Design of LED Chinese Character Wireless Information Display Board

introduction

LED Chinese character dynamic display screen is a display screen composed of multiple light-emitting diode dot matrices (8×8 dot matrices are used here). Compared with traditional display media such as colorful neon lights, pixel tube TV walls, four-color magnetic flip boards, etc., it has many advantages such as high brightness, strong contrast, good dynamic display effect, low failure rate, low energy consumption, long service life, flexible configuration, good visual effect, and all-weather operation, and has been widely used.

Overview

2.2 LED dot matrix display drive control

The drive control circuit can use 74HC595 (8-bit shift register/latch), as shown in Figure 2.

Among them, SCK is the shift pulse signal; SER is the serial signal. Data is input from the SER terminal, and each rising edge of SCK shifts the data right by one position. If a group of data, i.e. 8N, is to be input, the SCK signal generates 8N pulses. When the SCK signal ends, RCK outputs a negative pulse, and its rising edge causes the data to be output and displayed.

The driving circuit is composed of 4/16 decoder 74LSl54, 4953 driver chip, etc. Each 4953 chip can drive 2 rows of LED display. A row address is generated by the output of the 4/16 decoder, and the output is low level to control all displayed rows, and the LEDs in the same row are in a valid state. At the same time, an array transfer instruction is used to transfer the column data. That is to say, when the base of a MOS tube in the 16 rows is added with a low level (usually a high level), this MOS tube is in a state to be turned on. Then in the 64 columns, if a column is at a low level, the LED in the column will turn on and emit light, thus completing the display of a row. For the driving MOS tube of this column, its maximum withstand current and maximum dissipated power should be considered.

2.3 Principle of MCU Control Circuit Board

The single-chip microcomputer part of the wireless electronic information display board is the most commonly used single-chip microcomputer minimum system. It is mainly composed of a reset circuit, a crystal oscillator circuit (12 MHz), and a memory expansion circuit (expanded to 32KB). The output data uses the P1 port, while the P0 and P2 ports are mainly used to expand the external data memory. The P3 port only uses the RXD and INT1 terminals. The communication mode of the single-chip microcomputer is a serial asynchronous communication mode with a baud rate of 2 400 b/s, as shown in Figure 3.

2.4 Design of computer interface circuit

The communication between the wireless electronic information display board and the PC is set to simplex communication mode, that is, only the PC sends data to the display board. Therefore, there are only two wires connecting it to the computer serial communication interface, and only the data transmission terminal TXD and the signal ground wire GND are used as wired connections. Since the level of the single-chip microcomputer system is the standard TTL level, the MAX232A conversion chip is used here for level conversion.

2.5 Wireless data transceiver module

nRF2401 is a single-chip RF transceiver chip that needs to work in the 2.4-2.5 GHz ISM band. The chip has built-in functional modules such as frequency synthesizer, power amplifier, crystal oscillator and modulator. The output power and communication channel can be configured through the program. The chip has very low energy consumption. When transmitting at a power of 5 dBm, the operating current is only 10.5 mA; when receiving, the operating current is only 18 mA. Its DuoCeiver TM technology enables nRF2401 to use the same antenna to receive data from 2 different channels at the same time. nRF240 is suitable for a variety of wireless communication occasions, such as wireless data transmission systems, wireless mice, remote control unlocking, remote control toys, etc. Welcome to reprint, this article comes from Electronic Enthusiasts Network (http://www.elecfans.com/)

3. Debugging of wireless electronic information display board

For the single-chip system board, the main thing is the reliability design of the system. The power supply and ground wires should be properly selected, the wiring of the clock area components should be as short as possible, the analog ground and digital ground should be separately wired, and a decoupling capacitor should be added to the single-chip and other IC circuit ends. The I/O ports not used by the single-chip should be defined as outputs. The wireless transmitting and receiving parts should mainly pay attention to the selection of module power supply and the use of isolation measures. The power supply of the transmitting module is 12 V, and a rectifier power supply plus 7812 voltage regulator is used during production. When in use, the receiving module must be powered by a 7805 voltage regulator separately, and connected to the single-chip after adding an isolation driver at the signal output end. The receiving module should be shielded with a metal shell and then connected to an external antenna, otherwise the receiving module is very susceptible to interference from the single-chip clock multiplication. After all parts are debugged, joint debugging is carried out, and the feasibility of this design goal is experimentally proved.

4 Conclusion

The use of single-chip microcomputers is very important for many intelligent controls; it is very effective for saving hardware circuits; for LED electronic information display boards, it can only rely on the powerful data processing function of single-chip microcomputers, and the PC computer as a data transmission device is very important for saving circuit costs. Combined with PCs, LED dot matrix display boards will definitely play a greater potential and add color to the living environment.