Liquid crystal handwriting board

Abstract

The utility model discloses a liquid crystal handwriting board, which comprises a power grid power supply output module, an energy storage battery, a power supply conversion circuit, a control circuit, an infrared sensor circuit and a liquid crystal film, and the first output end of the power grid power supply output module, the output end of the energy storage battery and the input end of the power supply conversion circuit are mutually connected. The power conversion circuit is used for outputting a power supply to the liquid crystal film, the control circuit and the infrared sensor circuit; a first electric quantity detection end of the control circuit is connected with an electric quantity detection end of the power grid power supply output module, a second electric quantity detection end of the control circuit is connected with an electric quantity detection end of the energy storage battery, and a first control end of the control circuit is connected with a controlled end of the infrared sensor circuit. When a power grid is powered off, the liquid crystal handwriting board can still achieve a local erasing function.

Description

Technical Field

[0001] This utility model relates to the field of liquid crystal film technology, and in particular to a liquid crystal handwriting tablet. Background Technology

[0002] Most LCD handwriting tablets with partial erase functionality are currently powered by an adapter, while some products have a small internal battery for one-button erase. In the event of a power outage, although the one-button erase function can be activated using this small battery, the partial erase function will be unavailable. Utility Model Content

[0003] The main purpose of this invention is to propose a liquid crystal handwriting tablet that can still perform partial erasure function when the power grid is interrupted.

[0004] To achieve the above objectives, this utility model proposes a liquid crystal handwriting tablet, including a mains power output module, an energy storage battery, a power conversion circuit, a control circuit, an infrared sensor circuit, and a liquid crystal film. The first output terminal of the mains power output module, the output terminal of the energy storage battery, and the input terminal of the power conversion circuit are interconnected. The power conversion circuit is used to output power to the liquid crystal film, the control circuit, and the infrared sensor circuit. The first power detection terminal of the control circuit is connected to the power detection terminal of the mains power output module, the second power detection terminal of the control circuit is connected to the power detection terminal of the energy storage battery, and the first control terminal of the control circuit is connected to the controlled terminal of the infrared sensor circuit.

[0005] Preferably, the power conversion circuit includes a power conversion chip, resistors R13, R14, R16, R17, R32, and R60, capacitors EC3, C12, C21, C22, and C24, inductor L1, transistor Q8, transistor Q9, diode D1, and diode D7; the anode of diode D1 is used to connect to the mains power output module, the anode of diode D7 is used to connect to the energy storage battery, the cathodes of diode D1 and D7, the first terminal of capacitor EC3, the first terminal of resistor R16, and the source of transistor Q9 are interconnected; the second terminal of resistor R16, the first terminal of resistor R60, and the collector of transistor Q8 are interconnected, the base of transistor Q8, the second terminal of resistor R32, and the first terminal of capacitor C12 are interconnected, and the first terminal of resistor R32 is used to input a switch start signal; The drain of transistor Q9, the first terminal of resistor R13, and the VIN pin of the power conversion chip are interconnected. The SW pin of the power conversion chip, the first terminal of capacitor C24, and the first terminal of inductor L1 are interconnected. The second terminal of capacitor C24 is connected to the BST pin of the power conversion chip. The EN pin of the power conversion chip is connected to the second terminal of resistor R13. The FB pin of the power conversion chip, the second terminal of resistor R14, and the first terminal of resistor R17 are interconnected. The second terminal of inductor L1, the first terminal of resistor R14, the first terminal of capacitor C22, and the first terminal of capacitor C21 are interconnected. Their connection nodes are used to provide power to the control circuit and the infrared sensor circuit. The second terminals of capacitor EC3, capacitor C12, the GND pin of the power conversion chip, resistor R17, capacitor C22, and capacitor C21 are all grounded.

[0006] Preferably, the control circuit includes a control chip, resistors R36, R37, R85, R86, capacitors C1 and C72. The first terminal of resistor R36 is the first power detection terminal of the control circuit. The second terminal of resistor R36, the first terminal of resistor R37, the first terminal of capacitor C1, and the first voltage detection pin of the control chip are interconnected. The first terminal of resistor R85 is the second power detection terminal of the control circuit. The second terminal of resistor R85, the first terminal of resistor R86, the first terminal of capacitor C72, and the second voltage detection pin of the control chip are interconnected. The second terminals of resistor R37, capacitor C1, resistor R86, and capacitor C72 are all grounded.

[0007] Preferably, the infrared sensor circuit includes a resistor R15, a transistor Q11, and a diode D6. The first terminal of the resistor R15 is connected to the source of the transistor Q11, and its connection node is used to input the power supply of the infrared sensor circuit. The second terminal of the resistor R15 is connected to the gate of the transistor Q11, and its connection node is the controlled terminal of the infrared sensor circuit. The drain of the transistor Q11 is connected to the anode of the diode D6, and the cathode of the diode D6 is used to output the power supply of the infrared sensor.

[0008] Preferably, the LCD handwriting tablet also includes a charging circuit for charging the energy storage battery, the input terminal of the charging circuit being connected to the second output terminal of the mains power output module, and the output terminal of the charging circuit being connected to the input terminal of the energy storage battery.

[0009] Preferably, the charging circuit includes a charging chip, a resistor R50, a capacitor C26, and a capacitor C28. The VIN pin and EN pin of the charging chip, the first end of the resistor R50, and the first end of the capacitor C26 are interconnected, and their connection node is the input terminal of the charging circuit. The second end of the resistor R50 is connected to the CS pin of the charging chip, and the BAT pin of the charging chip is connected to the first end of the capacitor C28. Their connection node is used to output charging power to the energy storage battery. The second end of the capacitor C26, the GND pin of the charging chip, and the second end of the capacitor C28 are all grounded.

[0010] Preferably, the charging circuit further includes resistors R100 and R101. The first end of resistor R100, the first end of capacitor C26, the first end of resistor R50, the VIN pin of the charging chip, and the EN pin of the charging chip are interconnected. The second end of resistor R100 is connected to the first end of resistor R101. The connection node is used to output a charging protection signal. The second end of resistor R101 is grounded.

[0011] Preferably, the mains power output module includes a DC power adapter and a DC socket connected in sequence. The DC power adapter is used to input mains power, and the DC socket is used to output mains power.

[0012] Preferably, the LCD handwriting tablet also includes a Schottky diode D2, which is connected in series between the mains power output module and the power conversion circuit, and the cathode of the Schottky diode D2 is connected to the power conversion circuit.

[0013] Preferably, the LCD handwriting tablet also includes a Schottky diode D3, which is connected in series between the energy storage battery and the power conversion circuit, and the cathode of the Schottky diode D2 is connected to the power conversion circuit.

[0014] When the mains power output module of this LCD writing tablet is connected to AC power, electrical energy flows sequentially through the mains power output module and the power conversion circuit to the LCD film, control circuit, and infrared sensor circuit, respectively. This powers the control circuit and the infrared sensor circuit, keeping the infrared sensor circuit powered on, thus enabling the LCD writing tablet to perform partial erasure. In the event of a power outage, the power supply path, including the mains power output module, is disconnected. The energy storage battery then provides power to the LCD film, control circuit, and infrared sensor circuit, keeping the infrared sensor circuit powered on. Therefore, even during a power outage, this LCD writing tablet can still perform partial erasure. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an embodiment of the liquid crystal handwriting tablet of this utility model;

[0016] Figure 2 This is a schematic diagram of another embodiment of the liquid crystal handwriting tablet of this utility model;

[0017] Figure 3 for Figure 1 A schematic diagram of the circuit structure of an embodiment of a power conversion circuit;

[0018] Figure 4 for Figure 2 A schematic diagram of the circuit structure of one embodiment of the charging circuit;

[0019] Figure 5 for Figure 1 A schematic diagram of the circuit structure of one embodiment of the control circuit;

[0020] Figure 6 for Figure 1 A schematic diagram of the circuit structure of one embodiment of the mid-infrared sensor circuit. Detailed Implementation

[0021] The solutions in the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this utility model, and not all of them. Based on the embodiments of this utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of this utility model.

[0022] See Figure 1This utility model proposes a liquid crystal handwriting tablet, including a mains power output module 100, an energy storage battery 200, a power conversion circuit 300, a control circuit 400, an infrared sensor circuit 500, and a liquid crystal film (not shown in the figure). The first output terminal of the mains power output module 100, the output terminal of the energy storage battery 200, and the input terminal of the power conversion circuit 300 are interconnected. The power conversion circuit 300 is used to output power to the liquid crystal film, the control circuit 400, and the infrared sensor circuit 500. The first power detection terminal of the control circuit 400 is connected to the power detection terminal of the mains power output module 100, the second power detection terminal of the control circuit 400 is connected to the power detection terminal of the energy storage battery 200, and the first control terminal of the control circuit 400 is connected to the controlled terminal of the infrared sensor circuit 500.

[0023] When the mains power output module 100 is connected to AC power, electrical energy flows sequentially through the mains power output module 100 and the power conversion circuit 300 to the liquid crystal film, control circuit 400, and infrared sensor circuit 500, respectively. This powers the control circuit 400 and the infrared sensor circuit 500, keeping the infrared sensor circuit 500 powered on and supplying power to the infrared sensor (not shown in the figure), thus enabling the liquid crystal writing tablet to perform partial erasure. In the event of a power outage, the power supply path, including the mains power output module 100, is disconnected. The energy storage battery 200, through the power conversion circuit 300, provides power to the liquid crystal film, control circuit 400, and infrared sensor circuit 500, keeping the infrared sensor circuit 500 powered on and supplying power to the infrared sensor. Therefore, even during a power outage, this liquid crystal writing tablet can still perform partial erasure.

[0024] It is worth mentioning that, in order to retain the LCD handwriting tablet for partial erasing while maintaining operation for a longer period of time during a power outage, the control circuit 400 in this utility model also detects the remaining power status of the grid power output module 100 and the energy storage battery 200.

[0025] When the mains power supply is good, the control circuit 400 does not respond to the detected remaining power status.

[0026] When the power grid fails, the control circuit 400 detects that the mains power output module 100 has no remaining power and continues to monitor the remaining power status of the energy storage battery 200. It does not respond to the detected remaining power status until the control circuit 400 detects that the remaining power of the energy storage battery 200 has reached a preset threshold. At this point, the control circuit 400 controls the infrared sensor circuit 500 to enter a power-down state, stopping power supply to the infrared sensor. This temporarily disables the partial erase function of the LCD handwriting tablet, extending the tablet's operating time. In this embodiment, the control circuit can detect the remaining power status of the energy storage battery 200 in several ways. For example, it can determine the remaining power status by detecting the output voltage of the energy storage battery 200, or it can configure a dedicated power detector (not shown) to detect the remaining power of the energy storage battery 200.

[0027] See Figure 2 In a preferred embodiment, the LCD handwriting tablet further includes a charging circuit 600 for charging the energy storage battery 200. The input terminal of the charging circuit 600 is connected to the second output terminal of the mains power output module 100, and the output terminal of the charging circuit 600 is connected to the input terminal of the energy storage battery 200. Preferably, the energy storage battery 200 is a lithium battery.

[0028] It's easy to understand that when the mains power output module 100 is connected to AC power, in addition to providing power to the LCD panel, control circuit 400, and infrared sensor circuit 500 through the power conversion circuit 300, the energy storage battery 200 can also be charged through the charging circuit 600. Thus, when the mains power fails, the pre-charged energy storage battery 200 can directly provide power to the LCD panel, control circuit 400, and infrared sensor circuit 500, which is very convenient.

[0029] Please see Figure 4 In one specific embodiment, preferably, the charging circuit 600 includes a charging chip U2, a resistor R50, a capacitor C26, and a capacitor C28. The VIN pin and EN pin of the charging chip U2, the first end of the resistor R50, and the first end of the capacitor C26 are interconnected, and their connection node is the input terminal of the charging circuit 600. The second end of the resistor R50 is connected to the CS pin of the charging chip U2, and the BAT pin of the charging chip U2 is connected to the first end of the capacitor C28. Their connection node is used to output charging power to the energy storage battery 200. The second end of the capacitor C26, the GND pin of the charging chip U2, and the second end of the capacitor C28 are all grounded.

[0030] Furthermore, the charging circuit 600 also includes resistors R100 and R101. The first end of resistor R100, the first end of capacitor C26, the first end of resistor R50, the VIN pin of charging chip U2, and the EN pin of charging chip U2 are interconnected. The second end of resistor R100 is connected to the first end of resistor R101. The connection node is used to output a charging protection signal. The second end of resistor R101 is grounded.

[0031] Here, the charging chip U2 is a dedicated lithium battery charging integrated circuit with constant current, constant voltage, and trickle charging functions. It connects to an LED (not shown) via the CHRG and STDBY pins to display the charging status; for example, a red LED indicates charging, and a green LED indicates a full charge. Furthermore, the dedicated lithium battery charging circuit of the charging chip U2 supports safe charging of lithium batteries, operating within an ambient temperature range of 0–45 degrees Celsius. Charging will stop outside this temperature range to ensure lithium battery safety. The VIN pin of the charging chip U2 connects to the mains power output module 100, and the EN pin is the enable pin connected to the input power supply. The CS pin of the charging chip U2 is the current limiting control pin; different charging currents can be set by adjusting the resistance value of resistor R50. The BAT pin of the charging chip U2 is connected to the lithium battery charging input. When the lithium battery is within the normal voltage range and ambient temperature conditions, it can be charged normally. The TEMP pin of the charging chip U2 is connected to the negative temperature coefficient thermistor NTC. Usually, this negative temperature coefficient thermistor NTC is installed on the lithium battery, so that the actual temperature of the lithium battery can be fed back to the TEMP pin of the charging chip U2.

[0032] Please see Figure 3In a preferred embodiment, the power conversion circuit 300 includes a power conversion chip U5, resistors R13, R14, R16, R17, R32, and R60, capacitors EC3, C12, C21, C22, and C24, an inductor L1, transistors Q8 and Q9, diodes D1 and D7; the anode of diode D1 is connected to the mains power output module 100, the anode of diode D7 is connected to the energy storage battery 200, the cathodes of diode D1 and D7, the first terminal of capacitor EC3, the first terminal of resistor R16, and the source of transistor Q9 are interconnected; the second terminal of resistor R16, the first terminal of resistor R60, and the collector of transistor Q8 are interconnected, the base of transistor Q8, the second terminal of resistor R32, and the first terminal of capacitor C12 are interconnected, and the first terminal of resistor R32 is used to input a switch start signal; The drain of transistor Q9, the first terminal of resistor R13, and the VIN pin of power conversion chip U5 are interconnected. The SW pin of power conversion chip U5, the first terminal of capacitor C24, and the first terminal of inductor L1 are interconnected. The second terminal of capacitor C24 is connected to the BST pin of power conversion chip U5. The EN pin of power conversion chip U5 is connected to the second terminal of resistor R13. The FB pin of power conversion chip U5, the second terminal of resistor R14, and the first terminal of resistor R17 are interconnected. The second terminal of inductor L1, the first terminal of resistor R14, the first terminal of capacitor C22, and the first terminal of capacitor C21 are interconnected. Their connection nodes are used to provide power to control circuit 400 and infrared sensor circuit 500. The second terminals of capacitor EC3, capacitor C12, the GND pin of power conversion chip U5, the second terminals of resistor R17, capacitor C22, and capacitor C21 are all grounded.

[0033] In this embodiment, under normal power supply conditions, the voltage of the mains power output module 100 is higher than that of the lithium battery, so under normal power supply conditions, the mains power output module 100 mainly provides power. Transistors Q8 and Q9 form an electronic switch circuit. The base of transistor Q8 is connected to the control pin of the control chip (not shown in the figure) through resistor R32, and the collector of transistor Q8 is connected to the gate of transistor Q9 through resistor R60. When the power is on, the control chip provides a high level through resistor R32. After transistor Q8 is turned on, the collector voltage becomes low, and the gate of transistor Q9 becomes low. Thus, the drain and source of transistor Q9 are connected, and the input power enters the VIN pin of the power conversion chip U5. The power conversion chip U5 is a DC-DC converter chip that converts the input voltage to +5V for the control chip and the infrared sensor circuit 500. Inductor L1 is an inductor coil. Resistors R14 and R17 are connected in series to form a voltage divider circuit. The intermediate connection point is connected to the FB pin of the power conversion chip U5 to form a positive feedback circuit, so that the output voltage is constant at +5V. Capacitors EC3, C22, and C21 are input and output capacitors that play a role in voltage stabilization and filtering.

[0034] Please see Figure 5 In a preferred embodiment, the control circuit 400 includes a control chip, resistors R36, R37, R85, R86, capacitors C1 and C72. The first end of resistor R36 is the first power detection terminal of the control circuit 400. The second end of resistor R36, the first end of resistor R37, the first end of capacitor C1, and the first voltage detection pin GPIO1 of the control chip are interconnected. The first end of resistor R85 is the second power detection terminal of the control circuit 400. The second end of resistor R85, the first end of resistor R86, the first end of capacitor C72, and the second voltage detection pin GPIO2 of the control chip are interconnected. The second ends of resistor R37, capacitor C1, resistor R86, and capacitor C72 are all grounded.

[0035] Here, resistors R85 and R86 are connected in series to form a voltage divider circuit. The voltage is regulated and filtered by capacitor C72 before being input to the GPIO2 pin of the control chip. This GPIO2 pin has an analog-to-digital (ADC) conversion function, and the lithium battery voltage can be obtained after the ADC conversion. Similarly, resistors R36 and R37 are connected in series to form a voltage divider circuit. The voltage is regulated and filtered by capacitor C1 before being input to the GPIO1 pin of the control chip. This GPIO1 pin also has an ADC conversion function, and the output voltage of the mains power output module 100 can be obtained after the ADC conversion. If a power outage occurs, a low voltage will be obtained at GPIO1 (e.g., the maximum lithium battery voltage is 8.4V, and the output voltage of the mains power output module 100 is 12V). This tells the control chip that the lithium battery is currently being powered. Combined with the lithium battery detection circuit mentioned above, the power supply to the infrared sensor circuit 500 can be controlled. When the lithium battery voltage drops to a certain level, the control chip can shut off the power supply to the infrared sensor. This will cause the LCD handwriting tablet to switch from partial erase mode to one-key clear mode, ensuring that the LCD handwriting tablet still has the one-key clear function even when the lithium battery voltage drops to a certain value.

[0036] Please see Figure 6 In a preferred embodiment, the infrared sensor circuit 500 includes a resistor R15, a transistor Q11, and a diode D6. The first end of the resistor R15 is connected to the source of the transistor Q11, and its connection node is used to input the power supply of the infrared sensor circuit 500. The second end of the resistor R15 is connected to the gate of the transistor Q11, and its connection node is the controlled terminal of the infrared sensor circuit 500. The drain of the transistor Q11 is connected to the anode of the diode D6, and the cathode of the diode D6 is used to output the power supply of the infrared sensor.

[0037] In this embodiment, under normal power supply conditions, the GPIO3 pin of the control chip outputs a low level, and the source and drain of transistor Q11 are turned on. Therefore, the +5V power supply powers the infrared sensor (not shown) through transistor Q11 and diode D6. When the mains power supply is normal, transistor Q11 continues to conduct normally. When the mains power is lost, the control chip... Figure 5 The voltage detection circuit shown starts detecting the lithium battery voltage. When the lithium battery voltage is higher than a certain value, transistor Q11 continues to conduct to power the infrared sensor. The LCD handwriting board has a partial erase function. When the lithium battery voltage drops to a certain value, the GPIO3 port of the control chip outputs a high level, transistor Q11 turns off, and the +5V power supply cannot power the infrared sensor. At this time, the partial erase function of the LCD handwriting board is turned off, but the LCD handwriting board still retains the one-key clear function.

[0038] Please see Figure 2In a preferred embodiment, the above-mentioned mains power output module 100 includes a DC power adapter 110 and a DC socket 120 connected in sequence. The DC power adapter 110 is used to input mains power, and the DC socket 120 is used to output mains power.

[0039] It is worth mentioning that, to enhance circuit stability, this LCD handwriting tablet also includes a Schottky diode D2, which is connected in series between the mains power output module 100 and the power conversion circuit 300, with the cathode of the Schottky diode D2 connected to the power conversion circuit 300. Similarly, this LCD handwriting tablet also includes a Schottky diode D3, which is connected in series between the energy storage battery 200 and the power conversion circuit 300, with the cathode of the Schottky diode D2 connected to the power conversion circuit 300.

[0040] This technical solution uses a Schottky diode to connect the DC power adapter 110 and the lithium battery. By sampling and detecting the voltage of the DC power adapter 110 and the lithium battery, and intelligently controlling the power supply to the infrared sensor by setting appropriate values ​​within a range, it achieves the ability to continuously power the LCD handwriting tablet for several hours for partial erasure after a power outage. When the battery voltage drops to a certain value, the partial erasure function is turned off, while the one-key clear function continues to provide power for tens of hours. This satisfies the requirement that the LCD handwriting tablet can continue to perform partial erasure and one-key clear functions after a power outage.

[0041] It should be noted that the technical solutions of the various embodiments of this utility model can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this utility model.

[0042] The above description is only a part or preferred embodiment of this utility model. Neither the text nor the drawings should limit the scope of protection of this utility model. All equivalent structural transformations made using the content of this utility model specification and drawings under the overall concept of this utility model, or direct / indirect applications in other related technical fields, are included within the scope of protection of this utility model.

Claims

1. A liquid crystal handwriting tablet, characterized in that, It includes a grid power output module, an energy storage battery, a power conversion circuit, a control circuit, an infrared sensor circuit, and a liquid crystal film. The first output terminal of the grid power output module, the output terminal of the energy storage battery, and the input terminal of the power conversion circuit are interconnected. The power conversion circuit is used to output power to the liquid crystal film, the control circuit, and the infrared sensor circuit. The first power detection terminal of the control circuit is connected to the power detection terminal of the mains power output module, the second power detection terminal of the control circuit is connected to the power detection terminal of the energy storage battery, and the first control terminal of the control circuit is connected to the controlled terminal of the infrared sensor circuit.

2. The liquid crystal handwriting tablet according to claim 1, characterized in that, The power conversion circuit includes a power conversion chip, resistors R13, R14, R16, R17, R32, and R60, capacitors EC3, C12, C21, C22, and C24, inductor L1, transistors Q8 and Q9, diodes D1 and D7. The anode of diode D1 is used to connect to the mains power output module, and the anode of diode D7 is used to connect to the energy storage battery. The cathodes of diode D1 and D7, the first terminal of capacitor EC3, the first terminal of resistor R16, and the source of transistor Q9 are interconnected. The second terminal of resistor R16, the first terminal of resistor R60, and the collector of transistor Q8 are interconnected. The base of transistor Q8, the second terminal of resistor R32, and the first terminal of capacitor C12 are interconnected. The first terminal of resistor R32 is used to input a switch start signal. The drain of transistor Q9, the first terminal of resistor R13, and the VIN pin of the power conversion chip are interconnected. The SW pin of the power conversion chip, the first terminal of capacitor C24, and the first terminal of inductor L1 are interconnected. The second terminal of capacitor C24 is connected to the BST pin of the power conversion chip. The EN pin of the power conversion chip is connected to the second terminal of resistor R13. The FB pin of the power conversion chip, the second terminal of resistor R14, and the first terminal of resistor R17 are interconnected. The second terminal of inductor L1, the first terminal of resistor R14, the first terminal of capacitor C22, and the first terminal of capacitor C21 are interconnected, and their connection node is used to provide power to the control circuit and the infrared sensor circuit; the second terminal of capacitor EC3, the second terminal of capacitor C12, the GND pin of the power conversion chip, the second terminal of resistor R17, the second terminal of capacitor C22, and the second terminal of capacitor C21 are all grounded.

3. The liquid crystal handwriting tablet according to claim 1, characterized in that, The control circuit includes a control chip, resistors R36, R37, R85, R86, capacitors C1 and C72. The first terminal of resistor R36 is the first power detection terminal of the control circuit. The second terminal of resistor R36, the first terminal of resistor R37, the first terminal of capacitor C1, and the first voltage detection pin of the control chip are interconnected. The first terminal of resistor R85 is the second power detection terminal of the control circuit. The second terminal of resistor R85, the first terminal of resistor R86, the first terminal of capacitor C72, and the second voltage detection pin of the control chip are interconnected. The second terminals of resistor R37, capacitor C1, resistor R86, and capacitor C72 are all grounded.

4. The liquid crystal handwriting tablet according to claim 1, characterized in that, The infrared sensor circuit includes a resistor R15, a transistor Q11, and a diode D6. The first terminal of the resistor R15 is connected to the source of the transistor Q11, and its connection node is used to input the power supply of the infrared sensor circuit. The second terminal of the resistor R15 is connected to the gate of the transistor Q11, and its connection node is the controlled terminal of the infrared sensor circuit. The drain of the transistor Q11 is connected to the anode of the diode D6, and the cathode of the diode D6 is used to output the power supply of the infrared sensor.

5. The liquid crystal handwriting tablet according to claim 1, characterized in that, The LCD handwriting tablet also includes a charging circuit for charging the energy storage battery. The input terminal of the charging circuit is connected to the second output terminal of the mains power output module, and the output terminal of the charging circuit is connected to the input terminal of the energy storage battery.

6. The liquid crystal handwriting tablet according to claim 5, characterized in that, The charging circuit includes a charging chip, a resistor R50, a capacitor C26, and a capacitor C28. The VIN pin and EN pin of the charging chip, the first end of the resistor R50, and the first end of the capacitor C26 are interconnected, and their connection node is the input terminal of the charging circuit. The second end of the resistor R50 is connected to the CS pin of the charging chip, and the BAT pin of the charging chip is connected to the first end of the capacitor C28. Their connection node is used to output charging power to the energy storage battery. The second end of the capacitor C26, the GND pin of the charging chip, and the second end of the capacitor C28 are all grounded.

7. The liquid crystal handwriting tablet according to claim 6, characterized in that, The charging circuit also includes resistors R100 and R101. The first end of resistor R100, the first end of capacitor C26, the first end of resistor R50, the VIN pin of the charging chip, and the EN pin of the charging chip are interconnected. The second end of resistor R100 is connected to the first end of resistor R101. The connection node is used to output a charging protection signal. The second end of resistor R101 is grounded.

8. The liquid crystal handwriting tablet according to any one of claims 1-7, characterized in that, The mains power output module includes a DC power adapter and a DC socket connected in sequence. The DC power adapter is used to input mains power, and the DC socket is used to output the mains power.

9. The liquid crystal handwriting tablet according to any one of claims 1-7, characterized in that, The LCD handwriting tablet also includes a Schottky diode D2, which is connected in series between the mains power output module and the power conversion circuit, and the cathode of the Schottky diode D2 is connected to the power conversion circuit.

10. The liquid crystal handwriting tablet according to any one of claims 1-7, characterized in that, The LCD handwriting tablet also includes a Schottky diode D3, which is connected in series between the energy storage battery and the power conversion circuit, and the cathode of the Schottky diode D2 is connected to the power conversion circuit.

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