Wireless communication module development notes　

        Module must be modulated with a signal in order to work properly, common fixed-code coding devices such as pt2262/2272, as long as the direct connection can be very simple, because it is a special coding chip, so the effect is very good transmission distance is very far. 　　   

        Module also has an important use is to cooperate with the microcontroller to achieve data communication, this time there are certain skills:

1, reasonable communication rate

        Data module of the maximum transmission data rate of 9.6KBs, generally controlled in 2.5k or so, too high a data rate will reduce the reception sensitivity and increase the BER or even not work at all. 　　

2, reasonable information code format

        Microcontroller and module work, usually their own definition of the transmission protocol, regardless of the modulation method, the information code format to be transmitted is very important, it will directly affect the reliable receipt and transmission of data. 　　

Code group format recommended program 　　

        Pilot code + synchronization code + data frame, the length of the pilot code should be greater than 10ms to avoid background noise, because the first bit of data received by the receiver module is very easy to be interfered with (i.e., zero-level interference) and cause errors in the received data. Therefore, the CPU compilation code can be used to add some garbled code before the data identification bit to suppress the zero-level interference. Synchronization code is mainly used to distinguish the leading code and data. There are certain characteristics, so that the software can identify the synchronization code through certain algorithms, and at the same time to receive data ready. 　　

        Data frame should not be used non-zero code, not to mention long 0 and long 1. Manchester code or POCSAG code, etc.. 　　

3, microcontroller interference with the receiver module 　

        Microcontroller simulation 2262 is generally very normal, however, microcontroller simulation 2272 decoding will usually find that the remote control distance is shortened a lot, this is because the multiplication of the clock frequency of the microcontroller will be on the receiving module to produce interference, 51 series of microcontroller electromagnetic interference is relatively large, the 2051 is slightly smaller, the PIC series is relatively small, we need to adopt a number of anti-jamming measures to reduce the interference. For example, the microcontroller and the remote control receiver circuit are powered by two 5-volt power supply, the receiver board will be a separate 78L05 power supply, the clock area of the microcontroller away from the receiver module, reduce the operating frequency of the microcontroller, the middle to join the shielding and so on. 　　

Receiving module and 51 series microcontroller interface is best to do an isolation circuit, can better contain the microcontroller on the receiving module of electromagnetic interference. 　　

        Receiver module work is generally output a high level pulse, not DC level, so you can not use a multimeter test, debugging can be a light-emitting diode in series with a 3K resistor to monitor the module's output status. 　　

        Wireless data module and PT2262/pt2272 and other special codec chip use, the connection is very simple as long as the direct connection can be, the transmission distance is ideal, generally can reach more than 600 meters, if and microcontroller or microcomputer with the use of microcontroller or microcomputer clock interference, resulting in a significant drop in transmission distance, the general practical distance of 200 meters or less.