As an international standard protocol, DMX512 control technology was originally widely used in the field of stage lighting (Figure 1).
With the rapid development of LED lighting applications, DMX512 control technology relies on its standardization, protocol stability, parallel communication, strong anti-interference ability, long transmission distance, single lamp failure does not affect other lamps and other advantages, especially in the field of LED lighting, especially outdoors. The field of landscape lighting is becoming more and more important and is gradually taking the lead. Based on the above significant advantages, DMX512 control technology is especially favored by designers, and a large number of projects are overwhelmingly used. However, due to the large size and high cost of the traditional DMX control and decoding scheme, the LED outdoor landscape lighting fixtures are relatively small in size and the price competition is fierce. Therefore, in order to meet the design requirements and achieve small size, the manufacturers can achieve small size. The design and cost control have to adopt a lot of flexible ways to realize the versatile application of DMX512. It also makes the DMX512 technology develop rapidly in the field of lighting and realize more exciting evolution.
1 DMX512 Technical Description
The DMX512 protocol was first proposed by USITT (American Theatre Technology Association) and developed as a way to control dimmers from a console using a standard digital interface. Because the agreement is simple and practical, almost all lighting and stage equipment manufacturers support the control protocol, making it an international standard for lighting control. The DMX512 goes beyond the analog system, but it does not completely replace the analog system. The simplicity, reliability and flexibility of the DMX512 make it a fast-funding
In the case of the best protocol chosen, in addition to the dimmer, a growing array of control devices is evidence. DMX512 is still a new field in science, with all kinds of wonderful techniques based on rules. The DMX512 is designed around the industry standard EIA485 interface.
For the DMX512 control technology in the field of stage lighting, it should have the following characteristics in the strict sense:
1) The international standard DMX512 (1990) protocol has the advantages of standard, versatility, stability and reliability.
2) Designed around the industry standard EIA485 interface, which uses RS485 differential communication. The advantage is strong anti-interference ability and long transmission distance.
3) Parallel RS485 bus communication form. The advantage is that a single fixture failure does not affect other fixtures.
4) One DMX512 data packet contains a start code and 512 data frames. The data frame contains 1 start bit (low level), 8 bit data and 2 stop bits (high level), with no parity. DMX's signal data transmission rate is 250kbps, data frame width is 4^s per bit, and 44PS13 is required to send one frame.
2 DMX512 technology in the field of lighting applications
In the early days of entering the landscape lighting industry, DMX512 control technology used the DMX512 decoding solution in the field of stage lighting, but it soon faced problems. Because the stage light is generally large in size, the size of the decoding module is not high, and the value of the stage lamp single lamp is relatively high. For the decoding module part, the overall cost is not greatly affected. The LED lamps in the field of landscape lighting are more compact, and the number of applications is large, and the value of single lamps has certain limits. In this case, the stage lamp decoding scheme with larger size and higher cost cannot meet the application requirements. In this case, various types of economical solutions for DMX512 signal decoding have emerged.
2.1 Different forms of DMX512 decoding scheme
After the DMX512 control technology enters the field of landscape lighting, in order to adapt to the characteristics of landscape lighting applications, and respond to the low-cost, small-size market demand, the DMX512 decoding scheme has undergone many evolutions. For the terminal solution of DMX512 control technology, it is mainly The methods used include the following (Figure 2):
1) Based on the single-chip architecture, the 485 interface IC is matched with the peripheral protection circuit. The PWM dimming signal is directly driven by the single-chip microcomputer to drive the LED, or the LED is driven by the amplifier circuit. Its main features are large size and high cost, which is often used in traditional applications.
2) Based on single-chip + SPI shift IC scheme, it is mainly applied to multi-segment line lamps. After DMX512 data is processed by MCU, it is converted into SPI serial shift signal output serial SPI shift 1C, and then SPI shift The 1C outputs a PWM dimming signal that drives the LEDs to achieve control of any number of segments.
3) Independently developed non-programmable decoding chip, with DMX decoding function, but need external 485 interface circuit, can directly output PWM dimming signal, or convert output SPI serial shift signal. Compared with the single-chip application, the decoding chip does not need to write a program, and can be directly used, and the application is relatively simple.
4) Independently developed non-programmable decoder chip, integrated DMX decoding function and 485 interface circuit function, and some also have automatic write address function, the chip can directly receive DMX512 signal, and directly analyze the output PWM dimming signal to drive the LED. It can adapt to the transmission frequency of 250kb~ 750kb for easy expansion. At present, there are mature DMX512 chips in the market such as single-line TTL parallel/serial communication and two-wire RS485 parallel communication. It is characterized by high degree of integration and low cost, and it has basically occupied the mainstream.
Figure 2 DMX decoding module and decoding chip Fig. 2 DMX decoding module and decode IC
2. 2 different evolutions of DMX512 control applications
In order to meet the application of landscape lighting, DMX512 control has also experienced different forms of evolution in application. Some of them have blurred the significant advantages of DMX512 technology in order to reduce costs, and some are truly innovative, not only realized. Cost control also retains the significant advantages of DMX512 technology, which really makes DMX512 go to civilians and become popular. The following are introduced as follows:
1) Fully responsive standard DMX512 protocol and communication method (Fig. 3), that is, the most traditional DMX512 control, using a single-chip microcomputer, a decoding module composed of 485 interface chips, or an independently developed integrated DMX decoder chip. This method satisfies all the features of DMX512 (1990) protocol, RS485 differential communication, parallel bus transmission, and 250K transmission frequency.
2) Meet the DMX512 standard protocol, 250kb transmission frequency, and use serial transmission (Figure 4). This control method to meet two of the three necessary conditions, but not a parallel bus transfer, and therefore pose a problem only a single lamp failure, affecting the back of the lamp work. The advantage is that it can be addressed automatically without the need to set an address.
3) Meet the DMX512 standard protocol, 250kb transmission frequency, using serial TTL communication method (Figure 5). This control method only satisfies the communication protocol of DMX512, but does not use RS485 communication, and does not transmit in the form of parallel bus, but has the advantage of not having to set an address.
4) Meet the DMX512 standard protocol, 250kb transmission frequency, and use the parallel bus transmission method (Figure 6). This control method has the advantages of the standard DMX512 communication protocol and parallel bus transmission. The single lamp failure does not affect the other, but the RS485 differential communication is not used, and the transmission distance may be slightly weaker.
5) The extended DMX512 protocol uses parallel TTL communication (Figure 7). The main feature of this control method is to reduce the data frame width of DMX512, improve the standard communication frequency of 250kb, and realize more load. _ Generally use integrated non-programmable logic IC, adaptive 250kb ~ 750kb communication frequency, is a very good evolution!
6) Extended DMX512 protocol, using RS485 communication mode, parallel bus transmission application (Figure 8). Its feature is to reduce the width of the DMX512 data frame and change the communication frequency of 250kb, thus achieving more load.
7) Wireless DMX512 control, using wireless communication as a carrier to transmit DMX512 signals, which is characterized by borrowing a wireless communication frequency of 2.45 GHz to transmit signals in DMX512 data format. The actual project test proves that it works under the 2.45 GHz range. It can work normally, is not affected by wireless WIFI, mobile phone, wireless walkie-talkie, etc. It adopts single-point to multi-point technology, and the signal from the transmitter to the luminaire is independent, solving the problem of excessive interference. Wireless DMX512 control technology is rare in practical applications in outdoor landscape lighting, but it is also a kind of existence and has practical applications. Because the scope of application is narrow, this article will not do more detailed introduction.
3 Conclusion
DMX512 technology has been successfully applied in landscape lighting, and Figure 9 is one of its application cases. Although in a strict sense, perhaps these evolutionary DMX512 technologies are far from the essence and abandon some of their distinctive features, but from the practical application point of view, as long as the expected results can be achieved, and meet the stability and reliability, use Is it important to implement this form? From the perspective of development, as long as it is more stable, more practical and convenient, and cost-effective, all kinds of flexibility is a technological advancement! For the evolution of different forms, the author believes that there is value and significance of its existence! Such as higher cost of a single lamp, the mounting position irregular flood light, you can still employ parallel bus RS485 DMX512 control, so that more secure; and compact size, pixel density mounting lights, string, and other products are single-wire parallel TTL The DMX512 control design of the communication is more convenient and the cost performance is higher. Just like our demand for lighting products, lighting control also needs a lot of flowers!
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