Design of multimedia teaching curtain control system based on single chip microcomputer

Abstract: Aiming at the shortcomings of the current projection screen control method in multimedia classrooms, a simple and practical improvement method is proposed. This method is based on the AT89S52 single-chip microcomputer to realize control. The specific hardware circuit implementation method of the new multimedia screen control system is given in this paper.
Keywords: AT89S52 single-chip microcomputer; projection screen control

With the advancement of science and technology, multimedia teaching equipment has become an indispensable tool for modern teaching and many conference places. Multimedia mathematics equipment is generally composed of central control integrator, projector, screen, computer and audio equipment. At present, the common method for controlling the projection screen on the market is to directly control the rise or fall of the screen through the central control integrator or switch. The former is more expensive and complex to maintain; while the latter is direct and simple, but it is also found to have some shortcomings in actual use.
In response to these problems, this paper proposes a solution for automatic control of the projection screen based on the AT89S52 single-chip microcomputer. This control method can automatically start the projector and lower the projection screen when the computer is turned on; when the computer is turned off, the projector can be automatically turned off and the projection screen can be raised, and the screen can be remotely controlled and manually turned on and off.

1 Basic functions of AT89S52
AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8KB in-system programmable Flash memory. AT89S52 is manufactured using Atmel's high-density non-volatile memory technology and is fully compatible with the instructions and pins
of industrial 80C51 products. Its on-chip Flash allows program memory to be programmed in the system and is suitable for conventional programmers. It can provide flexible and effective solutions for many embedded control applications. The P0 port of AT89S52 is an 8-bit open-drain bidirectional I/O port. As an output port, each bit can drive 8 TTL logic levels; when "1" is written to the P0 port, the pin can be used as a high-impedance input. When accessing external program and data memory, the P0 port is also multiplexed as an 8-bit address/data. In this mode, P0 has an internal pull-up resistor.
The P1, P2, and P3 ports of the microcontroller are all 8-bit bidirectional I/O ports with internal pull-up resistors, of which the P2 output buffer can drive 4 TTL logic levels. When writing "1" to these ports, the internal pull-up resistor will pull the port high, and the port can be used as an input port. When used as an input port, the pin pulled low by the outside will output current due to the internal resistance. P3 port can also be used as a special function of AT89S52, such as P3.0 and P3.1 can be used as the receiving and sending ports of serial port data respectively.

2 Structure of multimedia projection screen controller
The structural block diagram of the multimedia projection screen controller (hereinafter referred to as the controller) is shown in Figure 1. The controller can send projector and screen control commands to the single-chip microcomputer through the computer's RS232 interface when "turning on/off" the computer, and control the "opening/closing" of the relay through the single-chip microcomputer. Thereby achieving the purpose of automatically controlling the lifting and lowering of the screen. The lifting and lowering of the screen can also be remotely controlled by a remote control. In order to be compatible with the original operation mode, the controller is also designed with a manual button.

3 Design of each module of the controller
3.1 Design of relay control circuit
Figure 2 shows the relay control circuit in this system. In the figure, pin 2 of the pin is connected to the 220V curtain power supply, pins 1 and 3 are connected to the rising and falling lines of the curtain end respectively, VCC is the relay +5V power supply, P1.0 and P1.1 are connected to the P1.0 and P1.1 pins of the AT89S52 P1 port respectively. When the single-chip microcomputer sets these two pins to "0", the relay can close the contacts through the single-chip microcomputer and under the drive of the PNP transistor 9012 to realize the forward or reverse rotation (i.e. rising/falling) of the electric curtain motor. Since the coil of the relay is an inductor, there will be a large reverse electromotive force when it is cut off. This reverse electromotive force is added to the transistor of the driving coil, which may break down the transistor, causing the relay to fail to turn off. Therefore, the high voltage needs to be bypassed. In order to protect the driving transistor, a diode 2A9P is added in Figure 2.

3.2 Serial port connection circuit
The serial port connection circuit in the system is shown in Figure 3. In the figure, the computer and the P3.0 and P3.1 (P3.0 is the receiving port and P3.1 is the sending port) of the microcontroller are connected through the MAX202 chip, and the 11th pin of MAX202 is connected to the P3.1 of AT89S52, and the 12th pin is connected to P3.0.

3.3 Manual button design
Since the teacher may use the blackboard during class and need to close the curtain, the original manual control method needs to be retained during the design. This design adopts a low-voltage button control method instead of the traditional 220V switch control method. Figure 4 shows its button circuit, where P1.2 is connected to the P1.2 pin of the microcontroller, and P1.3 is connected to the P1.3 pin of the microcontroller. In this way, when S2 or S3 is pressed, the corresponding microcontroller pin level will be pulled low, and the microcontroller will respond according to the pulled low pin and send a command to control the curtain action from the P1 port, thereby realizing the manual opening/closing function of the curtain. RST is connected to the reset pin of the microcontroller, so after pressing S1, the microcontroller will reset, so that the curtain will stop rising or falling midway. This not only maintains the traditional manual function, but is also safer than the traditional control method.

4 Conclusion
The practical results show that each function of the projection screen automatic controller can achieve the expected purpose, it is easy to use, simple to make, low cost and practical.