Short distance wireless transmission has the advantages of strong anti-interference performance, high reliability, good security, less limited by geographical conditions, flexible installation and so on. It has a wide application prospect in many fields. Low power consumption and miniaturization are the actual needs of users for current wireless communication products, especially portable products. Short distance wireless communication has gradually attracted widespread attention. The common short-range wireless communications include WLAN based on 802.11, Bluetooth, HomeRF and HIPERLAN (high-performance wireless LAN) in Europe. However, the hardware design, interface mode, communication protocol and software stack are complex, requiring special development system, high development cost, long development cycle and high cost of final product. Therefore, these technologies are not widely used in embedded systems. Common RF products do not have these problems, and short-range wireless data transmission technology is mature, simple function, easy to carry, so it has been widely used in embedded short-range wireless products.
The clock circuit and reset circuit of MCU are as followsIn the design of single chip microcomputer clock circuit, the frequency of crystal oscillator is 11.059 2 MHz, the communication rate between PC and single chip microcomputer is 9 600 B / s, and the corresponding capacitor is connected with the clock pin of single chip microcomputer to form a clock circuit. In the design of the reset circuit, the reset pin and the corresponding capacitance and resistance constitute the reset circuit. The principle circuit of interface between MCU and PTR2000 is shown in the figure.
Interface circuit between MCU and PTR2000AT89C52 MCU mainly completes data acquisition and processing, sends data to PTR2000 module and receives data transmitted by PC through PTR2000. The PTR2000 module connected with MCU modulates the data to be transmitted by MCU into RF signal, and then sends it to PTR2000 module of PC. at the same time, it receives RF signal transmitted by PTR2000 module of PC, and modulates TTL signal which can be recognized by MCU and sends it to MCU. RXD and TXD pins of MCU are connected with do and di pins of PTR2000 respectively to realize serial data transmission; TXEN, CS and PWR, which determine the working mode of PTR2000 module, are respectively connected with p2.0 ~ p2.2 of MCU I / O control port. When PTR2000 is working, its working mode is controlled in real time by the running control program of MCU.
The interface circuit design needs level conversion first. PC’s serial port supports RS-232 standard, while PTR2000 module supports TTL level. MAX232 device is selected for level conversion between the two. The interface circuit is shown in the figure. PTR2000 module carries out serial input and output, and pins Di and do are connected with PC serial port through level converter; Low power control pin of PTR2000. The PWR is connected to high-level VCC, i.e. PTR2000 works in normal state; The channel selection pin CS is connected to the GND low level, that is, the fixed communication channel 1 is adopted, and the fixed operation is 433.92 MHz; The RTS signal of PC serial port controls TXEN pin to decide when PTR2000 module is in receiving and transmitting state. The transmission rate of PC and serial port is 9 600 B / s, which is consistent with that of MCU.