Wireless communication modules are widely used in vehicle monitoring, remote control, telemetry, small wireless networks, wireless meter reading, access control systems, cell paging, industrial data acquisition systems, wireless tags, identification, non-contact RF smart cards, small wireless data terminals, security Fire protection system, wireless remote control system, biological signal acquisition, hydrometeorological monitoring, robot control, wireless 232 data communication, wireless 485/422 data communication, digital audio, digital image transmission and other fields.
1. Function of wireless communication module
1.1 Communication function: support GPRS and short message dual-channel data transmission; support multi-center data communication.
1.2 Adopted function: collect serial device data, such as serial instrument, collector, PLC, etc.
1.3 Remote management function: support remote parameter setting and program upgrade.
2. Communication characteristics of the wireless communication module
2.1 Industrial grade design, suitable for outdoor harsh environment.
2.2 Built-in software and hardware watchdog, no crash or disconnection.
2.3 Support data transparent transmission.
2.4 Support domain name resolution function.
2.5 Support various configuration software and users to develop their own software systems.
3. Advantages of wireless communication modules
In comparison, using the wireless data transmission module to establish a dedicated wireless data transmission method has the following advantages over other methods. The following introduces the advantages of using the DATA-6106 wireless data transmission module to establish a dedicated wireless data transmission mode compared to wired communication.
3.1 Low cost
The establishment of wired communication mode must erect cables or dig cable trenches, so a lot of manpower and material resources are required; while the establishment of a dedicated wireless data transmission mode with wireless digital radio does not require erecting cables or digging cable trenches, only needs to be connected at each terminal. It is enough to set up a wireless data station and an antenna with an appropriate height. In contrast, using the wireless data transmission module to establish a dedicated wireless data transmission method saves manpower and material resources, and the investment is quite economical.
Of course, in some short-range data communication systems, the wireless communication method is not less expensive than the wired method, but sometimes the actual on-site environment is difficult to wire.
3.2 Short construction period
When connecting remote sites with distances of several kilometers to tens of kilometers to communicate with each other, using the wired method, long-distance cables must be erected or long cable trenches must be dug. This engineering cycle may take several months. However, using the data transmission module to establish a dedicated wireless data transmission method only needs to erect an antenna with an appropriate height, and the engineering cycle only takes a few days or a few weeks. In contrast, the wireless method can quickly set up a communication link. The cycle is greatly shortened.
3.3 Good adaptability
The limitations of wired communication are too great. When encountering some special application environments, such as special geographical environments such as mountains, lakes, and forests, or application environments with difficult wiring such as moving objects, the wired network will be affected. Wiring engineering has strong constraints, and the establishment of dedicated wireless data transmission methods with wireless data transmission modules will not be subject to these restrictions, so the establishment of dedicated wireless data transmission methods with wireless data transmission modules will be better and wider than wired communication. The adaptability is almost not limited by geographical environment.
3.4 Good scalability
After users set up a communication network, new equipment is often added due to the needs of the system. If the wired method is used, re-wiring is required, the construction is more troublesome, and the original communication line may be damaged. The connection can realize the expansion of the system, which has better scalability in comparison.
4. Technical parameters of wireless communication module
Data format: 8 data bits, 1 stop bit, parity bit (odd, even, none) can be set.
Baud rate: 300, 600, 1200, 2400, 4800, 9600, 19200 (Bit/S) optional.
Communication error: ≤10.
Power supply: 10V ~ 30V DC.
Average current: <70mA/12V.
Working environment: Temperature: -40～+85℃; Humidity: ≤95%.
5. Data transmission of wireless communication module
Data transmission can be simply divided into wired (including erecting optical cable, cable or leased telecom line) and wireless (divided into establishing dedicated wireless data transmission system (433MHZ frequency band and 2.4G frequency band) or borrowing CDPD, GSM, CDMA and other public network information platforms ) in two categories.
Application fields of wireless communication modules
Applications:
The first concern of users is the transmission distance, and the distance is not a problem. In the near future, the 433MHz frequency band wireless data terminal DTD433 is used, and in the far distance, the GPRS transparent transmission data terminal DTP_S09F is used. The so-called "near" means that most factories and mines can be covered within 3 kilometers; the so-called "far" means that the communication distance exceeds 3 kilometers, even across different regions and different countries. Fortunately, China Mobile's network has covered the whole world, so distance is not a problem. . The combination of DTP_S09F and DTD433 can meet most of the wireless measurement and control requirements.
Connection application of wireless PLC data terminal and wireless MODBUS measurement and control terminal
PLC and 4DI/4DO wireless switch terminal DTD433H and 4AI/4AO wireless analog terminal DTD433F within 3 kilometers carry out MODBUS protocol wireless communication to realize wireless MODBUS transmission.
6. Precautions for wireless communication module
The module must be modulated by a signal to work normally. Common fixed code coding devices such as PT2262/2272 can be directly connected, which is very simple. Because it is a special coding chip, the effect is very good and the transmission distance is very long.
Another important use of the module is to cooperate with the microcontroller to realize data communication. At this time, there are certain skills:
6.1 Reasonable communication rate
The maximum transmission data rate of the data module is 9.6KBs, which is generally controlled at about 2.5k. Too high a data rate will reduce the receiving sensitivity and increase the bit error rate or even fail to work at all.
6.2 Reasonable message code format
When the single chip microcomputer and the module work, they usually define the transmission protocol by themselves. No matter what modulation method is used, the format of the information code to be transmitted is very important, which will directly affect the reliable transmission and reception of data.
Code group format recommendation scheme
Preamble + synchronization code + data frame, the length of the preamble should be greater than 10ms to avoid background noise, because the first bit of the data received by the receiving module is easily disturbed (ie zero-level interference) and the received data is caused by mistake. So using CPU coding and decoding can add some garbled characters before the data identification bit to suppress zero-level interference. The synchronization code is mainly used to distinguish it from the preamble and data. There are certain characteristics, so that the software can identify the synchronization code through a certain algorithm, and prepare for receiving data at the same time.
The data frame should not use non-return-to-zero code, let alone long 0 and long 1. Use Manchester code or POCSAG code, etc.
6.3 Interference of the MCU to the receiving module
When the microcontroller simulates 2262, it is generally normal. However, when the microcontroller simulates 2272 and decodes, it is usually found that the remote control distance is shortened a lot. This is because the multiplication of the clock frequency of the microcontroller will interfere with the receiving module. The 51 series microcontrollers have relatively large electromagnetic interference. Slightly smaller, the PIC series is relatively small, we need to adopt some anti-interference measures to reduce the interference. For example, the single-chip microcomputer and the remote control receiving circuit are powered by two 5V power supplies respectively, and the receiving board is powered by a 78L05 alone.
It is better to make an isolation circuit when the receiving module is interfaced with the 51 series single-chip microcomputer, which can better restrain the electromagnetic interference of the single-chip microcomputer to the receiving module.
When the receiving module is working, it generally outputs a high-level pulse, not a DC level, so it cannot be tested with a multimeter. When debugging, a light-emitting diode can be connected in series with a 3K resistor to monitor the output status of the module.
When the wireless data module is used with special codec chips such as PT2262/PT2272, the connection is very simple, as long as it is directly connected, and the transmission distance is ideal, which can generally reach more than 600 meters. The clock interference caused by the transmission distance is significantly reduced, and the general practical distance is within 200 meters.
