New progress in LED landscape lighting control system - DC carrier communication

LED lights have been used in the field of landscape lighting for more than ten years, and their control technology has also developed in several stages. Each stage has solved many problems and introduced new problems. The following is a further discussion on the development of LED control technology.

Phase 1, LED display Driver Control mode transfer method

The serial shift communication method based on 74HC595, DM115, MBI5026 and other similar chips is adopted . Each chip is cascaded and each lamp is cascaded. There are both constant voltage drive mode and constant current drive mode. The problem caused by this communication method is that there are too many signal lines on the lamp, reaching 4 or 5 (including ground wire), which not only increases the time cost and material cost of production and debugging of the company, but also increases the time cost and material cost of engineering installation, and at the same time leads to an increase in the failure rate. The biggest problem is that the chip or signal at the front end of a string of lamps is damaged, and the back end is also affected. Of course, its advantages are also indelible. HC595 is cheap, the chip is mature, the lamp and program design are easy, and there are many controllers supported on the market .

Second stage, RS485 bus of DMX512 protocol

The RS485 chip plus a single-chip microcomputer ( MCU ) is used to form an RS485 parallel system with 512 valid points on a bus. Each lamp is numbered with an address to receive different data respectively, so as to achieve the purpose of dimming and color adjustment. Compared with the first stage, this method reduces the number of signal lines and basically eliminates the phenomenon that the failure of a lamp affects the subsequent lamps. The signal transmission distance is relatively long, and the distance between lamps is not limited to a few meters or tens of meters. However, this method also brings other negative problems. First, the cost of DMX decoders is high. It is not only a little higher when purchased from outside, but also requires good design engineers to make it yourself. Then each lamp must be numbered. Automatic addressing without numbering requires additional signal lines. In addition, sometimes a decoder has a problem that affects the bus and is difficult to find the problem. In addition, each main controller has a limited number of lamps, which increases the hardware cost of the entire system. These negative problems are also the reasons that affect the large-scale use of DMX512 systems, and can only be used in some mid-to-high-end projects.

Phase 3: Single-wire communication

The emergence of 3-port and 6-port driver chips makes the design of LED lamps simpler

Representatives of single-line chips include ZQ1111, TLS3001, TM1803, SDMX5124, etc. They are all serially cascaded between chips through a single signal line. The I/O output port of each chip can automatically perform PWM scanning, so the communication rate on the signal line can be greatly reduced. If the distance between chips is less than 2 meters, HC245 can basically be omitted. This type of chip can not only meet high grayscale (256 levels) data transmission, but also increase the number of series lights. At present, it is widely used in point light sources and light strings (strips). Guardrail tubes need to be segmented, so more chips are used. The chips in the first stage are mature and stable, and it will take a process to gradually replace them. The innovative advantages of this stage are obvious. Only three output ports are designed for point light sources and light strings (strips), with internal PWM output, which greatly improves the data transmission efficiency, greatly reduces the data transmission speed, improves reliability, eliminates amplifier components , increases the number of cascades, and greatly improves the flexibility of lamp design. However, there are some shortcomings. First, most chips have just been launched, and their stability still needs to be considered and improved. The price of slightly stable chips is relatively high, and the application of single lamps that require multiple chips is limited. Secondly, the data is still transmitted in cascade mode, and the failure of the front-end chip or signal affects the subsequent chips and signals. Thirdly, there are not many controllers supported on the market, and customer choices are still limited.

Phase 4: DC carrier modulation communication applied to LED lighting control system

As the name implies, DC carrier is to load waveform on DC power line to transmit signal, so as to achieve the purpose of transmitting power and signal on the same line. Therefore, the lamps using this system do not need signal line, only power line. Therefore, the advantages of not needing signal line to lighting system are described as follows:

1. Reduce the time cost of welding and connecting signal lines when processing lamps in factories, as well as the material cost of signal lines;

2. Reduce the time cost and material cost of lighting connection and signal line layout in the project;

3. Improve the debugging and maintenance speed of the lighting system. The failure of a single lamp will not affect other lamps. The fault judgment is intuitive and you can find the faulty lamp.

The basic principle is that the power input end of the carrier modulator is connected to the switching power supply , and the signal input end is connected to the output port of the LED main controller. After the carrier, a group of power lines with signals are output. Each lamp is connected in parallel to this group of power lines. The carrier demodulator in each lamp demodulates the signal on the power line, and the single-chip microcomputer (MCU) controls the lamp after processing. In the future, a dedicated integrated chip can be used. The demodulator stabilizes the power supply, rectifies and filters it, and then supplies power to the lamp. Therefore, each switching power supply is equipped with a carrier modulator, and the lamp does not need a signal line.

The DC carrier has a wide range of rates, which can be selected from 0-1MHZ. The modem can be designed to be compatible with the DMX512 protocol or forward DMX512 protocol signals. All DMX512 master controllers on the market can be used, greatly expanding the customer's choice. DC carrier also has its disadvantages:

1. Because the power line is loaded with a signal, the impedance of the power line increases and the line voltage drop increases. Therefore, the power input voltage needs to be increased by a few volts to meet the voltage requirements of the rear-end lamps at full power load;

2. Because it is a bus connection, the lamps need to be programmed with address numbers to distinguish the signal data location;

3. Because the carrier has modulation and demodulation equipment, the total system cost will not be cheaper than the first and third stage systems, but it can be lower than the second stage DMX512 system.

Here, comparing the performance and price of the above four stages, the fourth stage is between the first (third) and second stages in terms of price, and the fourth stage is the most superior in terms of performance. The most cost-effective is the fourth stage - DC carrier communication system.

Of course, the development of LED lighting system will not stop at the fourth stage, there will be a fifth stage, what will the fifth stage be? I think it should be wireless communication, so that the power line does not need to carry signals, and the voltage drop returns to the same as the first, second, and third stages. Therefore, most of the disadvantages of LED lighting system are basically solved.