Short-range wireless transmission has the advantages of strong anti-interference performance, high reliability, good security, limited geographical conditions, flexible installation, etc., and has broad application prospects in many fields. Low power consumption and miniaturization are actual needs of users for current wireless communication products, especially portable products, and short-range wireless communication has gradually attracted widespread attention. Common short-range wireless communication includes 802.11-based wireless LAN WLAN, Bluetooth (BlueTooth), HomeRF and European HiperLAN (high-performance wireless LAN), but its hardware design, interface, communication protocol and software stack are complex, requiring special development. The system has high development cost, long cycle and high final product cost. Therefore, these technologies are not widely used in embedded systems. Ordinary RF products do not have these problems, and short-range wireless data transmission technology is mature, simple in function and convenient to carry, making it widely used in embedded short-range wireless products.
This paper introduces the design of wireless communication system interface and reset circuit module using NFC technology.
Circuit principle:
The clock circuit and reset circuit of the single-chip microcomputer: In the design of the single-chip clock circuit, the crystal frequency is selected to be 11.059 2 MHz, the communication speed between the PC and the single-chip microcomputer is 9600 b/s, and the corresponding capacitor is connected with the clock pin of the single-chip microcomputer to form a clock loop. . In the reset circuit design, the reset circuit is formed by using a reset pin and a corresponding capacitor and resistor. The principle circuit of the MCU and PTR2000 interface is shown in the figure.
Figure 1 Schematic diagram of the interface between the MCU and the PTR2000
MCU and PTR2000 interface circuit: AT89C52 MCU mainly completes data acquisition and processing, sends data to PTR2000 module, and receives data transmitted by PC through PTR2000. The PTR2000 module connected to the MCU mainly modulates the data to be transmitted of the MCU into a RF signal, and then sends it to the PTR2000 module of the PC, and simultaneously receives the RF signal transmitted by the PTR2000 module of the PC, and modulates the TTL signal that can be recognized by the MCU to the TTL signal. Single chip microcomputer. The RXD and TXD pins of the MCU are connected to the DO and DI pins of the PTR2000 respectively to realize serial data transmission. The TXEN, CS, and PWR pins of the PTR2000 module work mode and the P2 of the MCU I/O control port are determined respectively. 0~P2.2 is connected. When the PTR2000 is working, its working mode is controlled in real time by the running control program in the single chip microcomputer.
Figure 2 Schematic diagram of PC and PTR2000 interface
The interface circuit design first requires level shifting. The serial port of the PC supports the RS-232 standard, while the PTR2000 module supports the TTL level. The MAX232 device is selected for level conversion between the two. The interface circuit is as shown. The PTR2000 module performs serial input and output, and the pins DI and DO are connected to the serial port of the PC through the level shifting device; the low power control pin of the PTR2000. PWR is connected to the high level VCC, that is, the PTR2000 is fixed in the normal working state; the channel selection pin CS is connected to the GND low level, that is, the fixed communication channel 1 is used, and the fixed operation is at 433.92 MHz; the RTS signal of the PC serial port controls the TXEN pin. To determine when the PTR2000 module is in receive and transmit state. The transmission rate of the PC and serial port is set to 9 600 b/s, which is consistent with the microcontroller.
Editor's conclusion
The wireless communication system design of the single-chip microcomputer is based on the PTR2000 wireless data transmission solution, which can realize short-distance communication of less than 300 m. The system can be easily transplanted as a module in application, so as to build a more complex wireless communication network, which can be applied to small Wireless network, wireless meter reading, cell paging, industrial data acquisition system, safety fire protection system, etc., have certain practical value.
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