Most pixel types feature three terminals to drive them:
- VCC
- 0V
- DATA (DI)
However, with advancements in technology, manufacturers have developed chips that require four terminals. An example of tape that uses this technology is ENTTEC’s 8PX60-12-B pixel strip. This is based on the |WorldSemi WS2815 IC with a standard data line plus a backup data line to allow the data to still carry on down the strip if a pixel gets damaged or removed. These four terminals are:
- VCC
- DATA (DI)
- BACKUP DATA (BI)
- 0V
In the WS2815 protocol, it is possible to connect just VCC, GND, and DATA to your 3-terminal pixel driver. Better yet, you could splice the data output from the pixel controller to connect to both the Data and Backup Data terminals from your driver.
Another variation of 4 terminal pixels is for clocked protocols (i.e. APA-102). These separate the pixel data and clock data (usually embedded in the single data line). In these pixels, the terminals are as follows:
- VCC
- DATA (DI)
- CLOCK (CLK)
- 0V
In this system, the pixel receives data via the data line and then receives information via the clock line, which tells the pixel when to check for data. This helps overcome issues in very long runs of pixel strip, where the pixels might be slightly out of sync from start to end of the run and allows faster refresh rates (2 data lines = twice the bandwidth). If the Clock line is not connected, and if it is not receiving appropriate Clock information, the pixel will not be able to respond to the data it receives.
It is essential to remember that the data line and clock line do not carry the same information. You cannot splice the data line out from a 3-terminal controller to connect to the Data and Clock terminals. The pixels will not respond correctly if this is done. Using a Data + Clock protocol requires a controller that supports clock data.
Terminology
VCC/5v/12v/24v: VCC is a term used across the board, it stands for “Voltage Common Collector” this has a background in electronics, i.e. the rail that all the collectors (transistor pin) were attached to. It’s the collector voltage compared to the GND (0V referencd). – As the OCTO can handle between 4-60V DC we don’t mention discrete voltages on the label. Power (VCC) is non-directional on Pixel Strip
GND to 0v: Ground (GND) is non-directional on Pixel Strip, and is used as the common line for the pixels.
Data/DI: Data is one way, DI = Data In, DO = data Out, the data cascades down the chain. to put it simply, each RGB LED receives the data, uses the first 3 three control channels to set its colour, then removes them from the packet and passes a restructured packet down the chain to the next LED in the strip to do the same thing. – It’s due to this data reshaping circuit built into each LED that this data is unidirectional.
Clock (only on specific pixel strip): broadly speaking, there are two main types of pixel strip on the market, asynchronous and synchronous. The key differences are that asynchronous embeds timing and colour level into the data feed, meaning you only need one data connection and wiring is simple (all of ENTTECs strip is asynchronous). Syncronous however, requires a clock signal feed to be sent separately to the data feed. An example of this is the APA-102 chip type. Strips produced using these chips require both Data and CLK to be connected from the OCTO to the LED’s. – The benefit of this is that there is more bandwidth to push high refresh rates to the LED’s. However, given the ArtNet or sACN data being sent to them is likely to be 60FPS at the maximum, it’s difficult to even come close to the limits of asynchronous, the way we see it, more wires = more to go wrong.
Backup Data/BI (only on specific pixel strip): WS2815 is the Pixel IC Protocol used by our pixel strip (almost an identical signal structure to WS2812b), it encompasses the Data, and Backup line (backup is unique to WS2815). You could refer to our 12v black strip with the data and backup line as “a WS2815 pixel strip”. (In much the same way you would say that a moving light is a “DMX controlled moving light”).