LED Project Design Guide - Controllers

Controllers:

A controller comes in different types, the controller needs to be compatible with the LEDs or pixels that are being used. A controller receives data control(such as DMX) or local stand-alone color sequences and converts the values to an output for the LEDs.

Output, Constant Voltage: Most common type, does not regulate current and provides a consistent voltage, usually the output is PWM controlled to vary the channel intensity. Used to control LEDs such as standard 12 volt LED strip or modules.

Output, Constant Current: A less common type, regulates the output current to a constant selectable value, voltage is consistent but can be higher than the LED's rated voltage. Used to control high-wattage LEDs like 350mA or 700mA types, or smaller LEDs such as 5mm or 10mm types. Typically these controllers only work with a single current range.

Output, Pixel Controller: Becoming more common, these types of controllers are used to talk to smart/addressable pixels, such as WS2812, WS2801, APA102. These controllers do not control the LEDs directly, but rather produce a data signal that is received by the pixels and decoded into light intensity for the colored LEDs within the pixel.

Input, DMX-512, ArtNet: The most common control protocols that a software application will output. Packets are limited to 512 channels which is 170 RGB LEDs or 128 RGBW LEDs. Strands controlled with DMX/Artnet can not be longer than that unless the controller features universe merging.

Input, Serial, USB, Bluetooth, WiFi: A different way to transmit data to controllers. None of those are protocols necessarily, but are ways to interface from the transmitting PC(or other device) and the controller. WiFi could use protocols such as the NLED serial or even DMX/Artnet.

Input, Stand-Alone: Controller stores color sequences locally, either in memory or on an SD card. The user must load the sequences prior to usage. NLED products can trigger and control the stand-alone sequences through commands and software.

Pixel Controller:

Output Packet Rate: Also referred to as FPS(frames per second) which is how often the pixels are updated with new data. The pixels can not be updated with new data if the new data has not yet been received or transmitted. So the actual pixel packet rate is tied to the input packet rate. The maximum packet rate is limited by the pixel chipset. Asynchronous chipsets can not update as fast and commonly have a limit of 30 FPS with 1024 pixels at best. Synchronous chipsets can update faster and the upper limits is set by the controller's pixel output clock rate.

As an example, a WS2801 at 2.6Mhz(NLED default) clock output, with 1000 RGB pixels takes 9.2mS to send the packet to the pixels. 1000 RGB pixels of WS2812 at 800Khz takes 30mS to transmit to the pixels.

Input Packet Rate: DMX is typically 24 to 44 FPS, depending on software or console settings. Software applications will have internal values to use as the packet rate, but is also limited by how long it takes to send the data out.

Using other data sources such as serial, the input packet rate can be adjusted depending on baud rate of the serial data. To transmit data for 1000 RGB pixels at 1 mega baud(1,000,000) it takes 10uS per byte. There are 3000 bytes(one per channel) that are transmitted. Which takes 30mS to transmit the 3000 channels/bytes from PC(or other device) to the controller. Then that data is converted and sent from the controller to the pixels, which takes additional time. Reception of new data and transmission of the pixel data happens at the same time. There is a latency between what the PC sends and what is updated to the pixels, but there are numerous other aspects(such as drivers, USB enumeration, etc) that can delay the packet update even more. 100mS latency can be reasonably expected.

Stand-Alone Packet Rate: For NLED pixel controllers running Aurora stand-alone color seqeunes can perform extremely fast packet rates. Commonly that is 50 FPS, which creates very smooth color fades and transitions.

Smart Controllers: Supports stand-alone color sequences. Good for wearables, LED matrix, flow toys, infinity mirrors, and other projects that just need a simple way to play color sequences without other devices or computers attached. All of these controllers can also receive DMX, serial, USB, etc.

'Dumb' Controllers and Decoders: These controllers convert data signals such as DMX-512 or serial into outputs that control LEDs. Requires a computer or other device to transmit data to the controller. Good for LED matrix, wash lights, or any project that will be controlled remotely. DMX and serial can be both wired or wireless, there are many options for either solution.

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