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Neopixel 8x8 matrix doesn't work when driving from ZYBO FPGA
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Neopixel 8x8 matrix doesn't work when driving from ZYBO FPGA

by NanSheng on Thu Mar 08, 2018 4:47 pm

Hi, dear elites,

I'm new to Neopixel 8x8 LED matrix and now we bought some boards. However, when I got the board and designed a controller in ZYBO FPGA for testing, It's out of control. Thus I'd like to ask the following questions to clarify the understanding of the spec.

Q1: The 1st test pattern the FPGA controller output is to send out signal with LOW as reset code for 63us and then followed by a green color code for 64 LEDs and then end up with low for reset code. If FPGA controller only sends out the waveform ONCE, what would it expect to show in the Neopixel 8x8 LED matrix ? I expect it will keep showing green color since LED should latch the green color. Is it that case ? I don't see any lighting in the matrix in FPGA Testing.

Q2: The FPGA drives output with LVCMOS33 standard and a 200ohm resistor in series to the input pin of Neopixel 8x8 LED matrix . Is it OK ?

Q3: For power, we use 5V adaptor with 4A output without any RC circuit to the Neopixel 8x8 LED matrix. Is it OK ?

Q4: I followed the specification of WS2812B for timing control and use. The FPGA generates reset with 70us, TOH with 0.384us, TOL with 0.88us, T1H with 0.72us and T1L with 0.54us. Is it OK ?

Since it uses FPGA to control the matrix, it needs to design HW to drive the LED matrix. What kind of basic pattern would you suggest to drive first to check the baseline ?

https://www.adafruit.com/product/1487

If you need more information, please feel free to let me know. Thanks

All the best,
Nan-Sheng

NanSheng
 
Posts: 2
Joined: Thu Mar 08, 2018 4:02 pm

Re: Neopixel 8x8 matrix doesn't work when driving from ZYBO

by NanSheng on Fri Mar 09, 2018 7:54 am

After some attempts in debugging, I caught the root cause which is the output of FPGA 3.3V has potential issue to meet the VIH of Neopixel LED matrix, After placing a level sifter, it's resolved. Thanks

NanSheng
 
Posts: 2
Joined: Thu Mar 08, 2018 4:02 pm

Please be positive and constructive with your questions and comments.