Based on PLC LED digital tube dynamic scanning data display design - is analysed Industrial control -

PLC data display function has always been a problem in the PLC using. In the application of PLC, often to monitor some important data, but the PLC data display is usually an external display device, such as display or touch screen, and the price of these display devices tend to be expensive, more waste for some small system. Therefore, how to display the PLC data, and as far as possible do high efficiency, high stability, strong anti-jamming capability, hardware, less investment, is a lot of problems need to consider in the design of. The author USES the Siemens S7 - 200 PLC IN the special instructions to control the LED digital tube display, SEGIN, OUT instruction is four bytes IN the input low determine the hexadecimal number automatically converted to the corresponding code 7 segment LED digital tube paragraphs, and sent to the output bytes OUT side show. If using static LED digital display, PLC showed a decimal data needs to be 7 output point to control, if you want to show n bits of data, you need to 7 n dots. Digits, so use this way to display the data is large, need a lot of dots, and the price of the PLC is based on the input and output points to calculate, this led directly to the hardware costs rise, in view of this reason, looking for a cheap display technology is particularly necessary. Put forward using single-chip LED digital tube dynamic scanning display principle, according to the characteristics of the PLC cyclic sweep to catch PLC digital output directly drive the digital tube, PLC switch output can be divided into two parts, some are used for data output, the other part is used as the control of public digital tube end signal output. Using afterglow effect of the human eye, circular light each digital tube, this method is simple operation and low cost.

1 design implementation

dynamic scanning is the advantage of the characteristics of PLC scan periodically, to do each cycle only when programming a digital tube can form the electric circuit, and electric light, because of a scan cycle time is too short, only a few tens of ms, so the human feeling every digital tube is uniform electric light, without trailing phenomenon at the same time. Hardware design 1

design method of hardware circuit implementation is a starter button SB1 and a stop button SB2, two digital tube a, b, c, d, e, f, g respectively together, with the PLC controller output Q0 again. 0 ~。 7 through the current limiting resistor connected, the public end of the two digital tube com1, com2, respectively by using a transistor Q1 by PLC output end. 0 and Q1. 1 control, its wiring principle is shown in figure 1.

figure 1 double digital tube scan showed PLC driver circuit

by PLC controller output end Q1. 0 and Q1. 1 high and low level control in a switch triode, the working state of digital tube to com1 or com2 end cycle with the PLC public M conduction output, to select different digital tube, by PLC output Q0. 0 ~。 7 output corresponding data again according to the common signal to the corresponding digital tube a, b, c, d, e, f, g shows. Through software programming can be realized with a set of start-stop button control two sets of digital tube display the corresponding data.

2 software design by two different functions on the same hardware circuit design software realization example to elaborate the software implementation of a juice. An designing software example 1

this program implementation 0 ~ 99 s repeatedly counting function, press the SB1 start counting, pushing the SB2 make count stop counting in the stop position, then press the start button to start from 0 count, count to 99 after starting from 0 count again. The program ladder diagram as shown in figure 2. May generate the clock pulse counting of 1 s, using the data of PLC, transfer, transform the function of the transmission, processing, changes of count data, then use period of decoding SEG command driven seven segment digital tube, produced by the two timer cycle for 200 ms and reverse phase clock pulse count data control display changes. An designing software example 2

this program function of 50 s countdown pedestrian SB1 starting time, press the SB2 stop time, at the same time, digital tube, and then press the start button to 50 s countdown, timing to 0 s, digital tube out automatically. 2 end

design is mainly a double-digit divided into two groups of data in 10 and bits digital tube display, the program adopts cycle control method, then a scan cycle show a set of data, namely the cyclic display two sets of data. Assume that the program scan cycle for 100 ms, timer timer 100 ms, then each set of data update cycle is 100 * 2 = 200 ms, such display frequency enough to meet general industrial control requirements, can be used for real-time display. Also, if the display multiple sets of data, the data line connection is the same, only need to increase the control signal output points of PLC, digital tube common PLC output points of 7 + n, n number of digital tube; Software can be changed slightly. In this paper, the hardware and software design method are debugging success was made in the laboratory, and fully meet the design requirements, and reduce the hardware cost and good results have been achieved.

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