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Controlling LED strip with Nexys4 DDR


Question

Hello i'm a compsci undergrad and for a small project i have to drive a led strip using the Nexys4 DDR board.

My question is very simple and while the VHDL part of the project works alright I have a doubt about the intergraton with external hardware. As the title says I have to drive a led strip using the board, the led strip is composed by a series of WS2811 IC led controllers each connected to 3 5050 RGB LEDs. According to the WS2811 datasheet the chip needs 12V in but the board can't provide such high voltage so I have to use an external PSU for it. At the moment I'm just using the 5V USB to power the board, I'm unsure if it's okay to power the LED strip with an external PSU and the board using my PC and just connect the serial data pin OR if both the led strip and the board must be powered from the same source (eventually using a step down converter) with common GND.

The board is pretty expensive and I don't want to break anything so I figured out it was a good idea to ask here ahah thank you for your time

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Hi @lorenzouni,

My first gut reaction is that you should definitely make sure that your LED strip, Nexys A7 (the Nexys 4 DDR), and your PSU share a common ground, regardless of how they end up being powered since different sources of power can be (and often are) at different voltage potentials relative to earth ground, so it is always wise to get a common ground between systems communicating with each other.

I was also under the impression based on a WS2811 datasheet that I was looking at, https://cdn-shop.adafruit.com/datasheets/WS2811.pdf, that the power supply voltage had an absolute maximum rating between 6 and 7 V DC with a recommended value of 5 V DC.

But, if I am reading this incorrectly and the WS2811 LEDs need a 12V supply, I would check to see if the data input pin can accept and read 3.3V logic (since that is what the digital IO on the Nexys A7 operate at), and if so you can power the LED strip at 12V, use a step down converter to get a 5V line to power the Nexys A7 on JP3/J12.

For what it's worth, Digilent did something similar with WS2812 LEDs and a microcontroller many years ago; you can see what we did on Instructables here: https://www.instructables.com/900-LED-display/.

Thanks,
JColvin

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