DMX512 lighting control principle and engineering debugging problem sharing
Lighting control is the use of automatic control technology and intelligent management technology to control and manage the opening, closing, adjustment, combination and scene mode of the light source or lighting equipment of the building and environment lighting, so as to achieve the purpose of building energy saving, environmental art and sensor linkage.
the types of lighting control methods are varied, and the common ones include the following:
■ ON/OFF this is the simplest and most common control method: on/off, turn the light on/off. ■ 0~10V 0~10V is also a control signal, used to control the power supply part of the lamp, so that the lamp can receive 0~10V signal, a simple understanding is to adjust the brightness by adjusting the voltage, for example, 0V, the power output is zero; and 10V, can make the lamp output 100 brightness. ■ DALI DALI system is mainly used as a hotel, indoor lighting control system. Its biggest feature is that a single lamp has an independent address, and a single lamp or lamp group can be accurately dimmed through the DALI system. ■ P2 domestic independent innovation agreement control system. (with illicit cargo ^-^) ■ DMX512 DMX512 is mainly used for stage lighting and outdoor lighting. The specific control form is: WiFi, infrared induction, remote control, human body induction, etc.
The following will share with you the relevant content of DMX512.
DMX512 English is the Digital Multiplex With 512 pieces of information (ie multiple digital transmission).
The DMX512 protocol was first developed by the USITT (American Theatre Technology Association) as a way to control a dimmer from a console with a standard digital interface. In contrast to DALI, which is used to express static effects, DMX512 is mainly used to express the dynamic effects of the illuminated objects, that is, DMX-controlled lights give people the feeling that they are always changing, mainly in color changes, suitable for rendering atmosphere, so they are generally used in landscape lights and stage lights.
▲ DMX512 control system schematic diagram: several RGB lamps, each lamp contains a DMX module, the module at the same time received the power supply and controller signal, will drive the LED lamp beads bright and dark change, so as to adjust the color change.
■ Each output loop supports a maximum of 512 channels each output loop supports a maximum of 512 channels, and the maximum number of devices that can be brought to each port is determined according to the number of channels occupied by a single device.
▲ RGBW single pixel lamp connection diagram
■ 256 dimming gray scale (0-255) each DMX control byte is called a command frame, called a control channel, which can control one or more functions of the lighting device. A DMX command frame is composed of 1 start bit, 8 data bits and 2 end bits, and adopts unidirectional asynchronous serial transmission.
the S in the control instruction in the dotted line in the above figure is the start bit and the width is one bit, which is the start mark for the controlled lamp to receive and decode the control data; E is the end bit and the width is two bits, indicating the end of an instruction frame.
D0 and D7 are 8-bit control data, and their level combinations 1111 from 0000 to 1111 have a total of 256 states (corresponding to 0 to 255 in decimal numbers). When controlling the brightness of lights, 256 brightness levels can be generated, with 0000 to (0) corresponding to the darkest lights and 1111 1111(255) corresponding to the brightest lights. The DMX512 instruction has a bit width (per bit width) of 4 s, a frame width of 44 mps, and a transmission rate of 250 kbps.
■ Standard EIA485 interface The wiring mode is a bus topology and does not support ring or star networks. Up to 32 nodes can be attached to the same bus.
▲ The structure of various shapes, DMX512 to follow the first kind of bus structure, has a head and a tail.
▲ The above picture is a buried lamp project in Guangzhou. The signal line is relatively casual when wiring (as shown in the right picture), which will add a lot of work to the follow-up work.
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■ Transmission rate 250Kbps Bit rate refers to the number of bits transmitted per second, bit per second (bps). The baud rate is closely related to the construction specification, and the high baud rate signal has poor anti-interference ability.
in practice, sharing a few experiences can reduce some control problems:
the transmission distance of the super five network cable shall not exceed 100 meters; the distance between the controller exceeds 100 meters, the use of optical fiber; ③ The EIA485 protocol stipulates that the number of nodes carried by each repeater shall not exceed 32; ④ The wiring of each control loop must follow the bus structure layout; ⑤ The signal line and power line shall be laid separately.
Murphy's law, no matter how low the probability, bad things will always happen. Even if you use the DMX512 control system according to the standard step by step, you can always encounter various problems.
1. the entire control loop lamps flash uncontrolled how to do?
1. Confirm that the controller signal output is normal
when the whole control loop is out of control, if possible, first use the temporary controller to test whether the loop is controlled separately;
a. Controlled-there is a problem with the signal output of the original controller (or a problem with the wiring file, or a problem with the port hardware, or a problem with the port wiring); b. Uncontrolled-continued investigation; c. disconnect the lamp after the first lamp and test the first lamp separately to determine whether it is the controller problem or the signal interference caused by the rear lamp;
at this time, the first lamp is often OK.
2. Troubleshoot nodes or lamps
when the controller signal output is normal, slowly increase the lamps and find out the nodes or lamps that cause the abnormal loop signal; usually the "dichotomy" is used more quickly.
2. a control loop individual lamps flash uncontrolled
1. Confirm controller wiring is in place
the number of lamps in the wiring file of the controller shall be consistent with the number of lamps installed on site.
2. Test with full wiring file
first, use the test program to control the test, that is, the single-port wiring file is full of 1-512 channels.
A. random flashing lamps are controlled, and the problem can be solved by rewriting the code for the circuit lamps at this time; b. individual lamps are still not controlled, and the wiring of the signal output terminal of the uncontrolled lamps is correct or the lamps themselves have quality problems.
3. under what circumstances need to add a signal amplifier?
One function of the signal amplifier is to amplify the signal and restore the weakened signal to the strength of the starting point; the other function is signal isolation to prevent damage to the controller caused by the lamp failure.
In the standard case, accordingEIA485 protocol, every 32 nodes need to add a signal amplifier. In order to avoid the lamp signal becomes weak in rainy days or other circumstances, resulting in the phenomenon of flashes of lamps.
How many nodes can be taken in the output port of the 4. plus amplifier?
In the current EIA485 protocol, the standard is generally recommended to add an amplifier to 32 nodes. However, in actual operation, there can be more than 60 nodes, but there is a potential safety hazard of signal instability.
5. if the signal line is not shielded, can the signal be transmitted? If so, how far is the distance?
many domestic projects use network cables to make signal lines, which are basically unshielded. The transmission distance will definitely be discounted, but it still depends on what project is used to make the decision. The maximum distance can generally reach about 100m.
What should I do 6. the DMX loops are not synchronized in time?
There are several different ports in the same divider, and some of the individual port output signals will have obvious delay. What needs to be done at this time is to reset the parameters of the controller. Because the greatest possibility of this situation is that the parameter problem of the controller itself causes the output frequency of each port to be different, which causes the signal output of each port to be asynchronous.
7. the transmission rate is reduced, will synchronization be affected?
the transmission rate of DMX512 is 250Kbps, which cannot be reduced. If the transmission rate is reduced, it is another system. Another set of systems will have another set of protocols, which will not have any effect on the synchronization of the lamps.