Alarm circuit based on wireless temperature sensor

Abstract

The utility model discloses an alarm circuit based on a wireless temperature sensor, which relates to the technical field of alarm, and comprises a power supply module used for supplying power; the temperature detection module is used for temperature detection and over-temperature judgment, and when the temperature is over-temperature, the wireless transmitting module transmits a wireless signal; the wireless receiving and processing module is used for receiving the wireless signal, processing the signal and controlling the alarm work of the alarm control module; the infrared sensing module is used for sensing a human body and adjusting the voltage of a signal output by the volume control module when sensing the human body, and the volume control module is used for accessing an audio signal and processing the signal; and the alarm control module is used for performing power amplification processing on the audio signal and giving an alarm. The alarm circuit based on the wireless temperature sensor controls the alarm control module to cooperate with the volume control module to carry out alarm work and the infrared induction module to carry out human body pyroelectric induction in a wireless mode when the temperature is over-high, so that the alarm volume is reduced when someone is inducted.

Description

Technical Field

[0001] The utility model relates to the technical field of alarm, in particular to an alarm circuit based on a wireless temperature sensor. Background Technique

[0002] A wireless temperature sensor is a wireless sensor network product integrating temperature sensing, wireless communication, low power consumption and other technologies. It can detect the temperature at the location to be detected and perform remote alarm control when the temperature is abnormal. In order to improve the alarm efficiency, the alarm volume will be increased. However, when the user passes by the location where the alarm occurs, the relatively loud alarm sound causes discomfort to pedestrians and the user experience is not good. Therefore, it needs to be improved. Content of the Utility Model

[0003] The embodiment of the utility model provides an alarm circuit based on a wireless temperature sensor to solve the problems put forward in the above background technique.

[0004] To achieve the above object, the utility model provides the following technical solutions:

[0005] An alarm circuit based on a wireless temperature sensor includes: a power supply module, a temperature detection module, a wireless transmission module, a wireless reception and processing module, an infrared sensing module, a volume control module and an alarm control module;

[0006] The power supply module is used to provide the first electric energy and the second electric energy;

[0007] The temperature detection module is connected to the power supply module and the wireless transmission module, and is used to receive the first electric energy and perform temperature detection and over-temperature judgment, and is used to transmit the first electric energy to the wireless transmission module when the temperature is over-temperature;

[0008] The wireless transmission module is used to receive the first electric energy transmitted by the temperature detection module and transmit a wireless signal;

[0009] The wireless reception and processing module is connected to the power supply module, and is used to receive the second electric energy and the wireless signal and perform amplification, detection, rectification and decoding processing on the wireless signal, and is used to output a level signal;

[0010] The infrared sensing module is connected to the power supply module, and is used to receive the second electric energy and perform human body sensing, and is used to output a first control signal when a human body is sensed;

[0011] The volume control module is connected to the infrared sensing module, and is used to access an audio signal and perform voltage division processing on the audio signal, and is used to receive the first control signal and adjust the voltage division processing degree to adjust the voltage of the audio signal;

[0012] The alarm control module, connected to the power supply module, the wireless receiving and processing module, and the volume control module, is used to receive level signals and perform alarm operations, and is used to perform power amplification processing on the signals output after voltage division processing by the volume control module and adjust the alarm volume.

[0013] As a further solution of the present utility model: The power supply module includes a first storage battery; the temperature detection module includes a first thermistor, a sixth resistor, a seventh resistor, an eighth resistor, a first comparator, and a third switching tube;

[0014] Preferably, the first end of the first storage battery is connected to the first end of the first thermistor and the collector of the third switching tube and is connected to the inverting end of the first comparator and one end of the eighth resistor through the seventh resistor. The second end of the first thermistor is connected to the non-inverting end of the first comparator and is grounded through the sixth resistor. The other end of the eighth resistor and the second end of the first storage battery are both grounded. The output end of the first comparator is connected to the base of the third switching tube, and the emitter of the third switching tube is connected to the wireless transmission module.

[0015] As a further solution of the present utility model: The wireless transmission module includes a ninth resistor, a tenth resistor, an eleventh resistor, a first diode, a second diode, a sixth capacitor, a first potentiometer, a first oscillator, a seventh capacitor, and a wireless transmission device;

[0016] Preferably, the fourth end and the eighth end of the first oscillator are both connected to the VCC end of the wireless transmission device and the emitter of the third switching tube and are connected to one end of the first potentiometer through the ninth resistor. The other end of the first potentiometer is connected to the cathode of the first diode through the tenth resistor. The anode of the first diode is connected to the cathode of the second diode, the sixth end and the second end of the first oscillator and is grounded through the sixth capacitor. The seventh end of the first oscillator is connected to the anode of the second diode and the sliding end of the first potentiometer. The first end of the first oscillator is grounded. The fifth end of the first oscillator is grounded through the seventh capacitor. The third end of the first oscillator is connected to the IN end of the wireless transmission device through the eleventh resistor, and the GND end of the wireless transmission device is grounded.

[0017] As a further solution of the present utility model: The power supply module further includes a second storage battery; the wireless receiving and processing module includes a wireless receiving device, a first capacitor, a second capacitor, a first decoder, a third capacitor, and a first resistor;

[0018] Preferably, the first end of the second storage battery is connected to the VCC end of the wireless receiving device and the fourth end of the first decoder. The OUT end of the wireless receiving device is connected to the third end of the first decoder. The first end of the first decoder is grounded through a first capacitor. The second end of the first decoder is grounded through a second capacitor. The fifth end of the first decoder is connected to the sixth end of the first decoder and one end of a third capacitor through a first resistor. The other end of the third capacitor, the seventh end of the first decoder, the GND end of the wireless receiving device, and the second end of the second storage battery are all grounded. The eighth end of the first decoder is connected to the alarm control module.

[0019] As a further solution of the present utility model: The alarm control module includes a second switching tube, a power amplifier, and a first speaker; the volume control module includes an audio device, a fifth capacitor, a second resistor, a third resistor, a fourth capacitor, a first switching tube, and a fourth resistor;

[0020] Preferably, the collector of the second switching tube is connected to the first end of the second storage battery. The emitter of the second switching tube is connected to the power supply end of the power amplifier. The input end of the power amplifier is connected to one end of the second resistor, one end of the third resistor, and the collector of the first switching tube through a fourth capacitor. The other end of the second resistor is connected to the audio device through a fifth capacitor. The other end of the third resistor, the grounding end of the power amplifier, and one end of the first speaker are all grounded. The base of the first switching tube is connected to the infrared sensing module. The output end of the power amplifier is connected to the other end of the first speaker. The emitter of the first switching tube is grounded through a fourth resistor.

[0021] As a further solution of the present utility model: The infrared sensing module includes an infrared sensor and a fifth resistor;

[0022] Preferably, the VCC end of the infrared sensor is connected to the first end of the second storage battery. The GND end of the infrared sensor is grounded. The OUT end of the infrared sensor is connected to the base of the first switching tube through a fifth resistor.

[0023] Compared with the prior art, the beneficial effects of the present utility model are as follows: The alarm circuit based on the wireless temperature sensor of the present utility model performs over-temperature judgment by the temperature detection module and, when over-temperature occurs, transmits a wireless signal through the wireless transmission module, and is received and processed by the wireless receiving and processing module, so as to control the alarm control module to cooperate with the volume control module to perform alarm work. At the same time, the infrared sensing module performs pyroelectric induction of the human body, so as to reduce the alarm volume when a person is sensed, avoid the influence of the excessive alarm sound on the passing crowd, and improve the intelligence of the alarm circuit. Description of the Drawings

[0024] To more clearly illustrate the technical solutions of the embodiments of the present utility model, the following will briefly introduce the drawings required for the description of the embodiments of the present utility model. Obviously, the drawings in the following description are only some embodiments of the present utility model. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a schematic block diagram of the principle of an alarm circuit based on a wireless temperature sensor provided by an example of the present utility model.

[0026] Figure 2 It is a connection circuit diagram of a power supply module, a temperature detection module, and a wireless transmission module provided by an example of the present utility model.

[0027] Figure 3 It is a connection circuit diagram of a power supply module, a wireless reception and processing module, an alarm control module, a volume control module, and an infrared sensing module provided by an example of the present utility model. Specific embodiments

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present utility model with reference to the drawings in the embodiments of the present utility model. Obviously, the described embodiments are only a part of the embodiments of the present utility model, rather than all of them. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present utility model.

[0029] In one embodiment, please refer to Figure 1 , an alarm circuit based on a wireless temperature sensor, including: a power supply module 1, a temperature detection module 2, a wireless transmission module 3, a wireless reception and processing module 4, an infrared sensing module 5, a volume control module 6, and an alarm control module 7;

[0030] Specifically, the power supply module 1 is used to provide the first electric energy and the second electric energy;

[0031] The temperature detection module 2 is connected to the power supply module 1 and the wireless transmission module 3, and is used to receive the first electric energy and perform temperature detection and over-temperature judgment, and is used to transmit the first electric energy to the wireless transmission module 3 when over-temperature;

[0032] The wireless transmission module 3 is used to receive the first electric energy transmitted by the temperature detection module 2 and transmit a wireless signal;

[0033] The wireless reception and processing module 4 is connected to the power supply module 1, and is used to receive the second electric energy and the wireless signal and perform amplification, detection, rectification, and decoding processing on the wireless signal, and is used to output a level signal;

[0034] An infrared sensing module 5, connected to the power supply module 1, is configured to receive the second electric energy and perform human body sensing, and is configured to output a first control signal when a human body is sensed;

[0035] A volume control module 6, connected to the infrared sensing module 5, is configured to access an audio signal and perform voltage division processing on the audio signal, and is configured to receive the first control signal and adjust the degree of voltage division processing to adjust the voltage of the audio signal;

[0036] An alarm control module 7, connected to the power supply module 1, the wireless receiving and processing module 4, and the volume control module 6, is configured to receive a level signal and perform alarm work, and is configured to perform power amplification processing on the signal output after the voltage division processing of the volume control module 6 and adjust the alarm volume.

[0037] In a specific embodiment, the above-mentioned power supply module 1 may adopt a power supply circuit composed of a storage battery, and can provide the first electric energy and the second electric energy in a DC form; the above-mentioned temperature detection module 2 may adopt a temperature detection circuit composed of a thermistor, a resistor, a comparator, etc., and can perform temperature detection and over-temperature judgment; the above-mentioned wireless transmission module 3 may adopt a wireless transmission circuit composed of an oscillator, a wireless transmitter, a resistor, etc., and when receiving electric energy, emits a wireless signal; the above-mentioned wireless receiving and processing module 4 may adopt a wireless receiving circuit composed of a wireless receiver, a decoder, a capacitor, etc., and can receive a wireless signal and perform amplification, detection, rectification, and decoding processing on the wireless signal; the above-mentioned infrared sensing module 5 may adopt an infrared sensing circuit composed of a sensor and a resistor to perform pyroelectric induction of the human body; the above-mentioned volume control module 6 may adopt a volume control circuit composed of an audio device, a capacitor, a resistor, etc., and can access an audio signal and perform voltage division adjustment processing on the audio signal; the above-mentioned alarm control module 7 may adopt an alarm control circuit composed of a power amplifier, a triode, and a speaker, and can perform amplification processing on the signal output by the volume control module 6 and perform alarm control.

[0038] In another embodiment, please refer to Figure 1 、 Figure 2 and Figure 3 The power supply module 1 includes a first storage battery; the temperature detection module 2 includes a first thermistor NTC, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a first comparator A1, and a third switching tube VT3;

[0039] Specifically, the first end of the first storage battery is connected to the first end of the first thermistor NTC and the collector of the third switching transistor VT3, and is connected to the inverting terminal of the first comparator A1 and one end of the eighth resistor R8 through the seventh resistor R7. The second end of the first thermistor NTC is connected to the non-inverting terminal of the first comparator A1 and is grounded through the sixth resistor R6. The other end of the eighth resistor R8 and the second end of the first storage battery are both grounded. The output terminal of the first comparator A1 is connected to the base of the third switching transistor VT3, and the emitter of the third switching transistor VT3 is connected to the wireless transmission module 3.

[0040] In a specific embodiment, the above-mentioned first thermistor NTC can be a thermistor with a negative temperature coefficient; the above-mentioned seventh resistor R7 and eighth resistor R8 provide an over-temperature threshold; the above-mentioned first comparator A1 can be an LM358 comparator; the above-mentioned third switching transistor VT3 can be an NPN-type triode.

[0041] Further, the wireless transmission module 3 includes a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a first diode D1, a second diode D2, a sixth capacitor C6, a first potentiometer RP1, a first oscillator IC4, a seventh capacitor C7, and a wireless transmission device IC5;

[0042] Specifically, the fourth terminal and the eighth terminal of the first oscillator IC4 are both connected to the VCC terminal of the wireless transmission device IC5 and the emitter of the third switching transistor VT3, and are connected to one end of the first potentiometer RP1 through the ninth resistor R9. The other end of the first potentiometer RP1 is connected to the cathode of the first diode D1 through the tenth resistor R10. The anode of the first diode D1 is connected to the cathode of the second diode D2, the sixth terminal and the second terminal of the first oscillator IC4, and is grounded through the sixth capacitor C6. The seventh terminal of the first oscillator IC4 is connected to the anode of the second diode D2 and the sliding terminal of the first potentiometer RP1. The first shield of the first oscillator IC4 is grounded. The fifth terminal of the first oscillator IC4 is grounded through the seventh capacitor C7. The third terminal of the first oscillator IC4 is connected to the IN terminal of the wireless transmission device IC5 through the eleventh resistor R11, and the GND terminal of the wireless transmission device IC5 is grounded.

[0043] In a specific embodiment, the above-mentioned first oscillator IC4 can be an NE555 chip, which outputs a square wave oscillation signal in cooperation with the ninth resistor R9, the tenth resistor R10, the eleventh resistor R11, the first diode D1, the second diode D2, the sixth capacitor C6, the first potentiometer RP1, and the seventh capacitor C7; the above-mentioned wireless transmission device IC5 can be a T630-type integrated wireless remote control transmitter head.

[0044] Further, the power supply module 1 further includes a second storage battery; the wireless receiving and processing module 4 includes a wireless receiving device IC1, a first capacitor C1, a second capacitor C2, a first decoder IC2, a third capacitor C3, and a first resistor R1;

[0045] Specifically, the first end of the second storage battery is connected to the VCC end of the wireless receiving device IC1 and the fourth end of the first decoder IC2. The OUT end of the wireless receiving device IC1 is connected to the third end of the first decoder IC2. The first end of the first decoder IC2 is grounded through the first capacitor C1. The second end of the first decoder IC2 is grounded through the second capacitor C2. The fifth end of the first decoder IC2 is connected to the sixth end of the first decoder IC2 and one end of the third capacitor C3 through the first resistor R1. The other end of the third capacitor C3, the seventh end of the first decoder IC2, the GND end of the wireless receiving device IC1, and the second end of the second storage battery are all grounded. The eighth end of the first decoder IC2 is connected to the alarm control module 7.

[0046] In a specific embodiment, the above-mentioned wireless receiving device IC1 can be selected as the T631 type wireless remote control receiving head that is matched with the wireless transmitting device IC5; the above-mentioned first decoder IC2 can be selected as the LM567 decoder.

[0047] Further, the alarm control module 7 includes a second switching tube VT2, a power amplifier, and a first speaker BL1; the volume control module 6 includes an audio device, a fifth capacitor C5, a second resistor R2, a third resistor R3, a fourth capacitor C4, a first switching tube VT1, and a fourth resistor R4;

[0048] Specifically, the collector of the second switching tube VT2 is connected to the first end of the second storage battery. The emitter of the second switching tube VT2 is connected to the power supply end of the power amplifier. The input end of the power amplifier is connected to one end of the second resistor R2, one end of the third resistor R3, and the collector of the first switching tube VT1 through the fourth capacitor C4. The other end of the second resistor R2 is connected to the audio device through the fifth capacitor C5. The other end of the third resistor R3, the grounding end of the power amplifier, and one end of the first speaker BL1 are all grounded. The base of the first switching tube VT1 is connected to the infrared sensing module 5. The output end of the power amplifier is connected to the other end of the first speaker BL1. The emitter of the first switching tube VT1 is grounded through the fourth resistor R4.

[0049] In a specific embodiment, the above-mentioned power amplifier can be selected as a power amplification circuit composed of a TDA2003 chip; the above-mentioned audio device can be selected as an LQ46 chip to provide an audio signal; the above-mentioned first switching tube VT1 and second switching tube VT2 can both be selected as NPN type triodes.

[0050] Further, the infrared sensing module 5 includes an infrared sensor IC3 and a fifth resistor R5;

[0051] Specifically, the VCC terminal of the infrared sensor IC3 is connected to the first terminal of the second battery, the GND terminal of the infrared sensor IC3 is grounded, and the OUT terminal of the infrared sensor IC3 is connected to the base of the first switching transistor VT1 through the fifth resistor R5.

[0052] In a specific embodiment, the above infrared sensor IC3 can be selected as an HC-SR501 sensor.

[0053] In the alarm circuit based on the wireless temperature sensor of this embodiment, the DC power is provided by the first battery and the second battery. The temperature is detected by the first thermistor NTC. When the detected temperature is greater than the over-temperature threshold provided by the seventh resistor R7 and the eighth resistor R8, the first comparator A1 outputs a high level and controls the third switching transistor VT3 to conduct, so that the first oscillator IC4 is powered on. Cooperating with the ninth resistor R9, the tenth resistor R10, the eleventh resistor R11, the first diode D1, the second diode D2, the sixth capacitor C6, the first potentiometer RP1 and the seventh capacitor C7, a square wave oscillation signal is output, and a wireless signal is sent by the wireless transmitting device IC5. The wireless signal is received by the wireless receiving device IC1 and amplified, detected and shaped. The processed signal is decoded by the first decoder IC2 in cooperation with the first capacitor C1, the second capacitor C2, the third capacitor C3 and the first resistor R1. The first decoder IC2 triggers the second switching transistor VT2 to conduct, the power amplifier is powered on, the audio signal provided by the audio device is transmitted through the fifth capacitor C5, divided by the second resistor R2 and the third resistor R3, transmitted by the fourth capacitor C4, and processed by the power amplifier to trigger the alarm operation of the first speaker BL1. At the same time, the infrared sensor IC3 performs pyroelectric detection of the human body. When a pedestrian is detected, the first switching transistor VT1 is triggered to conduct, so that the fourth resistor R4 cooperates with the second resistor R2 and the third resistor R3 to perform voltage division work, and then the voltage of the signal input to the power amplifier is reduced, and the alarm volume of the first speaker BL1 is reduced.

[0054] For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic characteristics of the present invention. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting. The scope of the present invention is defined by the appended claims rather than the above description. Therefore, all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present invention. Any reference signs in the claims should not be regarded as limiting the claimed rights.

[0055] In addition, it should be understood that although this specification is described in terms of embodiments, not every embodiment contains only one independent technical solution. This narrative manner of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An alarm circuit based on a wireless temperature sensor, characterized in that: The alarm circuit based on the wireless temperature sensor includes: a power supply module, a temperature detection module, a wireless transmission module, a wireless receiving processing module, an infrared sensing module, a volume control module and an alarm control module; The power supply module is used to provide the first electric energy and the second electric energy; The temperature detection module is connected to the power module and the wireless transmission module, and is used to receive the first electric energy and perform temperature detection and over-temperature judgment, and is used to transmit the first electric energy to the wireless transmission module when the temperature is over-temperature; The wireless transmitting module is used to receive the first electric energy transmitted by the temperature detecting module and transmit a wireless signal; The wireless receiving processing module is connected to the power supply module, and is used to receive the second electric energy and the wireless signal and to amplify, detect, rectify and decode the wireless signal, and output a level signal; The infrared sensing module is connected to the power module, and is used to receive the second electric energy and perform human body sensing, and is used to output a first control signal when sensing a human body; The volume control module is connected to the infrared sensing module, and is used to receive the audio signal and perform voltage division processing on the audio signal, and is used to receive the first control signal and adjust the voltage division processing degree, thereby adjusting the voltage of the audio signal; The alarm control module is connected to the power module, the wireless receiving processing module and the volume control module, and is used to receive the level signal and perform alarm work, and is used to power amplify the signal output after the voltage division processing of the volume control module and adjust the alarm volume.

2. The alarm circuit based on a wireless temperature sensor according to claim 1, characterized in that: The power module includes a first storage battery; the temperature detection module includes a first thermistor, a sixth resistor, a seventh resistor, an eighth resistor, a first comparator and a third switch tube; The first end of the first battery is connected to the first end of the first thermistor and the collector of the third switch tube, and is connected to the inverting end of the first comparator and one end of the eighth resistor through the seventh resistor. The second end of the first thermistor is connected to the non-inverting end of the first comparator and is grounded through the sixth resistor. The other end of the eighth resistor and the second end of the first battery are both grounded. The output end of the first comparator is connected to the base of the third switch tube, and the emitter of the third switch tube is connected to the wireless transmission module.

3. The alarm circuit based on a wireless temperature sensor according to claim 2 is characterized in that: The wireless transmitting module includes a ninth resistor, a tenth resistor, an eleventh resistor, a first diode, a second diode, a sixth capacitor, a first potentiometer, a first oscillator, a seventh capacitor and a wireless transmitting device; The fourth end and the eighth end of the first oscillator are connected to the VCC end of the wireless transmitting device and the emitter of the third switching tube and are connected to one end of the first potentiometer through the ninth resistor. The other end of the first potentiometer is connected to the cathode of the first diode through the tenth resistor. The anode of the first diode is connected to the cathode of the second diode, the sixth end and the second end of the first oscillator and are grounded through the sixth capacitor. The seventh end of the first oscillator is connected to the anode of the second diode and the slider end of the first potentiometer. The first shield of the first oscillator is grounded. The fifth end of the first oscillator is grounded through the seventh capacitor. The third end of the first oscillator is connected to the IN end of the wireless transmitting device through the eleventh resistor, and the GND end of the wireless transmitting device is grounded.

4. The alarm circuit based on a wireless temperature sensor according to claim 3 is characterized in that: The power module also includes a second storage battery; the wireless receiving processing module includes a wireless receiving device, a first capacitor, a second capacitor, a first decoder, a third capacitor and a first resistor; The first end of the second battery is connected to the VCC end of the wireless receiving device and the fourth end of the first decoder, the OUT end of the wireless receiving device is connected to the third end of the first decoder, the first end of the first decoder is grounded through the first capacitor, the second end of the first decoder is grounded through the second capacitor, the fifth end of the first decoder is connected to the sixth end of the first decoder and one end of the third capacitor through the first resistor, the other end of the third capacitor, the seventh end of the first decoder, the GND end of the wireless receiving device and the second end of the second battery are all grounded, and the eighth end of the first decoder is connected to the alarm control module.

5. The alarm circuit based on a wireless temperature sensor according to claim 4, characterized in that: The alarm control module includes a second switch tube, a power amplifier and a first speaker; the volume control module includes an audio device, a fifth capacitor, a second resistor, a third resistor, a fourth capacitor, a first switch tube and a fourth resistor; The collector of the second switch tube is connected to the first end of the second battery, the emitter of the second switch tube is connected to the power supply end of the power amplifier, the input end of the power amplifier is connected to one end of the second resistor, one end of the third resistor and the collector of the first switch tube through a fourth capacitor, the other end of the second resistor is connected to the audio device through a fifth capacitor, the other end of the third resistor, the ground end of the power amplifier and one end of the first speaker are all grounded, the base of the first switch tube is connected to the infrared sensing module, the output end of the power amplifier is connected to the other end of the first speaker, and the emitter of the first switch tube is grounded through a fourth resistor.

6. The alarm circuit based on a wireless temperature sensor according to claim 5, characterized in that: The infrared sensing module includes an infrared sensor and a fifth resistor; The VCC terminal of the infrared sensor is connected to the first terminal of the second storage battery, the GND terminal of the infrared sensor is grounded, and the OUT terminal of the infrared sensor is connected to the base of the first switch tube through a fifth resistor.

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