Four Development Stages of DMX512

The New Progress in LED Landscape Lighting Control System - DC Carrier Communication

LED lighting in the landscape illumination field has journeyed through more than a decade, and its control technology has evolved through several stages, each solving many issues while also introducing new challenges. Let’s further explore the development of LED control technology.

First Stage: This stage adopted a control method transferred from LED display screen drive controls, using serial shift communication methods with chips like 74HC595, DM115, MBI5026, etc., where each chip and fixture is cascaded. It encompassed both constant voltage and constant current drive methods. The problem with this communication method was an excess of signal lines on the fixtures, reaching up to 4 or 5 lines (including the ground line), not only increasing the production and debugging time and material costs for companies but also adding to the installation time and material costs. Moreover, it led to an increased failure rate, with the primary issue being that if a chip or signal at the front end of a string of fixtures was damaged, it would affect those downstream. However, its advantages are undeniable, with HC595 being inexpensive, mature, and easy to design and program, supported by many controllers on the market.

Second Stage: The adoption of the DMX512 protocol and RS485 bus form, using RS485 chips partnered with microcontrollers (MCU) to create an RS485 parallel system with 512 valid points on a single bus, where each fixture is numbered to receive different data for dimming and color adjustment. Compared to the first stage, this method reduced the number of signal lines and essentially eliminated the phenomenon of one fixture’s failure affecting subsequent fixtures. Signal transmission distance was extended, and the distance between lights wasn't limited to a few meters. However, it also brought other negative issues, such as high costs for DMX decoders, either significantly more expensive when outsourced or requiring skilled engineers for in-house production. Additionally, numbering each light for address setting (automatic addressing would require adding a signal line), difficulty in troubleshooting when a decoder issues affect the bus, and the limited number of lights a master controller can handle increased the entire system’s hardware costs. These downsides influenced the widespread use of DMX512 systems, limiting them to mid-to-high-end projects.

Third Stage: The emergence of single-wire, 3-pin, and 6-pin driver chips greatly simplified the design of LED fixtures. Representatives of single-wire chips include ZQ1111, TLS3001, TM1803, SDMX5124, etc., linking chip to chip through a single signal line in series. Each chip’s I/O port could autonomously perform PWM scanning, thus allowing a significant reduction in the communication rate on the signal line, essentially eliminating the need for HC245 within distances of less than 2 meters between chips. These chips could support high grayscale (over 256 levels) data transmission and increase the number of lights in series. They have been widely applied in point lights and light strings (bars), with guard tubes requiring segmentation and the use of more chips, gradually replacing the first stage’s mature and stable chips. This stage’s innovative advantages were clear, designed for point lights and light strings (bars) with only three output ports and internal PWM output, significantly improving data transmission efficiency and reducing speed, thus enhancing reliability, eliminating the need for amplification components, and increasing cascading capability. However, drawbacks included most chips being new to the market, therefore questioning their stability and with slightly stable ones being expensive, limiting the application of single lights requiring multiple chips. Furthermore, data transmission still relied on cascading, where front-end chip or signal faults could affect chips and signals downstream, and there was limited controller support on the market, restricting customer choice.

Fourth Stage: DC carrier modulation communication applied in LED lighting control systems. DC carrier communication, as the name suggests, involves loading waveforms onto DC power lines to transmit signals, achieving the purpose of transmitting both power and signal through the same lines, rendering a separate signal line for fixtures unnecessary and only requiring a power line. This outlines advantages for the lighting system without needing signal lines: 1. Reducing the time and material costs for welding and connecting signal lines during factory fixture processing, 2. Minimizing the time and material costs for fixture connections and signal line arrangements in projects, 3. Speeding up system debugging and repairs, as a single faulty light does not affect other fixtures, simplifying fault diagnosis. Its basic principle involves connecting the power input of a carrier modulator to a switched power supply and its signal input to the output port of the LED master controller, then outputting a set of powered lines with signals, paralleling each light to this powered group. Each light's carrier demodulator then demodulates the signal from the power lines, processed by the MCU to control the fixture. Specialized integrated chips and demodulators can further be used for power stabilization, rectification, and filtering to power the fixtures. Thus, pairing each switched power supply with a carrier modulator eliminates the need for signal lines in fixtures. DC carrier’s rate range is broad, from 0–1 MHZ, allowing for arbitrary selection. Modulators and demodulators can be designed to be compatible with or forward DMX512 protocol signals, making them universally usable with DMX512 master controllers on the market, significantly broadening customer choice. However, DC carriers also have disadvantages: 1. The loaded signal increases the power line's impedance, enlarging line voltage drop, necessitating a higher input voltage to meet the voltage needs of end fixtures under full load, 2. The bus wiring requires fixtures to have address codes to differentiate signal data positions, 3. Carriers involve modulation and demodulation devices, thus the system's total cost won’t be cheaper than in the first and third stages but can be lower than the DMX512 system of the second stage.

In comparison, the fourth stage, in terms of price, sits between the first (third) and second stages, but in terms of performance, it is superior. The fourth stage—DC carrier communication system—represents the best value for money.

Certainly, the development of LED lighting systems will not stop at the fourth stage; a fifth stage will emerge. What could the fifth stage be? Likely, it would involve wireless communication, eliminating signal transmission through power lines and reducing voltage drops to those of the first, second, and third stages, thus fundamentally solving most drawbacks of LED lighting systems.