A few questions about daisy chaining 25 TLC5947s

Hi all,

For my project I'm creating a large-scale exhibit for which I intend to power 200 RGB LED's individually. My plan is to use a a series of 25 daisy-chained TLC5947's (each of supports 24 channels = 8 RGB LEDs). Control will be provided by a Raspberry Pi over SPI using a library like this one. Each LED has a max power dissipation of 150 mW, so the max total power used by the LEDs should be 150 mW * 200 = 30W. A 12V 5A switching DC power supply connected to one of the TLC5947's should be able to provide more than enough power for the whole series. From a control standpoint, a small amount of lag between the Pi sending an update signal to a specific LED and and it actually responding is okay, but hopefully not more than a few microseconds, as I want to do some coordinated light displays. My questions right now:

  1. Are there any obvious problems with this setup?

  2. The TLC5947's might be physically up to 5 feet apart. What kind of connecting cable might I be able to use to join them together for power and SPI data (ideally, one cable housing both)? Ideally, they would be joined via snap-in or friction connectors to make assembly and disassembly easy. I looked at using CAT5, but I don't think it can handle that much power and I'm not sure what other considerations I need to keep in mind.

Bonus question: Any suggestion on an easy and discreet way to connect the LEDs to the TLC5947's? Those distances will be about 2-3 feet long. I guess I'm looking for a nondescript-looking 4-wire cord.

Thanks in advance for any advice! Mark

. Are there any obvious problems with this setup?

Yes it is:-

The TLC5947’s might be physically up to 5 feet apart.

You have two problems with this.

  1. The fan out from the arduino, you will not be able to supply the current from one pin to drive 25 signals.
  2. Signal integrity, by the time a logic level signal travels 25 times 5 feet = 125 ft, it will be, to use a technical term shagged.

Basically this is the wrong sort of configuration for this chip.