Anyone having success with WS2812 via BitStream?

[TJC]

Hey folks,
Has anyone had success driving WS2812 LEDs using flint.io.BitStream?

I have a Lolin S3 board with a built-in WS2812 RGB LED on pin 38.
I'm trying to use this code to set it, but haven't had any luck.

EDIT: This turned out to be a bug in FlintESPJVM around large pin numbers. The actual use of WS2812 strips is confirmed as working on very small strips. Will come back soon after testing large numbers.

import flint.io.BitStream;

public class WS2812 {
    BitStream bitStream;

    public WS2812(int pin) {
        bitStream = new BitStream(null, 350, 900, 900, 350);
        bitStream.setOutputPin(pin);
        bitStream.open();
    }

    public void setColour(int r, int g, int b) throws Exception {
        byte[] colors = { (byte) g, (byte) r, (byte) b };

        bitStream.write(colors, 0, 3);
    }
}

[ElectricThanhTung]

Hi @TJC
Sorry for the late reply.
Did you succeed?

[ElectricThanhTung]

I tried it with your code, LED can light up but wrong color. Maybe I need to add a 60 µs at the start.

[TJC]

I came back to this and discovered some interesting facts:

• If I use an external LED strip on a lower pin number (pin=21) then it works.
• If I use the built-in LED on pin=38, it does not work.
• If I use an external LED on pin=38, it does not work. I also tried pin=40 and pin=41.
• If I use Micropython on the same board, pin=38, the LED works.

So I wonder if there is a problem with the way FlintESPJVM is mapping high pin numbers?

[ElectricThanhTung]

It looks like a 32 bit integer overflow error. I will check and fix it.

[ElectricThanhTung]

I already fixed it in this commit 0c820d4

[TJC]

Nice one.

[TJC]

Also - I note that the WS2812 protocol requires a 60 micro second delay at the start, where the voltage is low. Which I don't think the bitstream driver here achieves, except perhaps by accident. (ie. it drives the pin low at the end of the last bit. And then there is possibly some delay in code before it restarts..)

[ElectricThanhTung]

Yes. BitStream does not set the pin low for at least 60 µs at the start. However, after the data has been written, the pin is set low as the idle state.

[ElectricThanhTung]

And the pin will also be set to low when BitStram.open() is called.