1 Introduction
Short-distance wireless transmission has the advantages of strong anti-interference performance, high reliability, good security, less geographical restrictions, and flexible installation. It has a wide range of application prospects in many fields. Common short-range wireless communications include 802.11-based wireless local area network WLAN, Bluetooth (blueTooth), HomeRF, and European HiperLAN (high-performance wireless local area network), but their hardware design, interface methods, communication protocols, and software stack are complex and require special development The system has high development costs, long cycles, and high final product costs. Ordinary RF products do not have these problems, and the short-range wireless data transmission technology is mature, simple in function and easy to carry, making it widely used in embedded short-range wireless products.
2 PTR2000 pin introduction and design
2.1 PTR2000 device pin function
PTR2000 is a wireless data transmission module based on nRF401 device, which is designed with low transmission frequency and high sensitivity. The device uses the 433 MHz frequency band and is a true monolithic UHF wireless transceiver. Its working mode includes the setting of the working channel and sending, receiving, and standby states. It is determined by the three pins TXEN, CS, and PWM. Its working mode The settings are shown in Table 1.
2.2 PrR2000 module design
There are two main circuits around the device:
(1) Connection circuit with single-chip microcomputer The RXD and TXD pins of the single-chip AT89C52 are directly connected to the DO and DI pins of the PTR2000 module. The mode control pin of PTR2000 is connected with the control pin of the single chip microcomputer.
(2) The connection circuit with the PC uses MAX202 devices to perform RS-232 and TTL level conversion on the PTR2000 module and computer serial port, and connects the input and output signals of the PTR2000 and MAX202, and the converted signal is connected to the serial port of the computer.
3 Hardware design
In situations where wired transmission cannot be used, it is a more reasonable solution to use a wireless data transmission module and a single-chip microcomputer for data transmission. PTR2000 uses serial port for data transmission, and both single-chip and PC have serial ports. Therefore, PTR2000 can be used as a wireless interface for data transmission between single-chip and PC. Its hardware structure is shown in Figure 1.
The acquisition system mainly uses AT89C52 single-chip microcomputer as the control and processing core. It completes the data collection and processing and wireless transmission of control data. The AT89C52 microcontroller has a fast 8051 core, 8 KB Flash E2PROM, and 256 bytes of RAM. In order to realize wireless data transmission, the PTR2000 device with unlimited data transmission and reception integrated data transmission MODEM module is used. The device integrates high-frequency reception, PLL synthesis, PSK modulation / demodulation, parameter amplification, power amplification, channel switching and other functions, which is fully in line with wireless data communication Hardware requirements. In order to reduce costs, on the basis of the minimum hardware design, using C51 advanced C language programming, the system functions as much as possible with software programs.
3.1 Clock circuit and reset circuit design of the single chip microcomputer
In the design of the clock circuit of the single-chip computer, the crystal frequency is 11.059 2 MHz, the communication rate between the PC and the single-chip computer is agreed to be 9 600 b / s, and the corresponding capacitor is selected to be connected to the clock pin of the single-chip computer to form a clock loop. In the design of the reset circuit, a reset pin and corresponding capacitors and resistors are used to form a reset circuit. The principle circuit of MCU and PTR2000 interface is shown in Figure 2.
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