What does SPI, often heard with pixel-controlled LEDs, mean, and how does it differ from DMX512? We explain how it works, its advantages and limits, and which to choose in which project.
On a pixel-controlled facade, each LED group, that is, each pixel, receives its own color and brightness separately. There are two common ways to carry data to so many points: DMX512 and the serial pixel protocols known in the industry simply as SPI. Both can produce the same image, but they differ in many respects, from cabling to fault behavior.
SPI (Serial Peripheral Interface) is a serial communication method used in electronics to carry data over short distances between chips. In LED lighting, it is used as the general name for protocols in which pixel chips carry data by passing it on to one another. Chips such as WS2811, WS2812, WS2815, SK6812, UCS1903 and TM1814 are well-known examples of this family.
Most of these chips work with a single data line; some, such as WS2801 and APA102, use a separate clock line in addition to the data line. The control device must support the protocol of the chip used.
In an SPI system, the pixels form a chain. The control device sends the data for all pixels one after another to the head of the chain. The first pixel takes its share and passes the rest to the next; each pixel repeats the same job. That is why pixels are not addressed manually: each pixel’s address is its position in the chain.
This structure brings both advantages and limitations.
| Feature | SPI | DMX512 |
|---|---|---|
| Addressing | Automatic, by position in the chain | Each luminaire or pixel is given a start address |
| Signal structure | Single-ended (TTL) | Differential (RS-485) |
| Cable distance | Short; an amplifier may be needed | Long; up to 300 meters per segment recommended |
| Fault behavior | Without a backup data line, the chain may break | A faulty luminaire usually does not affect the others |
| Cost per pixel | Lower | Higher |
| Standard | Chip-specific protocols | Open standard (ANSI E1.11) |
In short, SPI is a strong option in projects where the luminaires are close to the controller, pixel density is high and the budget is decisive. In projects with long cable runs, luminaires spread over a large area of the facade, or devices from different manufacturers working together, DMX512 is the safer route.
There are also solutions that combine both worlds: data arriving over the network via Art-Net or sACN is converted to SPI in controllers placed right next to the pixels. This way the long distance is covered by Ethernet and the last few meters by SPI. We explain this structure in detail in our control signal article.
In most of our pixel-controlled products, SPI is standard and DMX512 optional. For example, our MidiPix P16 linear luminaire can be ordered with the SPI (standard) or DMX512 (optional) protocol; it has 16 pixels per meter, each controlled independently. Our PixiDot point luminaire is also made with SPI as standard and DMX512 as an option, so it fits both existing and newly installed systems.
We can evaluate together which protocol suits your project’s control infrastructure, the cable distances and the controller layout.
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