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What is the main purpose of LED hub, is it used only for RGB matrices to connect shift registers for every color or there are some other applications?

I'm working with HUB75 and that is the reason why I'm asking this.

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The question as stated at the time of this writing is a little vague, but I assume by "LED Hub" you're asking about the purpose of driver circuitry, to drive something such as this. There are a few reasons why you would use drive circuitry such as that; let's go over them:

  1. I/O Expansion: One of the primary limiting factors in driving an LED matrix by a device such as a microcontroller is the number of individual I/O lines available to drive the individual LEDs. Most microcontrollers offer 8~100 I/O lines; for applications which require more I/O, control circuitry (such as the LED hub) is generally called for.
  2. Ease of Computation: By offloading the LED driver functionality, control of the LEDs can happen in parallel to the primary processing unit, with minimal interaction from the microcontroller or other device (no need to have the microcontroller step through individual rows or deal with other computationally-intensive processes such as charlieplexing). This is a valuable feature, especially in lower-end devices which don't offer DMA and/or concurrent execution abilities (FPGAs, CPLDs).
  3. Power Concerns: Driving large numbers of LEDs requires significant amounts of current. A standard LED indicator will often require on the order of 20mA for operation. If multiple LEDs are run in parallel, their current draws can quickly add up, exceeding the maximum amount of current that can be run through a microcontroller or other device (as a rule of thumb, most contemporary embedded microcontrollers can pass 250-500mA of current; this figure is typically stated in the "Electrical Characteristics" (or related) section of the datasheet of a device in question).
  4. Constant Current Driving and PCB Organization: The main failure mode for LEDs is generally excessive heat build up ("thermal" failure). Depending on the LEDs in question and the application of interest, it may be beneficial to utilize circuitry such as a constant current driver to regulate the amount of current flowing through one or more LEDs. Control circuitry such as the LED HUB provides a nice, orderly way to add these features to your design without cluttering it.

Regarding applications, LED driver circuitry is primarily designed for driving arrays of LEDs. As far as other applications go, you might be able to drive large numbers of other small, low-current, DC-devices, such as piezoelectric buzzers. Outside of that, nothing particularly compelling comes to mind.

Hadley Research
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  • The answer provided by @Hadley Research is largely complete. I would only add another reason to a 'HUB' board like that (and countless others like it) is that driving R, G & B from separate 'channels' can be advantageous in colour control, but again that depends on the capabilities of the driver chip on said 'hub', again of which there are many. So it's not necessarily about a 'matrix' per se (i.e. 2D arrangement) either, that's really just a matter of physical organisation. – Techydude Jun 13 '15 at 03:59
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Its purpose is to seperate the driver end from the data processing unit and making the driver belonging to led matrice. The processing unit alone, with correct parameters, can serve to a higher number of variation of led matrice circuit. In this arrangement, the dependency probability is higher for low cost driver, and lower for high cost processing unit.

Ayhan
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