HUB75 RGB LED matrix with MicroPython on ESP32 NodeMCU?

[danielmader]

Hello,
I'd like to create a simple clock with a 64x32 LED matrix. I've found very valuable information on two websites about how to use this kind of display:
https://www.bigmessowires.com/2018/05/24/64-x-32-led-matrix-programming/
https://www.sparkfun.com/news/2650

My idea was to create the required "images" before and select them with some kind of look-up. Unfortunately, the loops are way too slow.
Is it impossible to run such a display with MicroPython? Do I need to use CircuitPython instead, with its rgbmatrix module?

while True:
    for row in range(16):
        for col in range(64):
            if col < 21:
                R1.value(1)
                G1.value(0)
                B1.value(0)
                R2.value(0)
                G2.value(0)
                B2.value(1)
            elif col < 41:
                R1.value(0)
                G1.value(1)
                B1.value(0)
                R2.value(1)
                G2.value(0)
                B2.value(0)
            else:
                R1.value(0)
                G1.value(0)
                B1.value(1)
                R2.value(0)
                G2.value(1)
                B2.value(0)
            CLK.value(1)  # a) CLK hi to shift in the color bit
            CLK.value(0)  # b) CLK lo to shift in the color bit
        OE.value(1)   # c) disable output
        LAT.value(1)  # d) LAT hi to load the shift register contents into the LED output
        LAT.value(0)  # e) LAT lo to load the shift register contents into the LED output
        A.value(row % 2)
        B.value((row // 2) % 2)
        C.value((row // 4) % 2)
        D.value((row // 8) % 2)
        E.value((row // 16) % 2)
        OE.value(0)   # f) re-enable output

Attached is my full code, maybe someone can point out a way to remove the bottleneck. Thanks in advance!
example_HUB75_Waveshare_64x32_LED.py.txt

[russhughes]

Here is one possible solution: https://notes.benjemmett.com/archives/114

[danielmader]

I have the same problem with your default pinout from the Hub75 Blaster PCB. The bitbanging approach works no problem (but too slow).

[benjohnemmett]

I'm guessing the dim colors are from limited power draw when running with the same power source as the ESP32. Blue LEDs typically require more current, so it would make sense that red & green light up but not blue. If you want dimmer lights with normal operation, you can control it somewhat by reducing the IlluminationTimeMicroseconds value. Also, using some kind of light diffuser would help it work better for use as a bedside clock.

Since you are seeing the same problem with a different pinout, then it's looking like a bug in the code. I'm still pretty swamped right now, but if I get some spare time I'll try to replicate the issue with my setup.

[benjohnemmett]

I broke out my logic analyzer today and traced down the issue. The updates are up on the main branch.

I discovered that the SoftSPI library leaves the MOSI pin at the level of the last bit transferred out. So, if the last bit (right-most pixel) of a given line is high then that pin would remain high while transferring the data for other two color channels causing the entire line to light up. There may be a setting in the SoftSPI library to fix this, however I just manually reset the pins low after shifting data out.

Last pixel illuminated before fix. (Note that the Red1 pin stays high for too long)

Last pixel illuminated after fix. (Note that the Red1 pin goes back to LOW before shifting green & blue data)

Thanks @danielmader for pointing out the issue and helping me track it down.

[danielmader]

This is great news! Thank you very much for your effort!

[danielmader]

@ALL: Ben was very helpful and further optimized his library. I find it very useful for simple Python-only applications that do not require high frame rates or a high amount of coroutine computation.

I've uploaded my code for a simple night clock which is based on it. It only requires an ESP32 module, a 64x32 HUB75 RGB-LED matrix and a power supply. Clock time accuracy is very good and maintained with a timer, and every 12hrs the time is synchronized via NTP:

https://github.com/danielmader/MatrixClock_MicroPythonESP

[mcauser]

Have you seen the ESP32-Trinity dev board, which plugs into the back of one of those HUB75 panels?
https://esp32trinity.com/

[danielmader]

Haven't seen it yet, but it looks interesting, definitely! Thanks!
However, my bigger problem is not the interfacing but to master the protocoll. Bitbanging is way to slow, and SPI is new to me. So there's a learning curve :)

[mcauser]

https://github.com/mrfaptastic/ESP32-HUB75-MatrixPanel-I2S-DMA
Using I2S / DMA will give you fast refresh rates.

[danielmader]

True, but this is not a "native" MicroPython solution. There are quite many libs available, it seems, but only very few which allow me to stay with Python.

[rsautomationembedded]

Actually P6 rgb module is purchasing, but at this time different type of pixel arragment, so what to do changes into the arduino_gfx library, because my data is not getting proper display

[benjohnemmett]

Do you know what protocol your LED matrix uses? I believe that P6 is probably referring to a 6mm space between each LED, not a protocol.