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What is a wireless interactive whiteboard
Wireless interactive whiteboard: The wireless interactive whiteboard can communicate with the computer, connect the whiteboard to the PC, and use the projector to project the contents of the PC onto the electronic whiteboard screen, with the support of a dedicated application. You can construct a large screen, interactive collaborative meeting or teaching environment. Using a specific stylus instead of a mouse to operate on a whiteboard, you can run any application that can edit, annotate, save, etc. any operation that can be done on the computer using the keyboard and mouse.
How does Rfid work?
A: The working principle of RFID is: after the tag enters the magnetic field, if it receives the special RF signal from the reader, it can send out the product information stored in the chip (ie Passive Tag, passive tag) by the energy obtained by the induced current. Or passive tag), or actively send a signal of a certain frequency (ie Active Tag, active tag or active tag), the reader reads the information and decodes it, and sends it to the central information system for data processing.
Introduction to EPC?
A: EPC (Product Electronic Label) technology, which is under the unified development and management by EPCglobal, an organization of the International Association of Article Numbering, is another new automatic identification technology after barcode technology, which can be uniquely given to each item. EPC code, thus achieving a unique identification of the item. EPC technology is the continuation and development of bar code technology. It is a useful supplement to bar code technology and an important part of the global unified identification system. EPC can further improve the logistics supply chain management level and reduce costs, and can realize the identification and tracking of all physical objects (including retail goods, logistics units, containers, freight packaging, etc.).
Realize RS-232 to TTL circuit with triode
1, DB9's 2 feet are RS-232 level signal receiving end, RXD; 3 feet are RS-232 level signal transmitting end, TXD;
2, DB9's 4 feet and 6 feet in parallel, 7 feet and 8 feet in parallel may be used for serial port power (with two poles 1N4148, Zener diode or three-terminal regulator 78L05 and other serial port to take power +5V circuit)
3, the Vcc in the figure should be +5V, TXD is connected to the single-chip TXD, and RXD is connected to the single-chip RXD.
Notes on the use of wireless data transmission stations
Since wireless data transmission has its particularity over wired and other transmissions, such as possible interference, transmission and reception conversion time, etc., the following matters should be noted when using digital transmission stations:
1. When using a fully transparent non-intelligent MODEM, some garbled characters will be generated on the RXD of the receiver (the transmitter is started to stabilize) and the tail (the receiver is muted off for a moment), which needs to be implemented by software. Filter", remove these garbled. At this point, according to our experience, the system software is best not to use VB, otherwise the serial port may cause a "dead" phenomenon, the specific performance of the COM port of the PC can not be sent. Of course, if the software is handled properly, this problem can be avoided. The above problem does not occur when using the smart MODEM, because MODEM has automatically filtered garbled characters.
2, should choose the appropriate DC stabilized power supply, requires strong anti-high-frequency interference, small ripple, and sufficient load capacity; it is also best to have over-current, over-voltage protection and lightning protection to ensure digital transmission The radio is working properly.
3. Do not use in a working environment that exceeds the environmental characteristics of digital radio stations, such as high temperature, humidity, low temperature, strong electromagnetic field or dusty environment.
4. Don't let the digital radio station continuously in the transmitting state, otherwise the transmitter may be burned out. Many digital radio stations or MODEMs have "long hair" protection, which can set the longest continuous transmission time limit to ensure that the transmitter is not damaged. So you should make good use of this feature when programming digital radio.
5. The ground wire of the digital radio station should be well connected with the ground wire of the external equipment (such as PC, PLC, etc.) and the ground wire of the power supply. Otherwise, the communication interface will be easily burned out. Do not plug or unplug the serial port with power.
6. Many RS-232C (or TTL) communication ports of digital radio stations, in addition to TXD, RXD, GND, must also have RTS to send request signals (control transmitter transmission), but many PLC serial ports can not provide RTS signals. At this point, you can set an output point to the RTS signal by programming the PLC.
7. When testing the digital radio station, it must be connected with a matching antenna or a 50Ω dummy load, otherwise the transmitter may be damaged. If the antenna is connected, the distance between the human body and the antenna is preferably more than 2 meters to avoid injury. Do not touch the antenna when transmitting.
8. It takes a certain amount of time for the radio station's transmitter to start (from the power of 0W to the maximum power called the transmitter start time) and the receiver's squelch to turn on (this time varies from a few milliseconds to several hundred depending on the station) It should be noted in the milliseconds, so when sending the data, please note: if the transmitter is turned on (ie, the RTS is valid), the data (TXD) is sent to the air, so that the transmitter is not stable yet, and the receiver is squelched. Also not open, the previous piece of data will be lost. The correct method is: after turning on the transmitter, wait for 100ms~200ms and then send the data. After the data is sent, delay the 10-50ms or so and then turn off the transmitter. For intelligent MODEMs such as FC-208 series or FC-206 series, this part of the work has been done in the MODEM software. Users do not have to do the above processing in their own software, and do not need to provide RTS signals, just press The correct rate and format will send the data to TXD. But don't forget that for wireless half-duplex radio, the transmission and reception conversion time is always there. It is better for the receiver to start the transmitter return data immediately after the data is received, but after the transmission and reception conversion time, start the party. Transmitter. Of course, the friend-speaking digital radio station can be adapted to the fast transceiving and conversion after being equipped with the FC-211 and FC-206 series intelligent MODEM, that is, the receiver can return the data immediately after receiving the data, without considering the transceiving conversion. Time. But for most other data stations and MODEM, this can't be achieved. Please pay attention to the software according to the conversion time of the products used.
Antenna selection and erection
1. Erection of the omnidirectional antenna:
When the omnidirectional antenna is erected, the distance between the antenna and the lightning rod is required to be greater than one wavelength, and the angle between the top of the antenna and the top of the lightning rod and the lightning rod is less than 45°. In principle, the antenna should be oriented toward the side of the communication distance (or the communication is difficult), and the antenna and the connecting part of the cable should be waterproof, and sealed with a special waterproof tape. If the communication distance is required to be far away, the antenna erection height should be increased as much as possible, and an omnidirectional high-gain antenna should be selected. If you want to enhance the signal in a particular direction, you can use a four-ring array or an eight-ring array antenna.
2. Erection and selection of directional antennas:
When the directional antenna is erected, the vibrator is required to be perpendicular to the ground, and the direction is as close as possible to the omnidirectional antenna of the central station. If the communication distance is far, the directional antenna should increase the height and gain as much as possible, and the connection between the antenna and the feeder should be waterproof.
Feeder installation and selection:
The feeder should be led to the station along the tower or pole, and tied in the middle with a wire to avoid being blown by the wind. The length of the feeder is just right, not too long, otherwise it will increase the loss. Feeders should avoid sharp bends and the curvature should be greater than 120 degrees. The central station should generally use low-loss feeders or feed pipes with a diameter of 12mm or more to ensure the communication signal of the whole system; the sub-station can select low-loss feeders with diameters of 7mm, 9mm and 12mm according to the distance, and the special requirements can be selected. Low loss feeder. In addition, whether it is an omnidirectional or directional antenna, it must be firmly erected and should have the ability to withstand 12 typhoons. In the multi-lightning area, it is recommended to string a coaxial arrester between the antenna and the feeder.
Advantages of using wireless communication
Data transmission can be divided into two types: wired (including erection of optical cable, cable or leased telecommunication line) and wireless (divided into a dedicated wireless data transmission system or borrowed from public network information platforms such as CDPD, GSM, CDMA, etc.).
In comparison, the use of the wireless data transmission module to establish a dedicated wireless data transmission method has the following advantages over other methods. The following describes the advantages of using the wireless data transmission module to establish a dedicated wireless data transmission method compared to wired communication.
1. Cheap cost
The establishment of wired communication methods must erect cables or dig trenches, so it requires a lot of manpower and material resources. The use of wireless digital radio stations to establish dedicated wireless data transmission methods eliminates the need to erect cables or dig cable trenches, and only needs to be connected at each terminal. Wireless data transmission stations and antennas with appropriate heights are all available. In contrast, the use of wireless data transmission module to establish a dedicated wireless data transmission mode, saving manpower and material resources, investment is quite economical. Of course, in some close-range data communication systems, wireless communication methods are not cheaper than wired methods, but sometimes the actual field environment is difficult to route, and customers will use wireless methods to achieve communication according to the needs of the on-site environment.
2. Short construction period
When remote stations connecting distances of several kilometers to tens of kilometers are to be connected to each other, wired lines must be used to erect long-distance cables or to dig long cable trenches. This engineering cycle may take several months. The digital transmission module uses the digital transmission module to establish a dedicated wireless data transmission mode. It only needs to set up an antenna of appropriate height. The engineering cycle only takes a few days or weeks. In contrast, the wireless method can quickly set up a communication link. The cycle is greatly shortened.
3. Good adaptability
The limitations of wired communication are too great. When encountering special application environments, such as encountering special geographical environments such as mountains, lakes, and forest areas, or applications where wiring is difficult, such as moving objects, the wired network will be Wiring engineering has a strong constraint, and the use of wireless data transmission module to establish a dedicated wireless data transmission method will not be subject to these restrictions, so the use of wireless data transmission module to establish a dedicated wireless data transmission method will be better than wired communication. Adaptability is almost unrestricted by the geographical environment.
4. Good scalability
After a user has set up a communication network, new devices are often added because of the needs of the system. If the wired method is used, it needs to be re-wired, the construction is troublesome, and it may damage the original communication line. However, if the wireless data transmission station is used to establish a dedicated wireless data transmission method, only the newly added equipment and the wireless data transmission station need to be added. Connected to achieve system expansion, compared to better scalability.
5. Easier to implement on equipment maintenance
The maintenance of the wired communication link needs to be checked along the line. When a fault occurs, it is generally difficult to find the fault point in time. The wireless data transmission module is used to establish a dedicated wireless data transmission mode. Only the data transmission module needs to be maintained, and when the fault occurs, the fault can be quickly found. The reason is to restore the normal operation of the line.