Realization of 5-inch TFT-LCD Remote Control System Using 51 Single-Chip Microcomputer

LCD has been widely used in industrial and civilian fields such as computer monitors, VCD display panels, and portable medical equipment due to its thin, light and low power consumption. In these products, the application of single-chip microcomputers can greatly improve their intelligence and ease of use, bringing comfort and convenience to people's lives. This paper uses the single-chip microcomputers AT89C2051 and AT89C51 of Atmel Company in the United States to design a remote control system for a 5-inch TFT-LCD. The system mainly consists of three parts: remote control transmitter, remote control receiver, and TFT-LCD drive circuit. It can remotely control the power switch, brightness, color saturation, contrast, and volume of the TFT-LCD, and has extended functions.
1 Hardware Design The overall hardware design block diagram is shown in Figure 1.

1.1 Design of remote control transmitting circuit

The remote control transmitting circuit consists of AT89C2051 single-chip microcomputer, keyboard, infrared transmitting circuit and power supply. Here, a 4×4 keyboard is selected to control the switch, brightness, contrast, color saturation and volume of LCD. The power supply is provided by 2 No. 5 (3V) batteries. 1.2 Design of remote control receiving circuit The remote control receiving circuit consists of AT89C51 single-chip microcomputer, keyboard, infrared transmitting circuit and power supply. Because the host (TFT-LCD) already has a DC power supply, the power supply of AT89C51 can be directly introduced by the host. The receiving circuit also uses a 4×4 keyboard, which also has function keys to control the switch, brightness, contrast, color saturation and volume of LCD. 1.3 Design of TFT-LCD driving circuit The driving circuit of TFT-LCD consists of two image signal processor chips







ADV7120 and ADV724. ADV7120 is a digital-to-analog conversion chip for image signals, which converts 8 B RGB digital signals into RGB analog signals. It is often used in color video systems. It is a D/A conversion chip that combines high-quality image processing with low cost. It consists of 3 high-speed 8 B video D/A conversions, 1 stable TTL parameter input and 1 analog signal output.

AD724 is a low-cost RGB to NTSC/PAL TTL converter. The chip operating voltage is +5 V and does not require additional filtering circuits or linear delays. When AD724 is not working, it will turn off the power.
2 Software Design 2.1 Remote Control Transmitter Program Design (1) Coding Format 8-bit binary coding is used. The coding format is shown in Table 1.

In the 8-bit code, the first 4 bits are check bits (0101) to reduce the bit error rate. The pins P1.2 to P1.5 correspond to the pins P3.2 to P3.5 and are connected to the keyboard array. The scan level is sent out by the P3 port, and the P1 port receives it and processes it by the microcontroller and sends it out by the serial port. The scan level sends a high potential on P3.2 to P3.5 in turn, and 8 ms is a cycle. The time is controlled by the timer of the microcontroller.

(2) Programming ideas

The main program initializes the microcontroller and sets the timer/counter to work in timer mode. The timer uses mode 1. Set the serial port and allow interrupts. Start timer 0 and wait for the timer interrupt.

The timer interrupt program outputs the scan word at the P3 port and receives the scan word at the P1 port. Check whether there is a high byte at P2.2 to P2.5. If there is, it proves that there is a key signal and processes the code, then the serial port outputs, the scan word is shifted left, and then the interrupt is returned. If P2.2~P2.5 have no high bit, that is, no key is pressed, the scan word is shifted left and the interrupt is returned. 2.2 Remote control receiving program design (1) Programming ideas The idea of ​​remote control receiving programming is basically the same as that of remote control transmitting programming. When the key information is determined, the signal processing program will be called, and the electrical signal will be sent from P3 and P2 ports. The outputs of P3.5~3.7 ports are connected to the three input ports of the 138 decoder. The 4-way D/A conversion corresponds to volume, brightness, chroma and saturation respectively. The output of P2 port is connected to the input of D/A. The output of P2 port is 8-bit adjustment offset. After D/A conversion, it is added to the original signal through the adder and then output to the TFT LCD to complete the adjustment function. P3.2 is used to control the TFT-LCD power supply. (2) Design flow chart The flow chart of the timer 0 interrupt entry program is shown in Figure 2.

The serial input interrupt program flow chart is shown in Figure 3.

The volume adjustment subroutine flow chart is shown in Figure 4.

The remote control signal processing program flow chart is shown in Figure 5.

(3) Taking the volume and brightness adjustment program as an example, the program list is given: LIGHTUP: MOV A, R2; Brightness up program

3 Conclusion After using the AT89C series microcontroller to install the remote control system on a 5-inch TFT-LCD, it is convenient to adjust analog quantities such as volume, brightness, color saturation and contrast. The remote control system can be promoted and applied to other series of non-remote control TFT-LCD products.

References

［1］ Li Weiti, Guo Qiang． Liquid Crystal Display Application Technology［M］． Beijing: Electronic Industry Press, 2001．
［2］ ADV7120 Manual［S］． Provided by ANALOGDEVICES．
［3］ AD724 Manual［S］． Provided by ANALOGDEVICES．
［4］ AT89C2051 and AT89C51 Manual［S］． Provided by ATMEL．