Method and apparatus for preventing eye burn from a robotic projector

Abstract

This invention discloses a method and device for preventing eye burns from a robotic projector, comprising: a light emitting group and a light receiving group located next to the projector lens compartment door. The light emitting group and the light receiving group are connected in a pair of tubes: a left emitting element and a left receiving element, a middle emitting element and a middle receiving element, and a right emitting element and a right receiving element. This invention adjusts the transmission and reception distance to approximately 0.5 to 1 meter by adjusting the resistance values ​​of six resistors in the circuit. Regardless of the direction from which an intruder approaches, the projector lens compartment door closes promptly. Simultaneously, for safety, the projector's light source is also turned off, effectively and promptly protecting people's eyes and ensuring the safe use of the projector.

Description

Technical Field

[0001] This invention relates to robots, and more particularly to a method and apparatus for preventing eye burns in robot projectors. Background Technology

[0002] In the existing technology, no technical literature reports have been found regarding methods and devices for preventing eye burns from robotic projectors. The applicant found a patent document related to projector assembly, invention patent application title: Projector Installation Assembly, application number: 201711199701.2. The working principle is as follows: when the projector is working normally, the projector lifting channel is in the open state. When the projector is not working, the lifting drive unit drives the lifting sliding plate to move, thereby moving the projector above the sliding sealing cover. Then, the sliding sealing drive unit drives the sliding sealing cover to move, thereby closing the projector lifting channel, thus achieving a good sealing and preservation effect for the projector.

[0003] Analysis shows that this patent cannot solve the problem of providing immediate protection when someone comes in front of the projector lens and is at risk of having their eyes burned by the projector's strong light.

[0004] In light of the above, people currently expect a technology that can immediately shut off the projector's light source when someone comes in front of the projector lens, especially active children who are likely to accidentally enter the projector's bright light area and potentially get their eyes burned by the projector's bright light. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies that "cannot provide protective measures when someone comes in front of the projector lens and may be burned in the eyes by the projector's strong light," and to design and manufacture a method and device for preventing eye burns from a robotic projector.

[0006] This invention is achieved by adopting the following technical solutions.

[0007] A method for preventing eye burns from a robotic projector includes: Step 1: Install an openable and closable projector lens compartment door in front of the projector lens, driven by the second microcomputer on the second motherboard. Step 2: Set up a light emitting group and a light receiving group next to the projector lens compartment door; the light emitting group includes a left emitting unit, a right emitting unit, and a middle emitting unit, and the light receiving group includes a left receiving unit, a right receiving unit, and a middle receiving unit; the left emitting unit and the left receiving unit are in a pair, the middle emitting unit and the middle receiving unit are in a pair, and the right emitting unit and the right receiving unit are in a pair. Step 3: Set the projector to be started and stopped by the second microcomputer, set the projector signal to be input by the first microcomputer, and set the projector operation instructions to be input by the touch keyboard of the LCD unit of the first microcomputer; Step 4: The first program memory of the first microcomputer on the first motherboard contains an LCD touch instruction program module, a communication program module with the second computer, a MIPI to RGB conversion program module, and a projection driver setting program module. The instructions of each program module are adapted to be loaded and executed by the first processor. The second program memory of the second microcomputer on the second motherboard contains a projector switch program module, a projector lens compartment switch program module, a projector fan driver program module, a left transmitter program module, a middle transmitter program module, a right transmitter program module, a left receiver program module, a middle receiver program module, and a right receiver program module. The instructions of each program module are adapted to be loaded and executed by the second processor. Step 5: Set the manual on / off buttons of the projector on the display touch screen on the robot's head. The first microcomputer calls the LCD touch instruction program module to select the content to be projected, calls the MIPI to RGB program module to provide the projector with a suitable image format, calls the projection driver setting program module to set the playback parameters, and calls the communication program module with the second computer to transmit the playback parameter data to the second microcomputer. Step Six: The second microcomputer calls the left transmitting program module, the middle transmitting program module, and the right transmitting program module to continuously output pulse signals from their three output pins within a unit time, and stores the number of pulses in the first temporary storage area of ​​the second program running variable register. At the same time, the second microcomputer inputs the pulses received by the left receiving unit, the receiving unit, and the middle receiving unit into its three input pins, respectively, and counts the number of pulses within a unit time. The counting result of the left receiving unit is stored in the second temporary storage area of ​​the second program running variable register, the counting result of the middle receiving unit is stored in the third temporary storage area of ​​the second program running variable register, and the counting result of the right receiving unit is stored in the fourth temporary storage area of ​​the second program running variable register. Then, the left receiving program module, the middle receiving program module, and the right receiving program module are called to compare the counting results of each temporary storage area with the data in the first temporary storage area. Step 7: Next, set the comparison error threshold to 1 / 300. When all comparison results are greater than the error threshold, it is considered that no human body is near the projector. When any comparison result is less than the error threshold, it is considered that a human body is near the projector.

[0008] The unit time selection range is between 0.2 seconds and 1 second, where a value is selected.

[0009] Step six describes outputting a pulse signal per unit time, the frequency of which is selected between 1KHz and 10KHz.

[0010] When a human body approaches the projector as described in step seven, the second microcomputer calls the projector switch program module to compare the count results of the second, third, and fourth temporary storage areas three times with the data in the first temporary storage area. If the count result of any temporary storage area is less than the error threshold after three consecutive comparisons with the data in the first temporary storage area, the projector lens compartment door switch program module and the projector fan driver program module are called to turn off the projector, the projector lens compartment door, and the projector fan.

[0011] A device for preventing eye burns from a robot projector, the device comprising: a projector disposed inside a robot head, a display touch screen in front of the robot head, and a projector lens compartment door behind the robot head, wherein opening the projector lens compartment door reveals the projector. A second motherboard is installed inside the robot's head, on which a second microcomputer is mounted; On one side of the projector lens compartment, a light emitting group and a light receiving group are set up. The light emitting group is connected to the following circuit units: left emitting unit, right emitting unit, and middle emitting unit. The light receiving group is connected to the following circuit units: left receiving unit, right receiving unit, and middle receiving unit. The left emitting element and the left receiving element are a pair of transistors, the middle emitting element and the middle receiving element are a pair of transistors, and the right emitting element and the right receiving element are a pair of transistors. The projector is turned on and off by a second microcomputer; The opening and closing of the projector lens compartment door is controlled by a second microcomputer; The left transmitting unit, right transmitting unit, and middle transmitting unit are circuitically connected to the second microcomputer. The left receiving unit, right receiving unit, and middle receiving unit are circuitically connected to the second microcomputer.

[0012] The projector fan, located next to the projector lens compartment door, is driven by a second microcomputer.

[0013] The robot's head is equipped with a first motherboard, which has a first microcomputer. The first microcomputer is connected to a display touch screen, receives projection playback commands entered on the display touch screen, and communicates with a second microcomputer through its own GPIO and PI12 pins.

[0014] The left receiving unit circuit is connected to a left shaper U11 at its end, which shapes the signal output by the first operational amplifier U1 and then outputs a potential of either "1" or "0" to a pin of the second microcomputer. The right receiving unit circuit is connected to a right shaper U31, which shapes the signal output by the third operational amplifier U3 and then outputs a potential of either "1" or "0" to another pin of the second microcomputer. The end of the receiving unit circuit is connected to a shaper U21, which shapes the signal output by the second operational amplifier U2 and then outputs a potential of either "1" or "0" to another pin of the second microcomputer.

[0015] A power supply is installed inside the robot's head, which outputs DC12V power for the color light strip unit and the projector switch circuit unit, as well as DC5V power for the first microcomputer, the second microcomputer, and related circuits.

[0016] When the resistance of resistor R3 in the left receiving unit circuit is 1KΩ, the resistance of resistor R2 is selected between 20KΩ and 120KΩ. When the resistance of resistor R8 in the receiving unit circuit is 1KΩ, the resistance of resistor R7 should be selected between 20KΩ and 120KΩ. When the resistance of resistor R13 in the right receiving unit circuit is 1KΩ, the resistance of resistor R12 should be selected between 20KΩ and 120KΩ.

[0017] The advantage of this invention lies in its placement of the light emitting and receiving groups next to the projector lens compartment door. The left emitting and receiving elements, the middle emitting and receiving elements, and the right emitting and receiving elements are connected in a tube-to-tube configuration. By adjusting the transmission and reception distance to approximately 0.5 to 1 meter, the projector lens compartment door will close promptly regardless of the direction from which an intruder approaches. Simultaneously, for added safety, the projector's light source will be switched off, effectively and promptly protecting people's eyes and ensuring the safe use of the projector. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention.

[0019] Figure 1 This is a schematic diagram of the application of the method and device for preventing eye burns from the robot projector of the present invention on a robot carrier. Figure 2 This is a schematic diagram of the robot head, the specific installation location of the method and device for preventing eye burns from the robot projector of the present invention. Figure 3 This is a schematic diagram of the assembly structure of the method and device for preventing eye burns from the robot projector of the present invention inside the robot head; Figure 4This is an electrical schematic diagram of the method and apparatus for preventing eye burns in a robot projector according to the present invention; Figure 5 This is a block diagram illustrating the principle of the program module settings in the first microcomputer of the method and apparatus for preventing eye burns in a robot projector according to the present invention. Figure 6 This is a block diagram illustrating the principle of the program module settings in the second microcomputer of the method and apparatus for preventing eye burns in a robot projector according to the present invention. Detailed Implementation

[0020] The present invention will now be described in conjunction with specific embodiments.

[0021] like Figures 1-6 As shown, a method for preventing eye burns from a robotic projector includes: Step 1: Install an openable and closable projector lens compartment door 121 in front of the lens of the projector 125, which is driven by the second microcomputer 92 on the second motherboard 130. Step 2: Install a light emitting group 122 and a light receiving group 123 next to the projector lens compartment door 121; the light emitting group 122 includes a left emitting unit, a right emitting unit, and a middle emitting unit, and the light receiving group 123 includes a left receiving unit, a right receiving unit, and a middle receiving unit; the left emitting unit and the left receiving unit are in a pair, the middle emitting unit and the middle receiving unit are in a pair, and the right emitting unit and the right receiving unit are in a pair. Step 3: The projector 125 is set to start and stop by the second microcomputer 92, and the signal for setting the projector 125 is input by the first microcomputer 91; the operation instructions for setting the projector 125 are input by the touch keyboard of the LCD unit 102 of the first microcomputer 91. Step 4: The first program memory 911 of the first microcomputer 91 on the first motherboard 140 is loaded with an LCD touch instruction program module 1021, a communication program module 1011 with the second computer, a MIPI to RGB program module 9041 and a projection driver setting program module 1191. The instructions of each program module are adapted to be loaded and executed by the first processor 914. The second program memory 921 of the second microcomputer 92 on the second motherboard 130 contains a projector switch program module 1201, a projector lens compartment switch program module 1211, a projector fan driver program module 1221, a left transmitter program module 2001, a middle transmitter program module 2002, a right transmitter program module 2003, and a left receiver program module 3001, a middle receiver program module 3002, and a right receiver program module 3003. The instructions of each program module are adapted to be loaded and executed by the second processor 924. Step 5: Set the manual on / off button of the projector 125 on the display touch screen 127 of the robot head 12. The first microcomputer 91 calls the LCD touch instruction program module 1021 to select the content to be projected, calls the MIPI to RGB program module 9041 to provide the projector with a suitable image format, calls the projection driver setting program module 1191 to set the playback parameters, and calls the communication program module 1011 with the second computer to transmit the playback parameter data to the second microcomputer 92. Step Six: The second microcomputer 92 calls the left transmitting program module 2001, the middle transmitting program module 2002, and the right transmitting program module 2003 to continuously output pulse signals from their three output pins within a unit time, and stores the number of pulses in the first temporary storage area of ​​the second program running variable register 923. At the same time, the second microcomputer 92 inputs the pulses received by the left receiving unit, the receiving unit, and the middle receiving unit into its three input pins, respectively, and counts the number of pulses within a unit time. The counting result of the left receiving unit is stored in the second temporary storage area of ​​the second program running variable register 923, the counting result of the middle receiving unit is stored in the third temporary storage area of ​​the second program running variable register 923, and the counting result of the right receiving unit is stored in the fourth temporary storage area of ​​the second program running variable register 923. Then, the left receiving program module 3001, the middle receiving program module 3002, and the right receiving program module 3003 are called to compare the counting results of each temporary storage area with the data in the first temporary storage area. Step 7: Next, set the comparison error threshold to 1 / 300. When all comparison results are greater than the error threshold, it is considered that no human body is close to the projector 125. When any comparison result is less than the error threshold, it is considered that a human body is close to the projector 125.

[0022] The unit time selection range is between 0.2 seconds and 1 second, where a value is selected.

[0023] Step six describes outputting a pulse signal per unit time, the frequency of which is selected between 1KHz and 10KHz.

[0024] When a human body approaches the projector 125 as described in step seven, the second microcomputer 92 calls the projector switch program module 1201 to compare the counting results of the second, third, and fourth temporary storage areas three times with the data in the first temporary storage area. If the counting result of any temporary storage area is less than the error threshold after three consecutive comparisons with the data in the first temporary storage area, the projector lens compartment door switch program module 1211 and the projector fan driver program module 1221 are called to turn off the projector 125, the projector lens compartment door 121, and the projector fan 124.

[0025] A device for preventing eye burns from a robot projector, the device comprising: a projector 125 disposed inside a robot head 12, a display touch screen 127 in front of the robot head 12, and a projector lens compartment door 121 behind the robot head 12, wherein opening the projector lens compartment door 121 reveals the projector 125. A second motherboard 130 is installed inside the robot head 12, on which a second microcomputer 92 is mounted; On one side of the projector lens compartment 121, a light emitting group 122 and a light receiving group 123 are provided. The light emitting group 122 is connected to the following circuit units: a left emitting unit, a right emitting unit, and a middle emitting unit. The light receiving group 123 is connected to the following circuit units: a left receiving unit, a right receiving unit, and a middle receiving unit. The left emitting element and the left receiving element are a pair of transistors, the middle emitting element and the middle receiving element are a pair of transistors, and the right emitting element and the right receiving element are a pair of transistors. The projector 125 is turned on and off by the second microcomputer 92; The opening and closing of the projector lens compartment door 121 is controlled by the second microcomputer 92; The left transmitting unit, right transmitting unit, and middle transmitting unit are circuitically connected to the second microcomputer 92; The left receiving unit, right receiving unit, and middle receiving unit are circuitically connected to the second microcomputer 92.

[0026] The projector fan 124, located next to the projector lens compartment door 121, is driven by the second microcomputer 92.

[0027] The robot head 12 is equipped with a first motherboard 140, on which a first microcomputer 91 is mounted. The first microcomputer 91 is connected to a display touch screen 127, receives projection playback commands entered by the display touch screen 127, and also communicates with a second microcomputer 92 through its own GPIO and PI12 pins.

[0028] The left receiving unit circuit is connected to a left shaper U11 at its end, which shapes the signal output by the first operational amplifier U1 and then outputs a potential of either "1" or "0" to a pin of the second microcomputer 92. The right receiving unit circuit is connected to a right shaper U31, which shapes the signal output by the third operational amplifier U3 and then outputs a potential of either "1" or "0" to another pin of the second microcomputer 92. The end of the receiving unit circuit is connected to a shaper U21, which shapes the signal output by the second operational amplifier U2 and then outputs a potential of either "1" or "0" to another pin of the second microcomputer 92.

[0029] A power supply 105 is installed inside the robot head 12. The power supply 105 outputs DC12V power required by the color light strip unit 205 and the projector switch circuit unit 119, as well as DC5V power required by the first microcomputer 91, the second microcomputer 92 and related circuits.

[0030] When the resistance of resistor R3 in the left receiving unit circuit is 1KΩ, the resistance of resistor R2 is selected between 20KΩ and 120KΩ. When the resistance of resistor R8 in the receiving unit circuit is 1KΩ, the resistance of resistor R7 should be selected between 20KΩ and 120KΩ. When the resistance of resistor R13 in the right receiving unit circuit is 1KΩ, the resistance of resistor R12 should be selected between 20KΩ and 120KΩ.

[0031] like Figure 2 , Figure 3 As shown, the projector 125 is located on the back of the robot's head 12, typically facing a wall or screen. Since the robot of this invention is mostly used in homes, there is a high possibility that children will wander into the bright light of the projector. To prevent eye injuries, it is necessary to protect the eyes of those who wander into the bright light.

[0032] like Figure 4 As shown, for this purpose, we installed a light emitting group 122 and a light receiving group 123 next to the projector lens compartment door. The light emitting group 122 is connected to the following circuit units: left emitting unit, right emitting unit, and middle emitting unit. The light receiving group 123 is connected to the following circuit units: left receiving unit, right receiving unit, and middle receiving unit. The left emitting element and left receiving element are a pair, the middle emitting element and middle receiving element are a pair, and the right emitting element and right receiving element are a pair. We adjusted the transmission and reception distance to approximately 0.5 to 1 meter. Regardless of the direction from which an intruder approaches, the projector lens compartment door will close promptly. Simultaneously, for safety, the projector's light source will also be turned off, thus effectively and promptly protecting people's eyes and ensuring the safe use of the projector.

[0033] The specific adjustment method is as follows: Adjust the resistance values ​​of resistors R16, R19, and R21, which is to adjust the current of LED1, LED2, and LED3, and thus adjust the light sensing distance. The resistance value should be selected between 100Ω and 500Ω. Under DC 5V voltage, the sensing distance is about 0.5 meters to 1 meter, which can close the projector lens compartment door in time.

[0034] The left, middle, and right shapers in the diagram ensure that the waveform is a standard rectangular wave. When irregular spike waveforms come in, the counting results will deviate significantly. These noise waves are filtered out by software control.

[0035] The above description is only a preferred embodiment of the present invention. For those skilled in the art, there will be changes in specific implementation methods and application scope based on the ideas of the present invention. The content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for preventing eye burns from a robotic projector, characterized in that, The method includes: Step 1: Install an openable and closable projector lens compartment door (121) in front of the lens of the projector (125), which is driven by the second microcomputer (92) on the second motherboard (130); Step 2: Set up a light emitting group (122) and a light receiving group (123) next to the projector lens compartment door (121); the light emitting group (122) includes a left emitting unit, a right emitting unit, and a middle emitting unit, and the light receiving group (123) includes a left receiving unit, a right receiving unit, and a middle receiving unit; the left emitting unit and the left receiving unit are tube pairs, the middle emitting unit and the middle receiving unit are tube pairs, and the right emitting unit and the right receiving unit are tube pairs. Step 3: The projector (125) is set to start and stop by the second microcomputer (92), and the signal for setting the projector (125) is input by the first microcomputer (91); the operation instructions for setting the projector (125) are input by the touch keyboard of the LCD unit (102) of the first microcomputer (91); Step 4: The first program memory (911) of the first microcomputer (91) on the first motherboard (140) contains an LCD touch instruction program module (1021), a communication program module (1011) with the second computer, a MIPI to RGB program module (9041), and a projection driver setting program module (1191). The instructions of each program module are adapted to be loaded and executed by the first processor (914). The second program memory (921) of the second microcomputer (92) on the second motherboard (130) contains a projector switch program module (1201), a projector lens compartment switch program module (1211), a projector fan driver program module (1221), a left transmitter program module (2001), a middle transmitter program module (2002), a right transmitter program module (2003), and a left receiver program module (3001), a middle receiver program module (3002), and a right receiver program module (3003). The instructions of each program module are adapted to be loaded and executed by the second processor (924). Step 5: Set the manual on / off buttons of the projector (125) on the display touch screen (127) of the robot head (12). The first microcomputer (91) calls the LCD touch instruction program module (1021) to select the content to be projected, calls the MIPI to RGB program module (9041) to provide the projector with a suitable image format, calls the projection driver setting program module (1191) to set the playback parameters, and calls the communication program module (1011) with the second computer to transmit the playback parameter data to the second microcomputer (92). Step Six: The second microcomputer (92) calls the left transmitting program module (2001), the middle transmitting program module (2002), and the right transmitting program module (2003) to continuously output pulse signals from its three output pins within a unit time, and stores the number of pulses in the first temporary storage area of ​​the second program execution variable temporary storage (923); at the same time, the second microcomputer (92) inputs the pulses received by the left receiving unit, the right receiving unit, and the middle receiving unit into its three input pins respectively, and counts the number of pulses within a unit time. The counting result of the left receiving unit is stored in the second temporary storage area of ​​the second program running variable temporary storage (923), the counting result of the middle receiving unit is stored in the third temporary storage area of ​​the second program running variable temporary storage (923), and the counting result of the right receiving unit is stored in the fourth temporary storage area of ​​the second program running variable temporary storage (923). Then, the left receiving program module (3001), the middle receiving program module (3002), and the right receiving program module (3003) are called to compare the counting result of each temporary storage area with the data in the first temporary storage area. Step 7: Next, set the comparison error threshold to 1 / 300. When all comparison results are greater than the error threshold, it is considered that no human body is close to the projector (125). When any comparison result is less than the error threshold, it is considered that a human body is close to the projector (125). Then, the projector lens compartment door switch program module and the projector fan driver program module are called to turn off the projector, the projector lens compartment door, and the projector fan.

2. The method of claim 1, wherein the robot projector prevents eye burn, and wherein: The unit time selection range is between 0.2 seconds and 1 second, where a value is selected.

3. The method of claim 1, wherein the method further comprises: Step six describes outputting a pulse signal per unit time, the frequency of which is selected between 1KHz and 10KHz.

4. The method of claim 1, wherein the robot projector prevents eye burn, and wherein: When a human body approaches the projector (125) as described in step seven, the second microcomputer (92) calls the projector switch program module (1201) to compare the counting results of the second, third, and fourth temporary storage areas three times with the data in the first temporary storage area. If the counting result of any temporary storage area is less than the error threshold after three consecutive comparisons with the data in the first temporary storage area, the projector lens compartment door switch program module (1211) and the projector fan driver program module (1221) are called to turn off the projector (125), the projector lens compartment door (121), and the projector fan (124).

5. A robotic projector eye-safty device, comprising: The device uses the method of claim 1, the device comprising: a projector (125) disposed inside the robot head (12), the front of the robot head (12) being a display touch screen (127), and the rear of the robot head (12) being a projector lens compartment door (121), the projector (125) being exposed when the projector lens compartment door (121) is opened; A second motherboard (130) is installed inside the robot head (12), on which a second microcomputer (92) is mounted. On one side of the projector lens compartment door (121), a light emitting group (122) and a light receiving group (123) are provided. The light emitting group (122) is connected to the following circuit units: left emitting unit, right emitting unit, and middle emitting unit. The light receiving group (123) is connected to the following circuit units: left receiving unit, right receiving unit, and middle receiving unit. The left emitting element and the left receiving element are a pair of transistors, the middle emitting element and the middle receiving element are a pair of transistors, and the right emitting element and the right receiving element are a pair of transistors. The projector (125) is turned on and off by a second microcomputer (92); The opening and closing of the projector lens compartment door (121) is controlled by a second microcomputer (92); The left transmitting unit, right transmitting unit and middle transmitting unit are circuitically connected to the second microcomputer (92). The left receiving unit, right receiving unit, and middle receiving unit are circuitically connected to the second microcomputer (92). The projector fan (124) located next to the projector lens compartment door (121) is driven by a second microcomputer (92); The robot head (12) is equipped with a first motherboard (140) with a first microcomputer (91) on it. The first microcomputer (91) is connected to a display touch screen (127), accepts projection playback instructions entered by the display touch screen (127), and also communicates with a second microcomputer (92) through its own GPIO and PI12 pins. The left receiving unit circuit is connected to a left shaper U11 at the end, which shapes the signal output by the first operational amplifier U1 and then outputs a potential of either "1" or "0" to a pin of the second microcomputer (92). The right receiving unit circuit is connected to a right shaper U31, which shapes the signal output by the third operational amplifier U3 and then outputs a potential of either "1" or "0" to another pin of the second microcomputer (92). The end of the receiving unit circuit is connected to a shaper U21, which shapes the signal output by the second operational amplifier U2 and then outputs a potential of either "1" or "0" to another pin of the second microcomputer (92).

6. The robotic projector anti-eye-burn device of claim 5, wherein: The robot head (12) is equipped with a power supply (105), which outputs DC12V power required by the color light strip unit (205) and the projector switch circuit unit (119); as well as DC5V power required by the first microcomputer (91), the second microcomputer (92) and related circuits.

7. The device for preventing eye burns in a robotic projector according to claim 6, characterized in that: When the resistance of resistor R3 in the left receiving unit circuit is 1KΩ, the resistance of resistor R2 is selected between 20KΩ and 120KΩ. When the resistance of resistor R8 in the receiving unit circuit is 1KΩ, the resistance of resistor R7 should be selected between 20KΩ and 120KΩ. When the resistance of resistor R13 in the right receiving unit circuit is 1KΩ, the resistance of resistor R12 should be selected between 20KΩ and 120KΩ.

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