Red light is displayed instead of expected white when trying to fill 32*16 panel with maximum white.

[shinych]

Hello. Thank you for the awesome library!

I am trying to experimentally see what is the power consumption when the panel is turned on with maximum brightness where all LEDs are on with #FFFFFF color. For some reason, the panel gets dark red instead of the expected bright white.

I am using this 32*16 panel https://de.aliexpress.com/item/32897324696.html with these options: --led-rows=16 --led-multiplexing=3 --led-row-addr-type=2 also added --led-slowdown-gpio=2 for Raspberry Pi 4 (as suggested in the issue 681). It all works very well when I am displaying some text or graphics.

This is my python function for filling the panel with the given color:

def display_fill(self, color):
    canvas = self.matrix.CreateFrameCanvas()
    canvas.Clear()
    for y in range(0,16):
        graphics.DrawLine(canvas, 0, y, 31, y, color)
    canvas = self.matrix.SwapOnVSync(canvas)

It works as expected when I pass any color up to approx. 243 brightness: graphics.Color(243,243,243)

But when I pass e.g., graphics.Color(255,255,255), the LEDs are on with a pale red color, which seems like some kind of a safe mode. (?)

Here is a video demonstrating the issue, when I change the color in the loop: https://youtu.be/0UC46oxHKms

I also noticed that when I reduce the number of lines in my function from 16 to 12 (so only 3/4 of the LEDs are on), then the fill with #FFFFFF also works fine.

What can be the reason for this behavior?

Thank you.

[fjansson]

Just a guess: could you be overloading the power supply? Red LEDs require less voltage to light than blue or green, so if the voltage drops the red ones would work the longest.

[shinych]

@fjansson thanks for your reply! Possibly, this was the issue.

With another power supply, it works properly now.

I am wondering if this "falling back to dark red" is by design or just a coincidence. Seems to be a neat feature for such cases!

[SchlenkR]

..same issue here, and: Reducing the number of LEDs helps. I didn't try another power supply, but I'll try. BTW: I'm using a complete different library :D So I guess you can close that issue here.