end of the DC-DC power supply chip is electrically connected with the 12V direct current voltage.

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