LORA wireless explosion-proof manual alarm button

Abstract

This utility model relates to the field of fire alarm technology and discloses a LORA wireless explosion-proof manual alarm button, including an alarm main control circuit, an alarm button circuit, an LED indicator circuit, a LORA wireless communication circuit, and a transformer filter circuit, all electrically connected to the alarm main control circuit. The alarm main control circuit receives signals from the alarm button circuit and controls the LED indicator in the LED indicator circuit to light up when an alarm is triggered, and sends the alarm signal out through the LORA wireless communication circuit. The LORA wireless communication circuit is connected between the alarm main control circuit and the user to realize the transmission of the alarm signal. The LED indicator circuit is used to indicate the working status of the alarm button. The system has low energy consumption, long wireless communication distance, and strong anti-interference ability, meets the safety requirements of explosion-proof scenarios, and can replace existing manual alarm buttons. It can detect the alarm button being pressed in real time and accurately, and send out an alarm signal, thereby reducing fire hazards, reducing economic losses, and ensuring safety.

Description

Technical Field

[0001] This utility model relates to the field of fire alarm technology, specifically to a LORA-based wireless explosion-proof manual alarm button. Background Technology

[0002] The high incidence of building fires is mainly due to the inability to detect fire hazards and issue timely alarms. Manual alarm buttons, a common fire prevention device, are activated by pressing a button to signal the occurrence of a fire. If the fire detector fails to provide timely audible and visual alarms, the manual alarm button can trigger the alarm, activating the audible and visual sirens and thus reducing property damage and protecting lives.

[0003] With economic development, fires cause enormous economic losses to the country and individuals, and have a significant impact on society. Therefore, how to promptly and accurately notify relevant departments and personnel has become a major social concern. Traditional manual alarm buttons employ two data transmission methods: one uses two-wire communication for data transmission, and the other uses RS485 communication for signal transmission.

[0004] Existing manual alarm buttons are divided into two categories: fire bus and RS485 communication. Wired manual alarm buttons involve the installation of communication networks, which is costly to use. The installation process requires extensive wiring, strong and weak current isolation, and the wiring method must strictly comply with relevant standards. It also has certain requirements for the application environment, and the wiring is very complex. If one alarm button malfunctions during use, a large-scale troubleshooting is required, resulting in high installation and maintenance costs. Utility Model Content

[0005] In view of the shortcomings of the existing technology, the purpose of this utility model is to provide a LORA-based wireless explosion-proof manual alarm button.

[0006] To achieve the above objectives, this utility model provides the following technical solution: A LORA-based wireless explosion-proof manual alarm button includes an alarm main control circuit, an alarm button circuit, an LED indicator circuit, a LORA wireless communication circuit, and a transformer filter circuit, all electrically connected to the alarm main control circuit. The alarm main control circuit receives signals from the alarm button circuit and, upon alarm activation, controls the LED indicator in the LED indicator circuit to illuminate, and transmits the alarm signal via the LORA wireless communication circuit. The LORA wireless communication circuit is connected between the alarm main control circuit and the user to transmit the alarm signal. The LED indicator circuit indicates the operating status of the alarm button. The transformer filter circuit converts an externally input DC24V voltage to DC3.3V and supplies power to the alarm main control circuit, the LORA wireless communication circuit, the LED indicator circuit, and the alarm button circuit.

[0007] In this utility model, preferably, the alarm main control circuit includes a main control chip D1, the main control chip D1 adopts the HC32L130J8TA series control chip, pin 6 of the main control chip D1 is connected to the alarm button circuit, pins 30 and 31 of the main control chip D1 are connected to the LORA wireless communication circuit, and pin 41 of the main control chip D1 is connected to the LED indicator circuit.

[0008] In this utility model, preferably, the LED indicator circuit includes a button X1. Pin 2 of the button X1 is connected in series with diode VD3 and resistor R9 and then connected to the G_CPU signal. Pin 3 of the button X1 is connected in series with diode VD2 and resistor R16 and then connected to the V_CPU signal. A capacitor C8 is also connected in series between the series circuit composed of diode VD3 and resistor R9 and the series circuit composed of diode VD2 and resistor R16. At the same time, one end of capacitor C8 is connected to pin 6 of the main control chip D1.

[0009] In this utility model, preferably, the LORA wireless communication circuit includes a wireless communication chip D1, which is an E22-400T22S series chip, and pins 7 and 8 of the wireless communication chip D1 are connected to pins 30 and 31 of the main control chip D1.

[0010] In this invention, preferably, one end of the indicator light circuit is connected to the V_CPU signal, and the other end is connected between pin 41 of the main control chip D1. The indicator light circuit includes a light-emitting diode HL1 and a resistor R14 connected in series.

[0011] In this utility model, preferably, the transformer filter circuit includes a rectifier bridge N1, a common-mode filter L1, an LC filter branch, and a step-down chip N2 connected in sequence. The rectifier bridge N1 is connected to the input DC 24V voltage, which is filtered by the rectifier bridge N1, the common-mode filter L1, and the LC filter branch, and then stepped down to DC 3.3V by the step-down chip N2.

[0012] In this invention, preferably, a capacitor C28, a variable resistor VP1, and a capacitor C14 are connected in parallel between the input terminals of the rectifier bridge N1. The two input terminals are connected in series with capacitors C19 and C21 respectively and then grounded. The input terminals of the rectifier bridge N1 are also connected in series with resistors R18 and R21 respectively and then connected to the input DC24V voltage. The output terminal of the rectifier bridge N1 is connected in parallel with resistor R19, then connected in series with diode VD1 and then connected to the common-mode filter L1.

[0013] In this invention, preferably, the LC filter branch includes capacitors C15 and C17 connected in parallel, with the two ends of capacitors C15 and C17 connected through inductors L2 and L3 respectively to form a π-type LC filter branch.

[0014] In this utility model, preferably, pin 5 of the step-down chip N2 is connected in series with capacitors C18 and C26 and then grounded; resistor R17 is connected in series between pins 4 and 5; pin 4 is connected in series with resistor R22 and then grounded; pin 6 is connected in series with inductor L4 and then connected to pin 3 through capacitor C25 and resistor R10; pin 3 is also connected in series with resistor R20 and then grounded; pin 6 outputs the V_CPU signal; pin 2 is grounded and simultaneously outputs the G_CPU signal; capacitors C23 and C24 are connected in parallel between pin 6 and pin 2; and capacitor C22 is connected in series between pins 1 and 6.

[0015] Compared with the prior art, the beneficial effects of this utility model are: The main control chip of this invention's alarm button supports deep sleep mode, waking up only when the button is pressed. Combined with the low-power characteristics of LoRa communication technology, it significantly reduces system energy consumption, making it suitable for long-term unattended scenarios. The DC24V local power supply solves wiring and communication issues, providing long wireless communication distances, strong anti-interference capabilities, and ensuring circuit stability at high decibel outputs, meeting the safety requirements of explosion-proof scenarios. It can replace existing manual alarm buttons, detecting alarm button presses in real time and accurately, and issuing alarm signals, thereby reducing fire hazards, minimizing economic losses, and ensuring safety. Attached Figure Description

[0016] Figure 1 This is a structural block diagram of a LORA wireless explosion-proof manual alarm button according to the present invention.

[0017] Figure 2 This is a circuit diagram of the alarm main control circuit described in this utility model.

[0018] Figure 3 This is a circuit diagram of the alarm button circuit described in this utility model.

[0019] Figure 4 This is a circuit diagram of the indicator light circuit described in this utility model.

[0020] Figure 5 This is a circuit diagram of the LORA wireless communication circuit described in this utility model.

[0021] Figure 6 This is a circuit diagram of the transformer filter circuit described in this utility model. Detailed Implementation

[0022] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0024] Please also see Figures 1 to 6This utility model provides a preferred embodiment of a LORA wireless explosion-proof manual alarm button that can replace existing manual alarm buttons. It can detect the alarm button being pressed in real time and accurately, and issue an alarm signal, thereby reducing fire hazards, minimizing economic losses, and ensuring safety. This wireless manual alarm button device has strong access capabilities, long communication distance, strong anti-interference ability, secure communication, and is easy to promote and apply. The alarm button includes an alarm main control circuit and an alarm button circuit, an LED indicator circuit, a LORA wireless communication circuit, and a transformer filter circuit, all electrically connected to the alarm main control circuit. The alarm main control circuit receives signals from the alarm button circuit and controls the LED indicator in the LED indicator circuit to light up when an alarm is triggered, and then sends the alarm signal out through the LORA wireless communication circuit. The LORA wireless communication circuit is connected between the alarm main control circuit and the user to realize the transmission of the alarm signal. The LED indicator circuit indicates the working status of the alarm button. The transformer filter circuit converts the externally input DC24V voltage to DC3.3V voltage and supplies power to the alarm main control circuit, the LORA wireless communication circuit, the LED indicator circuit, and the alarm button circuit.

[0025] In this embodiment, the alarm main control circuit includes a main control chip D1, which is an HC32L130J8TA series control chip. Pin 6 of the main control chip D1 is connected to the alarm button circuit, pins 30 and 31 are connected to the LORA wireless communication circuit, and pin 41 is connected to the LED indicator circuit. The main control chip D1 is powered by 3.3V, with an operating voltage range of 2V to 5.5V. Its power consumption in deep sleep mode is 0.5uA. It is used to complete manual alarm-related processing operations and is connected to the alarm button circuit, the LORA wireless communication circuit, and the LED indicator circuit. It receives signals from the alarm button, controls the LED indicator to light up when an alarm is triggered, and controls the LORA wireless communication module to send alarm information. The main control chip supports deep sleep mode, waking up only when receiving a fire alarm signal. Combined with the low-power characteristics of LORA communication technology, this significantly reduces system energy consumption, making it suitable for long-term unattended operation scenarios.

[0026] In this embodiment, the LED indicator circuit includes a button X1. Pin 2 of button X1 is connected in series with diode VD3 and resistor R9, and then connected to the G_CPU signal. Pin 3 of button X1 is connected in series with diode VD2 and resistor R16, and then connected to the V_CPU signal. A capacitor C8 is also connected in series between the series circuits composed of diode VD3 and resistor R9 and the series circuits composed of diode VD2 and resistor R16. One end of capacitor C8 is connected to pin 6 of the main control chip D1. Capacitor C8, connected in series between the two series circuits and with one end connected to pin 6 of the main control chip D1, can filter high-frequency noise in the signal, making the trigger signal transmitted to the main control chip more stable, reducing false alarms or missed alarms caused by signal fluctuations, and improving the accuracy of alarm judgment. The core function of the alarm button circuit is to receive manually triggered alarm commands. When button X1 is pressed, the KEY signal voltage decreases, and the main control chip D1 directly connects to this circuit through pin 6, enabling "no relay" transmission of the trigger signal. Compared to the signal splitting and delay issues that may exist in traditional wiring, this directional connection can shorten the signal transmission path to the greatest extent, ensuring that the main control chip can capture the trigger signal the moment the alarm button is pressed, thus gaining critical response time for subsequent alarm actions and avoiding alarm delays caused by signal transmission lag.

[0027] In this embodiment, the LORA wireless communication circuit includes a wireless communication chip D1, which is an E22-400T22S series chip. Pins 7 and 8 of the wireless communication chip D1 are connected to pins 30 and 31 of the main control chip D1. The wireless communication chip D1 uses LORA communication technology and is powered by DC 3.3V. It receives fire alarm information sent by the alarm main control circuit and forwards it to the user, promptly notifying the user and realizing on-site fire alarm. This allows residents to take timely measures, thereby reducing fire hazards and ensuring building safety. The wireless communication circuit adopts the new generation NB technology of E22-400T22S. Under the same base station conditions, LORA increases the number of accesses by 5-10 times compared to existing wireless technologies. LORA also has strong indoor coverage and strong anti-interference capabilities.

[0028] In this embodiment, one end of the indicator light circuit is connected to the V_CPU signal, and the other end is connected between pin 41 of the main control chip D1. The indicator light circuit includes a light-emitting diode HL1 and a resistor R14 connected in series. When the main control chip D1 receives a fire alarm message, it causes the light-emitting diode HL1 to work, and the indicator light illuminates to indicate that the fire alarm is working.

[0029] In this embodiment, the transformer-filter circuit includes a rectifier bridge N1, a common-mode filter L1, an LC filter branch, and a step-down chip N2 connected in sequence. The rectifier bridge N1 is connected to the input DC24V voltage. After being filtered by the rectifier bridge N1, the common-mode filter L1, and the LC filter branch, the voltage is stepped down to DC3.3V by the step-down chip N2. This method of using local DC24V power eliminates the need for additional wiring, solving the problem of complex installation in traditional wired alarms. The transformer-filter circuit, through a multi-stage design of rectification protection, π-type filtering, and precise voltage reduction, achieves efficient conversion from DC24V to DC3.3V, resulting in a clean and noise-free output voltage, avoiding chip misjudgment and communication interruption caused by power supply fluctuations. Simultaneously, the protective functions of components such as the variable resistor VP1 and diode VD1 reduce the risk of overvoltage and back current, lower circuit heat generation, and meet the electrical safety standards for explosion-proof scenarios.

[0030] In this embodiment, capacitor C28, rheostat VP1, and capacitor C14 are connected in parallel between the input terminals of the rectifier bridge N1. Capacitors C19 and C21 are connected in series between the two input terminals and then grounded. Resistors R18 and R21 are also connected in series between the input terminals of the rectifier bridge N1 and then connected to the input DC 24V voltage. Resistor R19 is connected in parallel between the output terminal of the rectifier bridge N1, followed by diode VD1 connected in series, and then the common-mode filter L1. The resistor R19 connected in parallel between the output terminal of the rectifier bridge N1 can achieve balanced distribution of the output voltage, avoiding voltage imbalance caused by differences in the characteristics of the diodes inside the rectifier bridge, preventing overload damage to a single diode, and stabilizing the output voltage amplitude, providing a stable DC signal for the subsequent diode VD1 and common-mode filter L1.

[0031] In this embodiment, the LC filter branch includes capacitors C15 and C17 connected in parallel. The two ends of capacitors C15 and C17 are connected via inductors L2 and L3, respectively, to form a π-type LC filter branch. The π-type LC filter branch, composed of parallel capacitors C15 and C17 and inductors L2 and L3, offers dual filtering advantages: Firstly, capacitors C15 and C17 can quickly absorb high-frequency noise in the power supply, while inductors L2 and L3 impede low-frequency interference signals. Together, they achieve interference filtering over a wide frequency range, significantly reducing voltage fluctuations input to the step-down chip N2 and preventing noise from affecting the chip's stable operation. Secondly, the π-type topology has significantly better filtering efficiency than single-capacitor or single-inductor filtering, providing a cleaner DC input for subsequent step-down circuits. This meets the stable power supply requirements of the alarm button's core circuit, reducing equipment malfunctions or communication interruptions caused by power supply impurities.

[0032] In this embodiment, pin 5 of the step-down chip N2 is connected in series with capacitors C18 and C26 and then grounded. Resistor R17 is connected in series between pins 4 and 5. Pin 4 is connected in series with resistor R22 and then grounded. Pin 6 is connected in series with inductor L4 and then connected to pin 3 via capacitor C25 and resistor R10. Pin 3 is also connected in series with resistor R20 and then grounded. Pin 6 outputs the V_CPU signal, pin 2 is grounded, and simultaneously outputs the G_CPU signal. Capacitors C23 and C24 are connected in parallel between pin 6 and pin 2, and capacitor C22 is connected in series between pins 1 and 6. Pin 1 outputs the V_CPU signal, and pin 2 outputs the G_CPU signal, forming independent power and ground signal paths. These can be adapted to the power supply logic of different circuits without the need for additional adapter circuits, simplifying the overall wiring. Simultaneously, capacitor C22 between pins 1-6 helps stabilize the voltage difference between the chip's input and output terminals, further improving the stability of the V_CPU and G_CPU signals and ensuring the synchronous and reliable operation of circuits relying on these signals. The stable power supply from the π-type filter and the step-down chip reduces circuit overheating and the risk of failure, meeting the electrical safety requirements of explosion-proof scenarios. Furthermore, the simple circuit topology and clear fault diagnosis path significantly reduce the difficulty and cost of later maintenance, ensuring the long-term stable operation of the alarm button and meeting the high reliability and easy-to-promote requirements of fire-fighting equipment.

[0033] Working principle: After the external DC24V power supply is connected to the transformer and filter circuit, the external DC24V voltage is first connected to the transformer and filter circuit to start the power supply link: Rectification and Protection Stage: The DC 24V voltage is current-limited by resistors R18 and R21 and then input to rectifier bridge N1. Capacitors C28 and C14 connected in parallel at the input filter initial high-frequency noise, and rheostat VP1 absorbs instantaneous overvoltage. Capacitors C19 and C21 connected in series further filter out common-mode interference, ensuring that the voltage input to the rectifier bridge is stable and safe. Rectifier bridge N1 rectifies the voltage into a stable DC. Resistor R19 connected in parallel at the output achieves voltage equalization and avoids overload of the internal diodes. Subsequently, diode VD1 conducts the voltage to prevent backflow of current and delivers the DC voltage to common-mode filter L1. After common-mode filter L1 suppresses the remaining common-mode interference, the voltage enters the π-type LC filter branch. Capacitors C15 and C17 absorb high-frequency noise, and inductors L2 and L3 impede low-frequency interference. Together, they achieve wide-range filtering and output a clean DC voltage. The pure voltage input step-down chip N2 uses capacitors C18 and C26 on pin 5 to filter out power supply noise. Resistor R17 between pins 4 and 5 and resistor R22 grounded to pin 4 form a voltage divider circuit to precisely adjust the chip's operating parameters. Pin 3 is filtered by capacitor C25, current limited by resistor R10, and grounded by R20, further stabilizing the internal signal. Finally, pin 6 outputs the V_CPU signal and pin 2 outputs the G_CPU signal, stabilizing the voltage down to DC 3.3V, providing reliable power to the alarm main control circuit, alarm button circuit, LED indicator circuit, and LORA wireless communication circuit.

[0034] In standby mode, the main control chip D1 enters deep sleep mode to reduce overall power consumption. When a fire hazard is detected on-site, the user manually presses button X1 in the alarm button circuit to trigger alarm signal transmission: After button X1 is pressed, its pin 2 is connected to the G_CPU signal via diode VD3 and resistor R9, and its pin 3 is connected to the V_CPU signal via diode VD2 and resistor R16. Capacitor C8 between the two series circuits filters high-frequency noise, causing the KEY signal voltage to stabilize and decrease, and then directly transmit it to the main control chip D1 through one end of capacitor C8. The main control chip D1 monitors the signal on pin 6 in real time. Because this pin is connected to the alarm button circuit, it can instantly capture voltage changes, avoiding signal delays in traditional wiring and quickly identifying alarm trigger commands.

[0035] After recognizing the alarm command, the main control chip D1 simultaneously triggers LORA wireless information transmission and LED indicator linkage. The main control chip D1 outputs a control signal through pin 41 to drive the LED indicator circuit. One end of this circuit is connected to the V_CPU signal, and the other end is connected to pin 41 via a series-connected LED HL1 and resistor R14. Upon signal triggering, HL1 quickly illuminates, providing direct feedback on the alarm button's status, facilitating confirmation of alarm activation by on-site personnel. This is particularly suitable for scenarios where auditory alarms fail in noisy environments. The main control chip D1 establishes communication with the wireless communication chip D1 in the LORA wireless communication circuit through pins 30 and 31. The main control chip sends alarm information to the wireless communication chip D1 via pin 30. The wireless communication chip D1 uses LORA communication technology and, under DC 3.3V power supply, forwards alarm information to the backend server or user terminal, enabling remote transmission of alarm signals from the backend to the user. This ensures that residents, fire departments, and others receive fire alarm information in real time through mobile apps and other channels, allowing for timely evacuation and rescue measures.

[0036] The above description is a detailed description of the preferred embodiments of the present utility model. However, the embodiments are not intended to limit the scope of the patent application of the present utility model. All equivalent changes or modifications made under the technical spirit of the present utility model should fall within the patent scope covered by the present utility model.

Claims

1. A LoRa-based wireless explosion-proof manual alarm button, characterized in that, It includes an alarm main control circuit, an alarm button circuit, an LED indicator circuit, a LORA wireless communication circuit, and a transformer filter circuit, all of which are electrically connected to the alarm main control circuit. The alarm main control circuit is used to receive the signal from the alarm button circuit, and control the LED indicator in the LED indicator circuit to light up when an alarm is triggered, and send out the alarm signal through the LORA wireless communication circuit. The LORA wireless communication circuit is connected between the alarm main control circuit and the user to realize the transmission of alarm signals; The LED indicator circuit is used to indicate the working status of the alarm button; The transformer and filter circuit is used to convert the externally input DC24V voltage to DC3.3V voltage and to power the alarm main control circuit, the LORA wireless communication circuit, the LED indicator circuit and the alarm button circuit.

2. The LORA-based wireless explosion-proof manual alarm button according to claim 1, characterized in that, The alarm main control circuit includes a main control chip D1, which is an HC32L130J8TA series control chip. Pin 6 of the main control chip D1 is connected to the alarm button circuit, pins 30 and 31 of the main control chip D1 are connected to the LORA wireless communication circuit, and pin 41 of the main control chip D1 is connected to the LED indicator circuit.

3. The LORA-based wireless explosion-proof manual alarm button according to claim 2, characterized in that, The LED indicator circuit includes a button X1. Pin 2 of the button X1 is connected in series with diode VD3 and resistor R9 and then connected to the G_CPU signal. Pin 3 of the button X1 is connected in series with diode VD2 and resistor R16 and then connected to the V_CPU signal. A capacitor C8 is also connected in series between the series circuit composed of diode VD3 and resistor R9 and the series circuit composed of diode VD2 and resistor R16. At the same time, one end of capacitor C8 is connected to pin 6 of the main control chip D1.

4. The LORA-based wireless explosion-proof manual alarm button according to claim 2, characterized in that, The LORA wireless communication circuit includes a wireless communication chip D1, which is an E22-400T22S series chip. Pins 7 and 8 of the wireless communication chip D1 are connected to pins 30 and 31 of the main control chip D1.

5. A LORA-based wireless explosion-proof manual alarm button according to claim 2, characterized in that, One end of the indicator light circuit is connected to the V_CPU signal, and the other end is connected between pin 41 of the main control chip D1. The indicator light circuit includes a light-emitting diode HL1 and a resistor R14 connected in series.

6. The LORA-based wireless explosion-proof manual alarm button according to claim 1, characterized in that, The transformer and filter circuit includes a rectifier bridge N1, a common-mode filter L1, an LC filter branch, and a step-down chip N2 connected in sequence. The rectifier bridge N1 is connected to the input DC 24V voltage. After being filtered by the rectifier bridge N1, the common-mode filter L1, and the LC filter branch, the voltage is stepped down to DC 3.3V by the step-down chip N2.

7. A LORA-based wireless explosion-proof manual alarm button according to claim 6, characterized in that, A capacitor C28, a variable resistor VP1, and a capacitor C14 are connected in parallel between the input terminals of the rectifier bridge N1. The two input terminals are connected in series with capacitors C19 and C21, respectively, and then grounded. The input terminals of the rectifier bridge N1 are also connected in series with resistors R18 and R21, respectively, and then connected to the input DC 24V voltage. The output terminal of the rectifier bridge N1 is connected in parallel with resistor R19, then connected in series with diode VD1, and then connected to the common-mode filter L1.

8. A LORA-based wireless explosion-proof manual alarm button according to claim 6, characterized in that, The LC filter branch includes capacitors C15 and C17 connected in parallel. The two ends of capacitors C15 and C17 are connected through inductors L2 and L3 respectively to form a π-type LC filter branch.

9. A LORA-based wireless explosion-proof manual alarm button according to claim 6, characterized in that, Pin 5 of the step-down chip N2 is connected to ground via capacitors C18 and C26 in series. Resistor R17 is connected in series between pins 4 and 5. Pin 4 is connected to ground via resistor R22 in series. Pin 6 is connected to pin 3 via inductor L4 in series, and then connected to pin 3 via capacitor C25 and resistor R10 in series. Pin 3 is also connected to ground via resistor R20 in series. Pin 6 outputs the V_CPU signal, pin 2 is grounded, and it also outputs the G_CPU signal. Capacitors C23 and C24 are connected in parallel between pin 6 and pin 2. Capacitor C22 is connected in series between pins 1 and 6.

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